Spring Projects - Ground Power - Heater Insulation
Added 4/1/2007 - approx. 205 Flying Hours
To finish my interior lighting
to the rear seats, I had to re-open the interior side panels, and to
add a ground charging circuit to both the main and aux batteries, I had
to open the flap tube areas, so I used this time to open up all of the
cabin panels again since I had wanted to insulate my SCAT tubing for
the heater feeds too. Now the SCAT tube shouldn't radiate heat
until aft of the fuel valve area, which was just one of those things I
intended to do to help ensure the fuel lines stayed cool. Spring
projects...
This gives a good look at the aux batteries and contactor. There
are 4 batteries, in 2 parallel pairs of 2 serial batteries.
They're 7Ah batteries, at 6v each. It provides power during
startup for the e-bus avionics, and it is completely separate from the
main battery other than a charging feed that can either come through a
diode or direct, depending on the e-bus switch position. My goal
of this project was to come up with a good way to charge both of my
batteries while the plane sits for any extended periods, to use that
time to maintain the battery to the best of my ability. I
purchased a Schumacher SC-2500A charger (actually I bought the WM-2500A...Wal-Mart's model number for that charger (owners manual)), that at least at one time was one of a couple smart chargers recommended by Odyssey (owners Manual)
for use with their battery. It charges the battery up to a
certain voltage for a certain time and then drops to a maintenance
charge of something like 13.6V. I haven't verified that it's
exactly the same as the OMAX-25A-1B
that they currently recommend, but I believe it probably is, and it's
at a lot lower cost, especially from Wal-Mart. It's a pretty cool
charger that is capable of charging at multiple rates, multiple types
of batteries, and it does have some diagnostic features to it also.
I liked it so much I bought a 2nd one for home use.
My requirements for the ground charge connection was not the same as
everyones. Some people want a plug for jump starting the plane if
the battery dies. I didn't care about that for myself, as I
wouldn't be flying home with a battery that had died that far without
first charging it anyway. But I did want a lighter weight
connector than some huge metal one, and I wanted one with some sort of
protection for the wires and terminals coming off the back to protect
from abrasion and shorting out. I also needed a form of connector
that had at least 3 pins...one ground, and one hot for each battery.
I searched high and low for what I wanted. Sure, there were
a couple of plugs that are more standard for ground power, that might
be nice, but the piper style couldn't handle 2 batteries, and it needs
to be modified to adapt for use. The other style is much more
expensive and I still don't know if I could charge 2 batteries and
still keep the connector "standard". After a lot of digging
around, I finally ran into what I wanted to use.
The 7-wire RV trailer connector
turned out to be a pretty great match. It's not tiny, but it's
nice. I really tried to look at the 4 and 6 wire round versions
too, since I didn't need that many conductors, but here's the problem:
Both of them didn't have great ways to connect the wires
internally. They used a cylinder to stick the wire into, and then
you crushed it with the threaded end of a screw to hold the wire.
I didn't want to do that for at least the 2 hot wires on the
plug. Also, the connectors didn't seem to be as "safe" from the
way the wires routed out the back of the plug...if one started coming
out, it would be easy to short on the metal plug or socket body that
they came with...and it didn't have a good wire support. In
contrast, the 7-wire model had a lot of plusses. First, it uses
screw terminals that you can use with ring terminals on the 6 terminals
around the edges...this is HUGE. Next, it has much larger
connector blades, that can easily handle the current. In
addition, you can use MUCH bigger wire with these plugs, as they're
made to handle charging RV batteries off the tow vehicle alternator,
and run electric brakes, and things like that. The wire spec can
handle better than 10ga on the center terminal...probably 8 or so, and
it easily handled my 10ga wire on the ring terminals. Not only
that, but the plug and socket were plastic, so they didn't add a lot of
weight, and the size wasn't all that bad. In short, it seemed a
very safe way to go.
So I hooked up a pin to each battery hot terminal, and the center I
hooked to the black battery neg. terminal. On the plug end, I cut
the clamps off the charger wires, and hooked up the ground and hot
terminals to feed my main battery, then added a 10ga jumper from the
main battery terminal to the aux battery terminal. So I have
achieved the goal of charging multiple batteries from one charger.
Yes, by the way, it's ok to charge batteries in parallel like
that....it's just as it is while you're flying. The nice thing is
though, you get a well conditioned and maintained charge, that should
help the battery last a long time, and keep it at full capacity.