A LOAD DUMP is a sudden large decrease in the dc output current of a battery charger. It may happen routinely, due to normal load control at a site, or abnormally, due to an emergency, system failure, or manual intervention.

If the disconnected load is inductive (a pump motor, for example), there could be a high voltage impressed on the dc bus. Normally, the battery can absorb the inductive energy, limiting the voltage rise. If the battery Ah rating is small, however, the voltage rise on the battery terminals could be substantial. This is a rare occurrence.

Another possible source of a voltage rise is the charger itself. A rectifier SCR, if it’s conducting at the instant the load is dumped, continues to conduct until the end of the half cycle at the line frequency. The energy that it passes through to the output charges the filter capacitors, which may rise by several volts (again, unless the battery is able to absorb the excess energy).

The voltage rise due to inductive energy can be handled by a free-wheeling diode connected across the rectifier bridge. This is a standard component in the AT charger, and is included in the optional motor starting kit for the SCR/SCRF charger.