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Old Mar 29, 2010, 02:13 PM
Merlin45 is offline
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flyit, crashit, fixit.
crsahing around in mid-europe
Joined Jan 2007
227 Posts
Quote:
Originally Posted by slipstick View Post
Can you repeat your tests because they don't seem to make much sense ? I assume you're using exactly the same motor and prop all the way through and each battery is freshly charged ? In which case what you have is

Test 1 20A @ 11V (on the 2200mAh 20C). O.K. that's a reference point
Test 2 15A @ 10V looks o.k but that's a much weaker battery (max 22.5A rather than max 44A in Test 1).

Now we get to
Test 3 18A @ 11V. With the same load (motor/prop) it shouldn't be possible to get less current at exactly the same voltage as Test 1. If it's running at 11V the current should be 20A again. If the current is really lower the voltage should be lower too.

Test 4 17A @ 11.5V. Even stranger you're now showing a HIGHER voltage but a LOWER current. That's not possible either if the load is still the same as in the other tests.

Something odd going on but perhaps it's not just the battery performance .

Steve
Interesting points, and has got me thinking, thanks. Iím figuring this out as I go along, so ideas help a lot.
First I can confirm that all tests are done under same circumstances, which are, I admit, not ideal (more below).

Are you sure about that relationship (V & I)? I mean different Lipos, different characteristics.
Test-3 had higher <C>, and therefore Volts wouldnít suffer (drop) as much as Test-2 Lipo, though supplying the same current. Correct me if Iím wrong.

I too am convinced that something is not quite right here: I think itís the <C> claims, but . . . (hereís the below bit, mentioned above!) . .

. . itís very hard doing these tests alone: I canít watch the powermeter, notice and write down values, operate the throttle, measure RPM, hold the plane, answer the phone and drink my beer all at once . You know what I mean! I did this at home, with no available assistants at the time.

Tests were short (>15 seconds), all with same load, and all lipos are fully charged to start. This was no endurance test.

As I was having problems with the RPM-measuring-gadget (not enough hands & feet), elected to leave that out, but wouldíve been good data to have. Though I did notice Volts/Amps/Watts in real time, when it came to writing-down time, I had to go for the values retained within the meter, (rounded to nearest 0.5-number): Amin, Vmax, Pmax.

I realise that this is not going to provide the most accurate results, but tíwas the best I could manage.
It wasnít my intention to go into this especially deeply, but got curious when the Kokam test disappointed, and then moreso after test-4.

So, the values were the extremes recorded and not averages, but the method used is consistent.
I will repeat the tests, but with a helper, and hopefully RPM too! (when I get time that is!).

Thanks for your suggestions so far.
Cheers, Bob
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