I have designed a circuit for in car use that operates at 12VDC. However I need to have the circuit have a backup power supply separate from that of the car battery. I have chosen a small 12V Lead Acid Battery. The problem I have run into is trying to charge the battery. I have been looking at charging circuits using the LM317 and so on but because of the voltage drop these won't work. The around 13V that I can get out of the cigarette lighter of the car when running should be enough to charge my battery, but I need a circuit that will stop charging the battery when it is fully charged, so I don't overcharge the battery. So a circuit that can take input of about 13V and charge the 12V battery is what I have spent hours looking for with no avail. Can anybody recommend anything or have any different advice on how to charge the battery.
Thanks In Advanced,
Dave
Thanks In Advanced,
Dave