Hot and puffy lipo after flight test- do I have correct C rating?

Flydigital

Member
I have 2 x 5000mAh 3s lipos used in series to create 6s power.
They are 20C rated.
I have made an octo and done a bench test after it crashed from over heated wires. In the test I ran it at mid power which was a current of around 35Amps.

After running down the batteries to about 3.4v per cell the batteries were hot and puffy.

Is the 20c rating too low?

I thought maybe 20c might mean maximum of 20amps current. But maybe in series it becomes 40amps for 2 or stays the same. If I need 40amps continuous in flight maybe I need higher c rating batteries?

Thanks for any help here.:)
 

STI-REX

Gettin Old
A 5000 mah 20c battery is actually 100 amps
5 amps x 20c = 100 amps

series = doubling of voltage amps stay the same
parallel = doubling of amps volts stay the same

I would think you would need at least a 40c battery to run an octo copter under full load

I run 45c-90c burst 4cell 5000 mah batteries on my qav500 v2 quadcopter and they stay warm not hot
So 5 amps x 45c = 225 amps with a 10 second burst at 90c of 450 amps

If you have too small of a "C" rating you will be drawing the batteries well below the safe voltage under climb out when hitting the throttle commonly called voltage sag
 

fltundra

Member
I have 2 x 5000mAh 3s lipos used in series to create 6s power.
They are 20C rated.
I have made an octo and done a bench test after it crashed from over heated wires. In the test I ran it at mid power which was a current of around 35Amps.

After running down the batteries to about 3.4v per cell the batteries were hot and puffy.

Is the 20c rating too low?

I thought maybe 20c might mean maximum of 20amps current. But maybe in series it becomes 40amps for 2 or stays the same. If I need 40amps continuous in flight maybe I need higher c rating batteries?

Thanks for any help here.:)
Hot and puffy because you ran them to low! Never below 3.6 volts under load.
 

econfly

Member
I would think you would need at least a 40c battery to run an octo copter under full load

I run 45c-90c burst 4cell 5000 mah batteries on my qav500 v2 quadcopter and they stay warm not hot
So 5 amps x 45c = 225 amps with a 10 second burst at 90c of 450 amps

If you have too small of a "C" rating you will be drawing the batteries well below the safe voltage under climb out when hitting the throttle commonly called voltage sag

It all depends on how you fly. Say you have a rig that can fly for 15 minutes on its battery power. Then, by definition, you are using no more than 4C on average. Big throttle punches or the like can of course require more than the average amount of current, but ultimately you can't have flight times of 10-20 minutes and, at the same time, say you need "at least 40C" to fly. An average burn rate of 40C means a flight time of under 2 minutes, after all. The most likely cause of hot/puffed lipos for most of us is not current demand, but rather running them down too low (as noted above).
 

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