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Old Jan 08, 2009, 03:43 AM
VK2TKW is offline
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Of course if you have a watt meter like "Wattsup" and i suspect most do, then plug it in to the battery and record the no load battery voltage. Next connect this now to your ESC and motor. Run the motor up to record a reasonable current then record the current and new voltage. The difference in battery voltage is the voltage lost due to the internal resistance (IR) (and of course connectors etc) Using the same maths above you can calculate the IR. eg using the same setup as the first example you measure unloaded battery as 8.4V and when supplying 9 amps it has dropped to 7.5 volts.

Voltage drop = 8.4-7.5 = 0.9 V

R=E/I = 0.9/ 9 = 0.1 Ohm

Same result but with a meter I already have and accurate enough for the exercise.

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