# Sump pump current draw

Posts: 39Solar Expert
Hello. I hooked up a kill a watt meter to my sump pump today and read the following watt > 910 Amps> 10.5.
The reason for all this is to figure out the surge current of the pump so i can purchase the right inverter. The numbers dont make sence since we are at 10.5
amps which is 120v x 10.5 amps = 1260w
I read a surge current for a pump can be 6 to 7 times its wattage
The kill a watt meter is telling me another story.
My question is that can i use the xantrex prowatt pure sinewave 2000w for this with out any problems.
Thanks

• Posts: 224Solar Expert ✭✭✭
Re: Sump pump current draw

Why not use a DC pump? Not sure how high you are pumping the water but maybe a bilge pump would work?

I have one of the small ones that pumps 500 gal per hour (granted at low lift) and only draws about 20 watts. I think it can lift 5-10 feet but the GPH drops and the power goes up.

These things are dirt cheap (way cheaper than an inverter, etc.)

Just throwing out an option.
• Posts: 39Solar Expert
Re: Sump pump current draw

My situation is unique i pumping 15feet up . I beleive its a 1/2 horspower home depo submersable pump. It works for me the only issue i have is that the float get stuck some times.
• Posts: 17,615Banned ✭✭
Re: Sump pump current draw

Basically, a Kill-A-Watt won't read the surge; it happens too fast for the meter to sample. There are some (very expensive) latching Ammeters that can do it.

Pumps are tricky. They don't have a fixed rate of draw. Put resistance against the motor (as in trying to lift a column of water) and the current draw goes up. Most sump pumps (pedestal type?) are about 1/4 HP. That would be 186.5 Watts if you try to calculate it from one electrical HP. See how far off the numbers are? You've already seen nearly 1 kW draw!

Rather than guess or buy an expensive meter or a much too large inverter, I like Peter_V's answer: the DC sump pump. If you want this for emergency power back-up, a pump like this one: http://www.canadiantire.ca/AST/browse/8/KitchenBath/Plumbing/WaterPumps/PRD~0623549P/Mastercraft%252BSump%252BPump%252BBattery%252BBackup.jsp?locale=en is cheaper than an inverter which could run a standard unit.
Re: Sump pump current draw

Like the other post I made about the lag of current flow vs the ac voltage waveform:

Power = voltage x current x cosine (current phase angle)

Inductive motors are not resistive loads where current follows voltage exactly (cosine of zero is 1.0).

With motors, the lagging phase angle is around a 0.6 power factor...

1/0.6 = 1.67

Or, your inverter will need to output 1.67x more current to account for the inductive qualities of an induction motor.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: Sump pump current draw

This is a complex issue and I cannot type much from my phone right now...

Centrifugal pumps use less power as flow is reduced/restricted and positive displacement pumps (like piston pumps use more).

A VFD (variable frequency drive) may also be an option for you.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 7,921Solar Expert ✭✭✭✭
Re: Sump pump current draw
andy300z wrote: »
My situation is unique i pumping 15feet up . I beleive its a 1/2 horspower home depo submersable pump. It works for me the only issue i have is that the float get stuck some times.

15' is a bit tall for a boat bilge pump, so you really need a sump pump.
pump reviews indicate 5' max lift
http://www.powerboat-reports.com/sample/bilge.html

The sticking float is a problem. that can either burn out the motor, or flood your basement, depending how it sticks. Niether is good.

What is your normal water input, 5 gallons a day? 1 GPM ? How much do you need to move ? maybe a smaller pump, with longer run times, is better than a large pump cycleing on - off - on all the time

Amazon.com has a pretty good listing and varity, but first, the amount and frequency of pumping needs to be known.

We'll try to get you to a workable solution
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