Sizing Inverters for Sump Motors

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ee.van

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Hi All,

I am attempting to size a Inverter Charger for 2x 0.5HP Pumps (115v 10.5A) as a backup solution in case of power outage.

I was thinking about a 3000VA Victron Multiplus Inverter Charger to Run the 2 Units.
I think I am a little confused between the 3000VA rating vs 2400w, both pumps running at the same time (after inrush) will technically overload the inverter.

Thanks for the help.
 
It would be far more efficient to use 24vdc pumps run directly off deep cycle or AGM batteries And simpler, less to fail.
 
ee.van said:
Hi All,

I am attempting to size a Inverter Charger for 2x 0.5HP Pumps (115v 10.5A) as a backup solution in case of power outage.

I was thinking about a 3000VA Victron Multiplus Inverter Charger to Run the 2 Units.
I think I am a little confused between the 3000VA rating vs 2400w, both pumps running at the same time (after inrush) will technically overload the inverter.

Thanks for the help.
Click to expand...
VA = Volts x Amps
Watts = VA x Power Factor.
Small 115V motors typically have about a .8 power factor, so the 3000VA unit x .8PF = 2400W capacity.

746W / HP, so 1/2HP = 373W, plus losses of about 5-6% = approx. 400W, x 2 motors = 800W load once running.

But...
10.5A FLA, on startup will be roughly 63A starting current, x 120V = 7560VA.
The inverter "Peak" output is 6000W, assuming .8PF = 7500VA, so you MIGHT be able to start ONE motor, but not if the other one is already running. You will likely trip this inverter on Overload.

Consider Tom's suggestion...
 
Thanks for the suggestion Tom! The pumps are a permanent fixture with no room to make any additional mechanical modifications.

I will likely go with 2x 2000VA (1600w) Victron Multiplus running in parallel with a motor soft starter(s) to attempt to limit current.
 
I suggested 24 vdc to minimize volt drop. Look in home power magazine, there is a lot of dc power equipment available for off grid users
 
Soft starters often don’t work well on the output of an inverter. Soft starts have to know where the Azeri cross point of the sine wave is, and dies so my detecting the rise and fall of the waves crossing each other. In an inverter output that is not as simple as it is in utility power. I’ve had about 50% success trying to make that work. Good luck.
 
Thanks Jreaf + Tom,

Its likely best to just source a 3000w inverter with a 9000w surge and just hard start each motor.

That or commit to mechanical changes to 24v pumps.
 
There is a significant efficiency loss with the inverter.
12VDC>inverter to 120> pump
Or
12VDC > pump
Also a sump pump tends to start and stop frequently, that would be hard on the inverter
There are package battery back up sump pump systems available…..
 
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