3.5 Battery bank midpoint
Battery unbalance can be detected by looking at the midpoint of a battery bank. If the midpoint is monitored it can be used to generate an alarm.
A midpoint alarm can mean the following: • An individual battery has failed, like an open cell or short- circuited cell • End of battery life due to sulfation or shedding of active material • Equalization is needed (only for wet cells) Both the battery balancer and the BMV 702 and 712 can generate a midpoint alarm.
The BMV 702 and 712 have a second voltage input that can be used for midpoint monitoring. It can be wired to the mid-point of the battery bank. The BMV will display the difference between the two voltages or as a percentage. For more info see: https://www.victronenergy.com.au/battery-monitors/bmv-700
In series/parallel battery banks it can be helpful to connect the midpoints of each parallel series string. The reason to do is to eliminate unbalance within the battery bank.
If you connect batteries in series/parallel, like the image on the right, you will see that the individual voltages will vary per series string and they will also vary within the string.
First make sure that each string has the same voltages by using a common negative and positive connection point or busbar
Once each string voltage is equal the midpoints can be connected. Make sure that the midpoint cabling is able to carry the full current between the batteries.
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