Midpoint Deviation Calculation; Setting The Alarm Level; Alarm Delay; What To Do In Case Of An Alarm During Charging - Progress Solar/Wind SLT 700 Series Operator's Manual

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

9.2. Midpoint deviation calculation

The battery monitor measures the midpoint and then calculates the deviation in a percentage from what the midpoint should be.
Where:
d is the deviation in %
Vt is the top string voltage
Vb is the bottom string voltage
V is the voltage of the battery (V = Vt + Vb)

9.3. Setting the alarm level

In case of VRLA (gel or AGM) batteries, gassing due to overcharging will dry out the electrolyte, increasing internal resistance
and ultimately resulting in irreversible damage. Flat plate VRLA batteries start to lose water when the charge voltage approaches
15V (12V battery). Including a safety margin, the midpoint deviation should therefore remain below 2% during charging. When, for
example, charging a 24V battery bank at 28.8V absorption voltage, a midpoint deviation of 2% would result in:
Obviously, a midpoint deviation of more than 2% will result in overcharging the top battery and undercharging the bottom battery.
These are two good reasons to set the midpoint alarm level at not more than d = 2%.
This same percentage can be applied to a 12V battery bank with a 6V midpoint.
In case of a 48V battery bank consisting of 12V series connected batteries, the % influence of one battery on the midpoint is
reduced by half. The midpoint alarm level can therefore be set at a lower level.

9.4. Alarm delay

An alarm delay is in place to prevent the occurrence of alarms during short-term deviations that will not damage a battery. The
alarm is triggered when the deviation exceeds the set alarm value for more than 5 minutes. If the deviation exceeds the set alarm
value by a factor of two or more, the alarm will trigger after 10 seconds.

9.5. What to do in case of an alarm during charging

In case of a new battery bank the alarm is usually due to differences in the initial state of charge of the individual battery. If
the deviation increases to more than 3% you should stop charging the battery bank and charge the individual batteries or cells
separately. Another way is to substantially reduce the charge current to the battery bank, this will allow the batteries to equalize
over time.
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Manual - BMV-712 Smart
Midpoint voltage monitoring