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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Peter Germann on August 11, 2012, 03:35:48 AM
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Measuring battery temperature before and after flight I have found this:
4 ea. 25C batteries (30-40 cycles): rise is 23 - 35°C (73 - 95°F)
1 ea. 65C battery (9 cycles): rise is 14° (57°F)
All batteries of the same type 2600/5S, recharged at 1.5C approx. by 2'000 mAh (77%). All load defining parameters unchanged.
The 25C batteries begin to show signs of fatigue, i.e. puffing, no-load end of flight cell voltage around 3.6 V and much (+50%) longer balanced-charge time. The batterie with the highest rise has triggered the low voltage cut-off after the clover and was retired.
The 65C battery remains significantly cooler and I now wonder whether this may contribute to longer cycle life? If so, does anybody have cycle numbers of the ThunderPower G6 Pro Power 2700/5S battery?
Thank you, Peter Germann
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It could ... but I do not think the temperature itself is the reason, because I have battery tempreature higner and I do much much more flights
I would say that the lower C rate means higher resistance (and it makes that higher temperature after flight as side effect) but the primary reason is that the higher resistance makes lower effective voltage and thus at the same final energy which is necessary for flight, the CHARGE (in mAh) is larger on that batter with lower C rate and thus you discharge it deeper, and that makes life time much shorter
IMHO when I see that battery after flight shows visibly less than 3.7V/cell, the battery will do only few next flight and it goes to basket
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Peter, I am sure all you say is true. Battery heating would be a function of C rate. The C rateing is a measure of battery internal resistance. The higher the C rateing the lower the battery's internal resistance. With a lower internal resistance less heat is generated, (IR losses). And heat is what kills a battery. All battries have some water in them (even so called dry battries). When you over heat a battrey and boil out some of the water you reduce the battery capacity.
When I worked on military hardware we derated every thing by 50%. So a part in a 5V circuit had to have at least a 10V rateing. So using this reasoning if you are pulling 25 amps you need a battery that will deliver 50 amps. A 2200 mah battry would need a minimum of a 23 C rateing. For this to be enough it depends on the amount of cooling air flow, Air temperature and other things. Also don't forget the center cells of a multi cell pack run hotter than the rest.
The above is a lot of words to say a higher C rateing is a good thing. That's why they cost more!
D>K
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They weigh more, too. I was skeptical of getting a 65C battery for a 15C application, but I'm getting convinced that the 65C is a good idea. They charge faster, so you need fewer batteries, and airplane cooling ducting can be dedicated to the motor and controller.
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Peter
165+ cycles on my 3each 5S2700's still going strong.
Norm
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Peter
165+ cycles on my 3each 5S2700's still going strong.
Norm
Norm,
25C or 65C?
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Peter
165+ cycles on my 3each 5S2700's still going strong.
Norm
Thanks and good to hear from you, Norm.Just two questions:
How much do you put in when charging?
What is your charge current?
rgds Peter
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Peter/Crist
About 1600-1650ma replacement charge for the 65C's. Not only do the 65's run cold they also take about 50ma less to charge than the 25C's.
I am using ThunderPower 5S2250 65C too. saves about 2 oz.
Regards
Norm