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Old Jan 26, 2006, 09:18 AM
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Question
Lipo resistance

How do you get the resistance for a particular lipo cell? ie thunder power or flight power?

Can you put a multimeter across the +ve and -ve to measure the rersistance or is that a bad idea
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Old Jan 26, 2006, 09:25 AM
TMetalMan is offline
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If you can find a way to measure amps (by using a watt meter or something else) you can figure the voltage drop at a given number of amps, and calculate the resistance that way. Voltage drop = Amps x Resistance
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Old Jan 26, 2006, 09:26 AM
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Quote:
Originally Posted by ionx
Can you put a multimeter across the +ve and -ve to measure the rersistance or is that a bad idea
Very bad idea, even more advanced (and expensive) DVM will burn.

Resistance of the cell is internal into the cell that has some voltage across it - You can imagine that it is resistor in series with batery, with no possibility to get inside this pair.
Two principles are used - first is to measure resistance using AC (pulsing to/from cell) current, often at 1kHz. This could tell You the number cloce representing real "resistance".
Second principe is to put known load onto cell/pack and measure how deep its voltage will drop (comparing to its no load voltage). This is not so exactly scientific, however can tell You more about pack/cell ability to "be usefull".
In general, Lipo resistance is very low, expected numbers are 10-50 miliOhm per cell.
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Old Jan 26, 2006, 09:31 AM
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Also the resistance is not static. It appears higher when the cell is cold and may change as the cell is discharged. The reason is that some of the resistance is due to current flow thru materials like we are used to measuring, but some is due to the chemical nature.
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