[Canberrauav] GEB Battery testing results

James Pattison james at auturgy.com.au
Wed Feb 4 16:24:34 EST 2015

Hi Chris,
Thanks for the info. In flight we've gone to 12.5v under load, I've gone to 12v on the bench (plus one test down to about 9v by accident - battery survived with little change to internal resistance).

I think your figure of 1.5C is going to be a pretty good number. Under 0.5C the rated capacity is generous, but at 1.7C we didn't get close, using 12.5v as cutoff. FYI my over-discharged battery (4S, 6000mah) took in 6800mah for a full charge, balanced fine and seems undamaged.



> On 4 Feb 2015, at 16:04, Chris Wilson <chris.wilson at hobbyking.com> wrote:
> Hello all this is Chris From HobbyKing,
> 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 can 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?
> Thanks
>> On Sat, Jan 31, 2015 at 11:45 AM, Andrew Tridgell <andrew at tridgell.net> wrote:
>> Hi All,
>> We've been doing some testing of the new 6Ah 4S GEB batteries in the
>> Ranger. These batteries have a claimed energy density of 260Wh/kg, which
>> if it is confirmed would be extremely good for longer range
>> aircraft. They have a very low C rating though - the rating is 2C
>> continuous, 3C burst, with 0.5C charge. We've got it setup with a 20A
>> current limit on the uavcan ESC in the Ranger, with 2 of the 6Ah 4S in
>> parallel, giving us a 12Ah pack, which means we are flying at max 1.7C,
>> and cruising at about 1C.
>> Last week we did a flight with this setup, and we were surprised to find
>> that the battery voltage dropped unconfortably low after just 5.2Ah had
>> been used of the 12Ah, so we landed it. It has flown for 30 minutes.
>> Today Grant, Greg and I did two more flights:
>>  1) first flight with a 5Ah normal LiPo (a turnigy LiPo)
>>  2) 2nd flight with the 12Ah of GEB batteries
>> the aim was to get a direct comparison of the discharge curve between
>> the two batteries.
>> The results are here: http://uav.tridgell.net/GEB-Batteries/
>> What we expected to see was that the higher capacity (12Ah) battery
>> would have less of a voltage drop on takeoff, and would go for more than
>> twice as long as the 5Ah battery before the voltage dropped to critical
>> levels.
>> From the graphs you can see that is not what happened. The voltage drop
>> on the 12Ah pack on takeoff was from 16.4V down to 13.4V, whereas the
>> drop on the 5Ah was from 16.5V down to 14.3V.
>> After 30 minutes of flying the 12Ah pack had gone through 5.3Ah of
>> capacity, and was starting to hit 12.5V under load, which is the level
>> at which we decided to land.
>> After 25 minutes of flying the 5Ah pack had gone through 4.4Ah of
>> capacity, and was also starting to hit 12.5V under load.
>> That means the 5Ah got to 12% capacity before it hit the low voltage
>> threshold, whereas the 12Ah pack used just 44% of its capacity before
>> hitting the same threshold.
>> What it really looks like to me is the GEB battery is behaving like a
>> 6Ah battery, not a 12Ah battery. It claims to be 6Ah per pack, and we
>> had two in parallel, so we expected 12Ah, but we clearly were not
>> achieving it.
>> I think we need to go back to the manufacturer for some advice. Perhaps
>> we are supposed to run these batteries down to a lower threshold voltage
>> than normal LiPos ? Or maybe they really just don't have anything like
>> the claimed capacity.
>> Cheers, Tridge
> -- 
> Chris Wilson
> Products Specialist
> Hextronik Limited
> Address: Rm K1, 9/F. MG Tower, 133 Hoi Bun Road, Kwun Tong, Hong Kong.
> 地址: 九龍觀塘海濱道133號萬兆豐中心20樓A1室
> Phone: (852) 3125 1900 ext. 181
> Skype: Products03 at hextronik.com
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