I use either 1N5401 or NTE5802 diodes ahead of my master
switch, so they are powering my whole panel. I understand
that they have a 3 amp capacity. I've never had any
problems with them. I recollect that they have a 0.6
V drop, so I don't have to worry about switching batteries,
the diodes do that automatically when the battery in
use drops to 0.6 V below the battery not in use. It's
very convenient. All I have to do is select my higher
voltage battery before I take off.

I can't take credit for the idea or design. I got
it from Nick Bonniere.

At 04:48 18 June 2005, Ian wrote:
On Thu, 16 Jun 2005 09:37:07 -0700, ContestID67 wrote:

I agree that a couple of diodes are the way to go
to place the
batteries in parallel without allowing one battery
to cause problems
with the other. However the key is the voltage drop
which is typically
0.6vdc for a power diode. Do you have a specific
diode number that you
have been using?

I used two IN5817's. I only use these to power a Volkslogger.
The rest of
the panel is still controlled via 'A/B' switches.

These are rectifying diodes with low forward voltage
drop, especially at
low currents. In my setup I think I loose less than
0.2V but it is tricky
to measure. These are small diodes with a Max current
rating of about 1A.
I don't think that you could power your whole panel
through them. (Google
should find you a data sheet).

Having the switches for the heavy current items (transponder
etc) is
useful. It is very difficult to test the health of
a battery on the
ground. So you normally only discover that the battery
is not up to
scratch when it dies while you are flying. At this
stage it is nice to be
able to switch over to battery B.


Ian