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Providing 12V Power to RV-Based Hardware?
jp93023 asks: "I am putting together a mobile computer lab in a converted RV. RVs have a 12v DC system for running most interior lights, built-in appliances, fans and so forth. They have a parallel 120v AC system for providing normal outlets, which is great when you are plugged in. It strikes me that when I am running from battery power (which will be most of the time) I will be expending precious watts converting the 12v from the marine batteries up to 120v, only to convert it right back down to 5, 9, 12, and 20v DC for all the PCs, laptops, etc. The equipment package will include desktops, laptops, digital tape decks, etc., so I'd be planning on bypassing the built-in transformers for everything but the laptops. Have any slashdotters put together a unified low voltage DC power distribution system for such a situation? Would the power savings be worth it? Any pointers to products or plans would be great!"
In my experience, you can simply run direct current (dc) from the battery or the cigarette lighter plug to wherever you need it while using the RVs AC inverter system at the same time. Shouldn't be a problem or need for special solutions. Just run the lines wherever it is convenient and use both DC and AC.
Hi,
:-)?
If the RV situation is similar to the boat situation, then the existing DC system is fine. The issue is getting appliances that expect DC input from the wall rather than from their own little transformer. I would be wary of taking 'normal' appliances and chopping the transformer off and sticking the wires into your DC system.
You can buy power tools, radios, even microwaves designed specifically for use with boat (and, I assume, RV) DC power systems. I'm sure the range is restrictive and maybe they are expensive, but they work.
However, an RV has a big old engine, right? So you aren't likely to be short of power, really, right? So why not just use the AC system and forget about the inefficiency
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I hope this link helps.
o bi letips/story/0,24330,3393834,00.html
http://www.techtv.com/screensavers/wirelessandm
Peter Norton showed a few laptop adapters (to charge bateries on 12v) and some inverters (12v to 110v).
For my personal usage (RV & travel) I will select the inverter, I just think it's more versatile. You can plug a boombox, recharge your GPS, recharge your cell phone, your PDA,... You just don't need to purchase a bunch of adapters.
Without an inverter I would be very afraid of the 'quality' of the electricity.
If you build your own solution, please let us know!
If all you want to do is power a computer from a car battery then just visit the DIY in-car mp3 player websites. There's pages on how to make a DC-DC inverter (not DC-AC-DC) that is designed to power ATX motherboards (so it provides 12V, -12V, +5V etc.)
I hate to be the first person in an Ask Slashdot thread to say search on google, but that's where you'll find them. Unfortunately right now I can't connect to google for some reason, but I'll post the URL to the supply I'm thinking of (and attempting to build incidentally)
Assuming you're running stuff that wants less than or equal to 12VDC, you might want to get and modify the "car power adapters" such as RadioShack adaptaplug. Keep an eye out for stuff with wall-warts that convert 120VAC to stuff 9VAC (like those Linksys Cable/DSL router/switches). Sometimes, though, you'll find some equipment that has an AC plug but a DC conversion internally, or stuff that doesn't care if it gets AC or DC. However, you don't want to test this experimentally unless you like releasing magic smoke or blowing things up. It's better to consult someone with electronics knowledge, or the manufacturer, first.
try here, here, and here, if you haven't already read them.
Will the computers be used when the RV is moving? If not, then why not simply buy a portable generator and use it to supply the AC power? Portable generators are very popular among the RV crowd, so I'm sure that you can find lot's of information on their use (such as here).
There are probably solutions for mounting and wiring the generator so that it can be used while the RV is in motion, but that sounds like a much more difficult problem and may be more than what you need.
This took me a long time to find as after all that google doesn't list it directly, but try here for what you're looking for.
mp3car This link is to the forums, check under power supply. You might look at LCD for low power and small displays. They should have what you need. enjoy.
I would be very afraid of the 12V coming out of the cigarette lighter adapter - I heard a story of someone working away on a laptop just fine using the car's 12V battery system and the car ignition turned off. However, they had their laptop fried when they turned the car ignition switch on. It send some crufty power through the cig lighter and into the equipment.
"I figure you're here 'cause you need some whacko who's willing to stick his finger in the fan. So who are we helping?
If battery conservation is important, stay away from the inverter- a large portion of the power will go away as heat- look into switching power supplies, which can run up to 80-90% efficiency. Look through surplus catalogs and so forth, buying them factory new will probably be prohibitively expensive, but they can be quite reasonable in surplus.
Also, try to stay away from linear power supplies- they also will convert a lot of your precious power to heat.
Running a desktop computer off a 12V system looks to be pretty easy at first, especially when you look at the common voltages (+/- 12, 5, 3.3V) But the problem starts when you look at how much current each one of those voltage rails use, it's pretty amazing- 30, 40 amps is not unusual.
With lower voltage DC supplies, you have high currents for the same amount of power delivered, so you're also going to want to use pretty thick wire to distribute the power around. This will minimize the loss of power to the resistance of the wire.
...because this is a project that a lot of amateur radio folk undertake in building emergency communications or stormchaser vans. Most amateur radio equipment runs on 12v DC, and these vehicles also usually pack a number of computers for digital text communications modes, processing weather info and satellite tracking.
Suggested keywords: "communications van", "emergency communications", "stormchaser", "RACES", "ARES"
-=Maggie Leber=-
This will (very easily, somewhat efficiently, and with with great accuracy) convert to all those voltages except 20V. A DC-DC step-up convertor (I don't know a part number off the top of my head, sorry) will do that for you.
:-)
Using that IC is a _very_ easy way to get started in an electronics hobby. Try it...
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
This would be far more useful to me as a way to replace the vast array of wall warts and chaotic tangle of black wires which warm my feet.
I'd chop off the devices' wall warts and replace them with some sort of quick-disconnect plug on both sides of the cut wire; this way I could use the wall wart again if I was out of this environment.
EE's, help me here. Let's say I have a single 24VDC bench supply (I'm starting at 110v at home)at 15-20A. I'm thinking that for any item drawing under, say, 500ma, I could build mini step-down regulators (in something like 35mm film canisters) using something in the 78xx series of regulators (i.e. 7805 for 5v). I'd put one of those quick disconnect plugs (mentioned above) on the output, so it would easily and quickly interface with the device.
As for the input to these regulators, I'd like to be able to run one 6-ft. wire around my equipment and let the regulators somehow "vampire" tap (I *think* that what it's called) this one wire (perhaps 12 gauge stranded? thicker? help?!), so the number of wires around my setup are drastically cut down. Is this realistic?
I definitely need input here, so please -- someone in the know reply and correct my errors here. I'm specifically concerned with my lack of knowledge in DC power distribution and power loss, not to mention if anything would be likely to leak power back into the regulator somehow.
This is likely more trouble than it's worth.
In automotive applications 12V is really 13.8VDC when the engine is running and anywhere from 11 to 13VDC when running off the battery.
I have an RV I use as a mobile office with computers and such, too. I just use regular inverters and the generator and have all the equipment running off standard off 120VAC UPS units.
Be aware that some inverters and generators produce a square wave AC output that is bad for some equipment (especially laser printers, I hear).
There are many RVer sites on the web with more info. Check out these sites and their message forums to get started: irv2.com, rvnetwork.com, rv.net.
I have a Laptop with a 12 volt power converter. I used this so I could drive around with friends and finger 802.11 networks around DC. Now, I got this converter from the manufactur. you shouldn't have a problem doing that for laptops. for PCs, you might need to swap out the power supply for a 12 volt one. Look around marine hardware suppliers for that, and get a soldering Iron.
The biggest problem will be with monitors. plasma and flat screen monitors are easy. just get a power converter that converts 12v to 9v or whatever the displays use. CRTs need the 120 volts, because they have that huge electro-magnet tucked in there. so, if you can afford it, use flat screens
Sig (appended to the end of comments you post, 120 chars)
Tread carefully here. You can go to any truckstop and buy a 2000W inverter for about $300. If you were to buy a 2000W inverter to power your home with all its expensive electric appliances from batteries (PV, wind, etc.), you're gonna pay $2-$5k for the same output, especially if you go true sinewave. Power quality is one of the main things you buy from these systems.
Yes, I know, there are many other things in those fancy inverters that also push the price: grid intertie, overload/temperature monitoring, battery charging/conditioning, data loggin, etc.. However, the old saying "you get what you pay for" usually holds true for inverters.
That said, I frequently run a laptop off a $30 400W inverter I got at Wal Mart and I haven't had any issues yet. But I disagree with the parent post's implication that an inverter would provide "quality" power.
Method of processing duck feet
First off, realize that most electronic equipment that uses a wall wart typically has a regulator in it anyway - ie, it may use a 9 volt wall-wart, but it has a 5V regulator in the device. So, basically if you can get a power supply with a 12 VDC line, and a 5VDC line, you are set. You then would have your pick of three voltages - the two already mentioned, plus 7VDC by using the 5VDC line as "ground" with the 12VDC line (this really isn't a great thing, not electrically sound, but I have yet to see anything fail because of it - but if you know of any problems using this kind of system, let me know). So, what power supply to use?
You want a PSU with the two voltage lines and ground. The power supply should provide relatively high current capacity on the lines. As a bonus, it would be nice to have extra lines for minor low-amperage things like fans and an LED indicator light. So, what did I use?
I used a switching powersupply I found used at a local electronics junk yard - it was a Sun power supply (not sure for what model, maybe and IPX/IPC). I mounted the PSU on the bottom of my desk (a cheap folding table), and ran wires (12 or 14 gauge auto wire, I think) from the power output lines to several "bus" terminal strips on the underside, in parallel. From the bus terminal strips I could tap into the power where I needed it. The power supply also had a couple of smaller connectors - one provided 12VDC and the other 5VDC. I hooked the 12VDC one to a fan I have mounted on my monitor (it gets hella hot without it), and the 5VDC went to an LED I have mounted in a hole in metal edge of the folding table, to show that the PSU is on.
While this isn't as clean as what you are proposing, it was all mostly off the shelf, and was easy to set up. The terminal strips used screws, so it is easy to hook into, plus the switching PSU should have a cleaner output than most wall warts...
Reason is the Path to God - Anon
If you are trying to enjoy your mobile computer lab in the country, running the engine (or even a generator) largely defeats the purpose of being somewhere peaceful and unpolluted. (The author did not say if he was working on vacation or touring schools and other events, so this might not be a factor.) The other detail is that most RV 12-volt electrical systems are run off the engine alternator, which probably puts out 150 amps for an extremely heavy-duty unit (typical HD is 70 amps). That's not going to run very many computers (1800 watts is only about 7 19-inch CRTs), so you can't run off the RV's engine very well; avoiding losses in the inverter is probably a smart move. A quick search found an ATX power supply which accepts 12 VDC in, and would probably be fine for this purpose.
Scientists restrict study to entire physical universe; creationist
The is the cheap one that mp3car.com people are having good success with:
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http://www.pcpowercooling.com/products/sleeklin
it is $129. refer to this thread if you need help:
http://www.mp3car.com/vbulletin/showthread.php?
Does the name Pavlov ring a bell?
If you're not, there are plenty of replies already here for you - get a cheap horribly polluting inefficient genset, run your RV motor all the time, etc. More gasoline = more dollars for Wahabi = more terrorist actions by Islamic fundies, but who cares as long as you've got Microsoft Solitaire?
/. crowd's disregard for anything beyond immediate gratification, sorry.
OK, I topped out my own irony-o-meter on that one. But I get pretty tired of the
Anyway, if you want efficiency, and you're handy, check out Home Power Magazine. The current edition has an article on choosing a laptop for low power consumption.
In your RV, you can use a standard laptop car power adapter, or you can build your own. Both my laptops run on DC (they have transformers and converters built into a pod in the middle of the power cord) and although they use odd voltages (14.5 VDC or something like that) I was able to get a DC/DC converter at the local ham radio store.
I have heard that some laptops do the AC/DC conversion internally, so if you have one of those you'll either have to crack the case open and add a connector or you'll need to sacrifice a battery pack to make a "fake battery" containing a simple voltage regulator circuit or else just a jack that you can connect an external PS to.
If you go the "fake battery" route don't be fazed by all those crazy connection points on your LIon battery pack - all but two of them are usually for charging the battery (to equally distribute the charge to all the cells) so you don't have to hook those up - just the two off by themselves, and you can use a cheap $20 multimeter to find polarity off a good pack.
Oh, and be careful if you dissect a battery pack, and dispose of the cells properly. Supposedly some of the laptop cells can blow up if you short 'em out (not sure if I believe that, but better safe than sorry).
Good luck!
---I live in an RV that is totally off grid. I pull an AC feed from my neighbors large 24 volt DC solar array, that has inverters tied into it that provide 120 and 240 VAC,, plus I have my own DC 12 volt solar setup. My small setup has three PV panels, a trace C-40 charge controller, with 4 6-volt deep cell batteries. I ran all new circuitry for my own juice I make. I run my laptops off of it, plus all my lighting. My 120 AC desktop I run from the feed I ran. Pulled the front passenger seat out of the rig and have my tiny computer office here, 4 computers setup, plus some radios and a small TV, etc. Some are 12 volt, some are 120 AC. The onboard converter "works", but as you mentioned, it's inefficient. My desktops I run on the provided AC feed, which measures a pretty constant 119.5 volts AC, heckuva UPS, yes it is.
You could adopt the RV's alternator to charge your large battery banks. If you have a built in genny, like I do, it's probably an AC alternator, so either way you'll be doing inverting and convertine. You probably have a 100 amp alternator, or something like that the RV's engine, but the voltage regulator is the problem, you want to occassionaly run an "equaliser" cycle for the deep cyckle batteries, for that, you need a much higher DC voltage than normal. You might could get by using an older like chevy manually adjustable external voltage regulator to do this, then just use your meter to run the voltage up to around 16 volts or so, instead of the normal 13.2 or whatever the alternator is set at. You would still need the charge controller, the most important piece of hardware, as batteries are quite picky on how they get charged if you want them to last. Panels put a variable voltage, it fluctuates, it can get as high as 20 volts from an alleged "12 volt" panel, so you really need that charge controller.
Now, AC power. Really, the modern good quality inverters just aren't that inefficient, check them out.
Here is my solar/alternative energy provider, owner's name is Roy, he has a generic question form on his main page for specific questions, feel free, and etc.
http://www.four-winds-energy.com/
If you want to see the large system I pull my AC feed from, go to this page,I don't have a pic of my RV solar rig, but if you scroll to the middle of this page and see the "mountaintop in georgia" pics and specs, you'll see some of Roy's work. He's quite knowledgable on this stuff, been doing it for years. He can fix you up with a mobile RV rig, to any specs you want.
http://www.infoblvd.net/4windpwr/about.html
Goodluck, hope to see a follow up slashdot article on what you wind up with!
---zogmeister
If you want to down convert the 13.8 volts that is standard in most vehicle power supplys the look at the 79xx and 78xx series of voltage regulators, whilst not as efficent as some of these super duper adaptors on the market they are easy to use there is also the LM317 adjustable voltage regulator for those odd voltages. I am not sure about in the US but most electrical hobbiest store should have data and application sheets on these devices here is a link to a dc-dc converter primer http://www.jaycar.com.au/pdfs/dcdcconv.pdf and this is a link to info on voltage regulators http://www.dse.co.nz/cgi-bin/dse.storefront/3d6431 9c00d7ecca2740c0a87f99073c/Export/catalogs/DTA0000 021.
Beware of some of the cheap plug in type converters as they only use resistors. I find it amazing that you can not buy decent equipment off the shelf in the US as there is plenty of demand for it I would have thought.
Anyhow I hope these links help