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I currently have a sump pump in my basement. I recently lost power during a rain storm and had to pump water out by hand until power was restored so I am looking to install a battery backup for the sump pump. I already have a 110 amp hour marine deep cycle battery which powers a 60 foot pound electric trolling motor for at least 4 hours so I believe that a sump pump should be able to be powered by this deep cycle battery.

I was looking at the sump pump and saw that it should take 920 watts when it is operating and I calculated that by multiplying 8 amps at 115 volts which is what the cap on the top of the sump pump says. I was looking at power inverters and I was wondering would a 1000 watt power inverter be enough power? I heard that when sump pumps first turn on they use more power than their continuous operating level.

EDIT- I was planning on keeping the sump pump plugged in to an outlet unless we lose power. If we did lose power, I was planning on unplugging the sump pump from the outlet and plugging it into the inverter that was being powered by the marine deep cycle battery.

  • Don't invert the power, it's too inefficient. Instead add a second battery powered to the pit, or replace the existing pump with battery powered. (They come with a charger circuit). If there's room in the pit second punps are nice to have as backup as well. – Tyson Feb 10 '18 at 19:32
  • Water powered backup sump pumps also exist, they're good as long as you aren't on well water. They use water pressure/venturi effect that is used to pump water. – Dotes Feb 10 '18 at 23:28
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There are a few aspects to consider.

Run time

Look at the history of how long power stays out when it goes out. Some causes can be corrected within a few minutes. If a crew needs to be dispatched to fix a downed power line, it could easily be hours. If there are many power lines down, it can be a lot longer than that.

Your 110 AH battery should power the pump for around 3 hours until it ages, given that the pump cycles on and off. If you're in an area that often gets serious storms, you might want a bigger battery, a second battery, or even a small generator.

Availability

But what if you're not at home to switch the power? Tyson's suggestion of adding a battery powered pump will, at a minimum, buy you some some time to get there and switch things if necessary.

Redundant pumps are a good idea, anyway, since sump pumps do fail independent of a power outage (pump or float switch; I've had to replace the float switch on ours about every 4 yrs.).

Inverter

If you go the inverter route, get one with a lot more spare capacity; 1000 watts is enough for the pump while it's running, but the pump takes very high current to start, which could pop the inverter's breaker; then you have no source of power. A battery-powered pump is better for this reason (in addition to Tyson's point that the proper charging circuit is typically built-in).

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I had a commercial battery back-up unit over 20 years ago. It powered a separate DC pump. The point I would add is during an extended outage, I pulled a battery out of a car and switched it with the back-up battery. Inconvenient , but rarely needed.

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