A few years ago when I was 14 or so I bought a small power inverter. It was only 120 watts and I never really had a use for it until one day during a snow storm our power went out. Bord I remembered the little inverter and thought... I hooked it up to an old car battery that was in the Gage and was able to run a lamp with a 40 Watt bulb and my TV and was able to watch television for a couple of hours before the car battery lost power. About four years ago I was stuck on a job site with no power. I had 18v Dewalt cordless drills so I was able to work but eventually after a few hours the batteries would die and I would have no way to drill holes for the wiring I was running for the house. And since the job site was well over an hour from my home I wanted to get as many hours in every day to make the trip worth while and I had a deadline to meet so the other crews could do their work. When at Walmart I walked passed the car care isle. I picked up a small 700 watt power inverter and went to the local junk yard and picked up a couple of salvaged car batteries. I brought the batteries home and charged them. The following Monday after lugging the batteries up the four flights of stairs and hooking the batteries in series (hopefully so they'd last longer) I connected the inverter up and plugged the Dewalt charger in to recharge the first 18v battery that went dead. It was sweet. I was able to work from dawn to dusk and keep the batteries charged as I worked and even attach a work light and a radio up to help with the boredom. Since them I bought a 5,500 watt gas generator and it worked great, but it wasn't always practical to lug it along all the time for short jobs. I then purchased a 3,000 watt power inverter for such things as running a jackhammer or floodlights and was more then pleased. I'd often just run it right off my truck battery for these short jobs. I'd have to either leave the car running or start the truck when I heard the warning chirp from the inverter warning me that the voltage was dropping too low to start my car... Great feature otherwise I'd be stranded. It's late and I'm bored but I was wondering. Is it possible to set up an alternator to a small motor. Most modern alternators have built in power regulators to prevent overcharging the battery. Allot of you guys come from different walks and I admit that I suck at math and pulleys and such are out of my scope. I'm not sure if it would be more efficient to run the motor off the inverter or the battery. My thought would be it would be difficult to find a strong enough and reliable enough 12v motor. So I'm thinking a 1/2 HP motor running off 120v would be more reliable though I'm going to lose a few watts off the inverter. And if you adjust the size of the pulleys the motor won't have to work as hard to turn the alternator and produce power. And if the alternator is working hard to keep the batteries charged it's going to require more torque and at the same time run at high enough rpm. Next is an alternator. I need to find one strong enough to keep the battery charged even if I'm drawing the full 3,000 watts off the inverter. I'm not sure of what the requirements are. Though there is a formula for figuring out how many volts/amps are needed from the battery supply depending on how much draw you are using on the inverter. Can you see what I'm trying to do here? The inverter in general wouldn't be practical for long term home use since it doesn't produce a "pure sign" and the inverter itself would produce interference. But for a job site or just out camping, power failure or whatnot it's nice to have. Extended use (days on end) I'd imagine would burn the inverter out. I don't want to go out and just buy a motor and alternator. I'm looking for ideas on how big of a motor and alternator along with the what size pulleys to use on the alternator and motor to make it efficient. And since the size pulleys can determine the rpm's... It's a bit confusing to me to say the least and this idea has been rattling around in my head for over a year now. Advice would be cool. Here's a pic of a similar power inverter.