# Capacitor for 3/4 hp 120/230v motor



## The_Modifier (Oct 24, 2009)

acro said:


> I've got an old Clausing drill press with what appears to be the original Doerr motor. The wiring has been altered by someone along the way. But 5 and 8 go to the capacitor, and I am not sure if there is a centrifugal switch, but I assume there is.
> 
> My questions are... what size capacitor is satisfactory? And am I correct in assuming the cap is a start, and not run?
> 
> Thanks


Fastest easiest method would be to ring out the fields and check their resistive values.


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## acro (May 3, 2011)

Well, 1 & 3 is one winding, 2 & 4 is the other. 5 & 8 go to the cap. 

It appears that it was still partially connected for 120v. 1 & 2 L1. 3 & 4 L2. But the cap was not connected.


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## CoolWill (Jan 5, 2019)

20 to 30 uF should be good to start it. It will probably be configured something like


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## acro (May 3, 2011)

You may be right on the cap size, but not sure about your diagram. 

I only have two windings, and my motor is dual voltage. So, series or parallel would be my options. Winding wires are black, cap wires are white. 

Keep on mind this is likely over 50 yrs old.


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## Galt (Sep 11, 2013)

5 and 8 are the start winding circuit not necessarily the capacitor for sure 5 and 8 won't both go on the cap.


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## CoolWill (Jan 5, 2019)

acro said:


> You may be right on the cap size, but not sure about your diagram.
> 
> I only have two windings, and my motor is dual voltage. So, series or parallel would be my options. Winding wires are black, cap wires are white.
> 
> Keep on mind this is likely over 50 yrs old.


Of course you have the ends of the coils. All the connections in my diagram are made externally. You have to figure out which coil is the start coil.


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## micromind (Aug 11, 2007)

This motor is almost certainly capacitor start, induction run. 

T1 & T2 are a run winding, T3 & T4 are an identical run winding. They are connected in parallel for 115 volts and series for 230 volts. These windings are directional, they need to be connected correctly or they'll fight with each other. 

T5 & T8 are the start winding connections in the terminal box. They go in parallel with T3 & T4 at either voltage. Generally speaking, T3 with T5 and T4 with T8 will give CW rotation with the shaft pointing away from you. 

The capacitor usually goes across T5 & T6. The other end of T6 is one side of the centrifugal switch and the other side of it is T8. 

On this motor, T5 and T8 will be in the terminal box (along with T1 - T4) and T5 and T6 will be sticking out of a hole in the top of the frame. This is where the capacitor mounts. 

The rating of the cap can be just about anything, there is no specific standard and very few manufacturers will give the rating. 

The voltage will usually be 125 or so and the uF can be just about anything.

A basic Baldor 3/4 HP cap start fan and blower motor uses a 460 - 552 uF cap while a general purpose model uses a 270 - 324 uF. 2 different jet pump models use the same 460 - 552 uF. 

I don't know about any other manufacturer. 

If the wrong cap is installed, it'll growl when energized, the shaft may or may not turn and if it does turn, there'll be very little torque. 

The only way I know to size the cap is to try a bunch of different ones until you hit the right one.


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## acro (May 3, 2011)

Upon closer inspection, I see there is a centrifugal switch in my motor. 
Micromind, I think you nailed it. 

I have several different caps to use, so I'll get to testing....

Unfortunately, the wires at the cap are not labeled, or it would have been be crystal clear. 

Thanks


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## acro (May 3, 2011)

It's alive! 

Started with a 53 mfd. The motor did start, but growled quite a bit. So I switched that one out for a 145-175 start cap. Motor starts quicker and growels less. 

The 145 is the biggest I have right now, but I think I will pickup a bigger one around 500 mfd. 

Incidentally, the run windings are about 0.9 ohms each, and the start winding is 5.4 ohms. Also, the run windings on this motor are 1 & 3 and 2 & 4. Which is different than most.


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