Battery Balancer - Victron Energy

Description

The problem: the lifespan of a battery bank, which is expensive, can be significantly reduced due to charge imbalance.
A battery with a slightly higher internal leakage current on a 24 or 48 V bank composed of multiple batteries connected in series/parallel will cause the batteries connected in parallel to be undercharged, and the batteries connected in series to be overcharged. Additionally, if new cells or batteries are connected in series, they must have the same initial state of charge. Small differences will dissipate during the absorption or equalization phase of the charge, but larger differences will cause damage either due to excessive gas release from batteries with a high initial state of charge (caused by overcharging), or due to sulfation of batteries with a low initial state of charge (caused by undercharged batteries).

The solution: battery charge balancing
The Battery Balancer equalizes the state of charge of two 12 V batteries connected in series, or of multiple strings of batteries connected in series, these strings being themselves connected in parallel. If the charging voltage of a 24 V battery system exceeds 27.3 V, the Battery Balancer will turn on and compare the voltage across the two batteries connected in series. The Battery Balancer will draw up to 0.7 A of current from the battery (or batteries connected in parallel) with the highest voltage. The resulting charge current difference will ensure that all batteries converge to the same state of charge.

If necessary, multiple balancers can be installed in parallel. A 48 V battery bank can be balanced with three Battery Balancers.

LED indicators

• Green: active (battery voltage > 27.3 V)
• Orange: lowest battery circuit active (difference > 0.1 V)
• Orange: highest battery circuit active (difference > 0.1 V)
• Red: alarm (difference > 0.2 V) will remain active until the difference is reduced to less than 0.14 V, or until the system voltage drops below 26.6 V.

Alarm relay
Normally open. Closed if the red LED is on, and open if the red LED is off.

Alarm reset
Two terminals are available to connect a push button. Connecting the two terminals resets the relay. The reset condition remains active until the alarm condition has expired. Afterwards, the relay will close again when an alarm is triggered.

More information and control through the median voltage monitoring function of the BMV702 battery controller.
The BMV-702 measures the median voltage of a string of cells or batteries. It displays the deviation from the ideal median voltage in volts or percentage. Separate deviation percentages can be set to trigger a visible/audible alarm, and to close a dry contact of a relay for remote alarm purposes. Please refer to the BMV-702 manual for more information regarding battery balancing.