Thread: Discussion A simple LiPo performance tool
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Old Jan 23, 2012, 12:54 AM
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Melbourne, Australia
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Some "real life" results

Since the whole purpose of the calculator on Mark Forsyth’s post is to provide practical guidance rather than encourage armchair debate I thought I would try it out that way and see how it stacked up against some reliable independent findings.

Still on the theme of small batteries I contacted nitrocharged (also known as Team 30 EDF ) who is in my opinion Mr Micro-EDF and who probably has more experience wringing the best out of small batteries than anyone around. The micro (30-35mm) fan guys are pushing the envelope (for continuous powered flight) for max power/weight with motor rewinds, custom fans and the best cells they can find.

I asked him what current he pulls from the Thunder Power 325 mAH 65C cells which are his current choice. His response was “I pull around +8 amps continuous from them. Besides a throttle back on the turns, they deliver till the end. Even though they are quite warm after a flight if the weathers in the 20's, they are still rock hard with zero puffing so far. And that is in a closed lipo bay - no cooling”. (thanks, Nitro)

Given the intensity with which these guys fly, and their extensive experience, I think we can assume this is a good “practical” current limit for adequate performance and decent life.

So how does this compare with the predictions of the calculator? I tested a 2S and 3S Thunder Power G6 325mAh 65c and also a 2S Hyperion G3 320mAh 25C which I thought would be their closest top-end equivalent. All three batteries are less than 5 months old, have never been stressed and have less than 10 cycles on them.

I got the results shown in “Table” measured at 23°C after resting overnight at 21°-23°C from a full charge.

So the calculator is predicting a recommended maximum current for the TPs of 7.8A almost exactly what the micro EDF guys use.

I then tested these batteries to see how they performed at the recommended C rating (24C = 7.8A for the TPs and 14 = 4.5A for the Hyperion). I converted everything to cell voltage to make comparison easier.

Results are in the graph “Recommended”. Looks pretty good. All three track almost identically at the recommended currents although the Hyperion runs longer of course because it is at a lower current. Voltage stays at about 3.5 mid –run which is about as low as you would want.

I then pushed the current up by a third to see what happened. See “Two rates”. The TPs are still coping pretty well but the voltage is getting below where I would be happy. The Hyperion is really out of the race IMO at this current with a mid-run voltage of only 3.3V.

None of the batteries got really hot – they were pretty well ventilated unlike inside a small foam jet - but the Hyperion is showing the stress at the higher current. See “Temp Rise”.

Overall, I think the calculator gives a reliable indication of a sensible maximum current. And it also shows why these particular Thunder Power batteries are the top dog at the moment for small EDFs. A FOM of over 1.0 is remarkable for sub-400mAh cells.

John
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Last edited by jj604; Jan 23, 2012 at 04:51 PM.
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