Desktop PC plugged into a car battery!

[Jeff Varga]

I want to bring my desktop PC into my RV. Just to see if it could be done, for cheap. I understand that I could go buy a pure sinewave inverter for about a thousand dollars. But that would just take the fun out of it. And I am not sure what would happen (to the PC) if I were to use one of the less expensive inverters that use a modified sinewave. <p>There are 420W UPS's at the surplus store for 25 bucks. The batteries are dead. I was wondering if it were possible to use the RV's 12VDC system to power the UPS and provide "backup power" for an extended amount of time? Should I take the time and money to figure this out, or are there obvious pitfalls that I am overlooking?

[JdOwNj]

I run my comp for hours like that in my car... it records data on the quarter mile.... Just make sure that the UPS board doesnt get to hot... you might need a fan to cool it.

[Chris Smith]

Also, thousand dollar convertors were in the last century!!! Circa 1990? You can purchase them now for under one hundred bucks, [even $40!] including pure sine wave. You can also hook up a one to one saturation core transformer for sine wave clean up and voltage maintenance. They cost around 60 bucks. Fans and cooling are prudent for extended use.

[cmcduff]

Another option, if you are going to be using the machine just on 12 volts, that is not switching back and forth from vehicle to house mains, is to change the power supply in the computer. KeyPower (www.keypower.com) sell various AT & ATX power supply that accept DC voltage input (12V, 24V & 36V). This would save multiple conversions (Just 12V --> Computer Power) not (12V --> 110V --> Computer Power)

[Jeff Varga]

It'll be a permanent install. Using a DC to DC PS for the PC would seem to be the most efficient as well. Allowing the computer to run longer between charges. I could then use the UPS to just power the monitor. In the future, to further save power, I could get an LCD monitor. I believe they use 12VDC as well.<p>Thanks!

[jollyrgr]

The inverters are not that expensive! Locate a UPS that no longer works that is capable of supplying the power needs of your PC and monitor. The 425 systems you mentioned should do nicely. Make sure it is a 12 volt "battery" system. (If you are lucky you can open the units up and see. Some can be opened to replace the batteries by removing a couple of screws from the bottom.) Now you will need to make a couple of modifications to the UPS. <p>First, REMOVE the dead batteries and RECYCLE them. Do not simply add them to the land fill. Radio Shack recycles old batteries. If not, drop them off at a proper recycle center.<p>Next connect heavy gauge wire (a high flex battery jumper cable is a good source) to where the batteries used to go. Be sure the wire gauge is at least that of the wire used to connect to the batteries. Run these outside the case. You will attach these to the 12 volt DC system of the RV or to a marine battery. Removing the original AC cable (if permanent) or the IEC connector makes a great location for running the power cable out.<p>If there are no vent holes in the UPS, drill a large number of small holes in the case on either side of the UPS to provide ventilation across the heat sinks. Mount a 12 volt muffin fan inside the case to increase air flow. If there is not enough room, simply mount it to the outside of the case and run the wires inside. Connect the wires to the 12 volt source (where the DC power enters the UPS). This is about the only problem you overlooked. The UPS is designed to supply power only long enough for the PC to be shut down or until the battery dies. In either case this is normally a very short time. You will need to dissipate the excess heat. Adding holes and a small muffin fan (salvage one from a dead computer power supply) will help.<p>Depending on the brand of UPS you may have to trick it into "cold starting" (starting without AC first being supplied). On some models you hold in the "test" button until the UPS beeps. You then release and immediately hit and release the button. On other UPS's the Piezo buzzer will constantly beep to alert you that the UPS is on battery. You might want to unsolder one leg of the buzzer to stop it from annoying you. Or you might want to add a switch so you can silence it as needed.

There you go! A power supply that was DESIGNED to run a PC from battery!<p>[ January 17, 2002: Message edited by: Jolly Roger ]</p>

[K8YS]

Your desktop computer uses a switching power supply, and a switching supply does not care if you feed it sine wave or pulsating dc.
I run a desktop on a UPS that used a 12v cell. Check the UPS before you look for a dead one, as many are 24 or 48v and not 12v.
Bob

[HomeBrew]

These days inverters are everywhere. You can pick them up at Wal-Mart starting at 140W to 600W for less than sixty-dollars. They do a pretty good job on most computers and have low-voltage shut down built in. There modified-sign wave and can introduce some noise in analog equipment unless you use filtering.