Dead Emco Compact 8 Motor

[itsme]

Hi there,

I was merrily machining away this afternoon when suddenly the motor on my lathe died - fortunately for me I was just about finished my final cut on the part. I know very little about how this motor works or what it even is really and was hoping for some advice on what may be wrong and what needs to be done in order to have a working machine again.

When I try to turn the machine on now, it makes a horrible electrical 'buzz' and when left on for more than about 4 or 5 seconds, it begins to smell a bit toasty. It does not rotate under power, however it rotates freely by hand suggesting the bearings are alright. I decided to take the motor out of the machine and turn it on without any load at all. When I did this, it did turn on, however it still made the horrible 'buzz' and for some strange reason it runs in reverse. ie. what used to be clockwise suddenly changed to anti-clockwise. It is obviously making barely any power, as just trying to turn the free spindle is too much for it.

I am assuming the motor is some kind of AC motor - it runs at a constant speed. Sadly my motor knowledge extends about as far as a simple DC motor, so I'm a bit stuck. For a bit of history on it quickly, it is around 20 years old and spent the first twelve years of its life making tensile test pieces for a company. It worked quite hard for those twelve years. In the last 8 years or so, it has probably seen less than 30 hours of total use.

Does anyone have any ideas what may be wrong? I have included a photo of the motor and another of the plate on the motor to help identify it.

Thanks
Warren

[Al_The_Man]

It appears by the plate to be a single phase - capacitor start motor, your starting switch (centrifugal) in the motor is probabally shot, if it already smells like toast, then it probabally is.
It is easy to take apart each endbell and check the switch for burnt contacts, if you are real lucky, a replacement switch may fix it.
But check the windings for burnt insulation first.
The fact it runs in reverse is an indication that the switch IS gone as it doesn't get the direction kick from the start windings.
Al.

[fkaCarel]

Consider yourself unlucky, if it smells, good chance it's dead.

Consider yourself lucky, your local motor dealer can sell you a 3-phase motor and make it fit. Emco motors shaft sizes deviates from standard motor sizes.

If you add a VFD to it, you don't know how you've ever done without it.

Edit: Al: no starting switch in these.

[itsme]

Hi there,

Thanks for the replies.

Al, it is indeed single phase (whatever that means???), as I am running it off a standard UK household socket. There is also a big capacitor situated near the switch on the machine.

From what I understand, fitting a 3 phase motor would mean that i need some kind of convertor in order to run it from a standard household socket. I'm not sure what advantages 3 phase would have, but I have always been happy with the motor that is on it now (when it worked, anyway...). If I can just get it back to how it was, I'd be more than happy.

I don't know what 'capacitor start' means, but fkaCarel, if you say this motor doesn't have a starting switch, does that make it is unusual and more difficult to fix (if it is fixable at all)? I'm really working in the dark here with my limited knowledge of these things...

Regards
Warren

[Al_The_Man]

Edit: Al: no starting switch in these.

I did not know that...

Maybe the Cap dried up after all those years.
As mentioned if you go with a 3ph motor you will HAVE to go with a VFD if you don't have 3ph. But I agree it is worth it.
You input 1ph onto the VFD and it outputs 3ph at variable frequency so you can either vary speed with a pot. or command signal from CNC S value.
That is only around a 1/3 hp so I would not imagine the cost being that high.
Al.

[fkaCarel]

Itsme, you have 220v single phase (as I do). The capacitor is used to create an offset for the sinusoidal to determine the direction off the motor. A VFD (variable frequency) generates 3-phase from 2 or 3 phase. The advantage is that the typical 2-phase rumble disappears. For me, the conversion to VFD gave an improvement in quality. Another advantage is direct response in clockwise, counterclockwise commands (threading).

And of course, the motor can be rewired. You will find a motor rewirer somewhere in your neighbourhood. As you compare the cost off a new motor, with maybe some modifications to make it fit, but available off the shelf, or rewinding a special (which Emco motors are) you will find that the new motor is a logical choice.

In february I had a motor special made. From the receipt:
Motor 0.75kw/1500/3phase: 88 euro
Modifications(axle to size, keyway and complete sealing): 150 euro
VFD: 209 euro

Around 1982 such a motor from Emco was around 300 euro....

[itsme]

Hi,

I can see that this is going to turn into a project within a project. It seems that Emco like to use components that are specific to them. The Compact 8 is also only compatible with Emco chucks, unless of course you modify it.

I will contact the Emco distributor tomorrow to find out what an original replacement motor would cost (just for the fun of it, if nothing else). I will also try and find a local motor rewirer and go and talk to them to see what they say.

I'm fairly confident that it is the motor that is dead and not the other electrics (the toasty smell is a good indication, I think). Just to be sure though, is there any way to test a capacitor without having to play with mains electricity?

Regards
Warren

[Al_The_Man]

That shows a 12µfd cap, if you substitute it you have to use a motor-run style. If you disconnect it you can use a meter to make sure it is not shorted, and if it is not and you have a high impedance meter, keep it on the ohms range and you should see a varying reading due to the slight decaying charge imposed by the meter, reverse the leads and you will see again a decaying reading, this is a very rough indication that it is still ok.
If it is shorted or open none of the above will be seen.
Al.

[itsme]

Hi there,

I phoned the Emco distributor this morning. The first thing he said after I told him what was happening, is that it is the capacitor. He also said something to the effect of 'those motors don't break'.

He told me to put the motor into the machine, turn it on and spin the spindle by hand. If the spindle then carried on running, it would be the capacitor. I did this and that is exactly what it did - it carried on running. I ordered a new cap and will try that. I also ran the motor for about a minute as it was and there was no toasty smell - maybe I was just over-reacting to a warm machine yesterday? Afterall, there was no smoke.

As you may have guessed, I am quite pleased that it may only be the cap. I'll wait and see now.

Thanks for the help
Warren

[itsme]

Hi there,

I just got the new cap in the post. I can't see any obvious markings on it that would suggest it is polarised. Can someone please confirm that this type of capacitor is not polarised before I install it. I'd hate to put it in the wrong way if it is polarised...

Thanks
Warren

[fkaCarel]

Not polarised. It's AC.

[itsme]

Ok, my last past may be slightly 'misleading'. The capacitor has got a 'bolt' mounting on the bottom and 4 terminals on the top. It may be polarised, BUT would all the terminals on the top be from the same pole. ie all of them be positive or negative? There are no markings that distinguish between them.

I have included a photo to make my sloppy description more clear.

Thanks
Warren

EDIT:Thanks fkaCarel, I was busy writing my own reply when you answered - that's all I needed to know