Compressor tripping thermal OL after 10 Seconds

[Kafer_meister]

Hi,

I bought this compressor about a week ago for £70. It was listed as spares or repairs as the run capacitor had gone, however it came with a new one.

I replaced the run capacitor and tried to fire it up, but it just kept blowing 13 amp fuses. The guy I bought it off said he happily ran it on 13 amps and only stopped using it when the capacitor went.

It was wired like this:

The pressure switch was a bit tired, so I decided that I'd replace that, wire it to a 16 amp plug and take the output direct from the tank rather than via the 1/4 switch outlet. I also sorted a few other little wiring defects.

I fired it up this afternoon and it runs quite happily for about 10 seconds before tripping the thermal overload switch. I don't think I've wired it incorrectly, but it is possible.

Any ideas on what might be the problem? I also need a run capacitor that is a physically smaller size as this one doesn't fit in the cover on the motor. Any suggestions where I can get a really small 40uf run capacitor?

Finally, any idea what make this compressor is? It's about 1990 and has a ***** Cheng Electric Industry Motor, 3hp 3000rpm motor. That's about all the info I can find on it.

 

[rtbcomp]

Normally compressors are fitted with a 1400 rpm motor for greater torque, could be the motor isn't getting up to speed and drawing too much current.

The trip appears to be connected in the neutral lead, it should still work, but presents a shock hazard.

 

[Kafer_meister]

Normally compressors are fitted with a 1400 rpm motor for greater torque, could be the motor isn't getting up to speed and drawing too much current.

The trip appears to be connected in the neutral lead, it should still work, but presents a shock hazard.

I thought that the motor speed was a bit high too, but going by the dates, it does seem to be the original motor. The guy I bought it from said that it had been in service for many years. Does it need less torque because it's two smaller pistons?

I think I rewired that switch differently after the photo was taken, but I'll check tomorrow and change it if necessary.

 

[brightspark]

Normally compressors are fitted with a 1400 rpm motor for greater torque, could be the motor isn't getting up to speed and drawing too much current.

The trip appears to be connected in the neutral lead, it should still work, but presents a shock hazard.

quite a lot of compressors are fitted with a 2800rpm motor. ive got one with a twin pump and motor set up the cutout is conected through the neutral the only time theres a shock hazard is if u take the motor plate of and stick your fingers in if its turned on then u deserve to get a shock

 

[Robotstar5]

Have you tried running it with the belt removed? maybe a motor fault

 

[Kafer_meister]

Have you tried running it with the belt removed? maybe a motor fault

I will try tomorrow. I hope it isn't a motor fault. It's going to turn it into a bit of an expensive purchase if it is.

 

[MoreWellie]

Have you tried replacing the oil?

My 3hp compressor often trips after 10 seconds when it is cold (10 deg C or less), if I put a fan heater on the pump for a few minutes and then try, it starts and runs fine

In the summer it never blows the trip

if you can find a capacitor with wires coming out rather than terminals then just mount the capacitor in a clip on the side of the motor

 

[Kafer_meister]

The motor runs fine when it's not connected to the pump. It trips when it is. I have removed any valves that may be causing excessive compression and it still does the same. The pump turns freely by hand. Is the motor goosed? Is there anything I can test on them?

 

[ford34/2]

What amps are on the motor?? maybe suspect thermal overload trip?? However 3 Hp on 13 amp plug is ambitious not surprised it blew fuses.
New thermal switches
http://www.ebay.co.uk/itm/Re-settab...r-fuse-5-10-15-20-30-Amp-ranges-/380556458408

 

[Kafer_meister]

What amps are on the motor?? maybe suspect thermal overload trip?? However 3 Hp on 13 amp plug is ambitious not surprised it blew fuses.
New thermal switches
http://www.ebay.co.uk/itm/Re-settab...r-fuse-5-10-15-20-30-Amp-ranges-/380556458408

I always got away with running my SIP 3hp on 13 amp, but it's not ideal. I had a load of 16amp stuff anyway, so I wired one to my 20 amp radial. It's not blowing fuses now obviously. It does flicker the lights a bit when it stops though.

The motor plate says 10amp. I could try a new thermal switch I suppose

 

[Kafer_meister]

Normally compressors are fitted with a 1400 rpm motor for greater torque, could be the motor isn't getting up to speed and drawing too much current.

The trip appears to be connected in the neutral lead, it should still work, but presents a shock hazard.

In had rewired it correctly thankfully. So hopefully all safe

 

[eil]

wire it to a 16 amp plug and take the output direct from the tank rather than via the 1/4 switch outlet. I also sorted a few other little wiring defects.

What exactly do you mean with this statement.

 

[the snooper]

I take it he means air line direct from tank and not connected to the pressure switch outlet

 

[Kafer_meister]

wire it to a 16 amp plug and take the output direct from the tank rather than via the 1/4 switch outlet. I also sorted a few other little wiring defects.

What exactly do you mean with this statement.

The compressor was wired with a 13 amp standard plug, but it was just blowing fuses. All of my previous compressors have recommended 16 amp feeds, so I wired on a 16 amp blue plug.

The standard air output for this compressor is through the 1/4 outlet that the pressure switch connects to. This is restrictive, so the air outlet is now direct from the large 1 1/2 outlet on the end of the tank. I've bushed this down to 1/2 inch to suit the regulators I have.

The wiring generally was a bit messy, terminals coming loose etc, so I tidied it up a bit. I didn't change it though.

I'm wondering if the new run capacitor is the correct size now, it's 40uf.

 

[eil]

I take it he means air line direct from tank and not connected to the pressure switch outlet

That's what worries me, the 1/4" outlet the unloading pipe or am I missing something.

 

[Kafer_meister]

That's what worries me, the 1/4" outlet the unloading pipe or am I missing something.

The pressure switch, unloading valve, pressure overload release valve and gauge are still attached to the 1/4 output as per normal. It's just that the actual air outlet, to the airline, comes straight out of the end of the tank.

 

[the snooper]

That's what worries me, the 1/4" outlet the unloading pipe or am I missing something.

there is an outlet from the tank which operates the switch and in turn also operates the unloading valve

 

[eil]

The compressor was wired with a 13 amp standard plug, but it was just blowing fuses. All of my previous compressors have recommended 16 amp feeds, so I wired on a 16 amp blue plug.

The standard air output for this compressor is through the 1/4 outlet that the pressure switch connects to. This is restrictive, so the air outlet is now direct from the large 1 1/2 outlet on the end of the tank. I've bushed this down to 1/2 inch to suit the regulators I have.

The wiring generally was a bit messy, terminals coming loose etc, so I tidied it up a bit. I didn't change it though.

I'm wondering if the new run capacitor is the correct size now, it's 40uf.

Aha that's a bit clearer now. The cap size sounds about right.

 

[the snooper]

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

 

[eil]

Have both caps tested by someone with a capacitance function on their meter.