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!"

Comments

RV power

[Anonymous Coward]

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.

Appliances are the problem

[Jon Peterson]

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 :-)?

Re:Appliances are the problem

[flonker]

As far as computers are concerned:

Laptops generally have a direct DC in, but that probably isn't relevant in this case.

Google returns MPBS1 - ATX DC-DC 12 Volt Car Power Supply, but not much else. (at least for the minimal searches I've done.)

Helpful information on inverters & laptop adap

[pmyre]

I hope this link helps.

http://www.techtv.com/screensavers/wirelessandmo bi letips/story/0,24330,3393834,00.html

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!

Same as in-car mp3 solutions?

[TinheadNed]

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)

12VDC-1.5 to 12VDC cigarette lighter adapters

[[null]]

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.

mp3car.com

[Sauron23]

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.

EZ

[shepd]

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... :-)

Probably not worth the trouble

[speleo]

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.

What I did...

[cr0sh]

I got tired of this as well - my solution didn't replace all of my wall warts, but it did replace most of them.

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...

The cheapest ATX DC to DC Powersupply

[Squeezer]

The is the cheap one that mp3car.com people are having good success with:

http://www.pcpowercooling.com/products/sleekline /a ccessories/sleekline_12Vps.htm

it is $129. refer to this thread if you need help:

http://www.mp3car.com/vbulletin/showthread.php?s =& threadid=9059