AC pump starting currents [RE-wrenches]

[Windy Dankoff, Dankoff Solar]

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>I have been told that they are very intolerant of silt.
>Allan

The Grundfos SQ and SQE pumps are intolerant of silt because they 
turn at about 10,000 RPM instead of the old standard 3450. Imagine!

Not all variable frequency (speed) drives are high speed however. 
This IS the up-and-coming thing in well pumps, folks. I would figure 
that in general they will require sine wave, and yes they do elimate 
starting surge by starting at low frequency and ramping up. The 
system is a rectifier then a 3-phase inverter (variable freq.), and a 
3-phase AC motor.

Efficiency is about the same as conventional AC pumps. The motor 
would be better, but there's some inverter loss. The pump head is 
generally the same, except for Grundfos who uses high-speed.

I've been looking at these because, any improved technology that 
contributes to better use of AC is competition for our DC pumps! 
However, for perspective, the WEEK that the Trace SW hit the scene, 
the sales of our Flowlight Booster Pumps immediately dropped by half. 
Most SW buyers had AC capacity to spare. However, it didn't take long 
for our sales to recover, because efficiency still matters, and those 
starting surges would blink the lights even through a 4KW SW.

A handy formula for calculating the power required, or the 
energy-efficiency of any electric pumping system, is at:

http://www.dankoffsolar.com/reference/calculating.html

Windy

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