E-Flight Power Sources Ask questions or read about power sources as they specifically relate to e-flight including Lithium-ion, Li-Poly, Nimh and Nicad battery packs.

IR and LiPo batteries

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Old 04-05-2015, 02:59 PM
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Boeing
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Default IR and LiPo batteries

Being relatively new to the area of electric flight, discussions mention that IR(internal resistance) as a method of monitoring the health and condition of your LiPo batteries.

Would appreciate your thoughts on this subject. Also, electric tools available to measure the pack's IR and each cell's IR.
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Old 04-05-2015, 06:02 PM
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chuckk2
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There are IR measuring chargers on the market, as well as IR Meters.
To confuse things, there is more than one method to measure IR.
The results can vary from one method to another, and even with different
amounts of charge on the same battery.

What should the cell IR be?
It varies, depending on the the Lipo as well as the measurement method.
Smaller capacity Lipos generally have a higher IR than higher ones.
Those I have vary from a low of less than 2 milliohms per cell to about 6.
New high capacity batteries are usually the lowest, and older or low capacity
the highest. I used an FMA DPL-8 for the measurement values. When measuring IR while charging,
the charge rates can change the readings.

Some of the chargers can only measure IR while charging, (Example DPL-8)
Yet, the IR under discharge is really the one to be concerned about, since it directly
impacts in use behavior..

At different points during charging, the IR can vary.

What I look for - - -
significant differences in IR from cell to cell in the same battery.
Twice the IR is usually of concern. One or even two milliohms may or may not be.

I'd also say that direct measurement of milliohms to lab accuracy is not the simplest thing to do.

Last edited by chuckk2; 04-11-2015 at 07:35 PM.
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