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Old June 20th 18, 12:21 PM posted to rec.aviation.soaring
Shaun McLaughlin[_2_]
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Posts: 10
Default A complicated question about LiFePO4 batteries, - and switching.

I have re-wired 2 glider panels in the last year or so and used John's
presentation as the starting point.

Fuse on each battery - a battery master switch for each battery (ON/OFF)
- IDEAL DIODES - +12V power bus - TYCO breaker for each device - DEVICE
- GND - DIODE - BATTERIES

I can recommend the Ideal Diodes and Tyco breakers (although they are not
cheap). I liked the idea of reducing the number of connections (separate
fuse and switch) by having a combined fuse/switch. Since first installing
the Ideal Diodes I know they have been used on a number of other gliders at
my club and everyone seems happy so far.

http://re-voltage.eu/

I installed the Diodes behind the panel rather than on each battery as I
didn't want to damage them while handling the batteries. However they can
be used to connect both batteries to the same charger safely.

This setup means I only need to switch a battery off if there is an issue.
It allows me to combine battery types (SLA/LiFePO4) if the need arises.

I went down this path of having both batteries always on and sharing the
load after having issues switching batteries in flight. If I wasn't quick
enough I would find my FLARM rebooting, then having to wait to download the
last 'trace' onto the SD card. I found this quite frustrating while running
ridges in the Alps! My stop gap fix to this was to add a capacitor and a
rotary make before break switch to select the batteries, but this was still
less than ideal and lacked redundancy.

Shaun

At 13:23 19 June 2018, T0hNIOKEpiBodHRwOi8vYXZpYXRpb24uZGVyb3Nhd2ViLm5ldA ==
wrote:
A beginning comment: With modern avionics drawing less power than their
pre=
decessors and LiFePo4 with greatly increased energy capacity, maybe only
on=
e battery is needed these days for most glider pilots. Just sayin'.=20

I agree that our batteries should not be run in parallel (without

diodes).
=
If one is of a significantly different voltage than the other, then the
hi=
gher one will charge the lower one possible at a high rate (current) that
y=
ou don't want. This can potentially blow one or both battery fuses (you
do=
have a fuse on each battery, right???), or might cause one battery to
fail=
in a bad way, either of which can leave you in a poor situation
especially=
during flight.

I have a presentation on my thoughts on the subject of two battery

systems
=
at http://aviation.derosaweb.net/presentations#wiring. =20

Here is my setup on my current glider.

- Two batteries (lithium)
- Each battery has a fuse.
- Two separate power buses with one battery powering each.
- One bus is for "communications" (radio, transponder, FLARM) and the
other=
bus is for "navigation" (GPS, Vario, etc.). =20
- Each bus has a separate breaker (5A) which is also a master switch (a
tru=
e breaker/switch by Tyco
http://www.aircraftspruce.com/catalog/elpages/pbci=
rcuitbrkr2.php?clickkey=3D5950).=20
- But I do have Schottkey diodes in each bus. Why, you might ask, do I
hav=
e diodes if I have two separate electrical buses? Because I can bridge
the=
two buses with another switch for that "just in case situation" (belts
and=
braces engineering over design). I have never have to use this switch

but
=
then again you never know ...

Thanks, John OHM =E2=84=A6