Electrics Problem – Lathe

[Justin ThymeParticipant @justinthyme24678]

[Justin ThymeParticipant @justinthyme24678]

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.

[john halfpennyParticipant @johnhalfpenny52803]

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

[Justin ThymeParticipant @justinthyme24678]

Posted by john halfpenny on 24/04/2023 13:56:11:

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.

[John HaineParticipant @johnhaine32865]

Are they induction motors or DC drives?

[Justin ThymeParticipant @justinthyme24678]

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

[JellyParticipant @jelly]

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

[John HaineParticipant @johnhaine32865]

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.

[noel shelleyParticipant @noelshelley55608]

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.

[john fletcher 1Participant @johnfletcher1]

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

[Dave HalfordParticipant @davehalford22513]

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.

[John HaineParticipant @johnhaine32865]

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.

[Justin ThymeParticipant @justinthyme24678]

Posted by noel shelley on 24/04/2023 22:09:31:

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.

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.

[Les Jones 1Participant @lesjones1]

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.

[Justin ThymeParticipant @justinthyme24678]

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)

[Chris Pearson 1Participant @chrispearson1]

Posted by Justin Thyme on 25/04/2023 22:47:15:

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

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.

[Justin ThymeParticipant @justinthyme24678]

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.

[Dave HalfordParticipant @davehalford22513]

Posted by Justin Thyme on 25/04/2023 22:47:15:

Posted by noel shelley on 24/04/2023 22:09:31:

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.

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.

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.

[noel shelleyParticipant @noelshelley55608]

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

[Nicholas FarrParticipant @nicholasfarr14254]

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

[Justin ThymeParticipant @justinthyme24678]

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.

[Dave HalfordParticipant @davehalford22513]

Posted by Justin Thyme on 28/04/2023 00:03:31:

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.

it's S1 rated which is continuous and it should go like that all day.

Class B says the windings can be 130C and they probably are, which means it can double as workshop heater.

I'm betting it draws more than the plated 4A, though why it only pops in one direction with the belt off I have no idea.

[Justin ThymeParticipant @justinthyme24678]

I could only get a reading out of one of the coils, and this is a diagram of the wiring. Does the centrifugal switch have to be engaged to get a reading from the other winding?

So a recap on what we have.

The forward Reverse switch seems OK and has now been rewired to work in the correct direction, it looks as though someone had clearly rewired it the wrong direction in the past!

With no belts on, the motor often runs well in both direction, but sometimes trips the fuse in anticlockwise (may be just when its hot)

With the belts attached it starts poorly and then runs well in clockwise, but mostly 95% of the time trips the fuse anticlockwise.

I am now wondering, if the capacitor has lost its umph (can that happen, I thought they just suddenly died), may be it can't get the motor to spin fast enough for the main winding to kick in ? (is that a silly theory?) this would explain it working better with belts off, but doesn't really explain the direction issue.

Anoteher thought on the capacitor. It is clearly not the original, real DIY soldering for connections. I am also wondering if it is of the correct size, if it was too small would that also cause starting problems?

What size of capacitor should a 370w motor such as this be using ?

The motor for the lathe works well but is 500w. could I try the cap off that on the smaller motor

[Dave HalfordParticipant @davehalford22513]

The Cap size is on the motor plate in box C1 100

According to your drawing the start winding is open cct. Check the centrifugal switch inside the motor end cover is free to move and the contacts make

[Justin ThymeParticipant @justinthyme24678]

the one that is on is 160µF could that be an issue ?

If the starting winding is open, why is it starting? I did double and triple check this winding with the cap removed and could not get a reading.

When the motor starts I hear a click as it picks up speed, and also hear it at similar RPM as it is slowing down after switching off – I guess this is the centrifugal switch ?

[Author]

Posts