question

hvalentim avatar image
hvalentim asked

How to calculate expected tail current when battery internal resistance while fully charged is know?

My lead acid batteries are brand new. The manufacturer supplies a value of 0.33mOhm of internal resistance when a battery is fully charged at 25°C.

We are talking about a 12x2=24v battery bank. So let’s forget about the cables connecting the batteries (2x70mm2 BTW) and assume a total resistance of 12x0.33mOhm = 3,96mOhm

Under an absorption voltage of 28,8v at 25ºC how much tail current should one theoretically expect when SOC=100%?

Does anyone know the proper math?

MPPT Controllersbattery chargingSmartShunt
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Image pinched from the SmartShunt manual.

tail-current.png

A tail current range between 2 - 4% would be considered normal.

Perhaps your battery manufacturer has a recommendation?


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kevgermany avatar image
kevgermany answered ·

Not sure why you want to calculate this. Easiest is to measure it. Keep the battery at absorption with lo load, wait until current finishes dropping and stabilises and that is actual tail current.

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