Electrics Problem - Lathe

Warco WMT 500

This is a machine of unknown history that we have recently acquired

The lathe itself works fine, forwards and backwards.

The milling machine however. This has a forward and reverse switch, when its on 'forward', the motor runs in reverse but otherwise seems to run well. (albeit the wrong way)

When the switch is turned to 'Reverse' the motor tries to run forward the (clockwise) but before it has turned half a dozen revolutions it trips the circuit breaker.

we do have pat testing equipment, and that shows it all to be in order. it would pass a pat test, if indeed it was a portable appliance, which clearly at about ¼ ton, it isnt.

Are you sure it runs the wrong way in mill mode? Check the direction of rotation of the mill head.

yes, absolutely, the milling cutters are spinning the wrong way, we realised this when they were not cutting.

Are they induction motors or DC drives?

Single Phase Induction

I have tried reversing the polarity on the capacitor, however it still won't run in a clockwise direction, it trips the fuse every time. Runs fine anticlockwise.

I have also tried it without the belts attached, (so its not some ratchet type fault on the milling machine jamming the motor!)

If the motor is fubarred, where would I try for a replacement ?

Edited By Justin Thyme on 24/04/2023 18:07:25

Induction motors are so widely available that your best option is to determine what frame size and mounting you need, then google to find the cheapest supplier of motors in that size and an appropriate power rating.

Unhelpfully your data-plate doesn't give the frame size and style, but you can easily determine the size by measurement and comparison with a chart (unhelpfully there are two standards IEC and NEMA) and the mount type by inspection (Downloadable reference here).

The "Type CO² 71 34" marking might be trying to say: "A face mounted motor (NEMA C-Mount), frame size 71 (an IEC size), with a 34mm long shaft", but if so is mixing it's standards, and should be marked IEC71 B14 (which would have a 14mm diameter, 30mm long shaft as standard).

Edited By Jelly on 24/04/2023 19:46:01

I suggest you replace the cap anyway and look at the switch for possible earth leakage paths that get selected when forward is selected. The motor has no preference as to which way it runs except as influenced by the capacitor.

The Cap gives the start windings a kick ! If it runs in one direction OK then the cap would seem OK ! Changing the cap polarity will do no good, it's the star windings that dictate rotation ! It sounds as though the reversing switch has a problem. What goes, an MCB or an RCD ? Where are you ? Noel.

Can you send a clear picture of the interior of the terminal box ? Before doing any thing take a picture or with a pencil and paper make a sketch of the terminal box layout and wire colours.

Your motor has two separate windings connected in parallel one to the other and the four are connected then connected to the mains supply. You have to identify each winding, have you a multimeter with a low ohms range ? You are attempting to locate the run winding, which will have a low resistance, lift a pair of wires, ( disconnect) probe around until you obtain a low reading. The run winding is the easiest as the start have the capacitor, the centrifugal switch and the winding itself all in series. Left us know how you get on. Home later John

As Noel implies the same parts of the motor operate regardless of direction the motor runs.

I would look at the switch wiring, including the motor end for chafing or poor terminations. I suspect someone has been fiddling and failed to find the switch issue.

Assuming that there is a centrifugal switch (motor isn't cap start and run), it may be on the way out and need cleaning/replacing.

tripping an MCB. but further to this we do have a PAT testing machine. and although I'm not a PAT tester (and a quarter ton lathe is hardly portable) The Lathe PAT test as entirely normal. even when testing the motor running forward, that being the function not working!

A little further update. I had another look at it today, and at first it was running well in both directions, and I let it run for a while (15 minutes) firstly I noticed a little smoke coming from it (but no smell of electrical burning, may be a bit of oil or dirt, I don't think the machine has been used for 10 years!!) and the motor was hot (nearly too hot to hold my hand on it, so casing 40-50 degrees?)

Then on trying to restart it when it is hot, just as yesterday, works fine in reverse, but trips the MCB on starting in Forward.

I think the switch on back to front may be a red herring, I wonder if before we were given the lathe the previous owner tried to fix something..

Im thinking the motor is buggered, but still curious why only one direction trips the fuse.

I agree with Noel Shelley's post on 24/04 at 22:09. I think a contact on the reversing switch is not closing in the forward direction. The reversing switch reverses the polarity to one of the windings. Depending on the design it may have a center off position in which case it also switches off power to both windings. showing us some good pictures of the reversing switch connections would be a help. Try to take pictures from different angles to make it easier to follow the wired to the terminals. This should help to avoid connections and some wires being hidden by others. Also tell us if the reversing switch has a center off position.

Les.

there is no central position - and would what you are suggesting result in a large heat build up ? and working well in both directions when cold?

will get some images, but probably won't be back in the workshop until friday. not sure how they will come out, most of the wires just seem black (may be they just need a little clean first)

Bear in mind that MCBs (and fuses) trip not only if there is a short, but also if there is a sustained overload. Heat and smoke suggests the latter.

triping only occurs in one direction when its hot.

The manual suggests it should be connected to a 20 amp supply - but there is only two motors on the lathe, one 500w and the troublesome one which is 370w. (and I cant invisage both motors run at the same time). Even with a start up surge, a requirement of 20 amps seems more than excessive.

That hot after 15minutes Is like my old motor, which also drew 10A instead of 5A, at 20minutes it tripped the built in thermal cut-out. A new motor fixed it.

Right ! Heat and smoke ! As others have said take pictures and do sketches of the wiring then conduct an insulation test (megger) IF this shows good insulation- no leakage then proceed to solve the problem. Check the the resistance on the start and run windings for short circuit . Check that the centrifugal switch if fitted is working as it sounds as though the start windings are staying in ! Check that the cap is at rated value. If you can run the motor on an ampmeter ( overscale ) = see that the run current is not above 4 amps. If any of the tests fail,  the motor has had it, either replace or rewind if a special. BUT understand the reversing switch before connecting as you may still have a problem ! If the test can be done hot it might be a good idea. It's times like this when an overload device ( the dear old MEM Automemota ) comes into it's own if properly ranged and set.. I fear many may confuse the No Volt release for an overload device ! A surge current of many 10s of amps is normal = even in smallish motors, and why a fuse or MCB offers NO protection. Noel.

Edited By noel shelley on 26/04/2023 11:53:24

Hi Justin, looks like your start/stop is like this one, which is the type on my Chester Champion mill, and as you say, has mostly black wires.

I had a similar problem a few years ago, and I think it would only go in reverse. If I recall, some how it wasn't latching properly. I managed to take it partially apart and fixed the problem, but I can't remember what is was. I already had this one as a spare, but didn't what to use it if I could fix the other one.

I don't know if Warco do these as spares, if that's what your problem is, however Chester do stock them On/Off NVR Switches though you would have to check if they are wired the same, but I imagine they are. The black mounting is 118 x 61mm and the hole centres are about 107mm

Regards Nick.

Edited By Nicholas Farr on 26/04/2023 12:05:02

Had the For/Rev switch off today, sorted the wires so that it now runs in the correct direction, switch works well, can't find any eath leakages!

But it still trips the fuse in the clockwise rotation, and slow to get to speed in reverse.

Will try and get some readings from the windings the morrow and report back.