Jan 26, 2006, 09:18 AM Registered User Joined Jan 2006 7 Posts 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
 Jan 26, 2006, 09:25 AM Registered User Huntington Beach, CA Joined Dec 2004 481 Posts 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
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.
 Jan 26, 2006, 09:31 AM Use the 4S Luke USA, TX, Euless Joined Aug 2003 9,318 Posts 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.