REFLECTOR: Battery options

[Jack Prock]

Hi Hiroo,

 

I just recently went through this.

 

I had one battery up front with an avionics bus switch to keep everything
off 

while I was starting the engine. The problem was that when I cranked the
engine,

the current drop was enough such that my Electronic Ignition would not fire
to start the engine.

Starting was incredibly difficult, although not completely impossible. It
sometimes fired off on just

the secondary Mag, but it was almost impossible.

 

So I decided to add a second battery in the rear, just for running the
starter. I figured I would still

have problems with the current drop even with two batteries, and I wanted to
eliminate the need

to have all electronics off when starting. I have a GRT HXr so all engine
monitoring is through that. 

I couldn't see oil pressure for more than a minute after starting. which
didn't make me comfortable.

 

I did some research and found a battery isolator.

http://www.powerstream.com/battery-isolator.htm

 

This keeps the two batteries separated ( one for avionics, one for the
starter) until 

15 seconds after it detects greater than 13 volts from the alternator, then
connects them together automatically.

No switch has to be thrown, it is all automatic.

This solved all my problems. I can now turn on the avionics before engine
start and I don't

have to worry about flipping a switch (which at some point, I would probably
forget)

to connect the batteries together after engine start.

 

I removed the need for an avionics bus. I changed that switch over to the
battery connect

override, which is not needed unless the starter battery gets drained for
some reason. I can

connect the front battery to the starter to help with starting.

 

The other advantage to this is that if something is left on in the plane, it
will drain the front battery,

but the starter battery will not be affected. So you can still start and
have the alternator charge

the front battery. 

 

I'm not flying yet, but so far it works great and does just what I wanted
for battery management.

 

I turn on the HXr, let it get settled, turn on the fuel pump and can see
fuel pressure, start the engine,

see oil pressure immediately, and about 15 seconds after start, I see the
voltage warning alarm

go off because the alternator gets connected to the front battery. Works
great!

 

Jack

 

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Hiroo Umeno
Sent: Tuesday, February 11, 2014 11:29 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Battery options

 

Fellow builders,

 

I have two Odyssey PC680s in the nose of my plane wired in parallel.  While
this setup works for the most part, starting the big 6 cylinder Franklin can
be a bit tasking.

 

I am considering doing something about it when we take the plane apart for
condition inspection and upgrade next winter.  So.

 

*         Would it make sense to move the batteries to the rear bulkhead
close to CG assuming the W&B issue can be worked out in the nose?  This will
reduce the wire run length.

*         Would it make sense to keep the batteries where they are now in
the nose and add additional 0-gauge wires (and back) to reduce current loss?

 

I know that going to 24V system will give me less current to drive the
starter but that is a fairly extensive change on the rest of the aircraft
systems.

 

Any other ideas?

 

Hiroo

 

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