[Canberrauav] GEB Battery testing results
chris.wilson at hobbyking.com
Wed Feb 4 21:21:23 EST 2015
Yeah at first when testing these batteries with standard rules of thumb
LVC, we were actually pretty disappointed, but after consulting with the
cell manufacture and getting more data these particular cells can safely be
discharged to 3 volts per cell no problem..so once we re-did our tests to
the new lower cut off, found the batteries to be slightly better than spec
surprisingly. I've got some fancy dancy charts from our battery analyzer I
can post if you guys want, but definitely the key was a 1.5 C or lower
discharge. The whole idea of this battery was to try and get conventional
multirotors in the air for an hour or better without the need of
a sliderule an engineering team behind you, LOL basically take a vantage of
these batteries. How we devised to do it and deal with the C rating was
simply not increase efficiency but decrease amp draw demand. Meaning
high-voltage..the higher the voltage the lower the amperage for the
same power being produced, lots of people assume higher voltage equals
higher efficiency and if engineered probably could but we found issues with
motor design and magnetic saturation etc the higher the voltage got. We
were able to design some 8S motors that are not necessarily more efficient
then a 4S motor just looking at Grams versus watts efficiency, they where
on par and still over 10 g/w so decent enough, however because the amp draw
was lower this is where the magic happens!!! the higher density batteries
GEB or Panasonic cells for the same given weight are now well within
C range of the total draw and can be used safely. Take our 3508 multi star
elite endurance motor it has a 268 KV and can swing an 18 inch prop
producing 1600g of thrust at only 2.7 A or a 15 inch prop at 6s for sub 4
amps..The key to utilizing these batteries and leveraging their higher
capacity comes down to matching a power system, figure out prop speed max
prop dis and thrust required and I can have a motor built and wound in 6s
and 8s kvs and then draw would probably be in the 1C rating. It would be
interesting to see what could be devised on fixed wing. On
multirotors we've achieved well over an hour flights utilizing standard 680
hex frames 13 inch props and just 8s set ups.
On Wednesday, February 4, 2015, Andrew Tridgell <andrew at tridgell.net> wrote:
> Hi Chris,
> Thanks for chiming in!
> > We have a ultra capacity battery line coming out soon based on the GEB
> > cells, from speaking with the factory and our test found these batteries
> > have a lower cutoff voltage than standard LiPo's and using the new spec
> > achieve spec capacity at 1.5c We geared the line for HV multi rotor setup
> > 8~10s that pull minimal amps, well with in the batterys C rating. What
> > voltage are you terminating your test?
> As James said we terminated at 12.5V loaded voltage on a 4S 12Ah pack
> (2x4S 6Ah in parallel). The load at 12.5V was around 19A. So that is
> 3.13V per cell at around 1.5C load.
> The unloaded voltage at that level of charge was about 14.7V (around
> What loaded cutoff voltage would you recommend for these cells to give
> us about 10 to 15% remaining capacity to bring the plane home?
> The other issue we noticed is that because the voltage drops so much the
> usual Ah rules of thumb get pretty bad, as the current draw to keep the
> plane in the air kept rising. So you really need to talk about Wh not
> Ah, and the usual autopilot failsafe code based on Ah consumed is
> perhaps not the best approach. Have you thought about that at all?
> Ideally we'd have an equation modelling the behaviour of the battery
> under different loads, so we can properly calculate the amount of
> capacity remaining for failsafe handling.
> Cheers, Tridge
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