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Measuring Open Circuit Voltage Of A Battery

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ujjwol77

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How can i measure the open circuit voltage of a battery with the load connnected!
 

You have to know the internal resistance of the battery, the exact resistance of the load and the current.
 

This is one possible method:

Let us assume:
unknown:
Vs = open voltage of the battery
Rs = internal resistance of the battery

known
R1 = resistance of the output load
Vb1 = battery voltage with R1 connected

In this case
Vb1 = Vs * R1 / ( R1 + Rs )
or
Rs = R1 * ( Vs/Vb1 - 1 )

Now Let us add a resistance R2 in parallel with R1, we get Vb2
Rs = R1//R2 * ( Vs/Vb2 -1 )

Therefore:
R1 * ( Vs/Vb1 - 1 ) = R1//R2 * ( Vs/Vb2 -1 )
In this equation only Vs is unknown.

When Vs is calculated, Rs can be found as well.
 
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