Compressor blowing it's fuse, possible run cap issue?

[indy4x]

Hi

I have a Clarke air compressor fitted with a 3HP single phase motor. It's been in bits for a while as it's previous owner had run it in a carpentry shop with a broken air filter so was full of sawdust.

I've stripped and cleaned the pump, fitted a new pressure switch and replaced the 3 core cable from the plug to the switch and switch to the motor

It ran for the 1st time yesterday and I have a problem with it blowing fuses.

The fuse blows on startup, the motor will start up, get almost to running speed and then the fuse blows. Doesn't happen every time but is getting more frequent.

Double checked my wiring and that's all good but the run capacitor is not pretty. Bottom of the case is bulging and the top cover where the wires go in looks stained as if something has leaked

The capacitor is 45 uf +- 15%, I have a new spare capacitor but it is 60 uf +-5%

Will this be ok in the motor even it it's only short term while I order a new one

 

[Wildefalcon]

Are you running it on a 3 pin plug? I think those motors are rated at 16 amps.

But that cap sound like it's dead, regardless.

 

[indy4x]

Yes, it's on a 3 pin plug, motor is 2.2kW

It's how it comes from MM

I've had the same model before and that had a 3 pin plug as well

 

[Wildefalcon]

See if you can download the manual, or look on the rating plate, to find the current draw.

 

[indy4x]

@Wildefalcon will do but the motor is 2.2kW so should be around 10A

In the interim, does anyone know if the 60uf capacitor will do short term to replace the 45uf?

 

[KimB]

You should be able to test the start capacitor with a DMM.
I had the same issue with my Clarke air compressor. Ended up being a burnt out motor. £100 for a new one

 

[indy4x]

@KimB don't think any of my DMM's measure capacitance, off to check

Edit: that would be a no

 

[Seadog]

Is it a start or run capacitor? If it's a start cap then the difference in value shouldn't matter. If it's a run cap then I think you'd be better off nearer the correct value.

 

[indy4x]

@Seadog it's the run capacitor

Internet searching as always has given me a variety of answers with no to +20% is OK

I'm being impatient, wanted it working as need to run the plasma cutter but will have to be patient and order the correct one

 

[waddycall]

You can kind of check a capacitor with a DMM if you measure resistance across the contacts after discharging it. Resistance should steadily climb to OL.

 

[MoreWellie]

the motor is 2.2kW so should be around 10A

The maths work for when it is running but when it is starting it takes a whole lot more much the same as the inrush on older welders.

on my 3hp I had to fit several 13A fuses before I found one that lasted

Apparently all fuses are not equal despite being brown and stating 13A on the outside

 

[Wildefalcon]

I use a 16a commando socket. If the compressor pump is tight, the motor will take more current to run, then with a run-in pump.

 

[MoreWellie]

if it is a belt drive then try turning it on with the belt removed to make sure the motor isn't faulty

 

[Nomad]

I had problems with a barn find compressor similar to yours. One started it would run fine, sometimes it would try to spin over but slowly, other times it would blow the fuse.
Pump piston etc looked ok, odd that it would always start ok if the cyl head bolts were loosened (so no compression), once started I could tighten the head and everything worked.
Removing the hardline to the tank made no difference so the problem was something with the motor or pump, not the tank.
Ended up stripping it for parts.

 

[MoreWellie]

One started it would run fine, sometimes it would try to spin over

typical symptoms for failed motor capacitor

 

[carbon]

In the interim, does anyone know if the 60uf capacitor will do short term to replace the 45uf?

I would only fit the 60 uf cap to check that the motor still works and not run it longer than necessary. If you have a clamp current meter you could check that the running current doesn’t exceed the current rating on the motor data plate

 

[indy4x]

So today I fitted the 60uf capacitor I had kicking about and it still blows fuses so it's not that

 

[indy4x]

Think I need to do some reading on how to test motors and get stuck into it

 

[Nomad]

I tried a couple of other (old & untested) capacitors on mine to see if helped, it didn't so maybe they were all faulty or maybe that wasn't the problem.
Keeps us uptated, it would be good to know for the next time I have a problem

 

[carbon]

Was that with the pump belt connected or just the motor on its own?