I want to build a 12volt emergency lighting system for my house with some old car batteries that I have. I'd like it to be when main power supply fails, it switches to emergency lighting of the batteries. I will be building a grid throughout my house to do this...it's going to be a lot of work since I will be placing lights pretty much everywhere, even on the staircase, on every step..... Any tips and/or suggestions?

Also, my cell phone (nokia 6230) is having problems in charging the battery.....it charges it up and depletes it in around 17 hours... I know it's not the battery because I have bought 2 brand new ones and the same problem.... When I checked the voltage being supplied to my battery from the cell phone when charging, I got 2.8 volts. My battery says 3.6v 850mAh. A friend I have told me that its probably the power regulator in the phone...is this easy to fix?? Thanks a whole bunch!!

No it's not easy to fix, you'll probably need a new phone. The emergency lightning system can be pretty simple. Just use an AC relay that has a normally closed contact for the main battery so that when the relay loses power it will switch on the battery output. The charging system for the main batteries can be as simple as a basic DC wallwart that outputs 13.5 volts with a decent current and run that off of an appliance timer so that it turns on every few hours for a few minutes to float charge the batteries. The only thing that would really require electrical knowledge is the relay, and that's hardly complex.

One of several things to address - that you've provided proper overcurrent protection so that the capacity of the wiring is not exceeded. While 13.8 volts isn't much the high levels of current available can cause fires or otherwise dangerous conditions. You might do this with a properly sized fuse or breaker at the batteries then fuses where wire size is reduced - possibly at points of use.

This is not as easy a project as it might first appear. A separate 12VDC lighting system feeding the whole house will first have to have a properly sized central 120VAC to 12volt DC power supply. It's current rating will have to be rated to handle every 12volt lamp in the house at the same time (how many amps, a lot??). Also the wiring may have to be a much large gauge then you might imagine to handle that load current without dropping too much voltage. So you really need to do some front end calculations to account for the total load required to properly size the AC power supply, battery amp-hour rating and the 12VDC house wiring.

After that it's pretty straight forward. One 120vac relay (with contacts rated to handle the total DC current requirement) can handle the normal/emergency switchover as well as charging of the battery when normal AC power is good.

Good luck

Left.

I've used these batteries for lighting....using car headlights which suck 55watts each and they have lasted about 2-4 hours....so I'm guessing that many little lights which are 2-5watts each should consume about the same.... 1 hour of electricity would be sufficient....