Colchester Student Mk1 Won't Start

hi Richard, have you checked that all the screws on the phase convertors contacter are tight? that is it in the last picture. you could start the lathe with the cover off the phase covertor to see if you can see anything arcing, but check all the screw connections are tight first. if the machine mart warranty covers it, I would suggest it is faulty, because the motor seems to run smooth and quiet as soon as the convertor stops rattling, and I don't think you could overload a 3hp convertor with a 1.5hp motor unless there is a poor connection through the lathe contactor, and the convertor is not consistently " seeing" all three motor windings. also check the terminals are tight on the convertor outlet socket.

phil

wiring diagram corrected and made readable! this is the one for your lathe as it should be. I have taken this from the manual you downloaded to my computer, cleaned and corrected it! N/O =normally open contact. N/C=Normally closed contact.

Thanks Phil thats absolutely fantastic

The contactor in the converter is all secure and fine with the wiring. I'll try starting the lathe with the components visible tomorrow morning and get back to you

Just back in from the garage, It's very cold in there!

I've taken the top off and run the lathe. The noise seems to be coming from a small component

I've tried to get a few videos of it, you can see some little paddles working and arcing occasionally.

Mal, the man who said he ran his pc40 on his student for years, messaged me back and said that his pc 40 made these noises too when it was on its last legs. So, i'm going to take this back to machine mart and order a pc60 which he says runs everything. Should also future proof it in case i ever get any more 3 phase machinery

I'll be interested to see if machine mart has any quarrels with me taking it back

Running with top off 1

Running with top off 2

I've taken it back to machine Mart but they've got to get their 'specialist' to test it before I can have my money back

I'll wait to hear back from them, then I'll order the new one

Good move Richard, until we know we have a reliable supply we are feeling around in the dark! In you video the noise is coming from the contacter in the base of the machine, and you can see the black centre of the contactor jumping in and out as it rattles, and there is also an arc from the contacts in the smaller relay inside the clear plastic box, but it does look like that convertor has been overloaded in the past, which has caused the contacts to burn and go faulty when it is loaded. Keep us all informed! Are you home for Christmas now, or still have another week at Uni?

double post

Edited By Phil Whitley on 15/12/2019 15:50:21

Hi Phil, I'm now back home till around the 3rd or 4th of January. Then back to uni till the 15th when I'm back home for another fortnight after exams.

The man in the shop said the specialist would be in tomorrow so could check it at some point this week. Hopefully sooner rather than later

Excellent! my feeling is that the small contactor in the plastic box, which I assume is single phase side, switches in the main contactor on the base of the unit, which is on the three phase side, it could be that servicing all the contacts in both relays would cure the problem, but not your job if it is under warranty. Also if there is some sort of overload protection in the unit, and I am sure there will be, that also could be faulty, and breaking down partially when there is load on the convertor. Having no experience with this type of phase convertor, I now realise I should have asked you to turn it on without the lathe connected, to see if it still rattled, which would condemn it as definitely faulty! No matter, we await the next thrilling installment with baited breath, and it distracts me from the triple shower and bathroom pump problem I also have on the go!

On a different tack, it could be that a fault on the lathe or the lathe wiring is causing intermittent loading on the phase convertor, and thus causing it to trip off and then restart, possible, but not probable. is the lathe contactor pulling in when you operate the lever on the lathe?, it could be that one of the contacts is not making properly. the lathe contactor must be working to an extent, because the C&D switch only completes the circuit to the coil in the contactor, and then the coil pulls the contacts in the contactor together to connect all three phases simultaeneously to the motor. Unfortunately, you cant observe this with the lid off, as removing the panel from the lathe disconnects the supply! Did you make a new contact to replace the one you found in the bottom of the box?

Phil

Edited By Phil Whitley on 15/12/2019 16:11:30

Hi Richard

Answer to your pm and if anyone else needs  to read up on this problem I thought It would be good to answer here yhat everyone can see ,if I can remember the pc40 use to trip out the house electrics when the suds pump run with the lathe so I just disconnected from the lathe and she run good , never got round to figure this out and have run it without suds pump ever since, still got the pc40 which runs my pillar drill 1/2 hp motor no problems bud will not run the lathe 3hp or the mill 2hp, I have tried plugging them in to the pc40 the lathe justs hums and the mill trips out the house [13amp feed ]

Richard I'am no way a electrician just giving you my experience on the clarke pc40 [ now running off a pc60 with no problems] I can take a vid or send pics if you like if it helps.

To Phill's post my pc40 rattles when nothing is plugged in and the 3 switches are on for 0.5 ...1....2...hp .

Mal.

Edited By mal webber on 15/12/2019 23:20:34

Edited By mal webber on 15/12/2019 23:28:51

Thanks Mal, thats interesting, possibly shows up how they fail when they do, although you would expect it to deliver its rated output reliably, but then again, it is probably made in Italy, like much of the machine mart electricals, which means some is good, and some not. I have a Clarke single phase mig from machine mart, and made in Italy, bought in the eighties, and still welding well after much use and abuse, it has had a couple of repairs, but I certainly have no complaints, and I am working on a SIP italian welder /battery charger, which is still going strong, and is suprisingly well built too!

Just a thought, did it rattle like this from new, or did it start rattling when it began going faulty?

Phil

Edited By Phil Whitley on 16/12/2019 10:47:00

I wouldn't assume the PC40 is necessarily faulty, or that replacing it with with a new PC60 will result in success!

Richard mentioned his lathe dates to 1955 and I'd have guessed earlier. The electrics appear to be original, 64 years old, and the lathe has not been kept dry. Furthermore someone has messed with the wiring, presumably in an attempt to get it going. To that I'd add the possibility that the drive train is gummed with old oil, or that new oil is stiff because of the cold weather. Maybe this adds up to more than the PC40 can cope with.

The other issue is the sort of device the PC40 is - static converters have distinct limitations! This type of converter isn't recommended for heavy or intermittent loads. From the manual:

The circuit shows the device briefly bodges an approximation of 3-phase with capacitors as a way of starting the motor. It doesn't output continuous 3-phase like a rotary converter or a VFD. The motor cannot develop full power.

Although the necessary capacitance is broadly related to the motor's output power, it's not that simple. The switches marked 1HP, 2HP and 3HP don't set power output, rather they add or subtract capacitors as necessary to match the motor to get enough phase-shift on the 3rd winding to start the motor. Page 8 of the manual shows 7 switch combinations for 0.5 to 3.5HP; the user should experiment for best starting.

Once the motor is rotating, I believe relay K1 disconnects the capacitors and leaves the motor running on two windings only. This considerably reduces the power output of the motor compared with what it would do with real 3-phase. I suggest the relay chatter is due to the PC40 thinking the motor has started and then detecting the motor is stalling, thus kicking again by reconnecting the capacitors. It's hovering on the brink of a successful start.

Note that the capacitors are only used during starting. Using this circuit for frequent stop-start work, as on a lathe or mill will shorten their working lives.

As the device is distinctly limited, they aren't suitable for all motors, or operating style. The manual says:

Thank you for purchasing this CLARKE Single to 3 Phase Converter. i.e. to run 3-phase asynchronous motors ONLY, from a 230V single phase supply.Please note that this device, because of its characteristics is for use primarily with constantly running motors. It is not desirable for use with stop start operations.

and

For some applications of small motors, or motors of unusual magnetic characteristics, it may be necessary to provide a pilot motor to obtain a balance of phases. Generally the pilot motor should be a 2 pole (2800 rpm) motor and as a general guide should be at least twice as big as the motor to be driven.

Why is the motor stalling? The PC40 must have done it's job as a starter, but maybe its autotransformer can't deliver enough amps to keep the motor turning. (A PC60 has a bigger transformer.) Or equally likely, it's because the lathe is stiff! Could be the motor would run OK on a warm day with clean bearings, but December in a clogged state is just too much. (Measuring my WM280 in a different context showed just turning its spindle, gears and leadscrew takes about 200W)

Longer term, I think a VFD would be a better solution than a PC60,. Apart from a VFD producing genuine 3-phase and getting the best out of the motor, a PC60 needs a 32A single phase supply!

Dave

Usually there are two banks of capacitors, start and run. All in parallel when starting, then larger set disconnects connects manually or automatically when up to speed. I helped a couple friends in the past and one had a manual rotary selection switch which adjusted the run capacitors in or out. When the motor hummed along that was the correct number of caps. If it sounded right it was right.The other had a current operated relay, which disconnected all of the start capacitor when the motor was up to speed, no adjustment, all or non, type of thing. When a pilot motor was fitted things really improved. Coolant pump was wire to Delta and fitted with I think, a 4 micro farad capacitor and ran from a 13 amp socket. John

the relay K2 can be seen arcing in time with the rattle from K1, I would suggest the rectifier is failing, allowing intermittent DC to K2 and causing the fault we see in the videos.

Or possibly C7 or R7? the fact that the PC 40 does this with the lathe disconnected is pretty damning! 3 phase motors will not start or run on 2 windings, when there is a "leg off" they just growl and sometimes turn very slowly.

Phil, to answer your question from a few messages ago, I have not replaced the contact i found in the bottom of the box. The lathe has been wired around that contact so it no longer needs it to turn on. I had my electronics friend look at it. The contactor must have broken so they wired around it, it was the other part of the contactor for all of the microswitches, so that's also why the yellow wire is not connected through the limit switch or to the circuit board.

As far as the use of vfds go, Initially i though i was dealing with a 3hp motor, so a phase converter was going to be much cheaper than a vfd, however now i know its only 1.5, a vfd would only be around £130.

But, I would have to rewire the lathe and i'd much prefer to keep it as close to original as possible.

I have a 2hp vfd wired up to a 3 phase motor for my belt grinder. Also, the motor for the lathe is original. I'm not sure it can be wired up for 230v or not, as vfds, as far as i know, do not produce 440v.

I would use the vfd, but only if its wired to where the plug for the lathe goes, which wouldn't work as I think the vfds need to be attached directly to the motor.

I have a 32 amp plug, so the pc60 seems like the more suitable option to me, as then i'll be able to use it with future machinery too, unlike a vfd where i'll need to buy one for each machine

Hi Richard,

You can get VFD's with 415v out but they are expensive. With a std VFD you would, as you say, have to rewire the motor in Delta, and connect straight to the motor, and it looks from your pic of the motor connections that the star point is inside the motor, you could try to test between the incoming blacks and the spare terminal on the connector block, as it is just possible that the star point is connected underneath the spare terminal, but it is a long shot. I think the PC40 should run the lathe easily, theoretically, the PC 20 should run it. I have detailed above how the PC40 works, and what is wrong with it, but we have seen from your videos that it WILL run the motor at full speed, but the starting is slow, and that is a fault on the phase convertor.

Back to the lathe contactor, if the missing contact has been bridged, the lathe must be starting on the other two contacts, the C&D switch cannot start the lathe without a contactor of sorts, as it needs to switch the three phases on simutaneously and seperately. I will look again at the pics of the lathe contactor and get back to you. Must go and cook Isobels tea!!

Phil

Edited By Phil Whitley on 16/12/2019 18:59:46

Mal, a video would be very helpful for comparison thanks