www.enerdrive.com.au Page 41
The above images are also indicating that busbars are being used to respectively join all positive
and all negative battery cables. Besides this, all positive and negative battery cables that are
wired to these busbars need to be of equal length. These precautions are made to avoid any
imbalance between the di erent series strings, to ultimately improve the overall accuracy of the
midpoint voltage measurement.
Practical Information
Typically, the midpoint deviation is smallest when the battery bank is not being charged or
discharged. However, even with only healthy batteries in the series string, a temporary imbalance
will occur:
• during the absorption charge stage
• when the battery bank is being deeply discharged
• when the battery bank is exposed to very high ch
arge- or discharge currents
Under these conditions, the midpoint alarm may trip. For this reason the default alarm On delay
is set to 300 seconds, as this is still considered a short enough time to not damage the batteries.
The default setting for the maximum deviation percentage (for formula see ) is 2%, which is
considered a good value for 24V systems. For 48V systems, this percentage should be around
1%. Despite these default settings, the user should still accept an occasional alarm during the
three above mentioned conditions.
In case the midpoint alarm trips frequently or unexpectedly, one or more batteries or cells may be
dying or reaching their end of life. The batteries or cells should be measured individually with a Volt
meter to nd the potentially defect battery. In case of paralleled series strings, please make sure
to remove the midpoint interconnection cable(s) rst before measuring the individual batteries.
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