Friday, August 11, 2006

pump surge

a technical lesson: motors draw lots of power when they start. why do we care? our well pump is a 3 horsepower motor that draws about 3200 watts when totally loaded. but, when it starts, it can draw 3 to 6 times that amount, sometimes more, so we're talking 9,600 to 19,200 watts! this means that our generator would have to supply this spike in power momentarily to get the pump rolling. this is wasteful because 99% of the time a generator capable of producing the peak would be woefully underutilized and inefficient, not to mention expensive.

but...i've discovered these things called soft-starters. they are devices that modulate voltage and current so that the motor starts smoothly and slowly, gradually increasing the speed of the motor until it's running full bore. this diminishes the peak load substantially and should allow us to start the pump with a generator. that's the theory anyway.

there are lots of makes of soft starters, with different configurations, complexity and pricing. one which is pretty nifty removes the need to have a pressure tank at all by keeping the pressure in the line constant. the pump, more or less, runs all the time, very slowly, using very little energy. but we can't use that one with solar, apparently. i'm working with the well driller and the manufacturer of the pump to figure out which soft starter would work best for us. ultimately, it needs to work with not only the generator but also our solar power.


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