Thread: Discussion turnigy ntm 50/50 motor
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Old Nov 20, 2012, 08:20 AM
jackerbes is offline
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Jack
USA, ME, Ellsworth
Joined May 2008
18,082 Posts
Was it 20.5V under load? Or before you put the load on it? That would be 4.1V per cell which is a typical charged and rested cell voltage.

What was the capacity of the pack? If it is falling to 3.5V quickly under load you may not have a pack with enough capacity. As an example, a 2000 mAH pack at 80A would be at a 40C discharge rate, while a 4000 mAH pack would be at a 20C rate. And if the pack quality was the same the voltage on the 4000 pack would fall less.

I like to see the voltage stay up around 4V or so under the full throttle at the start of a fliglt and seldom fly at continuous full throttle. So dropping back on throttle a little keeps the voltage up as the flight proceeds. And when a full throttle burst causes the voltage to fall to 3.5-3.7V or so I end the flight.

After a few flights and recharges you have a good feel for the duration in time and know when to land. If your recharges are putting about 80% of the capacity back (1600 on a 2000 mAH pack and 3200 on a 4000 mAH pack for example) then the all of the useful capacity is being used.

if you take the packs down to lower voltages they get warmer and lose their service life quicker. I never want to find a pack more than just a little warm when I wrap my hand around it and the cells should be back up around 3.9-4.0V or so shortly after landing. Sometimes when you get home it is hard to tell a depleted pack that has rested for an hour or two from a charged pack. But it will have little or no useful capacity left in it, put a small load on it and the voltage drops quickly.

Jack
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