Not All USB Power Is Created Equal

jfruh writes "We've reached a point in our electronic lives where most of our gadgets draw power from a USB cable, and we have lots of USB ports to choose from — some of which live on other gadgets, some of which live on adapters that plug into your wall or car. But those ports supply wildly varying amounts of power, which can result in hours of difference in how long it takes your phone to charge. The Practical Meter, the product of a successful Kickstarter campaign, can help you figure out which power sources are going to juice up your gadgets the fastest."

Comments

Or use what already exists

[cosmin_c]

Like this little thing and also learn what the numbers and values mean. Got two, they work great and they're consistent with more pricier measurement options.

Re:Or use what already exists

[cosmin_c]

http://www.amazon.co.uk/gp/product/B00DF2485S/ref=oh_details_o09_s01_i01?ie=UTF8&psc=1 Link wasn't processed...

Re:Or use what already exists

[marcansoft]

Or one of these (it also passes through USB 3.0, which is nice):
http://www.amazon.com/Centech-USB-Power-Meter/dp/B00DAR4ITE

This isn't new.

Re: Or use what already exists

[Anonymous Coward]

But that company isn't paying for a slashvertisement.

Re:Or use what already exists

[The123king]

I'd rather spend £10.00 on a charger and £2.50 on a stopwatch than £12.50 on that... At least that way i actually get a charger out of it...

Re:Or use what already exists

[wbr1]

And public education is consistent with more pricier education options.

Re:Or use what already exists

[Anonymous Coward]

There are even cheaper ones on DX.
http://dx.com/p/usb-av-usb-power-current-voltage-tester-translucent-blue-silver-235090 at $5.99
http://dx.com/p/usb-terminal-power-adapter-voltage-current-tester-grey-black-245604 at $10.99

Pretty much every hardware project idea I thought of, I found that China made them already at close to what I could in raw parts cost. :(

Re:Or use what already exists

[kelemvor4]

That's twice now, Charlie Mopps has saved us.

Re:Or use what already exists

[bobbutts]

How do you connect it without hacking a usb plug just like they're selling or otherwise altering your cable?

Re:Or use what already exists

[johnlcallaway]

Why bother with that either (unless you already have one .. which any self-respecting geek should already have). I have this thing called a 'clock' that I can use to determine how quickly something is charging. It's pretty simple to figure out which ones take the least amount of time to get to a full charge. I can then buy more of the ones that charge faster if I want to.

If someone has some money they want to waste on a device that only has one purpose, I won't argue with them stimulating the economy. But really .. $25US for this??? I'll pass.....

Re:Or use what already exists

[gl4ss]

business plan generator for 2013:

1. browse dx, find a neat product, that seems practical while being utterly useless for your usual hipster, preferably with nice lights.
2. ask around your hipster friends if they've heard of such a product. if they have go back to 1.
3. if not, then track down the manufacturer industry guy from china.
4. put the fucking thing on kickstarter with reduced features to put down cost(come on, going from a segment display to fucking FOur FUckING LEDS!!).
5. have them dropship the product from said china guys warehouse
6. you're in the moneeeyy you're in the moneeeeyyyy.

Re:Or use what already exists

[pr0fessor]

Very nice I may need one. Have you heard anything about how well USB Wall outlets work like these?

http://www.homedepot.com/p/U-Socket-15-Amp-AC-Standard-Duplex-Wall-Outlet-White-with-Built-in-USB-Charger-Ports-ACE-7169/203423602#.UozT2EAx7vQ

I've been considering getting a few.

Re:Or use what already exists

[Lumpy]

Turn in your Geek card. That will measure Current draw by the device, NOT how much current the device can deliver.

Re:Or use what already exists

[Lumpy]

Those are utter crap. I have bought and returned two.

http://www.smarthome.com/21680WH/Cooper-Wiring-TR7745-W-Dual-USB-Charger-with-15A-Duplex-Tamper-Resistant-Receptacle-White/p.aspx

This one however works flawlessly with an iphone, ipad, nexus7 and a Nexus 4.

Re:Or use what already exists

[pr0fessor]

I looked at that model at home depot but it was going for about $14 more than at smarthome. I think I'll be purchasing from there instead, thanks for the link.

Re:Or use what already exists

[macraig]

Since I already have a nice multimeter and don't see the need to waste money on yet another device that does exactly the same thing, I'd rather have a simple test lead adapter that lets me plug the multimeter into a USB ports instead of having to gingerly stick probes in there. If no one was entrepreneurial enough to address that need instead of trying to force people to buy another duplicate device, then I guess I'll have to make one myself.

Re:Or use what already exists

[Andy Dodd]

One issue with this (and many other power meters) is - What is the burden voltage of the ammeter? e.g. how much voltage does it drop.

Meters can often have a burden voltage of 0.1-0.2 volts when measuring currents on the order of an ampere. This might not seem like much, but considering that the original (2012) Nexus 7 drops charge current by approximately 200 mA for every 0.1 volt drop below 5.0 volts - http://forum.xda-developers.com/showthread.php?t=2065404 - 0.2 volts can drop your power by 400 mA (around 2 watts) - Many initial characterizations of Nexus 7 charging severely underreported charging current because the meter's burden voltage caused the device to reduce charging current.

Also, most devices now charge well in excess of 5 watts - so a meter that only shows that you're in the 5-10W range but not where in that range you are isn't very useful.

Last but not least - Forcing a device to pull more than 500 mA from a laptop can damage the laptop. That's a blatent violation of the USB charging standard. Yes, some hosts now support higher charging currents AND the method for reporting this is standardized as part of the USB charging standard - but making a device assume it is always connected to a wall charger could do damage if you connect it to an SDP (Standard Downstream Port) instead of a CDP (Charging Downstream Port).

(Unfortunately, only the very latest devices can successfully detect a CDP...)

Re:Or use what already exists

[CastrTroy]

The only problem with this is that the power my phone is using varies wildly. I'm not sure what my phone is doing in the background, but sometimes I'll plug it in, and it will charge at the rate of about 1% per minute, while other times it will charge much slower on the same charger, depending on what the phone is doing in the background. Also, it charges slower once you get past 90%. So to test out a bunch of chargers, you have to spend quite a long time discharging your phone, timing a large amount of charge, and even then the results could be inaccurate if the phone was busy doing something while testing one of the chargers.

Re:Or use what already exists

[Em Adespoton]

How do you connect it without hacking a usb plug just like they're selling or otherwise altering your cable?

The way it's always been done -- using probes. They look like long needles, have hand grips, and come with most meters. Some even come with a number of detachable tips to probe varying types of connections. You can even get some with a dedicated USB adapter these days, although that's not really needed and is more of a gimmick.

Re:Or use what already exists

[nblender]

Similarly, the Leviton T5630 one:

http://www.amazon.com/Leviton-T5630-W-Tamper-Resistant-Receptacle-125-Volt/product-reviews/B008O11IEY

also doesn't work reliably. It charges my iphone and Asus tablet, but not my son's Samsung Galaxy Ace. I haven't received my Nexus-5 yet so I don't know whether that'll work. What's tricky about the Leviton one is they pay lipservice to the multiple charging standards by making each port different presumably in hopes that your favourite device will charge in one or the other...

I haven't met many adapters and ports that won't charge my iphone but other smartphone vendors need to get their poop in a group and find a standard that they'll all stick to... Part of the appeal of an Android phone is they're all microUSB and chargers/cables would be easy to make universal but it's an epic fail in my opinion.

Re:Or use what already exists

[DaTrueDave]

How are you going to probe the power line inside the USB connection without tearing a spare USB cable apart?

Re:Or use what already exists

[BronsCon]

On your last point, the math you do by hand is only as accurate as the numbers you're basing that math on, which would be the numbers stamped on the device, which is what you're actually checking with the multimeter. If I stamp 5.1v 2A on a USB charger, you can do your math based on that stamping, or you can test the device itself and find that it only puts out 4.8v .75A, then to the math and get actual accurate results.

Re: Or use what already exists

[Darinbob]

And it's also not a kickstarter campaign, so clearly it's outdated technology. Only luddites would use a multimeter for this.

Re:Or use what already exists

[Darinbob]

Buy a $1 cable and cut it in half, strip the wires, and voila.

Re:Or use what already exists

[Darinbob]

Add a simple resistor, do some math, and problem is solved!

Re:Or use what already exists

[Darinbob]

That's the phone itself varying current in order to optimally charge the battery. However if you want to know which USB ports can put out the most current and is the best one to use for fast charging, then you measure on the port instead of the phone.

Re:Or use what already exists

[Darinbob]

I'm pretty sure if you head to the hardware lab at your school or place of employment and say "I was thinking of spending $20 plus shipping and handling in order to buy a device to bring out test leads from a USB port" that you would get several volunteers to make one for you in a couple of minutes for half that price.

Re:Or use what already exists

[LynnwoodRooster]

Why bother with that either (unless you already have one .. which any self-respecting geek should already have). I have this thing called a 'clock' that I can use to determine how quickly something is charging.

Clock? Some of us use a sundial, you insensitive clod!

Re:Or use what already exists

[Lumpy]

A simple resistor? so a random 1/4 watt will do?

No, you need a uncommon resistor, typically a 15-20 watt, and if you pick the wrong value you will not get a real reading, some of these things will significantly sag the voltage if the load is of the wrong impedance. and pick too high of a resistance and you dont get an accurate measurement.

So it's not a simple resistor, it's a very specific high power resistor that will emulate the proper device load that the power supply is expecting.

He still loses his geek card, you get to keep yours as you understand at least the basics of electronics and electricity :-)

Re:Or use what already exists

[tibit]

Heck NO! First of all, when measuring current consumption on a port that can deliver a measly 2.5W (5V at 500mA), you won't ever need a 15-20 Watt resistor, even if you used that resistor to short the power wires, much less when you use it in series with one of the wires.

Secondly, you do want as minimum of a dissipation on the current sensing resistor as your measurement amplifier will allow. There are two reasons for that.

The current sensing resistor is in line with the supply, so any voltage developed on it means less voltage to the device. Some devices consume fixed power and are thus negative resistances since they step-up the voltage using a switching converter. In those the more voltage drop your sensor develops, the higher the real current consumption since the load has said negative resistance. You definitely don't want that.

Also, whatever power the resistor is dissipating will necessarily heat it up, changing its resistance. Unless you measure that resistance (or the temperature of the resistor), you're facing an uncorrected error.

Alas, for USB use, you don't even need a discrete resistor. The resistance of the traces on your board (or a section of the cable) should be sufficient - 10mOhms is all you'd need, as it gives you a rather respectable 5mV at 0.5A. If you know your analog electronics, you should have no problem working with even 0.5mV at 0.5A, so just 1 mOhm is all you'd need. Even at 10A, such a "resistor" would dissipate a measly 0.1W, so with the currents seen in USB use, you're completely OK.

Re:Or use what already exists

[cheater512]

Actually a device is more useful in practical terms for comparing a specific device to an adaptor.

I have a 500 amp 5v USB charger. That means my phone charges in 30 seconds right?

You have to take in to account the device's ability to draw the power.

Re:Or use what already exists

[Algae_94]

Turn in your Geek card. That will measure Current draw by the device, NOT how much current the device can deliver.

Your geek card revoking powers have been stripped. The comment you replied to mentioned this exactly

Also this, AND the above mentioned devices will only tell your the voltage your device is currently drawing.

kickstarter link

[Anonymous Coward]

http://www.kickstarter.com/projects/david-toledo/the-practical-meter-know-your-power

External DVD drives

[jones_supa]

When it comes to USB DVD drives, some laptops cannot give enough energy to keep the disk spinning. There's a category of machines which seem to ditch the USB power regulation spec and just connects the USB Vcc rail to the 5V rail of the laptop. That's good and practical in my opinion. Then there's the another category which try to limit the power and have a polyfuse or something more smarter in place.

Re:External DVD drives

[SuricouRaven]

I've seen that before - USB to 5V direct. Someone vandalized a mouse, tearing the cable apart. It was smoldering and melting a hole in the keyboard when I found it.

Re:External DVD drives

[Joining Yet Again]

In what way is it "good and practical" to ignore a standard, possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current? At worst this is a fire hazard, as you'd end up delivering an unreasonably high current. If the device isn't intelligent enough to ask for the right current, it should be delivered a safe trickle - as the USB standard asks.

Re: External DVD drives

[AvitarX]

Any device that reacts badly to too much current is poorly designed or defective.
That's therese electricity works, you're half amp light bulb doesn't explode when there's nothing else in the house because there's too many amps available.
A device that issues is most likely already shorted out.

Re:External DVD drives

[jones_supa]

In what way is it "good and practical" to ignore a standard

For starters, it allows me to burn and read optical discs. Most external DVD drives want to suck all the power through USB and, while they might have a separate DC power connector too, finding just the right power supply is a pain in the ass. If everything was done properly, every external DVD drive would ship a discrete AC/DC power supply, because the USB spec does not actually allow delivering these crazy, over 1A currents which is needed. But what can you do...

possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current?

You are of course correct. As a comment above by SuricouRaven pointed out, letting big amounts of current through can cause hazardous situations.

Re: External DVD drives

[Joining Yet Again]

A USB port should react gracefully to a defective USB device - either limiting current or cutting power if draw is too high. It should not give the malfunctioning device the opportunity to catch fire by delivering it as much current as possible.

Liberal in what you accept; conservative in what you send.

Re:External DVD drives

[The123king]

As some other users mentioned, having USB attached to the 5V rail is not only a fire hazard, but a dangerous flouting of international regulations. On top of that, I have never met a USB-power-only DVD drive with anywhere near decent read-write speeds. I'll stick to my trusty Freecom 5 1/4" drive-in-a-caddy with it's 20x Read/Write and DVD RAM compatibility. Oh, and I can (and have) gutted it for an emergency PATA hard drive caddy. Best £50 i ever spent.

Re: External DVD drives

[rickb928]

Straight copper wire often reacts badly (in ours and the fire department's humble opinions) to too much current. In what way is it poorly designed or defective?

Or is it the design issue? Using copper wire where a resistive element would have been a better choice? Or perhaps connecting that copper wire to some more appropriate load? Maybe forgetting to include a much smaller wire (fuse) in the circuit?

Sorry, still getting enough caffeine in me to build immunity to the obvious. Devices don't react badly to too much current. They draw too much current and react badly to their own defect. Limiting current is a safety feature. Though 5W isn't a trickle in the real world.

Re: External DVD drives

[evilviper]

It's not the job of the power supply to protect malfunctioning devices from themselves. It's the job of the devices to have fuses, regulators, etc. This has been true, forever.

Your wall outlets will provided whatever is requested. Your car's alternator and battery will do the same. 12V devices plugged into a cig plug will get whatever they want, if they were designed so poorly as to not have a dammed fuse.

Re: External DVD drives

[niftydude]

This. A couple of years ago I plugged a defective DVD drive into an alienware notebook. It smoked the DVD drive, then blew up the entire USB subsystem of the notebook.

Needless to say, I don't recommend alienware to anyone anymore.

Re: External DVD drives

[Anonymous Coward]

Yeah, but the power supply should protect itself. If the damn thing is connected directly to the laptops 5V rail it's possible to make the laptops 5V drop by plugging in a defective decvice. That in turn means all kinds of weird shit might happen, including data corruption and hardware deaths.

Re:External DVD drives

[jones_supa]

I agree. Ultimately it's best to just have robust power delivery into DVD drives and not even try to run them through delicate USB power.

Re: External DVD drives

[plover]

Any device that reacts badly to too much current is poorly designed or defective.

Yes, and if I own such a defective device, I certainly don't want it starting a fire. The thing about electronics is that most people could own a defective component and not know until it's caused some other problem.

Electronic devices can have latent defects: poor insulation that's barely adequate to protect the device through testing, shipping, and installation, but as you use the device and move a wire repeatedly, the gap in the insulation causes a short. Should the purchaser be satisfied simply by knowing that he can sue the manufacturer for damages caused by fires? Does it mean the purchaser should never take other precautions, such as installing fuses, or buying equipment with current limiters?

Thanks, but I want to take all the measures available to me to ensure safety.

Re: External DVD drives

[silas_moeckel]

No your wall outlets provide up to what the wire running to them will support past that and the breaker trips or the fuse pops (granted it's often much after but still generally safe for the wire). Newer homes have arc faults in a lot of places that protect from even more.

Same thing for your car every branch circuit has a fuse of a given rating try getting more than 15 amps through your 12v accessory outlet.

Pretty much the rule is you can not step down the permanent wire size without an over current protection device.

Re: External DVD drives

[AvitarX]

The computer should cut power before it starts a fire (including if it's just strait 5 volt rail).

The computer should have a "dangerous current draw" fail-safe, not a "I killed an already broken mouse" fail-safe.

Fuses are pretty damned effective, and cheap. Devices should have them in case they short out, failure to have one is what I describe as poor design.

Re: External DVD drives

[AvitarX]

Yes, a strait copper loop, with nothing else would be what I call poor design.

As would a wrench laid across your car battery (and arguably the older jumper cables that don't have fuses, that allow idiots to short the battery).

Re:External DVD drives

[Joce640k]

Then there's the another category which try to limit the power and have a polyfuse or something more smarter in place.

ALL USB sockets are required to have a polyfuse, it's part of the specification.

Whether they're 500mA or 2A or whatever is another matter, but they have to have them.

Re: External DVD drives

[NJRoadfan]

USB ports are usually protected by a pico fuse on the motherboard. Back in the bad old days I had a 430VX chipset motherboard with a non-standard USB header. The manual documented the pinout so I wired in a port back plate Turned on the machine and the inside lit up like a Christmas tree. Somehow the fuse blew with just the USB header connected. Its likey that the manual's pinout was wrong and the back plate plug was dodgy. Its likely the metal back plate of the port (which is grounded to chassis) was connected to the USB port's power ground pin (are these supposed to be connected in any way?). The motherboard manual's pinout likely had the +5v labelled as the ground pin, so instant short.

Re: External DVD drives

[bobbied]

Any device that reacts badly to too much current is poorly designed or defective. That's therese electricity works, you're half amp light bulb doesn't explode when there's nothing else in the house because there's too many amps available. A device that issues is most likely already shorted out.

Safety demands that you *never* depend on the unknown thing to be properly designed or to function properly if you can help it. If you are providing power to something, you need to limit their power draw *somehow* to keep a malfunction from causing damage. It is why fuses and circuit breakers where invented and why modern power supplies will shut down if they are asked to supply more than their rated current/power. Any device that risks permanent damage because some other product draws too much current, especially if the device risks starting a fire, is inherently unsafe and should not be used.

Re: External DVD drives

[Khyber]

"Same thing for your car every branch circuit has a fuse of a given rating try getting more than 15 amps through your 12v accessory outlet."

Wonder what my 500w Inverter pushing dual 250w Altec Lansings would have to say to that, considering in my car the 12V accessory has a 40 amp buss fuse (the original one that came with the car when it was made in 1998, at that.)

Oh, look, my 90's S-10 has a 40-Amp fuse. again, the original one.

Well, hey! My 87 Tercel has a 35A, but that's still better than your 15.

Re: External DVD drives

[plover]

If you tie the 5V from the power supply straight into the USB ports, there is zero chance of preventing a fire. My 850W power supply is designed specifically to pump 30A into the cabinet on the 5V line. The power supply has no way of knowing if it's pushing that current into a hungry CPU or into a shorted out mouse wire.

It doesn't matter if a USB device is badly designed. There are several places that all need to implement safety measures. USB specifications require that a USB host limit the power to prevent these kinds of problems. A fuse in a mouse might be a fine design choice, but it is not going to improve my safety unless the USB current limiter is broken AND the mouse has some other internal defect limited to the board - a fuse in the mouse won't even protect me against a damaged mouse wire.

Re: External DVD drives

[AvitarX]

Fair enough, You and the other response rightly pointed out that a strait five volt rail connection is absurd to feed to the USB.

I'll still think that 2A fuse in each port (max USB spec) should be fine.

The 5A in USB 3.1 (for 12 volt) may need some negotiating, or more robust cables and fuses in the ports, or more robust cables.

Re: External DVD drives

[silas_moeckel]

Are those modern accessory outlets or old style cigarette lighter outlets?

Point still stands they are fused to protect the wiring as designed.

Re: External DVD drives

[Joining Yet Again]

Post flagged for being so hilarious I wet myself. In future, only use your powers for good, AC.

Re:External DVD drives

[Obfuscant]

because the USB spec does not actually allow delivering these crazy, over 1A currents which is needed. But what can you do...

Supply a dual-connector cable to plug into two USB ports, which USB DVD-RW and a couple of external disk devices I've bought have had. One is data and power, the other just power.

Re:External DVD drives

[jones_supa]

It didn't have any effect when I tried it. Maybe it works on some computers.

Re: External DVD drives

[evilviper]

No your wall outlets provide up to what the wire running to them will support past that and the breaker trips or the fuse pops

Yeah, but we're not talking about the WIRES. We're talking about a "defective ... device".

Your wall outlets absolutely offer devices that plug-in, "the opportunity to catch fire by delivering it as much current as possible."

Re:External DVD drives

[Darinbob]

Technically, USB ports are supposed to be limited to 500mA. Some laptops cheat on this though, such as those from Apple, but this is against the standard. Others cheat in different ways by increasing current for its own approved peripherals. But if you give more current than the device asks for you could damage it or your home.

Re: External DVD drives

[Khyber]

Cig lighter outlets. The kinds that can power real power inverters. I would have thought mentioning the year of vehicle would have made that apparent.

Re: External DVD drives

[JamieIanMacgregor]

I cant say I've seen a computer that outputs enough A@5v to melt a wire. I had a webcam with a solder blob which shorted 5v to gnd, it would just cause all of my computers to restart when plugged in, until I located the renegade blob and removed it.

Re: External DVD drives

[tibit]

This is not quite true. There's this thing called compliance, and your device won't ever get a UL listing (or pass CE compliance testing) if it doesn't provide power limiting on low-voltage outputs. It's braindead to do anyway, as you'll be a ripe target for lawsuits. A USB port should basically protect a 3m 24AWG power wire pair from melting when shorted or otherwise overloaded. In a house, that's what the circuit breakers are for: they protect the wiring from overloads.

Re: External DVD drives

[DarwinSurvivor]

Your power supply probably had a short-detection circuit which cut the power. One of my old laptops had a bad power cable (frayed, eventually fixed) that would hard-kill the laptop when the wire was in a particular position.

Re:External DVD drives

[DarwinSurvivor]

Maybe your laptop is limiting the total current to the entire USB bus instead of each individual port. Try figuring out which ports are using the same bus and plug it into 2 ports on different buses, that may fix the problem for you. Remember, the standard specifies how much power A port may consume, not the total of all the ports.

Re: External DVD drives

[JamieIanMacgregor]

you're probably right but I really thought all computer/laptop PSU's had short protection (at least from the 8088 days) which seems strange that others are able to smoke up a wire in their pc's - I've got some of the oldest shittiest pc's and PSU's around. I should point out that when I was doing repairs for PCDirect we had one customer's pc that managed to set it's RAM on fire while open on the workbench and at another repair shop one customer had cut the AC power cable to poke though a small hole in the desk and reconnected it wrong, blew the top of a chip on the motherboard. that is the closest I've seen to what people are reporting here in approx 20yrs on the job. I can just imagine the chaos that would ensue from a 100w usb port if it failed to negotiate the power requirements correctly.

Re: External DVD drives

[DarwinSurvivor]

Oh, definitely many of the system have either inadequate or defective protection circuits. I once had an ATX power connector (mine) short against the flat of a case's removable side panel and fry the HDD.

Re: External DVD drives

[plover]

Back in the day when it was common to simply have a row of header pins serving as a male connector, instead of containing them in a keyed-and-tabbed plastic socket, I once accidentally connected a ribbon cable backwards to the motherboard. Because we were just testing some devices in a lab, everything was spread out across a table instead of being shoved back into a small cabinet. When I powered up the machine, it looked fine, so we didn't pay much attention. But after a few seconds we smelled smoke, and when we looked around, we saw the middle of the ribbon cable was black and smoking. By the time we got back to the power switch, one of the conductors near the center of the ribbon had melted its way entirely out of the ribbon and was hanging downwards.

Somewhere in the middle of the cable, one of the wires carrying power to the device was short circuiting to a ground on the far end. Surprisingly, after we replaced the cable and hooked it up properly, neither device appeared harmed by the experience.

Simply being 5V is no guarantee of safety. Pump enough amps through a thin enough piece of copper, and it will overheat. We figured the 4' length of 28 AWG ribbon cable I was using offered 0.26 ohms of resistance. At 5V, that created a 96W circuit, which is about two thirds of the 150W my power supply was rated to deliver on the 5V bus. As far as the power supply was concerned, that was just a heavy load and was not detectable as a short circuit.

Don't really see the market

[mlk]

At work I could plug my phone into the computer or... Buy a second plug, that seams a bit pointless even it if it does knock and hour of the phones charging time.

At home I do have choice, but why would I really worry as each night it gets charged and has all night. So again an hour does not really matter.

What am I missing from this?

Re:Don't really see the market

[mean pun]

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Re:Don't really see the market

[heypete]

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

Re:Don't really see the market

[Teun]

Like when I've used the phone as hotspot and have Bluetooth on as well, power goes down rapidly and the day isn't over yet.

Having a quick top-up before getting on the train home is rather useful...

Re:Don't really see the market

[subreality]

This doesn't add up. The Nexus 7 has a 16Wh battery. The worst USB port possible (100mA) provides half a watt. Either a) your N7, rated for 10h active / 300h standby, is guzzling so fast that it would deplete a full battery in 32h of all-standby, or b) the USB port is defective.

Re:Don't really see the market

[unitron]

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping...

OK, we can stop right here and determine what the hell the problem is...and it's occurring before you even find a power source.

Go fix or replace your tablet. One should not be trying to power a black hole.

I may have accidentally modded the above "redundant" by starting to mod it "informative" and then deciding to read the rest of the thread to see if I was going to want to comment instead of modding.

If so, my apologies to the PP

Re:Don't really see the market

[pumpumpum]

Some devices may actually discharge when they are charged from port that don't supply enough power. See http://uros.com/public/blog/how-to-charge-your-mobile-device

Re:Don't really see the market

[bemymonkey]

Your Nexus 7 has runaway background processes. Otherwise there's no way it draws more than 500mA in standby - it would be empty after just a few hours. Check your battery stats to find the culprit...

My girlfriend's Nexus 7 charges just fine off of good old 500mA USB2.0 ports when it's in standby...

Re:Don't really see the market

[nightsky30]

I've noticed this as well when charging from a docking station usb port. It claims it is charging, and it doesn't lose charge as fast as when it's on pure battery power, but still loses charge over an extended period of time. Normal charging from the wall or other usb sources works fine. I think that particular usb port is just too weak. I don't have any issues with my battery life. I'm very happy with my Nexus 7 (2012).

Re:Don't really see the market

[Ash Vince]

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

I used to have the same problem with an old PC too. If I plugged most devices into my main computer they charged just fine, I had a really shit old small form factor packard bell thing I used to leave always switched on as a router though and if I plugged anything into that to charge via USB it ended up actually drawing power out of the device instead. This was not due to the device though, anything I plugged in to charge did the same thing.

Weirdly though I could plug anything that needed power to run like a usb stick, or usb modem and it worked fine without any issues.

Re:Don't really see the market

[nightsky30]

This very well could be the issue. With a recent wipe I will check to see if there is any improvement.
And still no KitKat :(

Re:Don't really see the market

[RabidReindeer]

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

The Color and Tablet Nook devices have two different charge rates. If you use the official "USB" cable with the LED indicator in it, it charges at a 1A (2A?) rate. If you use a stock micro USB cable, it charges at the official 500ma rate. The decision is made by the Nook itself, based on info from extra pins that are in the custom cable.

Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

Moral of story: always check new toys for screwball cables before buying.

Re:Don't really see the market

[jones_supa]

Mod parent interesting. Can anyone explain what happened in that scenario? Is it a load impedance issue? And, wouldn't there have been a diode to prevent current flow into wrong direction?

Re:Don't really see the market

[necro81]

How weak is your "weakly charging" USB port

The USB spec - ya know, that thing that every device carrying the USB logo is supposed to follow - permits a connected device to draw a maximum of 100 mA until it is properly recognized (enumerated) by the host. This is probably what the GP is referring to: 0.5 W of available power (less after conversion efficiency) isn't a whole lot for a device like a Nexus 7.

After being enumerated, the connected device can request higher current levels, up to 500 mA max. It isn't supposed to draw more unless the host permits it. For many modern portable electronics (e.g., smartphones) that have a 3-10 Whr battery, a 2.5-W maximum charge rate isn't much.

There are amendments to the spec that allow for greater power: in 2009, the spec created a Charging Downstream Port, which allows for up to 1.5 A from the host after enumeration; and the Dedicated Charging Port (DCP), which shorts the two data lines together and allows for 1.5 A charge power without enumeration.

Individual companies, such as Apple and Samsung, supply their own USB chargers that allow for even greater charge current, but do so in a way that technically violates the USB spec.

Re:Don't really see the market

[wbr1]

I have had two LG phones that either keep a static charge or lose charge when plugged into a cheap car charger with the GPS on. Without GPS it is okay, but I guess GPS and the nav app are such a drain that the poor charger can't deliver enough current. It would be nice to be able to test a charger to see what it's actual output is.

Re:Don't really see the market

[Speare]

A lot of the replies here are incredulous about Nexus 7 power.

My Nexus 7 2012 edition would charge up, even if the screen and wifi was on, if left on a 500mA laptop USB port (usb debugging / storage enabled).

My Nexus 7 2013 edition would not charge up, even if the screen and wifi was off, if left on a 500mA laptop USB port (even with usb debugging / storage disabled). It would drain slowly. It required a 1A from a wall-wart to tread water with the screen on. It took a 2A wall-wart to actually charge up while using it. I still have to find a powered hub that will give more than USB standard 500mA, so I can pass debug/storage data while charging.

Re:Don't really see the market

[evilviper]

What am I missing from this?

Your car charger would be a big one... Fire up Google Navigation for your weekend drive out-of-town, and connect it to your $2 cigarette lighter charger, and before you get to your destination, your phone shuts off because it has run out of juice. Other apps like the free MapQuest use less power and offer better routing, but even those commonly use more than the 500mAH basic old USB chargers can supply, so your battery will be drained rather than charge.

The second would be a living room USB charger... If you use your phone for lots of things, like reading eBooks or RSS feeds, listening to podcasts, playing games, looking-up information, etc., your phone won't make it through half a day on a charge. An extra charger in your living room allows you to keep things charged, and the FASTER that one charges your phone, the sooner you can un-tether yourself and return to pretending cell phones don't have horrific battery life.

Re:Don't really see the market

[evilviper]

In all those cases, though, I read the specs on the charger, and/or observe how fast my phone is charging, and don't NEED a stupid meter to tell me what I'll find out in a few minutes.

In fact it doesn't MATTER how much power your charger can supply, if it isn't wired in a way your cell phone recognizes it, it won't TRY to draw that much power, anyhow. And Apple and Android were oh-so-nice to choose mutually-incompatible methods of signaling this, so one charger cannot work for both. Though expensive "charging-only" cables offer a workaround.

IMHO, we should switch (back) to 12V DC barrel plugs ASAP, as those will supply enough power for any device, and are infinitely more durable connectors than flimsy and directional microUSB.

Re:Don't really see the market

[Skater]

I had something similar happen with my Samsung S3. It turned out the cable I was using (an Amazon Basics 6' cable) is bad - if you page through the reviews for it, you'll find a few reviews mentioning the same issue. The charger was delivering a full 1 amp or whatever, but the cable had too much resistance. If I was in an area with a weak cell signal and no wifi, my phone would take practically all night to charge, even with Wifi and Bluetooth turned off. Sometimes I'd even wake up in the morning and find it was only charged to 85%. Similarly, when using my phone as a GPS in my car, the charge on my phone would decrease even while plugged in with one of those cables. Unfortunately, I'd bought about 5 of those cables before I discovered the problem. I've replaced the three cables that were causing me the most headache. I replaced the one that was the biggest problem with an official Samsung cable just to be sure.

Re:Don't really see the market

[mean pun]

Exactly! For me the cable was the problem as well. The Nexus 7 2012 I mentioned comes with a wallsocket-to-usb charger, and a special USB cable. I managed to mislay that cable, and with most ordinary cables I had very long or even negative charging rates, even with the original charger. As far as I can tell the trick is to find a cable with low wire resistance, either because it is short, or because it has thick wires.

In any case, I think the whole discussion illustrates that some kind of measurement instrument to determine charging time or current is indeed helpful.

Re:Don't really see the market

[bluefoxlucid]

I plug into my computer even though I have a wall adapter that charges roughly 5 times faster. My phone's battery lasts 4-6 years instead of 1 before losing over 50% of its capacity.

Re:Don't really see the market

[dpiven]

[Nook Color/Tablet charging cables] ... (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

Better hurry over onto B&N's site and stock up on them, maybe.

Re trickle-charging, my experience is that the Nook Tablet wouldn't show any indication that it was charging at all if a standard uUSB cable was connected. I never left mine connected that way for any extended period to see if the battery charge actually went up. I might borrow it back from my wife and try it (if I can pry it away from her that long).

Re:Don't really see the market

[Medievalist]

The Nook Color I use in my car (with Torque app) stays connected to a regular USB cable in the dash that only supplies power when the ignition's on. It bluetooths to the ODBC. Running out of battery power doesn't seem to be a problem in a daily driver (which is good, because the car complains if the Nook boots, says the USB draw momentarily goes over spec and wants permission to shut down the USB port).

It used to charge reasonably quickly with the "official" cable and wall-wart ( which are actually very well designed (you can't hurt anything by using them incorrectly, because the cable head is longer so the extra pins don't touch anything if you plug it into a normal (not Nook) microUSB device)) but took forever without the special cable.

Re:Don't really see the market

[RabidReindeer]

Interesting. Back in July they were talking like a special production run would be made (no cables in inventory for months), but come July, nothing. Apparently they did it and didn't say anything - I had a pre-order in for all the good it did.

If you plug in a stock micro USB connector, even if it's jacked into a 2A power converter, the Nook will say "Not Charging". But come back in an hour or 2 and it will be back up to full power.

I don't think the trickle rate's enough to charge it while in use - especially with the Wi-Fi running, but it does work.

Re:Don't really see the market

[dpiven]

If you plug in a stock micro USB connector, even if it's jacked into a 2A power converter, the Nook will say "Not Charging". But come back in an hour or 2 and it will be back up to full power.

Interesting. I (or my wife) will have to try this; thanks for your observations.

Re:Don't really see the market

[mlk]

From the sounds if it you don't need a $25 dongle to say "this port is rubbish" and you could spend said $25 on either a powered USB hub or plug.

Re:Don't really see the market

[mlk]

But how does what looks to me like a cable tester help me with that?

The good usb cable I get. But that is not worth $25 is it?

Re:Don't really see the market

[mspohr]

This device seems to be able to bypass the "enumeration" thing and allow them to charge at max rate It also acts as a firewall to keep the USB port from downloading data from your device.

http://www.kickstarter.com/projects/1137339450/lockedusb-adapter-usb-charger-firewall-and-power-o

Re:Don't really see the market

[mlk]

In this case you are talking about the "better cable" rather than the cable tester, and would the "better cable" really help in the case of the car charger?

Re:Don't really see the market

[mspohr]

There is a known issue with some Android devices where they don't go into sleep mode and will discharge rapidly even when connected to a charger.
I had this with my Nexus 4 but it's been reported in many different devices.
Lots of random advice in forums on how to fix it but the problem still seems to exist.
http://androidforums.com/samsung-galaxy-s4-active/733289-s4-active-wont-go-in-sleep-mode-when-charging.html
http://forums.androidcentral.com/google-nexus-7-tablet-2013/314761-battery-drain-sleep-mode.html

Re:Don't really see the market

[xeoron]

I had the same problem with my Nexus 7 (2012), until I did these four things. 1) Go into the system settings and in the section for Apps and kill any process running that you don't want to run. 2) Uninstall the power hungry apps that are always running that you really don't use much or at all. 3) In the Play store go into your settings and tell it to not auto update 4) Install Deep Sleep Battery Saver Pro to tweak how the device will act with regards to power usage while asleep or with the screen merely off (there is a free version, but the pro gives you more power saving options). By doing these things I have went from having a N7 that had a fast power drain even when asleep, nor charge when asleep, to one that keeps power 10 times longer and charges while sleeping.

Re:Don't really see the market

[m.dillon]

Happens to me all the time on ALL my android devices. Totally non-deterministic. Sometimes my Nexus 7 (2012) can sit with the display turned off for several days without losing too much battery, other times I turn it off (display off) and it discharges overnight and is dead in the morning. Happens to both my android phones too. I'm not forgetting to turn off Pandora either.

Sometimes my phone is 'hot' just sitting in my pocket with the screen off. Sometimes it is 'cold'. When it's hot it's obviously eating power doing something, despite the display being turned off. It's totally random when this happens... usually the longer I leave the phone between reboots the more likely it is to get into that state. VERY annoying. NO services are running (nothing in the service bar at the top). Doesn't matter. Still random hot or cold.

Doesn't happen to any of my Apple devices. If I leave an Apple device turned off (sleep mode that is), it retains its battery level and drains at a very slow and highly deterministic rate. If I turn off my iPhone (and I'm not playing music on it), it goes to sleep. Always.

Honestly I don't understand why Google thinks this is ok. It's an obvious competitive advantage for Apple when its devices don't kill their battery and Android devices do.

-Matt

Re:Don't really see the market

[djdanlib]

That happened to me with a 10' $5 cable from Monoprice. Out of desperation after I broke it the other day, I bought a 3' $5 cable from the bargain bin in the cell phone accessories department at a big store that I usually don't go to... last resort, I know, but it couldn't wait until the next day. And the $5 cable works like the OEM cable.

Re:Don't really see the market

[evilviper]

you are talking about the "better cable" rather than the cable tester

And I have no idea what you are talking about, here...

I'm talking about USB charger/power supply, not cables specifically... And the "tester" is to determine if you've got a good one or not.

Re:Don't really see the market

[mlk]

If I've read the kick starter thing correctly (and I may have it wrong) this is two bits, a tester and a cable that will ensure you get the best charge from your USB port.

The tester only really works after you have bought a device, which is a little to late in my mind, esp. when you could buy a just $25 charger and be reasonably sure you are getting something good.

Sure you could say that send the charger back if you get a "dud" but that again will cost more (factoring in time) than just buying a good reasonably priced charger in the first case.

I'm sure it has uses (8000-odd people think it does), I just don't see them.

Re:Don't really see the market

[evilviper]

Spending more money won't help. Spend all you want on an expensive Apple charger, and it still won't fast-charge your Android phone.

Re:Don't really see the market

[sh00z]

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

there's a widget that will let you disable wifi, bluetooth and GPS from your homescreen. turn those puppies off before you sleep, and it'll charge in no time.

Re:Don't really see the market

[RabidReindeer]

If you plug in a stock micro USB connector, even if it's jacked into a 2A power converter, the Nook will say "Not Charging". But come back in an hour or 2 and it will be back up to full power.

Interesting. I (or my wife) will have to try this; thanks for your observations.

I'm going to up the time estimate, though. Overnight will do it. I was too lazy last night and it looks closer to 4 hours to get full charge.

Re:Don't really see the market

[Ash Vince]

My guess would be that the device simply consumed more power than it could draw from USB.

I doubt that was the case as it happened with more than one device and they charged fine from other PC's. Since this was a specific issue to that PC I always assumed the manufacturer skimped on the PSU somehow or it was caused be the USB modem that was permanently plugged in to the other USB port.

Re:Don't really see the market

[mjwx]

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

I have a Nexus 7 2013 edition and have experienced the same thing as the OP, as it turned out the power point was switched off.

My N7 lasts about 7 days in standby so the power draw is not high at all. I just spent a month travelling around the Americas and I only had to charge it every 4-5 days. I usually charge it from the wall but even from USB 2.0 ports on my laptop or desktop work well enough. The slowest charge I've had was from aeroplane USB ports which are deliberately restricted. I used my N7 to watch a few movies whilst charging it via the plane's USB port and at the end of the flight I had 10% more charge than when I started.

Re:Don't really see the market

[DarwinSurvivor]

There are amendments to the spec that allow for greater power: in 2009, the spec created a Charging Downstream Port, which allows for up to 1.5 A from the host after enumeration; and the Dedicated Charging Port (DCP), which shorts the two data lines together and allows for 1.5 A charge power without enumeration.

So the specification which was designed to protect devices that may pull too much current (possibly due to a short) is bypassed by shorting out the other 2 pins? Brilliant...

Re:Don't really see the market

[mlk]

We have a known bad combination - Apple charger, Android phone. How does this help? It will tell us it is bad, but we know that.

Re:Don't really see the market

[mcvos]

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

I've had this with my old Motorola Milestone. It lost power while charging on a weak charger. Even when turned off, it sometimes refuses to charge. Probably because it's old. I need higher powered chargers, or maybe a new phone.

Re:Don't really see the market

[evilviper]

Apple charger, Android phone. How does this help? It will tell us it is bad, but we know that.

Most people DON'T know these things, so there's that.

And while Apple-branded is one thing... There are plenty of other 3rd party, unbranded or similar chargers, which DON'T SAY whether they were designed for Apple, Android, old dumb phones, etc.

Hell, they can say they are designed to fast-charge Android phones, and NOT WORK.

USB charging is absolutely a confusing mess.

Re:Don't really see the market

[david_thornley]

I suspect background apps. I wasn't feeling happy with the battery life on my new iPhone 5s, so I went into Settings and turned off background updating for anything. It may take some apps a touch longer to come up properly and get the latest information, but I'm much happier with my battery life.

Re: Don't really see the market

[gzuckier]

Fastest charger I have is an RIM 700 ma i got at goodwill for $1.99. Faster than the oem samsung.

Re:Don't really see the market

[mlk]

> Most people DON'T know these things, so there's that.

But most people will not have what is clearly a geeky toy. So this only really helps reviewers of cables.

> USB charging is absolutely a confusing mess.

I've never really come across this confusing mess. Now I don't own any Apple devices, but my mix of Android devices have all charged fine with a mix of USB cables connected to a mix of plugs (ranging from battery packs to wall sockets). Sure the PC may charge slower than the wall socket but I don't see why most people would care.
The Apple charger might not charge the Android at all, but that is something that you will notice without a $25 tool.

Re:Don't really see the market

[evilviper]

I don't see why most people would care.

Yes you do, because I explained it in my first reply to you. At this point it's some kind of willful ignorance.

Re:Don't really see the market

[mlk]

No I really don't. But I think we have gone as far as we can can. I'm glad it meets a need you have, but I just don't see it.

Re:Don't really see the market

[evilviper]

Funny, you replied to my comment about just that without arguing with anything I said:

http://slashdot.org/comments.pl?sid=4463987&cid=45471781

It's not sex...

[Anonymous Coward]

Being the fastest might not be the best for your battery life.

Re:It's not sex...

[aliquis]

How do the boosting using the circuitry work? Why is it faster than Apples own cable for charging an Apple device? Or the cable work worse with PCs by design somehow?

Faster isn't always better

[Lennie]

I believe most types of battery when charged faster actually degrade faster.

Life fast die fast ;-)

Re:Faster isn't always better

[hcs_$reboot]

The Fukushima rods would indirectly charge anything very fast. But they won't die any time soon, unfortunately.

Re:Faster isn't always better

[Anonymous Coward]

If they could convert gamma rays to electricity directly, instead of messing around with steam, we wouldn't have Fukushimas.

Re:Faster isn't always better

[Joining Yet Again]

Smartass fast - run-on fast.

Re:Faster isn't always better

[Joining Yet Again]

Your threshold for what counts as stress + your tense overuse of italics suggest you may wish to consult your physician before you have a coronary.

Re:Faster isn't always better

[Sockatume]

The device should only draw as much power as it wants, which is controlled by the charging circuit in the phone, regardless of how much is available. Which raises the obvious question of how they're getting iPhones which want a 120-minute charge cycle, to charge in 90 minutes by using a special cable.

Re:Faster isn't always better

[PhrostyMcByte]

Remember, power over USB is negotiated. It doesn't just supply 2A to each port. The USB 3 spec allows for up to 900mA, but will only provide 150mA if the device doesn't ask for more. There is a separate "charging" spec which supplies up to 5A, though it wasn't supported by motherboards until fairly recently.

The phones want a 90 minute charge time; it's just that they communicate their want for more power in a way that not all USB hosts understand -- often they use some non-standard way that only their power adapter understands -- so the host ends up giving them less power than ideal. It looks like this cable is sort of like a universal remote: it has an IC embedded in it that performs power negotiation for the device.

Basically an Ammeter

[hcs_$reboot]

Instead of that ugly one, you may get something that gives an exact value, like this one. A new iPhone/iPad expects 2A, the MacBook (10W) expects also 10/5 = 2A.

Re:Basically an Ammeter

[thsths]

And a bad one, too, with a terrible resolution. Just get an amp meter and a cable, that should be under $10 together.

Typical slashvertising. I miss the good old days.

Re:Basically an Ammeter

[hcs_$reboot]

Typical slashvertising

Impossible, I disabled ads thanks to

As our way of thanking you for your positive contributions to Slashdot, you are eligible to disable advertising.

Re:Basically an Ammeter

[CODiNE]

That won't work as USB amperage is based on resister sensing.

Or....

[Anonymous Coward]

Or just use a voltmeter.

Re:Or....

[Joining Yet Again]

Perhaps AC has a spare voltmeter and was planning to add a shunt resistance in parallel?

Re:Or....

[Neil Boekend]

I can tell you the voltage: 5 V +-0.25V (assuming the USB port is within spec). What you need is the current, so an ampere meter is required. A multimeter is custom. However, that is clumsy. You need to get to the power leads, without shorting the power or data leads (as shorting the data leads defaults the current to 100 ma).
The idea is good but there are better solutions, as indicated by other posters.

Re:Or....

[bobbied]

An volt meter is just an amp meter that has a resister in series with it..

Also, it might be better to use a volt meter and a very small shut resister to measure a current in a circuit you don't want to disrupt. Such a scheme could be less disruptive to the circuit. Having all the current flow though your meter and the leads to/from the meter is more likely to be disruptive.

won't help for Samsung note 2

[leehwtsohg]

Samsung seems to measure the "reliability" of the supply or the cable, and limits power based on those values. Then the same supply will charge at different rates depending on the cable used.

Re:won't help for Samsung note 2

[AmiMoJo]

Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

Re:won't help for Samsung note 2

[ThatsNotPudding]

Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

This is why I build my own USB leads using #00 welding cable.

Re:won't help for Samsung note 2

[leehwtsohg]

I don't think it has to do with voltage drop. A cable usually will not show a voltage drop ~0 resistance for 2m of cable. And, same cable will charge other devices without any problem. A cable might burn out with too much current. Maybe that's the worry? I haven't really heard of that happening....
Even the originally supplied cable is rejected sometimes. And, if you get a bad charging rate, just unplug and replug the cable for another roll of the dice.
No, I think it is a simple bug in the charging control in the phone.

Re:won't help for Samsung note 2

[Anonymous Coward]

Voltage loss over such a cable is very real. At 0.14 mm^2 (AWG 26) you get 0.14 mOhm/m. For a 2m cable, 2 wires you end up with 0.56 Ohm. At 1.5 A that's a voltage drop of 0.84V.

Also note that such a cable is only rated for 0.36 A

Re:won't help for Samsung note 2

[m.dillon]

No no, resistance has nothing to do with it. The USB charger's output is current limited, which means that if the device tries to pull more current than the charger is programmed for, the charger's output voltage will drop. That is, the output will be limited to (for example) 500mA or 1A or 1.5A or whatever and if the device tries to pull more the output will STILL be limited to that value and the voltage will drop from 5V to compensate.

Smart devices can usually ignore the USB resistor-based programming pins (which run to different standards) and simply pull the charger's output down from 5V to 4V or something like that and measure the current (up to a reasonable limit managed by the device, of course), and figure out how much they can pull from the charger based on that.

Stupid devices will either not probe what the charger can actually do or will make assumptions based on the resistor-programmed pins (the one that has multiple standards) and not be able to handle the case where they guess wrong and crow-bar the charger's output by trying to pull too much current.

None of this has anything to do with the resistance of the wires inside or outside the charger.

-Matt

Re:won't help for Samsung note 2

[CSMoran]

Voltage loss over such a cable is very real. At 0.14 mm^2 (AWG 26) you get 0.14 mOhm/m. For a 2m cable, 2 wires you end up with 0.56 Ohm. At 1.5 A that's a voltage drop of 0.84V.

A factor of 1000 snuck out on you here. You went from milliohms to ohms in a second.

Re:won't help for Samsung note 2

[leehwtsohg]

I don't think this is true for some devices. As the grandparent said (me), for the Samsung Note 2, charging current depends strongly on the USB cable used - same charger will charge at different rates depending on the cable. (And sometimes the same cable + charger will charge at different rate depending on luck).

Re:won't help for Samsung note 2

[AmiMoJo]

~0 on what kind of measurement device? If you compare with say a 5 digit calibrated multimeter you will find a significant difference. 0.1ohms over the entire length of the cable will produce a 150mV drop at 1.5A. Most shit meters can't accurately measure down that low.

Re:won't help for Samsung note 2

[hamjudo]

The error was an extra "m". The poster meant 0.14 Ohms per meter. I've seen higher resistance USB cable than that in the real world. Think of how much copper they saved by using such thin wires...

Re:won't help for Samsung note 2

[GuB-42]

It's real. I have a Galaxy Note 2 and cheap long cables can't charge it correctly. These cables work fine on device requiring less charge current.
No amount of plugging and unplugging help, thin cables work 0% of the time, better cables (original or not) work 100%.

Re:This is News?

[Teun]

Yo doofus, it is because we know they can be different that we sometimes need to measure to know what's up.

Isn't there a spec on how much power ...

[Ihlosi]

... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

Re:Isn't there a spec on how much power ...

[RabidReindeer]

... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

There are several generations of specs. The original was hard-wired for 500ma max. Later versions can negotiate.

Re:Isn't there a spec on how much power ...

[necro81]

Most of the time a charger (proper one anyway) will set a certain voltage on the DATA+ and DATA- pins of the USB cable and the charging device senses this to know when it is appropriate to draw more power

Unfortunately, that method is not reliable, because every manufacturer implements it differently - it is not a part of the USB spec.

Following the spec, the only way to know the current rating is to either negotiate with the host (not usually possible for a standalone, "dumb" charger) or to have the data pins shorted together (a DCP according to the USB spec), in which case the available charge current should be 1.5 A min.

Re:Isn't there a spec on how much power ...

[silas_moeckel]

Which manufacturers blissfully ignored. Apple with there secret handshakes. Nearly all of the USB power specs required to much intelligence at the charger end thus cost. The latest is rather fun supping up to 100w. The previous supplying 1.5a assumed simply by shorting the data lines together.

Re:Isn't there a spec on how much power ...

[bobbied]

Most of the time a charger (proper one anyway) will set a certain voltage on the DATA+ and DATA- pins of the USB cable and the charging device senses this to know when it is appropriate to draw more power

Unfortunately, that method is not reliable, because every manufacturer implements it differently - it is not a part of the USB spec.

And you have hit the crux of this issue. There is no standard for this so manufacturers have implemented *dumb* ways around this which are incompatible.

Personally, I think there should be to additions to the standard that include the "dumb" option for devices needing up to 1 Amp. If the hub/charger can do 1 amp, hold the pins the right way and supply 1 amp. If the device requires more than 1 amp, then make it mandatory for the device to request what it wants using the USB data bus and the source device can choose to supply what it can in reply. We will need a maximum current in the specification, and I think 3-5 amps (15-25 watts) is about all that would be safe on the current cables out there.

Charging spec compatibility?

[Sockatume]

Different devices have subtly different ways of asking how much currently they can draw. Your iDevices and Androids and whatever are fairly interoperable with each other's chargers now, but there's still the occasional stupid outlier like the PS Vita that insists on having a specific shorting of the USB pins before it'll draw more than 500mA. I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

Apple vs. Other Devices

[coolmoose25]

I'm an Apple Abhorrent... I don't use any of their products, not even an Ipod. I'm an Android/Windows guy. But my daughter decided she had to have an iPhone and bought it with her own money. I have one of those little plugs you put in a cigarette lighter in the car. My car has two up front, one that is ignition keyed, the other is always on. The dongle is in the one that is always on. And I have a standard USB cable to charge phones and other devices from it. It charges all of my Android phones fine. It charges the GPS fine. It charges pads like the Galaxy Tab and the Nexus fine. It won't charge my daughter's iPhone, even with her white Apple USB cord. To this situation, my daughter tells me that the little dongle I have is a POS. I smiled and was reminded, yet again, why I won't buy Apple products.

Re:Apple vs. Other Devices

[dprimary]

I have never had any problems charging any apple product with a non apple charger or charging other products with an apple charger. Then again I don't buy $2 POS chargers. There might be a good reason the iPhone will not accept power from it.
Maybe you want to get out a meter and a scope and look at that charger closer before you have a car fire.

Re:Apple vs. Other Devices

[coolmoose25]

I only paid $1 for it, you insensitive clod! Seriously though, the thing has worked like a charm for over 2 years now... no car fires. No zombie apocalypse. Works for everything except Apple... hasn't damaged any device plugged into it. ...but yeah, it's the usb dongle that is the problem...

Re:Apple vs. Other Devices

[rjr162]

I also have a 1.5A cigarette light.. errrr "Power Port" charger that will charge my gt-i9300 S3 just fine but will NOT charge my wife's international Note II. It will for a short while if she's using it, then the phone will start making the charger connected sound over and over. The only way for it to charge her phone is to turn the phone off. The Note II just pulls too much power with the screen, battery etc and seems to overheat the charger. (Not that I'd expect this to happen with an iPhone but thought I'd share)

Re:Apple vs. Other Devices

[gl4ss]

the properiaty stuff is in the cable, it should charge. maybe it expects the datalines to be in other state though than they are on your charger.

Re:Apple vs. Other Devices

[m.dillon]

I have a multitude of Apple and Android devices and a multitude of Apple and non-Apple usb chargers and power sources, and also have a little non-Apple dongle charger in the car in the front.

It all works just fine. Apple might have weird charging cables but they still have usb on one end and they've worked with the dozen or so different usb charging sources I've got in the house and in the car.

Most USB chargers only throw out 2-5W. It's gonna take a while to charge-up Apple's big batteries with one of those but it will still work just fine.

-Matt

Re:Apple vs. Other Devices

[m.dillon]

What's happening there is that the phone is crow-baring the charger down to under 2V and then mis-interpreting its own voltage sensor (on the phone) thinking that the charger is connecting and disconnecting. Might also be tripping the short-circuit detector on the charger and causing it to cycle.

That's a problem with the phone. No phone should crow-bar the 5V the USB outlet provides, particularly not one that outputs >1A. (This is using your description of the charger being hot). All USB power sources are current-limited and the devices being charged have to deal with that properly.

-Matt

Re:Apple vs. Other Devices

[danomac]

Wasn't it not too long ago that there was an article here about how Apple is locking out unauthorized chargers on new iPhones? In other words, it absolutely refuses to charge unless it's an Apple branded charger.

People here sure have short memories.

Custom cables are almost always unnecessary

[sjbe]

Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

Exactly why I avoid devices with weird custom cables whenever possible in consumer electronics. It's been my experience that unless a custom cable is so popular as to become a standard itself (like Apple's Lightning) that eventually you are going to run into a problem. Furthermore it adds to the cost of the device (custom cables = $) and it usually means that the company making the device had lazy and/or incompetent engineers. Now admittedly the USB spec is pretty flawed, particularly when it comes to power, but even so I've still seen lots of devices that could have used standard USB (or Firewire etc) had they taken the time to do so.

Now sometimes the standard needs to be updated. I think USB should be beefed up to handle up to 100 watts with all due haste.

Bear in mind that my day job is to run a company that makes custom cables. Think about that. I make a living off of custom cables, have the ability and equipment to make a copy of pretty much any cable, and I still think they are a bad idea for most consumer electronics.

Re:Custom cables are almost always unnecessary

[toddestan]

I think it could be done, but the computer would have to smart about it, and the devices would have to do what they are told and not draw more power than the host tells then they can. The PC would know how much total power USB devices could draw, a device would request an amount of power up to 100W from the host, and the PC would then decide how much power the device could actually draw. The device would not be allowed to draw more than that. My guess is that in most cases, only one device would be able to draw the full 100W at a time. More than that would mean that not every device is getting the full 100W it requested. And that would be on a desktop, a laptop may only allow something like 20W total to begin with.

However, in the real world I would see too many problems with devices (and hosts) that wouldn't follow or implement the spec properly for this to work reliably.

Re:Custom cables are almost always unnecessary

[sjbe]

However, in the real world I would see too many problems with devices (and hosts) that wouldn't follow or implement the spec properly for this to work reliably.

You could make the exact same argument about pretty much any spec. There is always the possibility that someone will not implement it correctly and the market tends to weed out those devices. There is no insurmountable technical problem in doing 100 watt USB. There would need to be some changes in the controllers and the cables would have to be beefed up to handle the extra power but those are pretty straightforward problems to solve. Furthermore it would allow laptops to be powered by a USB cable instead of having to carry a power cord and transformer. It even makes wiring a building for DC power feasible at the consumer level. Picture having your outlets with on AC outlet and on USB DC outlet that can supply up to 100 watts. That would solve a lot of problems.

Change the spec

[sjbe]

I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

The answer is not a different gizmo to work around existing limitations in the spec but updating the USB spec to reflect real world conditions and handle more power and handle power more gracefully than it does now. There is some evidence that this might occur in the near future.

You don't need it

[koan]

I'll tell you the fastest, the USB wall wart plugged into the wall outlet.

Then turn it off while charging

[Marrow]

You probably arent using it then anyway.

Use a simple voltmeter

[sl4shd0rk]

This is /. after all. http://www.accesscomms.com.au/reference/usb.htm

Re:Use a simple voltmeter

[Khyber]

That isn't going to tell you how much power that port is capable of outputting or will output.

Bad phone design

[DrYak]

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level.

If you need a portable fusion reactor to power your tablet and/or phone *while it is sleeping* then there's something really wrong with your device.

(Bad hardware design, bad OS power management, or you installed too much background shit).

Cheaper alternative ($6)

[Ptur]

http://dx.com/p/usb-av-usb-power-current-voltage-tester-translucent-blue-silver-235090

Re:You should care more about safety...

[m.dillon]

Two-prong chargers just synthesize a ground. Well, there are two grounds actually... one for the AC side and one for the output side. On the AC side its the average of the AC sine wave between the two prongs taken off the middle of the rectifier. The charger's output is traditionally isolated with a transformer (a small transformer on the output of the switching power supply instead of a big one on the input), which isolates the output and also handles the flyback function for the switching power supply. The feedback circuit is traditionally isolated with an opto-isolator.

So the output side's ground is separate and isolated from the input side's synthesized ground. Which means that the output's ground will float to whatever it is connected to (which is what you want it to do).

The difference between the input side's ground (which is completely internal to the charger) and the output side's ground (which is exposed via the USB connector) is called the common-mode voltage differential. Obviously there are limitations since too much of a differential between the two grounds will cause arcing crossing the physical gap and/or transformer insulation. Most circuits are designed with insulation and gaps large enough to handle at least 600V of common mode.

(Common mode can be experienced directly by touching the 'ground' of a coax cable from your cable provider or touching phone wires whos 'ground' is the C.O. several miles away. The tingling you are feeling is anywhere from 60V to ~300V of common mode difference between the ground where the signal was generated and the ground your body has floated to... typically closer to the ground that your home is anchored to).

-Matt

Re:Let's talk

[wiredlogic]

USB has been amended many times over the years. You can't expect to plug into a 1.0 port and have modern features only developed within the last few years. Likewise you can't expect optional features such as 2.1A power supplies to be universally deployed. The only real problem is that charging ports aren't consistently labeled or color coded.

nobody else mentioned

[gzuckier]

If you can solder usb male and female connectors adafruit sells a 5 led 5 amp indicator board with connectors kit for $4. Or you guys who want accuracy can just buy a usb breakout board from them

Troll for parent comment.

[jo_ham]

I'd be very interested for someone to point out what part of the above comment is worthy of a troll mod. Or have we totally jumped the shark on what that particular mod option actually means?