AC induction motor capacitors

Thread Starter

erntech

Joined Feb 3, 2024
5
I'm trying to find out the values of the start and run capacitors that are missing in a Dayton Mod.# 4K853T ac induction motor. This model is obsolete and the replacement would be 30PT53. Windings check out good. The motor is dual voltage 115/230 single phase 60hz, 1/3hp, 1725rpm, 7.5a. Can someone help? Thanks
 

Thread Starter

erntech

Joined Feb 3, 2024
5
Are you sure it had a start cap?
I would not expect both on that small a motor.
Have you measured the winding resistance?
I only see where one would go. I based both caps after looking at the 30PT53. There may only be a run cap. Windings both measure 2.4 ohms, not shorted to ground or each other.
 

MaxHeadRoom

Joined Jul 18, 2013
28,696
Then if both windings are equal, it would appear to be PSC (Permanent start Cap) motor that is very easy to reverse just by a SPDT sw with centre off.
I would hazard a guess it would be around 7μf , oil filled paper run type cap.

1706998134508.png
 

Thread Starter

erntech

Joined Feb 3, 2024
5
Then if both windings are equal, it would appear to be PSC (Permanent start Cap) motor that is very easy to reverse just by a SPDT sw with centre off.
I would hazard a guess it would be around 7μf , oil filled paper run type cap.

View attachment 314317
Thanks Max, I figured the same 7uf after looking around online but wasn't trusting it. Now I do. Thanks again
 

Thread Starter

erntech

Joined Feb 3, 2024
5
Thanks Max, I figured the same 7uf after looking around online but wasn't trusting it. Now I do. Thanks again
Update. I installed the 7.5uf cap. Switched it on. Motor tries to turn, can hear the hum of excessive current and the breaker trips. I have 240v across the breaker to the motor switch. DPDT switch ohms out fine. There is only one external capacitor. Is there an internal cap I can get at. It must be shorted. Here's a pic at the cobbler shop.IMG20240112122520.jpg
 

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MaxHeadRoom

Joined Jul 18, 2013
28,696
Have you tried to give it a spin on power up, if the cap is not connected properly it is capable of running in either direction when spun,.
Are you sure you have the cap in series with one set of windings only?
 

Thread Starter

erntech

Joined Feb 3, 2024
5
Have you tried to give it a spin on power up, if the cap is not connected properly it is capable of running in either direction when spun,.
Are you sure you have the cap in series with one set of windings only?
It turns freely with no power. I connected the cap to the two wires that are under capacitor cover on the outside of the motor. Haven't tried helping the rotation on power up. It only stays on for about 1-1.5 seconds before the breaker trips.
 
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