Emco Mentor Wien Motor, missing ID plate, What voltage?

[Ian PParticipant @ianp]

I have an Emco mentor mill to which I fitted a VFD about 10 years ago and its proved totally trouble free. I run the motor at frequencies between 4 and 120Hz and it has never even got above very slightly warm to the hand.

The mill came without the motor rating plate and was wired as single phase. It seems to have three identical windings (Ohms test). I have since learned that Emco used 3 phase motors as standard and for single phase customers operated them in steinmetz configuration.

I am now beginning to wonder what voltage (in 3 phase) the motor is supposed to be operated on. It has never produced a lot of power (but always enough for my use) but the fact that it does not get warm make me wonder whether if it should be on 440V.

If anyone here has an Emco Mentor Mill I would be grateful if they could post the motor plate info.

Ian P

[SillyOldDufferModerator @sillyoldduffer]

I’m surprised that EMCO use 3-phase motors only, supplying 3-phase fitted for Steinmetz to single-phase customers; it’s possible though!

Some photos of a circuit diagram, or the motor and the inside of its terminal box would reveal what Ian has.  If it is Steinmetz, far from ideal because the compromise limits the motor to a maximum of 70% power and 25% torque at best.  Much worse if the capacitor isn’t in tip-top condition,  and ye olde capacitors rarely are.   If the EMCO really has a 3-phase motor, and the capacitor is dud, it’s a good time to consider a VFD, which would enable the motor to deliver full  power and torque, plus speed control.

Unlikely to be a voltage thing.   I find the difference between 440V and 230V 3-phase confusing, so I’m sticking my head over the parapet with what follows. Happy to be put right if my simplification is wrong or confused.

A 3-phase motor contains 3 windings, that can be connected in either of two configurations:  star or delta.

 

 

Thus the same motor runs on either 440V (windings connected in a star), or 230V (windings connected delta).  There are a bunch of pros and cons that decide if a motor is best connected star versus delta in a particular application, but power isn’t one of them: both configurations deliver the same power output.

A good reason for wiring delta is that single-phase to 3-phase converters of all types only have to output the same voltage as the single phase input.   Not having to boost mains voltage from 230V to 440V reduces cost and complexity whilst increasing reliability and safety.   (The cheapest way of producing 440V 3-phase if the need can’t be avoided is with a VFD, mainly because they don’t need a big transformer.   440V-out VFDs took a while to become affordable but a good option if one happens to buy a classic machine with a star only motor.)

Industry play to different rules, and star-wound motors often suit their purposes better than delta.  Consequently, although many motors bring out all six winding ends to separate terminals, many others hardwire the windings to a star point inside the motor, providing ony 4 terminals in the box – three for the phase inputs, plus neutral.

Star only motors can often be converted to delta by opening the motor, finding and breaking the star point, and adding wires to bring out all 6 winding ends to the terminal box, where they can be connected delta.   Difficulty of modifying an internal star point varies between easy-peasy and impossible, depending on where the manufacture chose to put the star point.  Often suits them to connect the star point very obviously at one end of the stator with easy access to all the wires, unfortunately burying it deep inside the motor is also common.   Sadly, manufacturers have absolutely no consideration for amateurs wishing to adapt their products!

In theory adapting a star only motor to delta is a bit risky because the manufacturer might have taken advantage of a star motor needing less copper and insulation compared with delta.  In practice unlikely to be a problem for amateur use.   Industrial motors are built to take a beating and hobby work is genteel!  Plus it’s been several decades since different grades of magnet wire were used to save money, at least in the size of motor a hobbyist is running (less than 7kW).

If a motor plate can’t be found, the terminals inside Ian’s motor box should reveal if it’s 3-phase with a choice between star/delta.  That informs what Ian might do next.

Faulty capacitor apart Ian’s EMCO motor not getting warm may be because it’s a well-made continuously rated motor.  We need to see the missing motor plate!  As the cost of a motor of given output is dramatically reduced when it only has to meet a reduced duty cycle, it’s unusual to find continuous rated motors fitted unless necessary.  This is one of the big differences between hobby and industrial kit, because industrial kit was built to work hard round the clock on a shift system, whereas hobbyists are unlikely to work anything like that hard.   Beware driving hobby machines heavily or for extended periods: overstressing the mechanicals and not allowing the motor and electronics time to cool down risks magic smoke and breakages!

Perhaps Ian is operating well within the capacity of his machine.  Motors and bearings that get hot quickly worry me far more than cool ones!    On the other hand, maybe the motor isn’t performing.   What’s needed is some form of dynamometer to measure the power actually available at the spindle: an interesting project if I had time and was feeling better!.

Whilst ancient capacitors are on the table, there’s an argument in favour of replacing them on suspicion alone because they are difficult to test properly.

• They often leak current, but most ohmmeters don’t apply enough voltage to detect this, not even a trusty 27V AVO.   The needle flicks as if the capacitor were storing charge correctly, but it isn’t!   Worse, although the flick is encouraging an ohmmeter can’t measure the capacitance to confirm the capacitor is within its original ratings.
• Many capacitance meters operate by measuring how long it takes to charge the capacitor, which works well most of the time.  Unless the capacitor is DC leaky, in which case the meter is confused.   Common to measure elderly capacitors and find the meter believes they are well above the original specification, with a 20uF unit reading 30 or 40uF.   Unfortunately not because the capacitors of yesteryear and improve with age like fine wine, it’s because they go bad in a way that bemuses a mid-range meter.   Instruments that aren’t fooled are outside my budget.

Dave

 

[Ian PParticipant @ianp]

This motor on the Mentor mill which with 4 speed geared head which I think preceded the FB2. I don’t have a wiring diagram but when I got the mill the seller advised me that it would never usually start in the high gear. I am sure I have seen mentioned (on the 100% accurate internet!) that Emco on this model used a 3 phase motor. My confirmation of it being 3 phase is based on the three windings being identical resistance to each other which I think unlikely on a single phase induction motor.

The motor does not have a terminal box and the windings are just brought out in a 4 core cable, one wire being green/yellow, I cannot easily check their colours now, but from memory  brown, black and grey. If on the offchance the motor was made in star mode the centre pint was not brought out.

I have googled until I am goggle eyed but have not yet found an image of the motor plate or any confirmation of the motor rating

The mill is due for some maintenance as it has a stripped gear in the head so I will have a chance to look at the motor wiring.

Ian

 

 

[vic neweyParticipant @vicnewey60017]

I have a Mentor mill,I don’t know how many versions there are but mine is an early one. I’ve had a look and there is no plate on the motor as such although there are a few numbers in the actual casting

 

[vic neweyParticipant @vicnewey60017]

They obviously were issued with a proper plate which must be missing on mine.

[Ian PParticipant @ianp]

Hard to see all the details on that plate (a good find BTW) but a 200V rating for the capacitor hints at it being a machine for North America running on 110V.

Ian

[Ian PParticipant @ianp]

Definite similarities between the casting stamps on Vic and my motors.

Both have a definite triangle (Delta?), both 180 (Wattage, 1/4HP?), the 1—-74 and the 1—75 could be date codes.

Ian P

Edit. 9—74 on my motor

[Robert Atkinson 2Participant @robertatkinson2]

That motor plate says 20uF 260V not 200V.
Likely a capacitor run motor.

Ian does not say what he used to measure the winding resistance or what the values were. Most commonly available multimeters are not very good at measuring low resistances and the winding resistance may be less than the connecting cable. To be sure of a 3 phase motor different techniques ae required. Either:
1/ Measure inductance of windings
2/ Excite each winding in turn with low voltage AC, say 12V,  and measure the voltage at the remaining connection.
3/ Spin the motor at constant speed and measure the voltage and phase of the voltages induced in the windings.

Robert.

[Ian PParticipant @ianp]

I did not state the resistance values as I did not note then at the time (many years ago) but they were within a few tens of milliohms on a six digit bench multimeter.

Its not easy getting to the motor wires now as I have mounted the VFD up close to the motor on the head of the mill, some dismantling is needed but it is on my todo list.

Ian P

[John Holmes 11Participant @johnholmes11]

Please see the attached photo of the WIEN motor plate on my Emco Mentor which I run directly from UK 220V mains. Hopefully this will answer some of your queries.

 

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