Comparing AC-Powered vs. DC-Powered Battery Backup Sump Pump Systems

Power outage can be a common occurrence during a severe rain storm and can lead to considerable water damage to the home. The sump system in a home typically relies on a heavy duty AC primary pump to discharge water entering the home through its drainage system. To compensate for the possibility of a power outage, the sump pit may include a battery-operated DC or AC driven pump in addition to the primary pump.

While pump qualities differ greatly, pump performance can be determined by an independent testing agency, thus assuring contractors of the highest quality pumps available. The values should have been generated at an 8-10 ft. head. The head is the distance that the pump discharges vertically (in a basement, it is usually 8-10 ft).

How do these AC/DC back-up pumps differ in function and performance? The best way to compare different available systems is to compare time and performance. This is based on the total amount of gallons discharged by a pump accompanied by a fully charged battery recommended by the manufacturer.

DC systems efficiently consume DC current and can run continuously for several hours (up to 10 hours continuously and intermittently for several days). A DC based back-up system typically consists of a DC pump, a 12 volt deep cycle battery (2 batteries if a 24 volt system), and a charger. Most DC pumps used as part of a back-up system were initially designed to be bilge pumps for boats and although not considered heavy duty, may still perform well.

A characteristic of a DC system versus an AC system is that the rate that it discharges is related to the degree that the battery power source is charged. A fully charged 12 volt battery will power the DC pump to its maximum capability. As the charge of the battery is consumed, the pumping rate of the DC pump diminishes. For example, a given DC pump will discharge at the rate of 30 gallons per minute with a fully charged battery, but may only be pumping at 15 gallons per minute when half of the battery charge remains. At the end when the battery is about to be depleted, the pump may be discharging at less than five gallons per minute.

An AC based back-up system typically consists of an AC heavy duty pump, a 12 volt deep cycle battery (or two batteries if a 24 volt system), and an inverter with a battery charger. An inverter converts the DC power of the battery to its AC counterpart. Unlike a DC pump, an AC pump will run close to its maximum potential capability until the battery charge is depleted. For example, if the AC pump can pump at a rate of 50 gallons per minute, it will continue at close to this rate (with minimal loss over time) until the battery power source is depleted.

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