Compressor tripping thermal OL after 10 Seconds

[the snooper]

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

they are not thermal in the sense that they operate from the heat of the motor, they work when too much current is drawn through them causing a bi-metallic strip to heat up and cut the power

 

[the snooper]

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

correct

 

[ford34/2]

Apologies hold my hands up, I was wrong, but still not a lover of thermal trips though, if you get it running get a dedicated, correctly rated DOL switch, I would be into the factory with the Motor and ask if they can advise the Cap rating.
Stan

 

[eil]

Take the black cover off the **** end of the motor to check if you can see the centrifugal switch. Regarding testing the motor, what meters do you have at your disposal to carry out tests

 

[Kafer_meister]

I got a reply from the chap I bought it off, who coincidentally lives about 1/2 mile up the road. He said that he took the motor and burned out capacitor to a motor specialist in Hereford and they matched a new cap to the old one. He's an astute chap so I have no reason to doubt that this is the correct information.

So if we assume that the run cap is correct and fine. What else is likely to be causing the problem? I'm still wondering if the start cap is on it's last legs?

I have a pretty tidy multimeter, but thats about it when it comes to test equipment.

 

[MoreWellie]

have you changed the oil?

my theory being that the trip would also go if the load on the motor was too high. So if the existing oil is way too thick, or significantly over filled, then it could cause the trip to go

I have never tried turning a compressor like this by hand (when the belt is off) so I don't know what sort of resistance you should feel but has to be worth a try and someone else here is bound to have done it in the past for a comparison

Also don't know what sort of temperature it is where the compressor is but if it is down at 10 or 11 degrees then have you tried warming the compressor unit up with a fan heater as per my earlier post?

 

[the snooper]

I got a reply from the chap I bought it off, who coincidentally lives about 1/2 mile up the road. He said that he took the motor and burned out capacitor to a motor specialist in Hereford and they matched a new cap to the old one. He's an astute chap so I have no reason to doubt that this is the correct information.

So if we assume that the run cap is correct and fine. What else is likely to be causing the problem? I'm still wondering if the start cap is on it's last legs?

I have a pretty tidy multimeter, but thats about it when it comes to test equipment.

if you can hear the centrifugal switch clicking in or out then that sort of rules out the start capacitor as the centrifugal switch disengages that circuit once upto a certain speed.

 

[mylesdw]

I would pursue the oil change avenue first. My compressor had exactly the same symptom when it was brand new. It had been built in some hot part of the world and the oil was too thick for our cooler climate. The distributor simply changed the oil for a thinner grade and the problem was solved. I'm guessing it is pretty cool in the UK right now.

It is quite possible that the guy you bought it from had a nice warm workshop or didn't use the compressor in the winter?

 

[the snooper]

what you could really do with is a clamp meter to see exactly what current is being drawn with and without the drive belt in place, if the current drawn is correct it could be a faulty cut out aswell

 

[Kafer_meister]

have you changed the oil?

my theory being that the trip would also go if the load on the motor was too high. So if the existing oil is way too thick, or significantly over filled, then it could cause the trip to go

I have never tried turning a compressor like this by hand (when the belt is off) so I don't know what sort of resistance you should feel but has to be worth a try and someone else here is bound to have done it in the past for a comparison

Also don't know what sort of temperature it is where the compressor is but if it is down at 10 or 11 degrees then have you tried warming the compressor unit up with a fan heater as per my earlier post?

I would pursue the oil change avenue first. My compressor had exactly the same symptom when it was brand new. It had been built in some hot part of the world and the oil was too thick for our cooler climate. The distributor simply changed the oil for a thinner grade and the problem was solved. I'm guessing it is pretty cool in the UK right now.

It is quite possible that the guy you bought it from had a nice warm workshop or didn't use the compressor in the winter?

I haven't changed the oil, but you're certainly correct that it's not in a nice warm workshop. My workshop is a big detached old brick building, with zero insulation, no heating etc. It's barely above 10 degrees. Lovely in the summer though as it really stays cool. His workshop was an integral garage in his house.

What oil would you suggest? Last time I changed the oil on a compressor I was told to use a non detergent motor oil. I think I went for Morris 30w. This is a pretty thick oil though. I have loads of more modern motor oil, but obviously that's full of detergents which I understand is very bad news for compressor pumps. I don't mind buying oil, I just begrudge paying for 'compressor oil' that's really expensive if it's essentially just engine oil.

 

[Kafer_meister]

what you could really do with is a clamp meter to see exactly what current is being drawn with and without the drive belt in place, if the current drawn is correct it could be a faulty cut out aswell

I'll see if I know anyone I can scrounge one off for a day.

Thanks everyone. I'm in France for the week, so I won't be able to make any progress for a bit. Will keep you all updated though.

 

[Kafer_meister]

What oil would you suggest? Last time I changed the oil on a compressor I was told to use a non detergent motor oil. I think I went for Morris 30w. This is a pretty thick oil though. I have loads of more modern motor oil, but obviously that's full of detergents which I understand is very bad news for compressor pumps. I don't mind buying oil, I just begrudge paying for 'compressor oil' that's really expensive if it's essentially just engine oil.

I found a few threads about this and there are 100 different answers. As it's hardly a new machine I think I'm going to just go with the best of my vast selection of 1/4 full 5ltr engine oils. I think I've got some 5w-30 somewhere which should be nice and thin when cold.

 

[eil]

Now your talking, try and scrounge one with a capacitance function on it if you can. (clamp meter I mean)

 

[Kafer_meister]

I'm back from France . Beautiful place. We've been house hunting and have found a place with a lovely house and a Huuuuge workshop that we like a lot. He wants too many monies though, so we'll wait till reality sets in.

I've changed the oil on the compressor for some nice thin 5/30. I only had about 750ml, so it needs a top up, bit for now it's fine. I also put a ceramic heater on it for 10 minutes to take the chill off.

The result was the same .

So I took the cover off the motor to see what the centrifugal switch is doing.

It works fine when there is no load on the motor, but when the belt is on the motor just doesn't get up to speed fast enough to spin the weights out. I guess it then overheats the start windings and trips the thermal.

The pump turns easily by hand (little finger easily) and I can move the weights about easily enough.

So why will it just not quite spin up enough to work properly? Worth trying a new start cap?

I've not tracked down a clamp meter yet....

 

[eil]

Seeing you haven't got a meter to test the caps, I would try a new start cap then you know both capacitors should be ok.

 

[Kafer_meister]

I finally got around to getting a new 400uf start cap. It's an ebay chiwanese special, but to be honest it looks well enough made from the outside.

Plugged it in, fired it up and it sprung straight into life, straight up to full speed. I can hear the centrifugal switch clicking in and out.

I need to do a little plumbing to get it properly sorted, but I'm very pleased. I reckon it owes me about £100 now.

 

[ford34/2]

its always nice to get an update, glad you seem to have solved the problem, even at a ton-- cheap compressor.
Stan