Author Topic: New Pump for off grid or battery backup.  (Read 487 times)

pumpq2

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New Pump for off grid or battery backup.
« on: September 22, 2021, 10:33:21 AM »

We are currently grid tied and have a 330 foot deep well with a static level about 40 feet down.

We would like to eventually be off grid (solar and microhydro), but as a stepping stone in that direction
have a small battery bank and solar panel set up to run the well pump when power is out.

My first look into power needs indicate a very high starting current for the well pump, and I had
read that a variable speed? variable frequency? pump has lower starting current.

What do you think may be a good solution here?


Cary Austin

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Re: New Pump for off grid or battery backup.
« Reply #1 on: September 22, 2021, 10:58:02 AM »
Sure a VFD will reduce the starting current from 6X to about 3X.  But you don't have to use A VFD to get a soft start.  Simply using the longest length of the smallest wire possible for the horsepower pump you have will create 36% less starting torque all by itself.  This reduces the current available to the motor for start up, which still works fine.  There are also pumps like the Grundfos SQ that have a soft starter built into the motor.  Studies show that you will spend 3 times as much maintaining a VFD pump system as a traditional pump system, so VFD should be the last resort.

pumpq2

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Re: New Pump for off grid or battery backup.
« Reply #2 on: September 22, 2021, 11:51:22 AM »
Regarding long thin wire...is the idea here to reduce the current carrying capacity of the conductor?  Would an inline resistor
do the same?

Looking at the SQ3-105, https://product-selection.grundfos.com/id/products/sq/sqc-3/sq-3-105-96510210?tab=variant-specifications , it says Power input P1 2.54kw, P3 1.74kw.  Do you know what P3 would refer to? 

I'm guessing my inverter would need to supply 2.54kw.

Thanks for your awesome help!

Cary Austin

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« Last Edit: September 22, 2021, 01:11:05 PM by Cary Austin »