Controlling Water Pump Speed

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Controlling Water Pump Speed

Post by WildBoar » Fri Mar 12, 2004 1:51 pm

Years ago (when I had the patience of a saint) I
experimented with every kind of SCR/Triac based
control circuitry. I breadboarded heating element
controllers, lamp dimmers, motor speed regulators,
etc. It was almost like being addicted to a drug!
Every new schematic I could find in a book or
magazine was immediately plugged into my
breadboard. <p>I've never heard the voice of God, but after several
months of experimentation a little voice in my thick
head said to me, "how many of these circuits are
you going to try before you realize that 99% of them
work properly 50% of time, at best!" In other words,
I can't ever remember breadboarding one of these
Triac based controllers that could be put in a box and
used in a real world application without the constant
worry that something might go wrong.<p>Now I've got a real world problem. I need to control
the speed of the most ubiquitous water pump ever
made. A common washing machine pump. (The kind
found in every $300.00 Sears top loading washer.)
I've replaced several of these pumps over the years
for friends and family. They are amazingly powerful.
You can easily fill a five gallon bucket in a few seconds
with one of these pumps.<p>Is there a truly reliable circuit for controlling the speed
of a washing machine pump? I would be just as happy
purchasing an already built and tested unit, as long as
the cost isn't outrageous.<p>Thanks guys!<p>WildBoar

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Re: Controlling Water Pump Speed

Post by MrAl » Fri Mar 12, 2004 2:21 pm

Hello there,<p>Does that particular motor have brushes?<p>I had built several triac controllers of
varying current handling capacity.<p>One used a 25 amp triac and it controlled
a big grinder, but the motor did have brushes--
that's a requirement for the kind of circuit
im thinking of.<p>Take care,
LEDs vs Bulbs, LEDs are winning.

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Chris Smith
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Re: Controlling Water Pump Speed

Post by Chris Smith » Sat Mar 13, 2004 5:07 am

NO,.... most appliances have the standard AC motor which doesn’t lend it self to motor speed control beyond a few rpms with out stalling. They don’t use expensive type motors in appliances and so your best bet is to control the flow, using restrictions in the out put or input of the water end of the pump.

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Re: Controlling Water Pump Speed

Post by dacflyer » Sat Mar 13, 2004 12:04 pm

there are ac brushless motors and they do not have start/run cycles in them,, i forget what they are called.. universal motors? like as in a window fan etc they do make them bigger and more powerful too... anyway you can use a regular fan speed controller on them ..they handle about 10amps if i rember right
and they would be fine on a pump like you talk about,,<p>what do you plan to use this pump for? you probably could use just a valve on it,, i know these pumps well they must have water in them to pump...i mean they are not self priming..thats why they are under the tub of the machine..and the hose is higher than the tub.. you could use a valve on them with out hurting the pump .altho you might want a screen on the input side to prevent trash getting into them,

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Re: Controlling Water Pump Speed

Post by perfectbite » Sat Mar 13, 2004 1:59 pm

For regulating centrifugal pumps, which is what this is, DO NOT regulate the fluid input to the pump body. A partially full (inlet regulated) pump chamber will cause cavitation (which can produce steam in the pump chamber under certain conditions), air binding of the pump, over heating and failure of the pump bearings, seals and the motor bearings (heat transmitted to them via the motor's shaft). Centrifugal pumps are designed to be run flooded. Positive displacement pumps are a different matter.

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Re: Controlling Water Pump Speed

Post by WildBoar » Sat Mar 13, 2004 2:08 pm

Thank you very much MrAl, Chris Smith,
dacflyer, and perfectbite.<p>I really appreciate all of your responses
to my posting.<p>WildBoar

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