Midpoint Voltage Monitoring; Battery Bank And Midpoint Wiring Diagrams; Connecting And Monitoring Midpoint In A 24V Battery Bank - Progress Solar/Wind SLT 700 Series Operator's Manual

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Manual - BMV-712 Smart

9. Midpoint voltage monitoring

One bad cell or one bad battery can destroy a large, expensive battery bank.

A short circuit or high internal leakage current in one cell for example will result in undercharge of that cell and overcharge of the

other cells. Similarly, one bad battery in a 24V or 48V bank of several series/parallel connected 12V batteries can destroy the

whole bank.

Moreover, when new cells or batteries are connected in series, they should all have the same initial state of charge. Small

differences will be ironed out during absorption or equalize charging, but large differences will result in damage during charging

due to excessive gassing of the cells or batteries with the highest initial state of charge.

A timely alarm can be generated by monitoring the midpoint of the battery bank (i.e. by splitting the string voltage in half and

comparing the two string voltage halves).

The midpoint deviation will be small when the battery bank is at rest, and will increase:

• At the end of the bulk phase during charging (the voltage of well charged cells will increase rapidly while lagging cells still need

more charging).

• When discharging the battery bank until the voltage of the weakest cells starts to decrease rapidly.

• At high charge and discharge rates.

WRONG: The midpoints are connected and without busbars

GOOD: The midpoints are not connected and without

or midpoint monitoring.

busbars or midpoint monitoring.

Due to the voltage drop over the positive and the negative cables the midpoint voltage is not identical.

In an unmonitored battery bank, the midpoints should not be interconnected; since one bad battery bank can go unnoticed and

could damage all other batteries.

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Midpoint voltage monitoring

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