Originally Posted by geebee
Multibiker, you may run into an issue with the 7812 regulator in that the input voltage has to be a certain amount above the output voltage (I can't remember the exact amount at the moment) and this point varies with load. When your battery approaches 12v you will find the regulator will shut off the output.
Recently I hit the same issue with a power supply.
Yes, you're absolutely correct. I think the spec says min. 3V differential but that's worst case. When I was testing the 7812s I tried various loads and found that the units I have maintain their output voltage (approx. 11.93V) until the input drops to 13.3V. At that point the regulator doesn't shut down, but as the input voltage drops, the output voltage drops by about the same amount.
Considering that at 13.3V the battery pack is almost 90% exhausted, and the worst that will happen is the lights will begin to dim, I figure I can live with it. In any case thanks for the info.