Battery Balancer - Victron Energy

Description

The problem: the lifespan of a battery bank, which is expensive, can be considerably reduced due to charge imbalance.
A battery with a slightly higher internal leakage current in a 24 or 48 V bank of several series/parallel connected batteries will cause the parallel connected batteries to be undercharged, and the series connected batteries to be overcharged. Furthermore, 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 charge phase, but larger differences will cause damage due to excessive gassing of batteries with a high initial state of charge (caused by overcharging), or sulfation of batteries with a low initial state of charge (caused by undercharged batteries).


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

If applicable, several 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 reduces 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 lit, and open if the red LED is off.

Alarm reset
Two terminals are available for connecting a push button. By connecting the two terminals, the relay is reset. The reset condition remains active until the alarm condition has expired. Subsequently, the relay will close when an alarm is triggered again.

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 percent. Separate deviation percentages can be set to trigger a visible/audible alarm, and to close a relay's dry contact for remote alarm purposes. Please consult the BMV-702 manual for more information on battery balancing.