Aux battery charger

[elippse]

I have a circuit that I am using in my plane to charge the auxiliary battery that approximates an "ideal diode", that is, it allows current to flow in one direction and blocks flow in the opposite direction and has almost no voltage drop. That's right; once the battery comes up to voltage the voltage drop is about 0.02V-0.03V, not the .35-.55 V drop of a Schottky diode so the battery gets up to full charge. It also incorporates a current limiter of about 2A so that you won't ruin the aux battery if it is discharged and you connect it to the main battery with the diode.
I had two occasions of this where the discharged aux battery, connected to the well-charged main battery, had so much current pumped into it that it went open, which is the reason I designed the circuit. It turns out that the aux battery was supplying keep-alive power to an avionics unit which would drain the battery over a few weeks time.
I will e-mail the circuit diagram to anyone who will, in turn, post it on this forum. BTW, you might check your aux battery to make sure it is really charged and hasn't gotten overcharged and opened up.

[Ironflight]

Here you go Paul:




Paul

[elippse]

OK, folks! Here's the schematic for the aux batt "ideal diode". I made mine on a copper-plated circuit board, either single-side or double, about 2" square. The parts cost should be less than $20 from Digikey. If you want, I can take a picture of it and see if Paul will post it as he did with the schematic.