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flafix (Mechanical) (OP)
28 Aug 06 8:28
Can I eliminate the centrifugal start switch ( which is broken, cannot find replacement parts) on a 1/2HP motor, with a solid state device such as a Supco R041?
jraef (Electrical)
28 Aug 06 14:14
No. That appears to be an overload protection device. The centrifugal switch is used to switch the starting and running capacitors in the motor. Without that, the motor will not turn. The centrifugal switch has nothing to do with overload protection (other than the fact that if the motor doesn't turn, it overloads!). It shouldn't be too difficult to replace that switch though.
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

flafix (Mechanical) (OP)
28 Aug 06 16:04
The R041 is a start relay/overload device. I have installed them on refrigerator compressors with or without start capacitor. The motor is a Superline Frame A71 Type SP-KR made by Murai Kiki Corp. Japan under licensed by Mitsubishi. I cannot find an any parts suppliers for this motor. The drive dogs for the centrifugal throw out are broken. If you can direct me to a supplier that may have parts I would replace them. If not I will work on a solid state start relay solution. I also have a Supco Starter Pow-R-Pak Model SPP that I picked up at the parts house the other day. I was wordering if a split phase start motor would work with a solid state start device.
aolalde (Electrical)
28 Aug 06 17:43
You can use a  NO Contactor to bypass the centrifugal switch. The contactor will be operated by a relay sensible to the line current. It will make with the inrush current and will open when the line current drops to around 150% full load current.Probably you will be able to get the same logic with solid state circuits.
itsmoked (Electrical)
28 Aug 06 19:01
I had a gas dryer that had the start winding running thru the 'Start Cycle' switch.  You had to turn and hold the switch long enough for the motor to start. Rather like starting a car.  I don't know what was used to latch the motor ON once it was up and running..

Keith Cress
Flamin Systems, Inc.-

waross (Electrical)
28 Aug 06 19:07
Hi Keith;
In a drier the centrifugal switch is commonly double throw.
The normaly open contacts turn off the heat if the motor stops and are also used to seal in the motor control circuit.
This arrangement seems to be unique to motors on clothes driers.
itsmoked (Electrical)
28 Aug 06 19:14
Ahhh! Thanks waross for that.  Makes total sense to how I remember that dryer working.  I was in it all the time.  It was one of those 'fiddling required' models.  It had a buzzer for an igniter that interfered with half the stuff in the house. The contacts burned out constantly, (since they lived in the flame).

Keith Cress
Flamin Systems, Inc.-

flafix (Mechanical) (OP)
4 Sep 06 0:14
The RO41 worked fine. The ice shaver is back up and running. Making snow cones once again.
mc5w (Electrical)
4 Sep 06 1:37
The centrifugal switch is a clothes dryer also has an additional normally open contact that activates the burner or the electric heating element.

Some of the solid state motor starting relays on the market can self adjust for a particular size motor, partiularly the ones that can add a starting capacitor. A so called hard start kit converts a permanent split capacitor refrigeration compressor to capacitor start capacitor run and uses the voltage across the start winding rather than the current through the run winding.

The classic split phase starting relay was made by Texas Instruments and had the coil in the run winding and a normally open contact for the start winding. These were gravity sensitive and used gravity to open the contact. To get a relay that would work for a goofy size refrigerator motor that was made in Italy I had to get a smaller size relay, unwind all of the winding turns ( 70 ) and then rewind on the number of turns ( 60 ) that would get this motor to work.

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