[Canberrauav] GEB Battery testing results

Chris Gough christopher.d.gough at gmail.com
Sun Feb 1 00:40:03 EST 2015


Oops! you did say 4s.

It's a lot less shocking, I don't think efficiency explains the result anymore  but there is still a potentially interesting difference in efficiency at different %C(max). Obviously, reading numbers off a chart on my phone is quite inaccurate even when I use the correct axes, but it looks as though battery efficiency is something like:

 3A  (0.25C) very efficient
 9A (0.75C) 95% efficient
 17A (1.4C) 85% efficient

This is based on looking at discernible periods closest to the (almost) zero current period at either end of the flight, and assuming the resting voltage is about the at adjacent times.

start. 16.5v 0A
~10:50. 14v 17A output 240W total 280W
~10:51. 15.5v 10A output 155W total 165W

end. 11:16 14v 0A
~11:15 13.3v 8A output 106W total 112W
~11.15 13.9v 3A output ~42W total ~42W

Is 30 minutes of ~15W heating enough to make a temperature problem for the battery?

Chris Gough

> On 31 Jan 2015, at 9:30 pm, Andrew Tridgell <andrew at tridgell.net> wrote:
> 
> Hi Chris,
> 
>> For example, looking at the plot, zero load on a fresh charge was
>> about 23v. At ~10:51, the current went up to 14 amp and the voltage
>> dropped down to 17v. So the output was about 240W (14A * 17v). 
> 
> I should have explained that voltage is on the right axes, current on
> the left. The batteries are 4S, and don't go above 16.5V
> 
> Cheers, Tridge
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