Midpoint Voltage Monitoring; Battery Bank And Midpoint Wiring Diagrams; Connecting And Monitoring Midpoint In A 24V Battery Bank - Victron energy SmartShunt Manual

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Manual - SmartShunt

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.

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

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

damage all other batteries.

Always use busbars when applying midpoint voltage monitoring. The cables to the busbars must all have the same length.

Midpoints can only be connected if corrective action is taken in case of an alarm.

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Midpoint voltage monitoring

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