Midpoint Voltage Monitoring; Battery Bank And Midpoint Wiring Diagrams; Connecting And Monitoring Midpoint In A 24V Battery Bank - Victron energy SmartShunt 500 A Manual

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.
•

9.1 Battery bank and midpoint wiring diagrams

9.1.1

Connecting and monitoring midpoint in a 24V battery bank

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.
28
OK
GOOD
WRONG
Vbatt+
Aux
SHUNT