Compressor cuts out before reaching pressure

[dave h 2]

Just remember that adjusting the pressure like that is a one off, you need a separate air regulator to make the pressure suitable for any tools.
As I said above if the centrifugal is stuck on, the start winding is always powered and the motor draws extra current. This can damage the start winding, which was never intended to work for more than a few seconds and means the motor may not spin up to speed.

 

[Dcal]

Just remember that adjusting the pressure like that is a one off, you need a separate air regulator to make the pressure suitable for any tools.
As I said above if the centrifugal is stuck on, the start winding is always powered and the motor draws extra current. This can damage the start winding, which was never intended to work for more than a few seconds and means the motor may not spin up to speed.

Very valid point.
It's not often they fail closed but possible.

 

[Anguz]

still most likely the non return/decompression valve isnt bleeding the air off, and its starting under load

 

[dave h 2]

still most likely the non return/decompression valve isnt bleeding the air off, and its starting under load

I've just check my 3HP CompAir version with a moving coil clamp. On a 13A socket - Start up flicks to 22A - run 9 to 10A.
Mine vents loudly at 40psi
I do get the short release of air once it reaches pressure but obviously i don't when it stops but hasn't reached pressure. The centrifugal switch could be the problem though? SO i'd need to open the motor up to find it?
There's your problem - you should, buy a new valve and hope pushing it hasn't creamed your motor.

 

[timgunn1962]

If you can get a clamp meter on one of the wires (Live or Neutral, but not both together) and measure the current being drawn, it'll help to determine whether the problem is "real", or if it's "just" the overload tripping at less than its rated current. The overloads are invariably the cheapest thing that will get the job done and they do tend to fail occasionally.
The centrifugal switch is inside the motor and I'd check absolutely everything else it could possibly be before mauling about inside the motor. If pulling the motor apart really seemed necessary, I'd be inclined to do it with the motor in-situ: there are never any jacking screws to adjust the motor position and it's usually easier to measure the depth/protrusion of the shaft in/from the motor pulley and make sure it's the same when you put it back together and wind on the belt in the quick-and-dirty manner. Doing it correctly and moving the motor inwards tends to result in a whole load of frustration when it comes to tensioning ghe belt and aligning the drive.
I had a similar issue with a compressor supplying a pneumatic valve control system a few months ago. It was the duty compressor of a duty/standby compressor set up with non-return valves to make the changeover automatic. It was a fairly new 3 HP, 150L belt-drive compressor running on a 15-20% duty cycle and it was was intermittently tripping the overload. It had been fine for several months prior to the first trip. The overload was marked for 15A, maximum current measured with clampmeter was 12.8A. The manufacturer wanted to replace the compressor under warranty, which would have been a major PITA. I spoke to them, managed to convince them I had half an idea what I was doing, that the measurements I'd taken suggested it was just a dodgy overload, and got them to send out a replacement overload to try. It was going to take a few days to arrive, so in the meantime I ordered a couple of replacement overloads from Amazon for next-day delivery. The compressor had been lasting no more than 6 hours on the original overload without tripping. It lasted nearly 2 days on the Amazon-sourced overload, then tripped. The factory one was fitted when it arrived and the compressor has lasted a several months so far on the factory replacement overload with no problem.
In your shoes (presumably without a clampmeter) I'd be ordering a replacement overload before doing anything else.

 

[not done it yet]

The centrifugal switch could be the problem though? SO i'd need to open the motor up to find it?

Would not running the motor without the drive belt fitted and listening for the switch to re-engage, after turning off, as the motor slows be good enough. I‘ve never had a welded switch in a motor, so I might be wrong on this.

 

[AHTI123]

Tested with a clamp meter and measured a steady current of 16.9A. Overload protector is rated at 20A, Ive got a new overload on its way.

 

[dave h 2]

What does the motor plate say the current should be?

 

[not done it yet]

Not 16.9A!

 

[dave h 2]

Wait for it! The start-up draw would likely bend the needle on my clamp.

 

[Jack_K]

As it trips before the pressure switch opens then the pressure switch probably won't release the pressure between the tank and pump meaning the motor has to restart under load. Even a working compressor may fail to restart in this condition. What others have said for testing is what I would do too as to determine why it trips in the first place.

 

[AHTI123]

As it trips before the pressure switch opens then the pressure switch probably won't release the pressure between the tank and pump meaning the motor has to restart under load. Even a working compressor may fail to restart in this condition. What others have said for testing is what I would do too as to determine why it trips in the first place.

Yes, that is the conclusion I have come to. When it trips, I push the pressure switch which releases the pressure and it will restart fine.

 

[AHTI123]

Sticker on motor....something about 16.2a here

 

[AHTI123]

Replaced the pop out overload switch and its back working as it should. Thanks for the helpful replies.