Backup Power Supply for a Sump Pump

Primary Pump

Most homes with a basement have a low point in the foundation, called the sump pit or basin, that collects water. During a rainstorm, it will begin to fill with water. A pump in the basin switches on when the level rises to a certain point, but well before it can reach the basement floor. When the water level drops below its normal level, the pump shuts off. The home builders select a pump with enough capacity to remove the water in a few seconds. This pump gets its power from the household alternating current, or AC wiring that runs the rest of the house. During a power failure, the pump stops, and water can overflow the well into the basement.

A secondary pump can take over if the primary pump loses power. The secondary has an independent, separate pump and electric motor. It shares the same outlet pipe as the primary, and the outlet pipe will have check valves to prevent water from one pump from leaking back out the other. A deep-cycle lead-acid battery provides power for the secondary pump.

The charger for the secondary pump's battery ensures that the battery stays fully charged as long as the AC outlet is on. As long as the power stays on, the backup pump is kept idle. The controller may have a meter to indicate the battery's condition and an audible alarm to alert the homeowner that the backup pump's running, or that the battery needs service. When the power goes out, the controller senses the loss of voltage and enables the backup pump.

Backup pumps are sold either alone or packaged with a primary pump as a combination unit. If the home has an existing primary pump but no backup, the homeowner can install a backup pump. She can have a combination put into a new home or to replace an old primary pump.

The secondary pump will run as long as its battery holds out. Because the pump doesn't run continuously, the battery could last many hours. Homeowners in rural locations may opt to use a gasoline-powered portable generator. A generator can produce electricity for the sump pump and other critical appliances. It will keep a sump pump going as long as it's fueled, but you have to be there to operate it. A more expensive standby generator will operate automatically.