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Pump powered by a modified sine wave inverter not functioning
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NO Way

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angry.gif Pump powered by a modified sine wave inverter not functioning
Pump powered by a modified sine wave inverter not functioning

From: No Way
Subject: Re: Grundfos SQ pump used on modifed sine wave inverter
Date: Sunday, 02/01/2015 18:04

This 1 horsepower, 5 gpm pump was installed about a year ago, 375 feet down in a 400 feet deep well. It worked fine, with "soft start"starting current ramping up gradually on startup as advertised. Suddenly about 2 weeks ago it stopped working. Warranty expired about 6 months ago.

Now when switched on there is a pause for about one second, then about a second of low power draw (less than 20% normal load), a one second pause, then another second of low current draw, a pause, then a surge large enough to quickly draw down 4500 watts of solar panels and the storage batteries to the point that the inverter kicks off due to low voltage. Surge amperage is too brief to measure. Inverter input and output voltages are steady until the big surge hits.

Inverter is 2500 watt, 240 volt, modified sine wave output (5000 watt peak).

Previous pump was another Grundfos SQ, but 1/2 horsepower, 5gpm, installed about 3-4 years ago..This pump was powered by a 2500 watt, 120v modified sine wave inverter. It was replaced to have a higher lift, deeper installed pump. Old pump was then installed in another well and is still working fine.

Thank you


On Thursday 01/29/2015 at
14:48, No Way wrote: My 3/4
hp Grundfos SQ pump died 2 weeks ago after one season of
use. This is the Grundfos response -

Sorry for the

The SQ and SQE pumps
are designed to use AC power (electrical requirements shown
below). Having said that, you can used DC power as long as
you use an inverter to convert to 1x200-240V with a +6% and
-10% tolerance as dictated by the requirements below. The
problem I am seeing with your setup is the use of a modified
sine wave inverter instead of a pure sine wave inverter. The
modified sine wave causes problems due to its inherent
current spikes as compared to the pure sine wave where the
current alternates smoothly. This type of setup will likely
cause excess heat buildup, potentially damaging the motor. I
suspect this is why you are experiencing issues with the
ramp-up, as it should be build current smoothly for the
"soft start" feature of the SQ electronics.

Grundfos Product Suppor
02-02-2015 11:47 AM
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