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1P 240V Lafert Motor In Colchester Student Lathe - Wiring Help

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Martin Winlow25/11/2019 15:31:44
5 forum posts



I have acquired a Colchester Student lathe which has clearly had a non-original drive motor (for the cutting side, not the coolant one) put into it.  The wiring for this is disconnected at the motor.  I can't get any sense out of Lafert and it appears to have some sort of early 'electronic' speed sensing circuit comprising of a relay and another component that neither I nor the UK Lafert agents can ID.

There are only 4 wires emanating from the motor windings; 2 small and 2 large, the latter are marked 'A' and 'C'.

I would assume that the smaller wires go to a starting field coil and the bigger to the run coil and the components switch over power from the former to the latter once the motor reaches a certain RPM.  The mystery component would appear to monitor the speed of the rotor and activates the relay to switch from starting coil to running coil.

Photos below and if anyone has any clues as to how this all goes back together, I would be pleased to hear them.

Martin Winlow

Isle of Colonsay

Edited By Martin Winlow on 25/11/2019 15:37:02

Edited By JasonB on 18/01/2020 15:11:39

Edited By JasonB on 18/01/2020 15:13:15

Martin Connelly25/11/2019 15:49:35
2177 forum posts
226 photos

Could be start coil. Possibly a timer and relay to cut it off after starting instead of a centrifugal switch. Are there remote mounted capacitors?

Martin C

john fletcher 125/11/2019 16:04:09
805 forum posts

Could it be a current operated relay as fitted to a fridge, connections look a bit iffy.

john fletcher 125/11/2019 17:29:03
805 forum posts

Back again. I notice identification markers attached to the motor four wires.If you have a multi meter locate both pairs of windings, one pair will have a much higher resistance than the other pair, that will be the start winding. Join together one end of each winding, that will connected to say the LIVE. (NOT YET) Using the meter again, if my assumption is correct the black box has a low resistance coil inside.One connection of the coil is connected in series with the low resistance winding (the run) and the other side of the coil is connected to the supply Neutral. That BLUE square box looks to be a capacitor with two RED wires attached. Connect one of the RED wires to the second wire of the start winding and the other RED wire to the unused terminal of the black box. So now if I'm correct, when you connect the two wires to the mains electricity and press the GREEN button you should hear a click or clonk as the motor starts indicating that the relay has pulled the contacts closed and which opened again almost immediately, as happens in a fridge. Please be extremely careful and have a second person standing by.

A picture is worth a thousand words

The third wire, is connected to the second wire of the capacitor. If you send me a PM with your email address I'll send you a diagram.

A picture is worth a thousand words.

Clive Foster25/11/2019 18:33:03
3172 forum posts
113 photos

I agree with John that the motor may be a capacitor start & run type and that the blue box is a start capacitor with there is a relay in the box controlling the start capacitor. However there are two types of relays that can be used for this duty.

Current operated relays are generally used for capacitor start motors with the relay coils in series with the run windings. When the motor is up to speed the current drops opening the relay and taking the capacitor out of circuit. They can also be used with capacitor start and run motors connected as described by John but there is an alternative set up using potential relays.

Potential, voltage, operated relays are used with capacitor start & run motors. The relay coil connects across the start winding and disconnects the start capacitor once the voltage is high enough to indicte that the motor is up to speed. The main capacitor remains in circuit connecting the "live" ends of the run and start coils. Start and run windings are joined at the "neutral" connection and "live" power connection is made to the run winding.

I've never encountered such a motor in real life but understand that the start capacitor can be physically surprisingly small due to better control of the voltage across it. General purpose start capacitors need to safely withstand full mains voltage plus a decent safety margin. Capacitors linked via a potential relay only have to be rated up to the relay opening voltage. Current through the coil of a potential relay is less too.


Martin Winlow27/11/2019 18:37:48
5 forum posts

Hi All,

Thanks v much for the replies (I would have responded sooner but I didn't get any notifications of the thread having been updated - now remedied).

I have had another look and the skinny wires (~0.5mm2 CSA) show 7.6R and the thicker ones (~1.0mm2 CSA) 4.1R (including probes etc).

Lafert said that one of the 2 rectilinear components is a probably a relay and the other a sensor to change from start to run. He wasn't any more specific except to say that these motors defo did not have the old-fashioned type (centrifugal?) speed switches for this purpose and clearly there is no sign of them.

Given that the blue box has only 2 connections and the black one 4, it would appear that the black box is the relay and the blue the sensor.

There were 2 large cylindrical capacitors with the motor; one is 25uF and the other 125uF both rated for 400V. Both have 2 'fast-on' (spade) terminals.

Please email anything to the first letter of my first name at my surname dot co dot uk.

Thanks again for all your help.

Regards, Martin Winlow.

Clive Foster27/11/2019 19:47:35
3172 forum posts
113 photos


Two capacitors suggest that this is a capacitor start - capacitor run motor. The skinny wires will be to the start coil.

If so the relay will be a voltage / potential operated type. The blue box may well be something to do with trimming the relay coil response curve for more positive behaviour.

Clearly a good and rather sophisticated motor. We need to find someone who knows exactly what it is and how to wire it up so the control gear works correctly. Perhaps one of the guys on the American "Practical Machinist" site would know. If you want I could ask.

That said the last time I had a motor designed to work with an external start control relay through my hands I simply wired an extra button and contactor into the control box to handle the start capacitor and simply held the button down until it came up to speed. Crude but effective. When you have just intercepted a high quality Brook 2 HP single phase motor that "won't start" on its way to the bin a certain amount of improvisation is in order.

As your s is on a lathe with a clutch and will always start up off load a simple time delay really would work well enough. A couple of seconds with the start capacitor in circuit should get it going just fine.


peak427/11/2019 23:21:01
1776 forum posts
193 photos
Posted by Clive Foster on 27/11/2019 19:47:35:


Two capacitors suggest that this is a capacitor start - capacitor run motor. The skinny wires will be to the start coil.

If so the relay will be a voltage / potential operated type. The blue box may well be something to do with trimming the relay coil response curve for more positive behaviour.

Clearly a good and rather sophisticated motor. We need to find someone who knows exactly what it is and how to wire it up so the control gear works correctly. ...................


I was having a search around whilst Jane was cooking, it seems that Lafert also make stuff under AEG's name
I've failed to find the correct wiring diagram, though I'm sure it's out there.
A search for Lafert LMR 100LC4 is more fruitful, however the only copies of the diagram I can find are on sites such as SCRIBD which offer a month's free access and $9.99 per month thereafter.

LM refers to Single Phase and the 100 is the motor size, 100=2.5HP ; Plain LM are start capacitor (I think, but might be Run, either way, single cap.)

The R has me slightly puzzled, but the LME series have have higher start torque capacities and Start + Run caps, the switching being done by an Electronic starter. Unfortunately that diagram didn't help as it has 5 wires not 4, and completely different colour coding, with no mention of the blue box.

I wonder if LMR are the forerunners with a simpler voltage sensed Relay starter??

Sorry, best I can do for now, as one of the more dubious links locked up the browser and disabled the part of task manager which would allow me to close Opera manually. Only just finished the malware scan. surprise

Maybe someone running Linux is able to assist.


OK , now checked my history and found a link to the pdf of the LME, on Lafert's own web site, which seems safe enough with Avast and Malware bytes.



Edited By peak4 on 27/11/2019 23:41:50

Martin Winlow30/11/2019 17:12:11
5 forum posts


Thanks again for all the help.

I have +vely ID'ed the larger black box as a relay ( but nothing at all for the blue thing which has next to 0R resistance across its leads and no capacitance.

I accessed but it refers to modern motors. That said it is titled 'Single Phase Motor - Capacitor Start & Run Connection Diagrams (Single & Dual Voltage)' with the same colours for the start (as well as being labelled 'A' and 'C' and run motor winding wires, which is hopeful ...

Another page shows a similar modern motor (LM(E)80S2) which has a 25uF run and 124uF start cap (almost identical to mine). The same data sheet ( refers to a 'LME Current Relay' being SE02 (listed elsewhere as a 'G3-072 Start Switch' but no details), but I can't find any more on this (although the first PDF file shows a box marked 'SE' with 5 connections and I suppose this could be a combined black and blue box...? Not that that helps!

(Démarrage means 'start' and 'Principal' means... 'Main' (but you probably guessed that!) Haven't a clue what 'A' means)

Meanwhile, I have tested both capacitors and they roughly match their specs.

If someone feels up to combining the 2 diagrams above into something that makes electrical sense, I'd be very grateful.

Regards, Martin.

Martin Winlow18/01/2020 11:07:47
5 forum posts

(Sorry about the broken pic links above - I've changed ISPs - working on it...)

In case anyone else needs it (finally obtained from Italy)...

... and what's more, it works... but if someone could check the current readings (taken with an AC clamp meter of reasonable quality) I'd be grateful. They were with the motor running under no load and its a 1.5kW motor)...

john fletcher 118/01/2020 15:39:28
805 forum posts

I'm glad to see you have the motor running after all the searching around. By your circuit diagram that relay is a current operated type as fitted to lots of fridges, has to be one that matches up with motor starting current, not any old one. You can easily wiring a reversing switch it be needed, but do also fit a proper motor starter with No-volt release and use it for starting after selecting DOR. John

Phil Whitley18/01/2020 15:50:35
1449 forum posts
147 photos

I don't see anything wrong with the current readings, the amps marked on the motor are the full load amps, often abreviated to FLA, so you would expect it to draw much less off load. Get it on and make some swarf!


Martin Winlow18/01/2020 17:34:16
5 forum posts

Thanks to you both (all) - the motor is already re-fitted on the lathe and it's about to face its first job. Stupefacente!

ARNOLD LIVINGSTON 125/04/2022 15:40:23
1 forum posts
1 photos

I konw this is an old thread but do you which hp your motor was & what klixon relay was fitted?

I am doing up an old 1hp Lafert which is similar but the relay is trash, just wondering which to get to have proper startup

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