Phase converter failure help-rotary

[redtom]

WEll, my well meaning brother decided to come to town to help at dads. He wanted air so he went around turning things on-the compressor is not 3 phase. My dad has a 3hp idler motor phase converter with a sealed capacitor start box with push button for starting the idler, for his Bridgeport mill. Long story-short, the idler motor got left swiched on without running for days without the starter box being pushed to start. Now it won't run. I checked the power supply which is good. Question is will the caps be bad orwill the motor be burned up? I don't know how to check the caps, (2).

 

[bison]

Did you try the reset button?
i believe there is one on the converter motor as well.

 

[guido]

Hello redtom,
I would check and see if the overload is tripped also as suggested.
You can check the capacitors with an ohm meter.
First make sure they are discharged. Use a screw driver from one lug to the next. Put the volt meter on ohms scale and touch the connection on the capacitor. Now take the meter and go through all the ohms scale. Reverse the leads and do the same thing.
Ones you find the scale that works, if the capacitor is good, will charge up and show some reading. If it acts the same way everytime you reverse the leads, the capacitor should be good.
This test is for a digital meter. Analog meter will work as well, againg you'll have to find the range that works. When you find the range with an analog meter, the needle will spike up and them come down towards the zero range.
Good Luck..............Guido.

 

[redtom]

She's an old cast iron 3hp idler motor so I think its pre-overload. Don't recall seeing any kind of reset.

 

[DH in Carolina]

Isolate the three leads feeding the motor and check for resistance between two of them with a ohm meter. Repeat with the third wire and one of the other wires. Readings should be close between all three leads. If you get no reading between any two you have a open circuit. Most three phase motors will not have a reset buttion as they are externaly protected. The capacitors need to be isolated to check also. DH

 

[redtom]

I quess one my main questions is will the motor burn up up if the switch is thrown on and left on and the starting caps never pushed?

 

[DH in Carolina]

First is this a factory built phase converter or a home made converter? Yes the motor could burn up if power is applied to the motor and it has a manual start system. Some home made converters have to have the idler motor started rotating by hand to get them going. You may have a manual push button that uses a start relay and start capacitors to get the motor running. If yours is like this and power was left on the motor windings would overheat and burn out unless you do have overload protection. If this motor is burned out you should be able to smell burned windings. If you do a internet search for phase converters there is a lot of information on how to build one and how they work. DH

 

[redtom]

This is a home built, sort of, my dad bought the "special" box which was riveted shut and the place gave him instructions how to wire it into his idler. Upon opening the box it is only two caps with a button switch. I just tested the caps as mentioned here and they bulid up with the ohm meter then stop and do it the same way when switched terms (while isolated). I found a fuse blown on one leg in the disconnect. I can get the idler motor to roll real slow then fuse blows again, as if the caps are doin nothing when pushed. But if they test good as described, my new question is, Can the motor be "partly" bad? It doesn't have the tell tale fried smell but shes a heavy cast job thats sealed up pretty good.

 

[DH in Carolina]

OK from what you say it sounds as if you have one start cap and one run cap in the box. The push button puts the start cap into the circuit to give the motor a boost to get it going. Don't hold the button in more than 1 or 2 seconds as the cap may explode. The reason the fuse is blowing is because the motor is drawing locked rotor amps trying to start on two phases (single phase). If the motor has the shaft on it, wrap a flat belt around it and pull it to get the motor rotating at the same time you apply power to the motor. If the motor starts than the motor is probably ok. I would suspect the run cap is bad. The run cap is the one in the metal can. Look and see if the top is pushed up or deformed. The start cap will bee in a plastic case. Hope this helps. DH

 

[redtom]

Working from memory since its down at my dads, I believe the two caps are wired in series and are identical. Plastic 216-259MFD. one wire in-two wires between the two- then one wire out, roughly. No bulging or burned smell or look from either of them and I meteres them as described earlier. Thats why I was sort of looking towards the motor. I can spin it up tommorow and see if it runs.