SQ pumps on mod sine wave [RE-wrenches]

[Brad Bassett]

Kirk,

My first guess would be that the water level at the SQ intake is low. I 
don't remember what the required head over the intake is, but if it's 
too low you can get cavitation and lack of performance. This is not 
usually as much of a problem with soft start pumps, but can be more of a 
problem with high speed pumps and the SQ is 10,000 rpm or so once it 
gets going. If you want to send me a sketch of the system (keep it to 
<300kb if possible)(or contact me for a fax #) I'll take a look and if 
necessary check with the Grundfos techs. I don't think the mod sine wave 
is the problem, and if you turn the pump off and on again and still have 
the same symptoms, I'd be even more inclined to dismiss the inverter as 
the problem.

My experience with pumps is that 99 out of 100 work fine and 1 out of 
100 have wierd problems that are a bugaboo to track down.

Kirk Herander wrote:
> Group,
> I have a customer running a 1/2 HP Grundfos SQ series (soft start) pump 
> on
> an old Trace U 2024 mod sine inverter. Occasionally, like once every two
> weeks, the pump won't fill the pressure tank when cut-in pressure(30 
> psi) is
> reached. The pump turns on, but the pressure hovers around 10-15 psi. 
> There
> is also a dc pump plumbed to the tank from a spring. Once we switch over 
> and
> allow the DC pump to pressurize the tank, then switch back to the 
> Grundfos,
> it will work fine for a couple of weeks until this happens again. Any 
> ideas?
> Battery voltage is not low when this occurs.
> 
> Also when cut-in is reached, the pressure will drop from 30 to 0 psi for 
> a
> second, then rise normally as the pump pressurizes the tank. Is this 
> sudden
> pressure drop to be expected from a soft-start pump?
> 
> thanks
> Kirk
> 
> Vermont Solar Engineering - a Xantrex / Trace Certified Dealer
> Kirk Herander
> PO Box 697
> Burlington, VT. 05402
> www.vermontsolar.com
> www.backeastsolar.com
> 800.286.1252 - 802.863.1202
> fax 802.863.7908
> 
> 
> 



Brad Bassett
Schott Applied Power 
Tumwater, WA office
bsbassett at earthlink.net

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