Hi,
I have an application (a VHF repeater) that requires 12V for about a week when it's set up once each year. We've been using a leisure battery but this needs changing halfway through the week.
I'm looking for a way to run multiple batteries without needing to physically swap them over (the repeater is in a tricky location).
Firstly, is it possible (and safe) to run leisure batteries in parallel? My internet research says that this is common practice and that for well-matched batteries (same capacity, same level of charge) this is fine, as long as each battery is fused individually. I'm aware that common practice isn't often best practice.
I need to make the set-up idiot-proof, and was thinking about making a battery select circuit that, say, connects the load to the battery with the highest terminal voltage.
I am aware that a couple of diodes would be a simple solution, but I'd prefer a more efficient approach that doesn't drop the battery voltage, even by the 400mV of a Schottky (at 8A or so, during transmission).
Also, 400mV x 8A is 3.2 Watts so heat sinking becomes an issue, especially in the worst case scenario of an open mic causing the repeater to transmit continuously.
I was thinking of using a couple of high-side P-channel MOSFETs, with one or other selected by a comparator (or even a microcontroller, which could be a bit more flexible) comparing terminal voltages. Some hysteresis (and/or time limiting) will be necessary to stop the on-load voltage drop from causing the thing to oscillate between batteries.
Does anyone have any suggestions, or pointers to existing circuits, to manage two (or possibly more) batteries in some way? I would imagine it's a common problem but Internet searches haven't revealed much. Maybe people just put the batteries in parallel and have done with it.
Thanks in advance,
Andrew
0xADF