Charging Onboard Small Gel Cell Batteries

[tx_jayhawk]

I have a dual alternator setup, but I am also considered a small gel cell standby battery to purely power my standby instruments (elec gyro and lights). I know...I'm a belt and suspenders type of guy, so please no "overkill" comments.

Question is this...I would be interested in seeing what solutions people have employed to charge these small onboard gell cells?

I understand that you should not charge them at a rate greater than 10% of their capacity (.3 amp charge for a 3 ah battery), so that effectively eliminates the regular onboard charging system for the very small batteries.

Thanks,
Scott
7A Finishing

[Ironflight]

My little 4.5 aH Aux battery is continuously trickle charged off the main battery bus through a resistor and diode (the dioded prevents back-current from the aux battery into a dead main battery, and the resistor limits the charge current. You can limit the charge current to anything you feel appropriate by sizing the resistor properly.

Paul

[airguy]

And as we've discussed before, use a Schottky diode to keep the pass-through voltage as high as possible for top charging.