What you need is a REGULATED lab power supply that has adjustable
voltage and current adjustments. I use a 0 to 33 volt at 0 to 30
amp power supply that has digital readouts for voltage and current
that I bought surplus.
Set the charge voltage and max charge current and plug it in. As the
battery charges the supply will switch from current limit mode to
voltage limit mode automatically.

You cannot feed the power into the APU port for a long time (more than
10 minutes) or it will generally fry the APU port relay because most
are not rated for continuous operation.
Install a charging jack on an inspection panel and wire it direct to
the battery with a FUSE at the battery that will support the expected
charging current from your power supply.
For 12v systems set the power supply to 14.00 to charge overnight or
13.45 for long term float charge. Double these voltages for a 24 volt
system. These voltages need to be adjusted some what if the
temperature is not close to 70F. This voltage verses temperature data
can be found on the internet for the type of battery you are using.

You do NOT want to use a low cost common UNREGULATED trickle charger
or you will surely fry your expensive battery by over charging.
Don't take the battery caps off unless you intend to charge at very
high rates or the acid will cover everything near the battery.
John

On Thu, 17 Mar 2005 15:08:05 GMT, Kyler Laird
wrote:

David Lesher writes:

I don't suggest this lightly, knowing the BS and $$, but have you
considered adding a 2nd jack, smaller in size? That COULD be fused
at say 60A, and live. That could accommodate both a charger, or your
power-tug, with no risk to your aluminum friend...or you while in it.

Standing at the plane a few nights ago, I considered the same thing.
I've been working on blending a small charger and some old batteries
(from my electric lawn mower) to make a compatible charger.

I decided that I should add some resistance just in case one of the
batteries (plane or charger) gets really low. I don't want a sudden
rush through it. Then I realized that if I'm going to do that I might
as well just use small connectors and wire. And if I'm going to do
that I don't really need to use the high-power port.

However...using the existing power port is handy. The best thing about
it is that it's externally accessible. I can put a charger on it
without leaving the nose open. I leave expensive stuff (headsets) in
the nose so even in my (shared) hangar it's worthwhile to keep it
locked, but it's especially advantageous if I'm on the ramp somewhere
leaving the cabin and engine and heaters on.

Perhaps the answer is to bridge the relay contacts with a low-current
toggle circuit breaker? That would allow me to easily control whether
or not trickle charging or discharge can occur through the port but if
I happen to leave it enabled and a short or reverse polarity condition
occurs the circuit would be broken.

See any problems with that?

Thank you.

--kyler