Battery switching without tears

On Sat, 04 Apr 2020 18:23:41 -0700, 2G wrote:

On one of my flights last year I had to switch between my avionics
battery and engine battery when the avionics battery voltage dropped too
low (I had left the master on after the last flight and could only
partially charge the avionics battery before launching).

Some years back I had a momentary disconnection problem with the XLR plug
supplying power to my panel: it carries a common ground plus a positive
line from each of the two batteries I carry - one supplies flight
instruments, the other drives radio and T&B.

I added small capacitors (18mm diameter x 35mm long, 35-50v, so 1000-2000
uF capacity or thereabouts for each capacitor - thats a guestimate since
I can't read their markings without major surgery), one for each battery,
and with a 0.1 ohm resistor in series with it.

This solved the problem completely, but my current draw is lower than the
yours: 500 mA for flight instruments and 200 mA with T&B running and
radio on and receiving.


--
Martin | martin at
Gregorie | gregorie dot org

On Sun, 05 Apr 2020 12:15:53 +0000, Martin Gregorie wrote:


I added small capacitors (18mm diameter x 35mm long, 35-50v, so
1000-2000 uF capacity or thereabouts for each capacitor - thats a
guestimate since I can't read their markings without major surgery), one
for each battery,
and with a 0.1 ohm resistor in series with it.

Correction: still don't how big the capacitor is but the current limiting
resistor in series with it is 10 ohms (just measured it) so the capacitor
won't charge or discharge more at than 1.2 amps. The resistor is a big
wire-wound resistor in a rectangular ceramic case with the capacitor
taped onto it, so is both mechanically and electrically strong.

But, as I said, since this fixed the problem thats enough to prevent
vario and radio resets if I smack the XLR connector powering my panel. Nav
is fine - got its own internal battery.

The same setup may well sort out a break-before-make switch too, with the
advantage that fitting it across the +12v and ground lines on the panel
side of the switch can most likely be done without disturbing anything
that's already in your panel and is both inexpensive and easy to make and
install.


--
Martin | martin at
Gregorie | gregorie dot org

MAKE before BREAK, not the reverse, which will momentarily interrupt
power to your panel.Â* Of course, if you're really, really fast, you
might get by...

On 4/5/2020 6:28 PM, Martin Gregorie wrote:
The same setup may well sort out a break-before-make switch too, with the
advantage that fitting it across the +12v and ground lines on the panel
side of the switch can most likely be done without disturbing anything
that's already in your panel and is both inexpensive and easy to make and
install.

--
Dan, 5J