HELP, Electric Motor Guru's

[JimR]

HELP, Electric Motor Guru\'s

Today my 6.5 HP 220 volt 1PH. air compressor quit on me. The compressor tried to start up and blew the breaker. So I reset it and it blew again. The motor just made a loud hummmmm. I pulled the belt and the motor spins freely. It still just hums and blows the circuit breaker. It is a capaciter start motor with two capacitors mounted on top under a cover. One is white and the other is black. Both have 3 wires attached to them. Can anyone here tell me how to check these or the motor? TIA

 

[SPIKER]

Re: HELP, Electric Motor Guru\'s

Jim:

you more than likely do not have ability to check the caps but you MAY be able to check the motor it's slef. if you have a good meter (DOM or ANALOG will work)

measure all of the leads from lead to lead and to ground on the leads going INTo and OUT OF the motor. be carefull as some caps may hold a charge for a LONG TIME. three are meters made to check capasitors but they are rather expensive. some morot repair stores may have one and may check them for you right there call ahead and ask.


one other way to check is to remove the belt and see if the motor will run un-loaded by the compressor. also check to make sure the compressor motor still turns.

MarkM

 

[JimR]

Re: HELP, Electric Motor Guru\'s

Thanks for the info. The motor does not run unloaded. It just humms along and blows the breaker.

 

[v8dave]

Re: HELP, Electric Motor Guru\'s

As Spiker suggests check to see if the compressor turns freely. If it does then try replacing the capacitors (caps). They do go bad, usually cook out from the heat.

Surplus Center has both motor start and motor run caps for a cheap enough price to check by substitution. The microfarads (MFD) size is the easiest way for you to tell the difference between MS and MR caps. You most likely have motor start, MS, caps.

Check the caps that are on the motor now. If you can't get the exact voltage and MDF, you can safely go up in voltage, do not go down in voltage. You can go up in MFD, but try not to go over by more than ~50%. You can go under in MFD by 10% if necessary.

 

[JerryG]

Re: HELP, Electric Motor Guru\'s

<font color="blue">The microfarads (MFD) size is the easiest way for you to tell the difference between MS and MR caps. </font>
Which one is usually the largest?

 

[Junkman]

Re: HELP, Electric Motor Guru\'s

I can't offer any more than what has already been offered, but I can tell you that if you need to take it off and have it repaired, there is a company on Rt. 20 in Auburn, just past the Fair Plaza on the East bound side of the road that does motor repairs. I have used them in the past, but not recently, so I don't know how there prices are now. In the past, they were quite inexpensive... Junk..

Brown Alfred L Assoc Inc
Route 20
Auburn, MA 01501
Phone: (508) 754-5682

 

[TBAR]

Re: HELP, Electric Motor Guru\'s

Sounds like it is single phasing. Have you checked the voltage on both 110volt legs going to the motor???


TBAR

 

[_RaT_]

Re: HELP, Electric Motor Guru\'s

I have sometimes taken the belt off the motor, tried to see if it would start with no load. I have also been able to "push" start it by hand rotation with no load. If it will start and run fine under these situations, I usually find replacing a capacitor or two if that is the case to work.

 

[johnbilt]

Re: HELP, Electric Motor Guru\'s

Hi

An electric motor shop will have everything to check it out right. No guesses.

The humming indicates current is flowing to the motor and the breaker certainly verifies that. You could also have a shorted winding.

A cap can be checked by removing one lead and shorting to the other through a resistor. Don't short it directly as this creates a large energy dissipation and is harmful to the windings in the cap. After discharging, Put an ohm meter across the cap and verify it is not shorted. The resistance should rise steadily and then stabilize, indicating a charging cap voltage at the meter.

John

 

[v8dave]

Re: HELP, Electric Motor Guru\'s

Usually motor start caps are the larger capacity, 20 or so microfarads and on up. Physical size is not the measure.

But, I just looked at Surplus Center's caps and I see that is not the always the case. The motor run caps they have are in a more durable, metal, case than motor start. Motor start caps I've been familiar with (and the ones shown at supus center) are in a bakelite or hard plastic case.

I've used AC caps that look like Surplus Center's Motor Run caps as Motor Start caps. They were what I had at the time and I used them to diagnose the problem. But then, for safety reasons (to fit in the original space) I went and bought some correct size Motor Start caps and used them after trouble shooting with the bigger caps.

Look to see what you have, metal case or plastic case? Then select from the similar style capacitors.