Colchester Student Mk1 Won't Start

Right richard, here we go, the clearest and best wiring diagram is in the free download manual from the Colchester site, even though it is for a Mk1.5 with a different make of contactor, they are electically identical.

Refering to the drawing you will see what we call the limit switch (because that is what it says on the case) is referred to as the Craig and Derricot release switch.

Starting at the contactor coil, you will see that one side of the coil is connected to L1 which is an incoming phase. Remeber that the coil works between two phases, there is no neutral in this set up!

The other side of the coil connects to terminal 2 on the contactor, and then to the red wire which goes to the C&D switch terminal 3.

The other phase used is L3 which goes via a link wire through terminals 10 and 9 on the contactor, which are the overload cut out switches, and then on through the yellow wire from terminal 9, through the end cover and lock switches to terminal 1 on the C&D switch. Note a mistake on the drawing, in that the yellow and red wires which cross adjacent to terminal 3 on the C&D switch are NOT connected but the semicircle has been ommitted from the drawing!

When the end cover is fitted, and the key switch is on, terminal one, yellow wire on the C&D switch is "live".

When the switch is lifted from the off position to the intermediate position, (we will call the unmarked terminal on the C&D switch 4) 1 and 4 are connected together, and 2 and 3 remain connected. the live goes from1 to 4, down the link to terminal 2 across the switch to 3 and back to the coil on the red wire, and the contactor pulls in/motor starts.

on the contactor, the holding in contacts close the circuit between 1 and 2, and as the start handle is moved fully in to the on position, the C&D switch opens 2 and 3, and 1 and 4 remain closed. Machine is now running, and terminals 1 and 4 on the C&D switch have become part of the holding in circuit and the machine will continue to run till the contact is broken by pushing the lever to stop, or if the power fails, the end cover is removed, or the key switch is turned off.

Refer to the wiring diagram whilst reading this, as I did when writing it, or it will make no sense! My money is on the key switch being in the off position. Good luck with it, and I will still be here for any further questions you have, and any further assistance you may need,

I'll make a sparky of you yet!

Phil

Edited By Phil Whitley on 07/12/2019 18:10:45

Link to manual.

https://colchesterlathe.groups.io/g/main/files/Colchester%20Student/Colchester%20Student%20-%20Mk1%20%28Round%20head%29/Colchester%20Student%20Mk1%20-%20Instruction%20and%20spare%20parts%20manual.pdf

Been back to have a play today, had a look inside the "limit switch" and it doesn't look the same as Phils.

Thoughts?(apart from it being filthy)

Hi Richard, all the wiring diagrams using this type of switch use three wires to the switch, the yellow is missing, and it is the yellow wire that takes the "live" through the end cover switch and the key switch to the C&D switch! the red is connected to the terminal where the yellow should be, see if you can trace the red back to the starter and see where it goes. even if it has been wired in some way to make it start, the NVR cannot work unless tyhere are three wires at the C&D switch.

Phil

Take the red tape off the yellow wire in the starter area, leave the end cover on, remove the panel round the key switch and see if you can test from the yellow wire in the starter to the key switch to see if you can find out where the yellow wire goes to. It should start at C1 on the contactor, go through the end cover switch, through the key switch, and to terminal one on the C&D switch.

Phil

Richard, the switch mechanism seems to be working correctly, but I would guess it is lacking the correct live feed, I am going to reproduce the wiring diagram out of your original manual in a more readable format, with the errors taken out, but I am working tomorrow, so will do it at the weekend. in the meantime, see if you can find any other disconnected wire ends, especially yellow ones!

Phil

The lathe is alive. I spent quite a while using a multimeter testing for continuity in the circuitry, however I couldn't find anything wrong except from the way someone has changed the wiring. They have changed it so it no longer has the safety features, so the key switch, switch in the left of the headstock for the gear cupboard and others don't affect it. No longer has a no volt release either.

So I had a play with the wires in the isolator, swapped two of the phases round and it worked. Someone suggested this a while ago.

However, even though the lathe is now spinning a bit, it's still not happy about it.

Phil, I mentioned that your lathe spun a lot more easily than mine did, I think there's too much resistance as the static converter is struggling to power the lathe.

The converter has different power settings, from 0.5 to 3.5hp. but it works best on 2hp for the 1.5hp motor. I'll get some footage of the lathe on different speeds and the effect it has on the converter and post it later. I took the brake apart and it's not causing any resistance (apart from when pushed).

Any thoughts? Videos to follow

On second attempt, trying every speed, it seems to be able to get into most but the higher speeds. Also running the phase converter at full 3.5hp instead of the 2hp stated before

52 speed video

86 speed video

118 speed video

192 speed video

272 speed video

445 speed video

It doesn't seem to want to get up to speed when the 445 speed is set

I'm not sure what condition the motor is in, Its the original from 1955 so it could be knackered?

But, also the phase converter may be old already since I bought it from the back reduced section of machine mart

My money would be on the converter not having enough oompf. The "phantom" 3rd phase approach of thesedevices is not ideal.

Also if it as not been run for a while, ltet it warm up for a while before trying the top speeds. It may need the oil needs warming up. When I first got my Chipmaster it wouldn't go a full pelt (3000 rpm).
There is not much that can go wrong in an induction motor, so I expect the motor is OK

A couple pages ago A guy called Mal said that he ran his colchester student on a static converter for 4 years before it gave up. He said that it slowly lost energy and ended up not being able to get into the higher speeds. Especially given that the motor is only 1.5hp with a 3.5hp converter, surely 2hp extra is more than enough?

I bought the converter from the reduced section in machine mart, so it could have been used before. It's definitely not brand new. So possibly that could be the issue, in which case i'll have to try and take it back to machine mart and get a working one?

As far as warming up goes, i'll try that tomorrow as the lathe has not been used for potentially years. ive had it since august and only just been able to turn it on.

The motor may not be the full issue, but could definitely do with some care. Its 65 years old and judging from how dirty the lathe is, It's probably full of crap too

Hi Richard, the phase convertor should be fine provided it is working correctly, and I dont think the motor would turn the lathe at all if it only was getting two phases. Take the belts off, check the motor turns smoothly and freely, then power it on and see if the motor runs quietly, if it hums loudly or growls, it is likely to be off a phase or phase imbalance. let the motor run for say, ten minutes with no load on it, and see if it gets warm. Those Lancashire dynamo motors are pretty bulletproof, I doubt there is anything wrong with it. Strip the brake mechanism inside the input pulley to see if one of the brake shoes is binding, or possibly one of the linings has come unbonded and is jamming the pulley, it should be free to turn. It is possible that there is a bad bearing in the motor, but if there is, you will hear it when you run the motor without the belts on. I thought when you posted up the switch that it had been rewired to provide a straight on/off operation. No reason for it to be wired like that unless someone has tried to get the safety and key switch out of circuit, but has not understood how to do it, or not had a wiring diagram. who knows. Did you replace the missing contact in the contactor?

Phil

Edited By Phil Whitley on 13/12/2019 21:01:01

we need some sound on the videos!!

Phil

also noticed that you have the leadscrew and feed rod in gear, put the very short lever on the front of the headstock in the mid position and the end gears and screwcutting gearbox should stop turning. If the saddle is tightor something alse is wrong that may be why the lathe input shaft is difficult to turn, you need to find out why that is! Remeber we discussed the brake mechanism in the pulley? check it out!!

Phil

The videos should all have sound, not sure why you're not getting any. There should be a speaker at the bottom left you can click on

I had the motor out before and it seemed to be spinning fine, but I didn't leave it to run for long.

I also took the brake to pieces and its working fine.

All the safety switches have definitely been cut out of the circuit as it shouldn't run with the end cover off, but it does. There's no logical reason that they would have been taken out though, so you may be right. I still think the contactor is broken and is just being used to transfer the power, with no no-volt release. The contactor is always in contact with the circuit, it never stops being attached, so perhaps the spring went and they decided to cut it all out.

The same yellow wire from yours is disconnected at both ends on mine

I know someone who's tearing down a colchester student so even though the lathe is working for now, i'll see if i can get her to sell me the control panel and components from her lathe. So I can just replace the whole thing.

This is a video of the motor by itself and you should have audio, it runs okay, not the smoothest, but decent enough. Perhaps a little rattley, but nothing serious. I'll run it tomorrow by itself and have a play around

motor free spinning video

Is that rattle at the begining of the motor running free vid the contactor chattering, or is it coming from the motor?

Phil

getting a new control panel and especially if it has the later contactor, sounds like a good idea to me!!

phil

The rattle is the noise that the converter is making. As far as i know, it should be silent, so maybe thats why there's something up

Yes Richard, that definitely sounds suspicious to me, might be an idea to whip the top off and check out the capacitors to see if any of them are bulging or leaking, you get that sort of rattle from loose transformer laminations too, and they settle down as the current falls when the motor runs up to speed.

Phil

Hi Richard, the videos are working with sound today, or at least some of them are , I get a 404 error on the 118 speed one but no matter. What I see on the 272 speed video tells the story, the noise from the phase convertor seems to be a relay chattering as the light flickers in time with the rattle, and then when the relay finally pulls in the motor immediately runs up to speed, and goes quiet and smooth, look in the phase convertor for loose connections or dirty relay contacts and get back to me! Watch out for the capacitors!! they hold a charge but should have discharge resistors across them. short them with a well insulated screwdriver across the terminals to discharge them and make them safe.

Phil

Taken the top off the converter, I can't see anything wrong particularly. I've had issues with capacitors before so I could probably notice. My multimeter doesn't measure farads since it's just a cheap one, so I can't test the capacitance of each with that method.

It's definitely an old converter though, it's last safety test was in 2017.

I have the receipt and I have a video of it making the clunking noise. So machine Mart should just take it back with no quarrels. But it depends what people would recommend me to do next

Thanks