Automatic industrial battery chargers (e.g. EA-BCI series of automatic battery chargers) feature a false polarity check. The above mentioned test rig should also contain this. When connecting a BUT (battery under test) to such test rig or EA-BCI series charger, the output relay status is OFF. Both, test rig and BCI would then do the following:
a) Check the connected BUT for correct polarity.
Note: if a battery is connected to a DC power source with reverse polarity it will cause something similar to a short-circuit and can heavily damage the DC source’s output circuit (see figure 2).
In case the polarity is correct, it would then:
b) Check the BUT’s voltage to set the DC source’s output voltage to the same level as of the BUT. Note: a switching mode DC power source has a very energetic capacitance on the output, serving as output filter. If this filter is discharged and a battery is going to be directly connected to it, the result will be a sudden high-energy discharge from the battery into the filter and subsequently cause a heavy spark (see figure 3). Only if correct polarity is detected and the voltage levels of DC source and BUT have been equalized, the output relay will be set to ON status and sub- sequently connect DC source to battery, allowing to initiate the charging process.