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I have 1/3 horsepower sump pump currently plugged into my home's 120 volt outlet. I have a 105 amp hour 12-volt battery and a 1200 watt pure sine inverter ready to go when the power goes out.

The only issue is if the power goes out, I would need to be home to physically unplug the sump pump plug from the wall outlet and plug it into the power inverter and also switch the power inverter on which is connected to that 12 volts 105 amp hour battery.

Is there a switch of some sort that I could get to automate the process where the inverter could be switched on and the sump pump automatically get power from the battery without me having to be home to physically move the plug over?

Justin Todd
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6 Answers6

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Another answer by Fresh Codemonger suggests having two pumps, one on regular power and the other on your inverter.

I would like to suggest a similar option that I think is more efficient.

As the other answer says, you should have a second pump. However, instead of connecting it to your inverter, your second pump should be one that is designed to run directly from 12VDC and have a battery charge controller. That way, the pump itself maintains the battery charge and automatically turns on when needed. That removes the need for the inverter, resulting in a simpler and more energy-efficient setup.

There are also a number of sump pump companies that actually make a 2-in-1 pump which has both a 120VAC pump and a 12VDC pump in the same unit. It automatically switches between them as needed.

Moshe Katz
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I think the easier thing to do is to have two sump pump connected. The first on household power and the second on your battery. The first would have a start sensor at a lower spot than the battery sump sensor. This way the battery one only runs if the water reaches above a high spot. This will also give the added benefit that if the household sump pump fails independent of power the battery based one will still take over.

Fresh Codemonger
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You don't want to do that.

An inverter powerful enough to start a sump pump will also have high standby losses. It will burn your battery down in short order.

When you're dealing with a 12V system this small, you want all the loads to be DC.

It might be tolerable if you only spun up the inverter for the second per day the pump was actually in operation. However, leaving it spinning 24x7, the inverter will account for 95% of the battery's capacity; very little will actually pump water.

Pumping water is cheap (energywise). Get a 12VDC sump pump that is 100% off when it's off.

One option I have considered is to have a supervisory system (like an Arduino) spin up the inverter on some event (hourly?) then monitor until current draw goes below what a fridge draws, then shut off. shut down the inverter on low current draw. If the fridge or sump pump was needed, they'd run until done, then the inverter would see they've stopped drawing, and shut off.

By the way, you should seriously consider augmenting your battery with a modest sized solar system. A solar panel can keep that battery topped up.

Harper - Reinstate Monica
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Depending on how handy you are with electrics and/or basic electronics, you could build a relay circuit that switches your pump over to the inverter (and a second relay to connect the battery, to avoid the inverter idle drain sucking your battery dry before it's actually needed).

(I don't yet know how to add diagrams to a post here, else I'd draw up a minimal circuit for that function..)

WooShell
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I accomplished the almost exact setup you are looking for. 1 - 1/6 hp ac sump pump that switches sources when power goes out. I wired up a 2 pole relay that has the sump connected to the common terminals. Normally open contacts connect to the city power and normally closed contacts connect to the inverter. With the coil connected to the normally open contacts(city power), it stays energized until power goes out then switches power sources. I have a smart charger connected to the batteries to maintain the battery life.

user68386
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Why not use a smart inverter with all this built-in? They charge the battery with city power, then automatically switch to inverter power when city power goes out. The sump pump is plugged directly into the inverter.

DIY-Doc
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