ml3456

Does anyone know how to determine the capacity of a Li-Po cell? I have circler's that work with nicads or NimH, but lithiums operate differently. I think it is important to know how your batteries run, just not base it on voltage. Like to know that if I fly for an hour, how much capacity is left. After a few years of use, does the battery still meet its design criteria.

Thanks, Mark

OhD

Mark,
1) Charge the battery.
2) Discharge the battery with a known load that is roughly what you believe you will use during operation. Something like 500 mA.
Measure the voltage every ten minutes.
3) Plot a curve of voltage vs. time. You should see a fairly linear curve until the battery is nearly discharged. Don't go below 3 volts per cell.
4) From this curve you will see a critical voltage where it starts dropping very fast. Quit flying well before you get to this voltage when you test with a loaded voltmeter between flights.
5) After flying a safe number of flights, go home and discharge the pack to the critical voltage to determine roughly what was left.
If there was a lot left you know you can fly to a lower voltage next time out. However, always allow a large safety factor.

You will find that these cells have a fairly good correlation between voltage under load and remaining capacity. After a few years they will not perform as well but will still fly your airplane.
Good luck.

rajul

My Feedback: (58)

Can the Triton cycle Li polymer batts ? Maybe this is an easier way to verify the capacity ?

ml3456

OhD,

Thanks for your help. Looking for something that may be a little more automatic. Sirius makes a analyzer for Nicads/Nimh batteries. Any way toy modify it or fool it to stop at 3 volts instead of 4.4 volts. I am pretty good with mechanical things, but I don't know electronics.

mark

OhD

Set it to 5 cells and it will turn off at 5.5 volts. That should still be okay. That will give you the capacity but you still need to know when it is getting low before it is too late.

OhD

I assumed you had a two cell pack.

ml3456

Yep. Still requires constant attention though.

Thanks

doctor jason

i have used the above method works well