# Testing 200ah TS

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I am using a CBAIII and testing some 160ah TS cells. What should the sag be if pulling 10amps? How about 20amps?

thanks
Francis
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#### DavidDymaxion

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Sag = (Internal resistance) * (Current).

Note if you go from 0 to some current you can get a higher sag than if you go from I1 to I2 currents -- batteries can have a "surface charge" that gives them high voltage right off charge that dissappears quickly.
I am using a CBAIII and testing some 160ah TS cells. What should the sag be if pulling 10amps? How about 20amps?

thanks
Francis

#### Tesseract

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I am using a CBAIII and testing some 160ah TS cells. What should the sag be if pulling 10amps? How about 20amps?

thanks
Francis
It's going to be tough to determine the internal resistance (Ri) data on a 200Ah cell if you can only load it at 0.05C or 0.1C. You are trying to measure a resistance in the milliohm range, and 10A across 1 milliohm results in 10mV of drop. You need a damn good meter to measure that accurately. If you can make the difference in testing currents at least 100A then even a crappy hardware store meter will let you make a decent Ri calculation.

Oh, and definitely test at two different currents, not 0A and some current, to get Ri. Surface charge is very minor in LFP, but on a TS 200Ah cell I have right here it is 16mV going from 0A to 3.4A of load. That totally swamps the actual internal resistance I've measured for this cell of 1.7 milliohms.

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