[Canberrauav] GEB Battery testing results
james at auturgy.com.au
Wed Feb 4 16:24:34 EST 2015
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?
>> 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
>> 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
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