Battery switching without tears

On Sunday, April 5, 2020 at 9:19:23 AM UTC-7, Martin Gregorie wrote:
On Sun, 05 Apr 2020 09:10:53 -0700, stu857xx wrote:

On Sunday, April 5, 2020 at 10:18:00 AM UTC-5, Dan Marotta wrote:
Wouldn't a make-before-break switch solve the problem in a much simpler
fashion?Â* That's what my Stemme uses and switching between main and
tail batteries is a non event.


Depends on what happens between make and break.

There will be some amount of surge current from the full battery to the
empty one. If the current times the time exceeds the fuse IT, you can
blow a battery fuse.

Long wires out to the tail and quick switching could make this less
likely.

So would a schottky diode inline with each battery. It will cost you a
whole 0.25v voltage drop and even make the switch unnecessary if you
don't mind drawing from both batteries at once. I power my logger that
way, but split the panel feed so one battery runs flight instruments and
the other does radio and T&B.

Backups? My nav system is a PNA thats good for at least a couple of hours
on internal battery and my backup vario is a Borgelt B.40 thats good for
8 hours plus off the fresh PP3 dry battery it uses for an alternate power
source.



--
Martin | martin at
Gregorie | gregorie dot org

Schottky diodes are unnecessary and I would not recommend them do to their voltage drop. The cap works just fine and isn't invasive (it is wired in parallel to the existing voltage bus).

Tom