Backup or “Uninterrupted Power Supplies” are extremely common in the computer industry. They are simply pure sine wave inverters that automatically switch from wall power to inverter power when the power goes out. The smaller 350 watt units run on an internal 12VDC sealed battery that will give a computer about 10 minutes of run time for you to shut everything down safely.
( A common 350 Watt backup power supply running off a car battery)
The problem is, the batteries are readily available, but they are expensive $25.00 – $40.00 depending on where you buy them. I pay $10.00 for a top quality battery that is removed from equipment and has more life in it than a new poorly built one. (BGMicro.com) A lot of people don’t want to spend the money and end up dumping the backup power supply when the battery goes dead.
I asked an IT friend if he would save them and I had several in a week. The problem is, what’s an inverter with a dead battery good for. I take the battery out and replace it with a short cord and set of alligator clips. Make sure you keep the polarity correct, red to positive, black to negative. That allows me to use it on my car battery or any number of good charged batteries I keep around the shop. Last week we lost power for several hours and I was still able to work with my backup power supply running some 100 Watt Compact Fluorescent bulbs (CFL’s). They use 23 Watts each but put out 100 Watts of light.
Make sure you use a heavy wire, twice as heavy as what the inside wire running from the unit to the battery should be fine.
A large truck battery with a 350 Watt inverter will comfortably run two 100 Watt CFL’s, my laptop and a small boom box for music for hours. When the power comes back on, simply recharge the battery until next time. If it’s going to be a day or two, use it sparingly and charge the battery from a vehicle or use the car battery to power it, starting the car on regular intervals to charge it. Just make sure you don’t let it drop to low.
I also scored at the battery store where they had some inverters with dead batteries they didn’t want. The local computer store gets them all the time and often upgrades the client to a new unit.
The only down side is some of them beep. I disconnected the beeper on mine, but you can put it somewhere else and run an extension cord.
These things are everywhere, particularly yard sales and thrift shops. Even if you paid a few bucks for one, it’s still one of the best deals around.
Let me know if you like this type of story, I have a bunch more.