Compressor tripping thermal OL after 10 Seconds

[Kafer_meister]

have you identified that that is actually the start capacitor and not the run capacitor

How do you mean? I think that the start cap is fine. The motor has no problem starting and rotates in the correct direction. The guy I bought it from said that the run cap had gone. It came with the new one, but not the old one, so I never saw it. He said it had the classic 'smoke' marks on it.

 

[eil]

Are the capacitance values not on the rating plate of the motor.

 

[Kafer_meister]

Are the capacitance values not on the rating plate of the motor.

The start one is. 400mf, but it doesn't state the run one.

 

[the snooper]

I thought you said start cap had gone, so I got them mixed up, wrong run cap could cause it to trip

 

[Kafer_meister]

I thought you said start cap had gone, so I got them mixed up, wrong run cap could cause it to trip

Ahh, i see

The reason I wonder about the run cap size is a) the tripping and b) the physical size. I can't find a run cap anywhere that would fit inside the cover that the motor came with, not by quite a long way.

 

[eil]

That's helpful by the motor manufacturers isn't it.

 

[eil]

Most of my 3hp motors have between 30 and 35uf

 

[Kafer_meister]

That's helpful by the motor manufacturers isn't it.

I guess adding another column on the plate was 'too 'ard' .

I can't find any reasonable answers on how to work it out either.

 

[the snooper]

some run capacitors go as low as 2.5 could the type sc-4 also double as service capacitor 4mfd you never know with the chinglish

 

[Kafer_meister]

I'm still no wiser as to why this compressor isn't working. I tried running it with no run capacitor and the result was exactly the same. I've ordered a 20uf run capacitor to see if this make any difference, but I'm also wondering whether the start cap is suspect now. The motor doesn't seem to get up to speed under load. I might order a very cheap start cap to see if that makes and difference.

 

[the snooper]

if it ran exactly the same with no run capacitor then its either the wrong one or the windings are damaged, if the start capacitor had gone it wouldn't start up they usually just buzz and nothing else

 

[Kafer_meister]

if it ran exactly the same with no run capacitor then its either the wrong one or the windings are damaged, if the start capacitor had gone it wouldn't start up they usually just buzz and nothing else

I read somewhere that the start capacitors can lose their capacity, so they will provide enough oomph to start the motor, but often not enough to get it up to speed under load. Does this sound plausible?

Is there a manner in which I can test the windings? Measuring the resistance maybe?

 

[the snooper]

I suppose it depends on how slow its turning, it could also be the centrifugal switch so may be worth pulling the motor apart and check things out

 

[Kafer_meister]

I suppose it depends on how slow its turning, it could also be the centrifugal switch so may be worth pulling the motor apart and check things out

I don't think it's the centrifugal switch. When you run the motor with no load, it runs fast and smoothly. As it powers down you can hear a very definite click as the switch springs back to its start position.

I might pull the motor apart anyway and have a look, but to be honest I don't really know what I'm looking for with regards to damaged windings. I guess burn marks etc if it's overheated.

 

[ford34/2]

I`m no expert, but if its an older motor, do be careful with any wiring that has insulation on it, it can become very brittle and just fall off at the slightest touch. Then you got even more problems, not advocating trying, but it the motor reaches full RPM off load, if you were to slightly wedge some 2" X 2" against the pulley -- a 3 Hp motor is not going to slow down.

Stan

 

[the snooper]

if you can hear the centrifugal switch operating then I would think the start cap is ok, the problem you have is, if the run capacitor is the wrong value then the motor will be out of phase, you will need the exact value the motor was designed to have, if they guy you bought it from just fitted the closest value he could get his hands then its only good for a door stop as you will never know what value to buy and the wrong cap will just cause heat damage to the windings and cause it to fail, unless that is what has already happened and you've been had

 

[Kafer_meister]

if you can hear the centrifugal switch operating then I would think the start cap is ok, the problem you have is, if the run capacitor is the wrong value then the motor will be out of phase, you will need the exact value the motor was designed to have, if they guy you bought it from just fitted the closest value he could get his hands then its only good for a door stop as you will never know what value to buy and the wrong cap will just cause heat damage to the windings and cause it to fail, unless that is what has already happened and you've been had

It has always had a thermal overload protector, so would this not prevent any damage?

I e-mailed him earlier to see if he still had the old one by any chance. He wasn't the type of chap to deceive someone deliberately. He said he'd been to a motor specialist who had sold him the 40uf run cap. I think I'll hold off buying more bits then and consider the possibility of a new motor .

 

[the snooper]

yes it should prevent damage but its a bit of a false positive as it wont allow it to run and you cant find the correct value unless he has the original or remembers if the original was 40 uf

 

[ford34/2]

By the time the Thermal overload has tripped a lot of damage may have already been done, they are not the safest protection for a motor,Thermal being "HEAT" when its cooking it trips.
Stan

 

[Kafer_meister]

By the time the Thermal overload has tripped a lot of damage may have already been done, they are not the safest protection for a motor,Thermal being "HEAT" when its cooking it trips.
Stan

Ahh Ok. I figured that they would be designed to kick in before the damage was done.

I've just found that TEC motors are about 15 minutes from my house, I might see if they have any very cheap deals going on a replacement.