PA-30 External Power Mod?

[Frank Brunot]

I'd like to use an external charger to keep the battery in top condition, but the way a PA-30 is wired, the Master Switch must be ON in order to energize the External Power Security Relay and the Master Relay. This in turn powers ON several items in the plane.

Since the External Power jack becomes "hot" when the Master switch is ON, and the plane is flying, would there be any adverse effects to running a #4 cable directly from the Ext Pwr jack to the battery, bypassing the two relays, in order to use the jack to charge the battery on the ground?

[Charles Schefer]

I've considered doing this but have elected not to. My reasoning is that a battery being charged (or battery tended) should be done in a well ventilated area. The battery box in our aircraft does have ventilation tubes but I believe they are designed to provide ventilation when the aircraft is in motion being operated. I have a new Bogert battery box with new vent tubes and a sealed AGM Concorde battery but still - I think it's best only to charge when the battery is in the open, not sealed in the battery box - other's will disagree.

I will also note that I've heard that some Comanches are wired such that the external power port (GPU plug) is always hot regardless of the master battery switch position. Mine is like yours - when the master switch is on a relay connects the GPU port to the battery.

If it's helpful to you check out this thread here on the forums -> viewtopic.php?f=94&t=7747&hilit=battery+charger

In that thread you will find I posted the instructions / comments of Dr. Mike Schloss who is also an A&P / IA. Mike provided instructions for doing it in what he claims is an FAA legal way. Again I choose not to do this for the reasons stated. I pass this on in case it's helpful to you.

- Charles

[N3322G]

My approach to keeping battery happy is to fly pretty much every week whether there is somewhere to go or not. Change ships battery every 4 years. Lycoming recommends regular flying to keep engines happy anyway and I get to practice landings. Except for stupid owner tricks, battery has not failed except in 46 years when both alternators died on a single flight and even then, turned off everything and it recovered enough to put the gear down.