DC servo motor wiring question

[ManofkentParticipant @manofkent]

[ManofkentParticipant @manofkent]

I recently bought Boxford 11 inch industrial lathe.

The spindle motor is a permanent magnet DC servo motor. (SEM MT 40W4 -45), together with a Parker driver.

Now I had always understood servo motors to have 3 wires, DC in, signal, and DC 0.

But this motor seems to have only 2.

This motor has 3 pairs of connection pins and wires.

A1 & A2 (armature).

T1 & T2 (tacho voltage)

K1 & K2 .

I am guessing from the motor schema that K1 & K2 are for a thermo cut out.

Needless to say the cable cover with wiring diagram is missing.

So can anyone point me in the right direction. Can this be a simple PWM controlled motor with 2 wires, and if not what am I looking for to find the third (signal) connection?

Many thanks

John

[mgnbukParticipant @mgnbuk]

Not sure what you mean by a "signal" connection ? What sort of "signal " ?

Your description of the SEM connections is as I remember them & the K1/K2 connection are a simple thermal switch not a thermistor. The DC servo drives that we used with SEM MT series motors at my previous employment were either Norwin (PWM transistor drives) or Indramat (thyristor drives), both of which just had a DC+ and DC – output to the armature & received speed feedback from the DC tachogenerator (9.5v/1000rpm for the MT series IIRC). I would expect that the Parker drive would have those connections – does it not ?

Nasty overly small connection "box" on those motors – always a struggle to get all the wires in & the box assembled with it's lid without getting something trapped.

Nigel B.

[ManofkentParticipant @manofkent]

Thanks Nigel.

Yes the Parker drive has those connections (and a load more – mostly on a 10v control circuit).

Your reply is most helpful. I thought I was losing my marbles trying to wire up this motor. I think the designation "Servo" took it to beyond my understanding.

I fabricated a new connection box cover. As you say, too small for some pretty thick cable.

Is there a way to tell if the thermal switch is still working. Were they normally closed or open do you recall?

Once again thanks. Your reply has been very helpful.

John

[mgnbukParticipant @mgnbuk]

John,

From memory they were normally closed. They were of limited value, as they were mounted in the frame of the motor & the heat was generated in the armature. By the time the frame had heated up via the air gap to the point that the switch tripped, the armature was usually toast anyway. The original SEM MT series brochure is available as a .pdf here

Not that usual to use a permenant magnet servo motor as a spindle drive – they are a continous torque motor with no constant power range -, though in effect that is what the Chinese use on hobby machines (but without the tacho feedback). Your motor appears to be an 8.5Nm continuous torque 4000 rpm maximum speed @ 180 V DC. The tacho on that motor is shown as 7v /1000 rpm (35mA max).

The Parker drive should just have the armature & tacho connections to the motor. There will probably be a choke in series with the armature wiring, which would normally be twisted. The tacho should be connected with a screened two core cable, with the screen grounded at the drive. The thermal switch would normally be connected in series with the drive enable circuit, the Emergency Stop circuit or as a control input, depending on the whim of the designer. Other connections to the drive other than power input (which maybe via a transformer) would be a 1-10 V velocity demand signal (two core screended cable), a "Run" or "Enable" signal and some monitoring – "Drive OK" and, depending on the drive type, maybe an "At speed" and a "Zero speed" output. If you can get the drive model details I'll see if I can pull up a manual. My previous employer used Parker 540 series DC spindle drives, though it is a while since I last comissioned one.

We used to use MT40 series motors on larger machines such as Butler Elgamills. My main recollection of this type was that they seemed hard on brushes – I changed more worn-out brushes on that motor family than the smaller MT30 series (used on Bridegport sized machines) or the larger MT52 series. Tacho armatures occasionally went open circuit on one segment – I doubt tach armatures are available as spares now, but they were around £400 + Vat 20 years ago – the brush plate was another £100 or so.

Nigel B.

[Jason HahnParticipant @jasonhahn10319]

Hi Nigel,

I believe it's John's question brings me here.

I have a servo drive from an old EDM machine, please see the picture.

Servo Drive

I'd like to make it work with a 48V DC motor, it is a SANYO DENKI M818T-031 which has two wires(+/-) to get power, and two wires from its tachogenerator.

DC Motor

My question is how to wire the drive with the motor, what are those terminals on the panel for?

I'll be appreciated if you can pull up a manual.

Thanks,

Jason

[mgnbukParticipant @mgnbuk]

Hi Jason.

From a quick Google that appears to be a Charmilles part, which fits with your EDM machine history. The only references I find to it are from industrial parts suppliers (with no module specifications – just like-for-like replacements), and nothing from Charmilles. It is likely that the drive pre-dates digital documentation, so the best to hope for would be a .pdf scan of a paper manual and, if this is a Charmilles specific part, there may not have been manuals made available to users.

There do not appear to any armature connections on the front panel – are there any more connections to the rear of the case ? Guesstimating, +/- 10v to 0V could be the velocity command analogue signal from the controller, TG to 0V could be the motor velocity input from the tachogenerator (black & white wires from your motor). Over current & overvoltage maybe fault signal outputs to the machine control circuit. Which leaves the 36V – maybe input power, but strange to see it on the same connector as the +/-10V and TG inputs – and no connections for the motor armature ( red & blue wires on the motor).

I oculdn't say if your servo motor would work with that drive. It is unfortunate that the tacho wiring obscures the armature voltage rating & what may be the continuous torque rating on the motor data plate in your picture. Are there any rating plates on the drive module giving, say, input voltage & current or output voltage & current ? If the drive had a lower output voltage than the motor that would not be the end of the world – the motor maximum speed would be less than at rated voltage. But current is another matter – a lower current capability from the amplifier would lead to lower torque at the motor & loading the motor beyond the drive current rating may damage the drive.

Nigel B.

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