Slashdot Mirror
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!"
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)
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 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.