On 07/25/2018 08:44 PM, kinsell wrote:
On 07/24/2018 08:16 PM, Craig Funston wrote:
On Tuesday, July 24, 2018 at 2:22:09 PM UTC-7,
wrote:
On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω
http://aviation.derosaweb.net wrote:
On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the
longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both
batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω
http://aviation.derosaweb.net wrote:
Andy,

I have used the ideal diodes mentioned by Shaun McLaughlin
(http://re-voltage.eu/ US$27 each) as I was given a pair to test
with.Â* They do what they say with minuscule voltage drops across
them.Â*Â* Full disclosure, I am currently using two 1N5821 Schottky
diodes in my panel right now (page 74 of my presentation) -
small, simple, cheap, plentiful, robust, and easy to mount.

That being said - the availability of inexpensive ideal diodes
has exploded in recent years mainly for use in systems like solar
panel arrays.Â* See
https://www.ebay.com/sch/i.html?_fro...es%29&_sacat=0.
I also like the increasing range of mounting styles available
allowing for placement options behind our increasingly cramped
panels.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of
the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select:
Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3
(tail). I use a bank of capacitors connected through a power
resistor to energize the circuit when the switch is between
batteries.

If I had to do it again I would use ideal diodes (though as others
have mentioned this is really not nearly a necessary with LiFePO4
batteries since they go through voltages below 11v quite quickly
on my battery tester). I would also separate the batteries to
individual switches to eliminate the switch as a single point of
failure.

Andy Blackburn

9B

--
Dan, 5J

Dan - Do you have diodes in this circuit to prevent cross-charging
of the batteries?

I will repeat something I said above that (without diodes) putting
the batteries in parallel can cause a large current to flow from the
"high" battery to the "low" battery.Â* Effectively one battery is
charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on
your batteries (you do have a fuse right at your battery's positive
terminal, right??).

On lithium batteries, which probably have intelligent current
limiting electronics inside, this should not be an issue.Â* But
notice the words "probably" and "should".

YMMV.Â* Be careful out there.

- John OHM Ω

How much current do you project when switching from a low LiFe at
12.4 volts(pretty much done) to high at 13.7? I have been doing this
switching with SLA batteries for 25 years. Switch new one on- switch
old off a second or two later. Have not blown up anything yet.
UH

Plus one. KISS principle.


Two switches and two fuses should work fine, certainly an improvement
over some of the Rube Goldberg solutions proposed here.

But two batteries, two fuses, and two Schottky diodes would be an
improvement.Â* Perfect for everyone except jet jockeys who want more
switches to flip.

Finally, one properly sized battery with a fuse is probably the best
solution, half the number of BMS boards to blow up.Â* Can't get much
simpler than that.Â* There's a lot to be said for reducing component count.



Speaking of losing the panel, Garret Willat just posted a video on FB of
flying in the Czech Republic with no avionics power, which also took out
his engine controller. Did have a paper map and mechanical vario.