Appendix 1: Measuring The Midpoint Voltage Of A 24V Or 48V Battery Bank - tbs electronics Expert Modular Bedienerhandbuch

Appendix 1: Measuring the midpoint voltage of a 24V or 48V battery bank

Being able to measure the midpoint (or center-) voltage of a battery bank that contains multiple
series connected batteries or cells, is an important feature that can save you a lot of money in case
one of the batteries or cells is dying. One bad battery or cell can for example show a high internal
leakage current, causing an excessive terminal voltage deviation compared to the other batteries in
the series string. During charging, the healthy batteries or cells are then exposed to a too high
charging voltage, causing damage to these batteries as well. When connecting several series strings
in parallel, a bad battery or cell can cause even more damage to the surrounding healthy ones.
Wiring
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When installing a series string of batteries or cells, please make sure to only use
batteries of the same age and with identical initial State of Charge (SoC). When you
are not certain if the SoC of each battery is equal, please perform a full charge cycle
on each battery individually before connecting these in series.
When using only one series string of batteries in a 24V or 48V setup, a midpoint voltage
measurement setup can be made easily. The +B1 input should be connected to the positive terminal
of the 'upper' battery and the +B2 input to the center connection between the batteries (between
battery 1 and 2 in a 24V system and battery 2 and 3 in a 48V system). Please see the diagram below:
Please note that when using the +B2 input for midpoint voltage measurement, you should set
Function F2.0 to 'MIDPNT'. You can also configure the +B3 input for midpoint voltage measurement,
but only one of these two inputs can be used at the same time for this purpose.
When connecting multiple series strings in parallel to increase the total battery capacity, things are
getting slightly more complicated. Normally such series strings should not have interconnected
midpoints like indicated in the next image:
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