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Old Mar 28, 2010, 04:59 PM
Alan Hahn is offline
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Chicago 'burbs
Joined May 2006
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Quote:
Originally Posted by Merlin45 View Post
@everydayflyer

Hi, and thanks for fast response and associated links with info.
I have read a lot of your posts and respect your knowledge in this field.

Using my starter base: that is, my system pulling 20A at 11V, being supplied by a more-than-adequate source operating at 10C even though it’s rating is 20C.

I bought the Kokam 1500 20C thinking that it would easily be able to supply my required 20A without too much volt-drop, and was very surprised that it didn’t reach the 20A target, only delivering 18A at 11V. Almost, but not quite. I can live with it, but it bugs me that it doesn’t cut it 100%, only 90% !

Can you please explain why can it not deliver the current? I can only think quality, or Kokam‘s optimism.
As it‘s regarded as a high quality Lipo (I thought, anyway), I am disappointed, as I thought it would manage 20A without much trouble.

Obviously as we’re talking planes here, weight and physical size are major considerations, so I was looking for a suitable Lipo which could give me 20A. That’s full gas, which I wouldn’t be using non-stop anyway.

Thanks for your trouble.
Cheers.

I am not sure why you think smaller lipos, with C ratings (1500-15C, 1500-20C, equivalent 2000-15C) will provide the same current at the same output voltage as as a 20C 2200mAHr pack--which as you say is too heavy and big for the application.

It is obvious that the C rating (even though it is an ill-defined quantity) doesn't directly correlate into providing your definition of acceptable power--even the 20C 2200 pack would fail to provide your definition of acceptable power for the C rating I think.

I will agree with you that cost is not always a good indicator of the internal resistance of a pack. However it isn't completely anti-correlated either ("high"cost does not equate with high resistance).
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