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DC Power distribution - Nix the Transformers?
MailtoDelete asks: "I have most of my electronic gear plugged into a couple power strips hanging off a UPS. Most of these devices have big block-type transformers which, besides being bulky, are a bit of an eyesore. I have been trying to find a product out there somewhere that would allow me to have one central transformer that would distribute DC power at variable voltages, depending on what devices I wish to plug into it (think one AC input and 9 or so DC outputs individually adjustable). I found this device that resembles what I have in mind, but it does not have sufficient output for my router, switches, and various other devices. Is there a product on the market already that would do this? Can I build one with my marginally above average soldering and electrical schematic skills? Have any of you found a better way to eliminate these blocky plug-hogs?"
"This is Reddy Kilowatt, reporting a dangerous, overloaded octopus connection in sector five!"
"Flyin' in just a sweet place,
Never been known to fail..."
The device you're looking for is a power supply -- they're not just for computers. Just get one that will put out enough amps for peak demand on all your devices, mount some molex connectors onto a board of some sort, color code them by their voltages, and stick the whole shebang in an old PC case.
Of course you'll have moved from a bunch of smaller blocky transformers to a large honking thing with a fan, you'll have to wire up your own cables. Watch that you don't overload it, or you let out the magic smoke and none of your devices have power (and you'll be ventilating your room of noxious fumes). And none of it will be portable. It's going to be loud with the fan, and don't skimp on that, or it's magic smoke again.
This is probably even more misguided than the guy who wanted a raised floor.
Forget replacing wall warts with one very large wall wart.
Where is my wireless power?!
We wont be truly untethered until we have wireless power.
(Not entirely kidding. Is there any safe way to deliver wireless power? Or am I just asking to turn my house into a very large Microwave Oven?)
- For the complete works of Shakespeare: cat
Can I build one with my marginally above average soldering and electrical schematic skills? Have any of you found a better way to eliminate these blocky plug-hogs?
Sure, but you'd need a transformer with multiple sets of windings, one for each voltage you want to put out, and one for your line input... But you're not likely to find one that fits your exact needs.
Nevermind concerns about drawing too much current from your device, and failing gracefully.
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Instead of helping someone build the circuits they require and possibly learn something in the process, let's just remind them that they're only above average, and thus shouldn't even bother.
This doesn't fit what you're looking for exactly, but it fill help the problem of having to plug wall worts into your power strip. It is basically a 12 inch extension cord that plugs into your power strip so that the transformer doesn't take more than one outlet up./ SearchTool s/item-details.asp?EdpNo=392776&CatId=1284
"Get full use of your power strips and UPS outlets with this premium power cable from Cables Unlimited! Just plug this cable between your bulky power adapter and any unused outlet and this revolutionary designed space saving cable acts as a 1' extension, giving you a little extra length to get into hard to reach places."
http://www.tigerdirect.com/applications
The link you provided to the "ELK-PD9 Power Distribution Module" is telling.
Do you understand why devices such as that are used?
A power distribution module such as that is used to power devices like remote video cameras, remote security sensors, and other remote monitoring devices.
Key word being remote.
Devices such as these use structured wiring with data (video) and power coming in to the device over one cable bundle. This is done for ease of installation to the remote site, and because the security camera on your neighborhood Target store being 100 feet from the nearest power outlet makes a wall-wart is unfeasible not unsightly.
I dub thee... Sir Phobos, Knight of Mars, Beater of Ass.
Why bother? If each device has it's own power brick, it's safer. If one fails, the others won't.
If you combine all of them into a single point of failure, you might reduce what you think is an "eye sore" but at the cost of a higher risk of failure.
Is making your setup less sturdy worth a cosmetic fix?
It's designed for large scale server rooms, and as such won't particularly adapt to what you want, but this does show that others have had the same thoughts and are applying them to various niches. They do also explain what they see as the benefits of this arrangement.
http://www.rackable.com/products/dcpower.htm
...now that I think about it, so could just obtain a hobbyist DC power supply of sufficient amperage and hook all your devices up to the appropriate voltages.
It's possible that a spare PC power supply might even suffice, but be careful that you get one that doesn't detect and auto-off when a motherboard isn't plugged in.
Lots of power supplies from somewhere like this: http://www.kepcopower.com/prodmod.htm
If you do this, be sure to check for unexpected shorts. A piece of equipment we install at work has a big warning to only use it with its own power supply. Of course, it's so much easier to tie it to the beefier supply running the other panels it associates with, so many techs do just that. And it works just fine. Until...
Turns out, due to some wierd design decision, the common pin for the serial port isn't really "common". If we plug into it with our laptops, and then plug the laptop into AC power (with ground pin intact on the PS) it shorts the power supply through the serial port, the laptop ground, back to the grounded power supply on the main panel. (This little panel "doesn't require" grounding - wonder why...)
So, if your devices all connect to each other in some way make sure this sort of loop doesn't occur. Especially if you use a single beefy supply - you might be in for fireworks!
I swear reading most of these ask slashdot's are slowly killing me from the inside out.
e =CTLG&category_name=CTLG_009_001_003_000&product_i d=61-2755 , but if you want ONE DC converter with various voltages, you're just asking for trouble. An eyesore they may be, but they're quite safe for the most part and do their job properly.
If you're pissed that a block takes up like 3 ports on a surge protector, get a short extension cord like this: http://www.radioshack.com/product.asp?catalog_nam
-Adam
The PC power supply will give you the wattage/current you need to operate most if not all your DC devices. You will need to wire the power supply so that it will stay on without being hooked up to a motherboard. For ATX p/s' here is an article on how to do it.
That will give you +/- 5 VDC and +/- 12 VDC. To get the 9 VDC used by many devices you need to add some circuitry. Basically you want to use a voltage regulator to reduce the +12 VDC to 9 VDC. This can be done with as few as 1 part but adding a few more for safety is recommended. Here is a quick primer on the LM78XX series voltage regulators (your looking for a 7809, like this) .
Regardless of what some posters say this does not have to be a big ugly noisy box. You will need some sort of case with ventilation for the ATX p/s and additional circuit. The fan in the ATX p/s should be enough to cool both the ATX p/s and the additional voltage regulators. If you use a bypass transistor to increase the current output of your voltage regulator or if you run the voltage regulator close to the max current you should attach them to a heat sink.
Also, from places like Digikey (or Jayco in AU) you can by barrel connectors (like the wallwarts have) to hook up so that you can plug/unplug your low voltage cables from your spiffy new box.
Overall this is a great first project to try so hop to it. Just make sure to post all the pictures and description of your project so we can /. your server. :-)
The above is not intended as a step by step howto instruction. It is intended as a starting point to research the correct way to construct your project. Tread carefully. You can also find lots of electronics sites that probably have the circuits you want and you can post to sci.electronics for help.
Merlin.
DC power distribution is used in telecomm applications. They use a 48V bus and use DC/DC converters to get the required voltages. The DC/DC converters are expensive, and the AC->48V converter is also expensive.
You could just get auto-adapters for all your crap and then use an AC->12V converter. However, I imagine that this is more work than it's worth.
Why not just do what everybody else does and get more outlet strips?
The coils are there to provide electrical isolation. If they were left off then you'd be exposed to at least one side of the 120VAC in what may be a poorly isolated unit. The coils are large because electromagnetic inductive efficiency drops with the input frequency. Efficiency is the major reason why the switching frequency in PC switching power supplies are so high, most can get away with just using air cores rather than metallic cores.
The IC you mention is useful for completely isolated devices (no external connections) such as night lights.
As far as the things we plug into wall outlets, I think it would be very wise for all electric devices that uses a transformer to use an external transformer rather than build it directly into the device. this way, if you later switch to solar you can run the device directly off the DC from the solar panel, only perhaps having to adjust the voltage. DC is preferable with solar technology, which produces DC output, whenever possible, since an invertor to convert from DC to AC cuases you to lose energy and are somewhat innefficient. DC works best with short runs as well, such as from the panels into your house. AC for distribution was chosen since the voltages can be easily stepped down after high voltage runs, since high voltage carries better over long distances. It would be great if we could find clean, renewable, safe, practical, non-toxic energy sources, like improved solar, so we could get rid of AC and its EMF fields and all of those ugly high voltage power lines crossing the country.
The problem is efficiency. You can drop 120V to 12V on this, but that means that the regulator has to burn up 108 V. If you're drawing 1A, then that's 108W being wasted just to step down the voltage, and 12W actually being used by the device (90% wasted).
However, a transformer can step down voltage with a very high efficiency (google says 80 - 90% efficient).
A stepped down signal of 12V and 1A means an input of 120V and 0.1A, plus loss due to resistance. With 90% efficiency, that means an input of about 13W for the same output as the regulator alone.
Of course, there will be some loss due to using a DC regulator after the transformer, but nowhere near the 108W lost above.
Please, if you don't know anything, shut up. Converting from DC to AC is just as efficient as converting from DC to DC. Unless your solar cells happen to put out the exact voltage your device requires (they don't), you still need some kind of switching power supply. Whether it takes in or puts out DC or AC is almost completely irrelevant.
In the Army we used DC power for some applications, it's an nasty problematic way of distributing power and tends to be unreliable, if at all possible avoid it. If you are wondering why, it reinforces the fact you don't know enough about real-world power distribution to do it with out it cause more problems than it creates.
DC is dangerous, if you get shocked by it it holds on to you more, there is no pauses in the current to allow you to get off the conductor. DC is dangerous, generaly it needs much more current for a give power because the voltage is lower, short curcuits tend to arc-weld together; Avoid DC power distribution when ever possible.
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This, in fact, is what's happening when you have devices powered off USB, FireWire, or Ethernet. Read this discussion of how USB power distribution works.
So the parts exist to do what the original poster wants to do. But they're not typically packaged for the end user.
IEEE 802.3af aka Power-over-Ethernet and USB 2.0 both provide DC power in a standardized form factor.
USB 2.0 is good for 5.0 volts and a max of 500ma (2.5 watts) for the bus.
IEEE 802.3af is good for 44-57 volts and a max of 15.4 watts.
Many devices currently on the market, such as PDAs, iPODs, and a few cell phones will charge from USB ports.