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Cellpro 10s question

Old 10-29-2008, 11:02 PM
  #1  
Curtster
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I have a question related to one of the Cellpro 10s charger functions, and no doubt someone has an answer.

When reading thru the instructions (What instructions? There weren't any in the box!?!? Ohhhh, the ones a buyer must download and print out themselves? Yeah, those.... grrrrr!), it says that if the battery is connected using the balancing plug and the discharge wires, during charge the pack's internal resistance will be displayed in milliohms.

Ok, now what do I do with the readings? As an example, a recently charged relatively new Rhino (zippy) 3s 2150 pack registered 7.3, 5.2, and 5.5 milliohms internal resistance. What does that mean? Is a flay rod askew on the treadle (Monty Python)? Or is it suffering from sinusoidal deplenaration (The Retroencabulator)?

Seriously, what does it mean?

Thanks in advance!

Curt
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Old 10-30-2008, 03:27 AM
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coro
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Internal resistance determines, what voltage drop will occur inside the cell if the pack is loaded by certain power.

Since 7 mOhm versus 5 mOhm is not that high difference, as it means 0.007V versus 0.005V per 1 ampere of load current, it seems to say nothing valuable.. However, at 60 amperes it gives 0.42V versus 0.3V voltage drop.. Still not that high, but..
But the heat produced inside the cell at that 60A load, is 25.2W versus 18W..
Well, if both cells will stay below critical temperature, it may still mean nothing. But even if the better of them will get warm but still OK, the worse one may outreach the border and it will say bye-bye to You. Hopefully, not in flight..
:-)

You do not need to take care about it, but it says a lot..
The difference of internal resistances between cells, is what determines the health of Your cells in a pack, and one cell higher then others, means that it was probably hurt somehow. Or it was manufactured with a little defect, perhaps..

And, the absolute value, determines pack age, and pack capability of delivering power.
And, the increase of Ri of the certain pack, compared to Ri of the same pack when it was new, may unveil that it is getting old, or it is abused by Your way of using it.. and its power is fading away.

Or, it may just show that it is getting cold, outside - Ri of Lipos is increasing if cold..
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Old 10-30-2008, 03:57 AM
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Coro,

Thank you so much for taking the time to write such a detailed explanation in terms that even I can understand. It seems as though the worst difference so far in my packs is about 2-2.5 milliohms, so I won't worry about it for now.

Thanks again!

Curt
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