Lathe motor gone cactus

Lathe motor went 'pop' in a blinding flash of arclight when attempting to start mid-job today. Popped a 20 Amp RCD/Breaker.

Have pulled it out of the lathe, this is what I know about it:
Brook Crompton Parkinson
Single Phase
750 Watt
240v
Compressor duty
Capacitor
Centrifugal switch
Reversible
5 (winding?) wires

If I flip the start switch in either direction, it immediately trips the breaker/RCD with no motor movement.

Whats the default troubleshooting procedure for something like this? Check the windings (the 5 wires?) for continuity & resistance? The capacitor looks good (not ruptured, as would be consistent with a total failure and blinding flash). Centrifugal switch shouldn't come into it as it's not even spinning up before the RCD trips. Motor is mechanically fine - free spinning, no abnormal noises or heat.

Replace? Send for rewinding? Or should I just bite the bullet and go to a 3 phase & VFD setup? Where do I even start to look here, electrons aren't my specialty.

Hi there,

I hope you get this sorted soon. All I can suggest is that if it's the RCD, that would indicate an earth leakage somewhere rather than excessive current draw from active to neutral. I don't think a dodgy cap will trip the RCD. It can still be the start up circuit including the cetrifugal switch since this is already connected on start up and disconnects once at a pre-determined speed of the motor.

If I was to have a wild guess (bearing in mind I'm not an electrician) I would say that there is a breakdown in the insulation between one of the windings and the body of the motor. It's not a cheap Chinese motor I assume so maybe it's just old and finally the enamel insulation has finally broken down or perhaps you were doing some heavy cutting and the motor gor warm and the insulation finally gave up?

It may have nothing to do with the motor and perhaps it's the switchgear that has created a short?

Anyway, remove the motor and bench test it for continuity and go from there. That won't cost you a cent. If it is the motor and you want to consider a 3 phase transplant with VFD, a 1 -2 HP 3 phase motor can be had for around $50 secondhand on ebay etc if you look carefully.

If electrons are not your specialty, I would suggest you do some research into what is required BEFORE you make the decision. While it's not what I would call overly complex, it does require a certain amount of electrical/electronic knowledge. People here will give you some pointers and help but ultimately you will have to do the work and be happy that you did it safely.

First port of call will be to get the motor out and test it with a continuity tester, or take it to an electrician for testing.

Cheers,

Simon

Short answer, if you aren't comfortable working with electrical systems, take it to your local motor rewinder for testing.


Long answer, arcs and flashes from the motor, tripping RCD. definitely take to a motor repairer/rewinder. Don't even fiddle with it, keeping the evidence intact can be invaluable to the guy diagnosing the fault.

If the motor has shorted windings or failed insulation you may or may not pick that up with a general purpose multimeter. By that I mean the motor winding is low ohms, how can you tell if it has shorted turns? Likewise the insulation might only breakdown at higher voltages than you general purpose meter can provide. A megger is required to test the insulation.

Ray

Right... so given I want my lathe back in action ASAP, it sounds like my best option here is a new motor, and deal with getting the old one checked and possibly rewound at a later date, given at 1 horse, even as a quality motor, it's probably going to cost a significant portion of its replacement cost to be rewound.

So I guess I should start reading up on 3phase and VFD setups.

I had a problem with my lathe motor when it first arrived and so sent it to the rewinders. They did not fault find because that would cost more than the job was worth - the process was 1. confirm a fault 2. cut off the windings 3. Rewind.
That was a 4HP jobbie. A 1HP may not even be worth rewinding.
Take it in and ask the question I guess.

Michael

Before you go any further, head Ray's advice first.
You might just be lucky and it's only a cable connection come off or broken, touching the motor frame inside the covers. Motors vibrate and therefore metal fatigue happens. Seen lots of that over the years. Sometimes all it needs is a bit of cable cut off and reconnected or a new cable. But as Ray said, don't do anything until the rewinder or MOTOR KNOWLEDGABLE sparky has had a look for evidence.
If it is a failed winding, small chances are you would have smelled it before it blew.
If it needs rewinding, the quote will give a starting point for your budget of replacement and/or change to VFD (much better option in my opinion, but more expensive overall).
If electrons aren't your thing, that option may very quickly become tricky too, with changes to switchgear etc. Most domestic type electricians aren't much help to you then either. You really have to ask the right questions to see if they have a clue.....

Just finally, DON'T fiddle with electrical things "in case you might figure it out" - your life, health and safety is worth a lot more than a sparky's bill!

Where in NSW?

Metro Sydney, but in a place that 'just popping in to the nearest rewinders' is still a bit of an expedition.

I say 'electrons aren't my thing', but I'm selling myself short there. I've previously built my own CNC controller, am more than capable of doing basic electrical work safely, the switching gear for a small 1 horse motor doesn't phase me. I've looked into doing a 3ph/VFD setup before and it's within my capabilities. However I consider the inside of the motor casing to be 'dark arts and voodoo' and would just prefer not to invest too much time into learning to troubleshooting something I probably can't fix or diagnose myself anyway.

Follow the soot trail.

If it went pop with a blinding flash, there will be an obvious soot deposit.

I'd be starting with the plug / leads and switchgear first PM. In my experience with a blown cap the motor will still hum (unless the terminals are shorted) - just not rotate or not rotate fast. You have a major short which you should be able to isolate with a multimeter before you start making life too complicated or spending big bucks.
Also remember when testing that the big capacitors store dangerous charge for a while after disconnection and need to be shorted with an insulated screwdriver or similar.
All the best with that. davo

Is this motor original to your lathe? The reason I ask is that if it is rated for compressor duty I would question it's suitability as a lathe motor. While compressor motors have large starting torque they are designed to run intermittently rather than for long periods at their rated load and this may have contributed to cooking the windings if that indeed turns out to be the problem. A lathe motor should have a continuous rating. I reckon it might be worth having a chat with your local motor supplier / rewinder. For what it's worth I would go with a 3 phase motor and VFD, the user friendliness is worth the marginal extra expense.
Cheers,
Greg.

OK - been a while, but I finally got the round tuit I needed to look at this.

I lured next door's sparky and his megger over with a cold one, and confirmed that the motor has a ground leak. At this stage, I'm considering it dead. So I need a replacement.

Existing motor was 1 horse, 1440rpm, 1ph. There's Tianjin Specials on eBay for under $200 that would match those specs. Are these even worth considering for a lathe application? It would certainly be a fast, easy, and cheap solution.

I'm willing to spend the extra to go to 3ph and a VFD, however, but don't even know where to start beyond sourcing the motor. going this route I'd move to a 2 horse motor to make up for the 30% loss running 3ph from 1ph rectified. I'm confident I could wire it up, but selecting a VFD leaves me stumped. Can anyone suggest what to look for there? Recommended brands and sources would be much appreciated.

Hi There,

Whilst agreeing with all thats been said, is this motor vented ? if so have you checked visually for any swarf or turning that has got into one of the vents and shorted things out. I've seen bits of swarf weld themselves to the motor frame and start switch before, with just the description you gave.

If you go here
Electrical Motors Online - Royce Cross Agencies
and go to their specials section on the right, a 1 hp motor will be $207. Shipping will add a bit but I would trust it more than something from O/S without a presence to back it up.

Michael

I have bought a couple of motors off Conon Motors and have been happy with their service. They have a good range and are reasonably priced. They have a shop front in Glen Waverly and also an eBay store http://stores.ebay.com.au/CONON-MOTO...p2047675.l2563 No affiliation, just a customer.