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speed control on single phase motor
2

speed control on single phase motor

speed control on single phase motor

(OP)
Is there a way to wire a 1/4hp capacitor-start motor so that you get a slow and a fast speed?  I am trying to replace a blower motor on a hydronic ceiling unit in a gym and they are wired for slow and fast speeds, yet the nameplate of the existing motor is single speed, 1725 rpm.

RE: speed control on single phase motor

The short answer is if you need multiple speeds, buy a multiple speed motor. Some air moving motors are part of a motor ballast package. Some just use some series reactors to slow the motor but you will be taking a chance replacing one with a generic single speed motor.
The other option is a two speed motor, but a 2:1 speed ratio is not much good for fans.
The motor may have been changed from the OEM motor already.
But if you take a chance and connect a single speed motor to an existing speed reducing reactor, monitor the current. If the motor runs slower and the current is below the nameplate value you may be safe.
Disclaimer; You are on your own. If you come back complaining that you changed a special purpose motor to an off the shelf generic motor and it failed, I will disavow all knowledge of this conversation, change my handle and disappear.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: speed control on single phase motor

2
New PostwlbIII; To answer your question, generally not.

There are some motors in air handler service that seem to have 3 or 4 speeds when you run them on different taps.

Keith Cress
kcress - http://www.flaminsystems.com

RE: speed control on single phase motor

There are variable speed drives (controllers) for 1 phase motors, but they are not designed to be used on capacitor start motors. they can be used on PSC or Shaded Pole designs.


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RE: speed control on single phase motor

if you notice the prices of any kind of single phase AC motor speed controllers, you will see that you could buy an eBay 3 phase motor and a standard VFD for less - and hence avoid any freak shows.

Keith Cress
kcress - http://www.flaminsystems.com

RE: speed control on single phase motor

"What Itsmoked said."  A Star for Keith.

RE: speed control on single phase motor

My furnace has a motor wired for slow and fast speeds.  I can't imagine I could make it work (easily) with a VFD and a 3 phase motor.  The motor has to match the existing control board.  Basically you have the wrong motor and need to get the correct one.  

RE: speed control on single phase motor

I replaced a very old gravity feed furnace with one that had a three speed motor.  The old duct work was over  12 inches in diameter and offered none of the restriction new duct work has.  Even at the slowest speed it pushed too much air!  I ended up using an auto transformer to drop the voltage and restricting the inlet air size to get the airflow I wanted.

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