# Two Speed Reverse Single Winding Motor



## Nick Hacking (Jan 31, 2017)

I hope I'm doing the right thing. I've drifted from asking about general wiring of the the whole machine to looking at the wiring inside my motor, so I've started a new thread....

The motor is three-phase, 415V.

The switch is a Kraus & Naimer A442 and a bit of digging on the internet showed me how it's wired. If I've understood it correctly, in position "1" the three live feeds go to the corners of the delta (T1, T2, T3).

In position "2" the three live feeds go to the middle of arms of the delta (T4, T5, T6) _and the corners are shorted together_ so that the configuration is two Wye circuits, in parallel.

From this, am I correct in assuming that the motor will run from 240V (3 phase from a VFD) in position "2" - but with only about half the power - something akin to the performance of the motor running from 415V and the switch in position "1"?

I presume, if this is correct, that to get the machine to run at full tilt, I either need to find a 415V power source, have the motor rewound professionally, or fit a substitute motor?

Any advice, folks?

Kind wishes,

Nick


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## hvontres (Jan 31, 2017)

I will need to puzzle on thins some more when I get home tonight (a little rusty on my wye-delta transromations), but I think you should be able to wire it in the "2" configuration to the VFD and get full power, however, you will need a VFD that can supply 2x the full load Amps @415 V. The motor should give you the low speed rpm in this configuration. To get your full speed output, you could run the VFD @ 120Hz, since your mechanical setup should handle the increased speed.


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## Nick Hacking (Jan 31, 2017)

Dear Henry,
Brilliant! I hadn't thought of driving it at 120 Hz. Thank you so much: you have given me hope.

Kind wishes,

Nick


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## hvontres (Feb 1, 2017)

Ok, I did some more research and here is what I figured out. In order to run at low speed and lower voltage, I think you would need to seperate the windings at T6,T4 and T5 and then reconnect them  like the Low Voltage setup in the lower left corner of the picture. This is theoretical, and of course would require getting into the inside of the motor. Hope this helps












Motor_windings



__ hvontres
__ Feb 1, 2017


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## Nick Hacking (Feb 1, 2017)

Thank you again, Henry.

At the moment I cannot get the wretched motor open. I need to remove the pulley stack to do that and (despite removing grub screws and circlip; and using heat) so far all I've managed to do is to damage the bottom pulley flange.

You don't think there's any mileage in the high frequency idea with a parallel Wye configuration? Given that it's a 2 HP motor, even a 25% inefficiency loss will still give me 1.5 HP at the business end. And, it's not as if the machine is going to be running flat-out all day. Overheating should not be too much of a problem.
Or am I clutching at straws?

Kind wishes,
Nick


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## Nick Hacking (Feb 2, 2017)

Well, I could procrastinate forever but sometimes one simply has to get on and do.
After asking around, I've ordered a Mitsubishi 240V VFD. It goes up to something ridiculous like 400 Hz and is rated at 2.2 kW.
I shall put my mill back together, try it with the VFD and if it performs well enough, the trial is over. If it doesn't then the motor is going to have to come off again and I'll have to find some way into it to hack the internal wiring.
(Or take it to someone who knows what they're doing: but that's less fun.)

Either way, I shall report back in due course....

Kind wishes,
Nick


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## Nick Hacking (Feb 8, 2017)

An update:

I cannot get the stacked pulley off the motor spindle for love nor money, but I managed to improvise a pair of jacks, using nuts and bolts, to pull the bottom plate off the motor, and the rotor, the motor spindle and the top bearing came out as one lump, leaving the windings in the stator in the motor housing. The shaft of the motor still goes through the plate and remains trapped by the pulley stack.

With the motor housing now upside-down, the wires all go in to the bottom of the housing which appears to be welded shut. There's a ring which (again) appears to be a permanent fixture, holding the stator and  obscuring the view down the outside of the windings so I still cannot see which wires to cut and where to connect my new leads. Pulling this motor apart in a non-destructive way is proving to be a huge challenge. The angle grinder may have to come out, but I'm nervous about that because there's a real risk of turning the windings into scrap copper.

Meanwhile, my Mitsubishi VFD has arrived - it has a 500-odd page manual but, fortunately, has an easy-run mode for idiots.

There should be time for more experimentation at the weekend. I certainly think it's worth trying the high-frequency option before I imperil the integrity of the windings for ever. I can measure current output on the VFD and I have an optical tachometer to measure spindle speeds. I suppose that if I chart frequency, current and rpm, I'll be able to see when the current keeps increasing for no appreciable increase in speed, and that'll be the point where there's flux saturation, and so the maximum working frequency of the motor.

Thinking aloud, really, in the hope that someone will stop me if my idea sounds unutterably stupid....

Kind wishes,
Nick

[Edited after watching the induction motor 101 video, to correct my use of terminology]


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## Nick Hacking (Feb 11, 2017)

Carrying on my one-sided conversation 

I've discovered that my motor has an aluminium case. The stator is held in place by three allen-head screws and a _very_ tight interference fit. I tried heating the case and cooling the stator, but I couldn't get it to budge, so I resorted to the angle grinder. The lid of the motor has four large solid lugs on the underside, in-between which are gaps for cooling. I cut through the lugs to take off the top and then carefully slit the side of the case. Apart from the case, I managed not to damage anything. The stator then came out and I've hacked the wiring as Henry suggested. Now I'm about to go back out to the workshop to try to put it all back together. I only have a DC TIG, and anyway, I've no experience of welding aluminium so there _will_ be bodging, I'm afraid.

A quick question: with my AVO the DC resistance of each coil (there are six) appears to be of the order of 12 ohms. Does this sound about right?

Kind wishes,
Nick


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## Nick Hacking (Feb 12, 2017)

Not sure if anyone is reading this, but if you are: SUCCESS!

Many thanks again to you, Henry, for pointing out what I needed to do.

At 50 Hz the motor draws about 6 amps under no load: roughly twice the rated current on the plate for operation in "series delta mode" at 420 V - so that seems about right.

Interestingly, it quite likes 70 Hz, and the no-load current drops down to 3 A at that frequency. However, at higher speeds it gets rather upset and intermittently stalls with currents reading 12 A or more and a lot of heat generated. It cannot be good for it to emulate a three-bar electric heater: I'll set the frequency limit to 70, I think.

Now for spindle speed tests and then I need to make the electrics permanent, set the mill up and start to learn how to use the beast. I've got a _working_ Bridgeport and I'm as happy as a dog with two tails!

Kind wishes,
Nick


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## Nick Hacking (Mar 18, 2017)

Just in case you all thought that I'd gone away....

Between skiing holidays and work, I haven't had a lot of time in the workshop recently, but I have managed to gather the electrical components that I need for my re-wire and low-voltage conversion. I found a rather dodgy Chinese "step up / step down" PSU on eBay for not very much. When I took it apart it is, as I suspected, an auto-transformer, but the 120 V it gives out from its centre tap works my cross-table feed with no difficulty. The motor is rated at 90 W and the transformer says it can handle 200 W, so even if the transformer's label is a little optimistic, it should still work. I've also bought a small 12 V DC PSU. I'm going to convert the 50 V work light to 12 V LED and the PSU will also serve for the control circuitry. All I need to do now is to wire it all together.

There's a second-hand machine dealer near here and I bought the biggest machine vice that I could afford from him. I've had the beast running and have actually done a little bit of milling and drilling. As YouTube's _AvE_ says, a Bridgeport serves as a mighty solid drill press.

I have a 1J head and with the third pair of pulleys (marked 180 rpm in back-gear / 1,500 direct drive) I'm measuring 1,540 rpm at 50 Hz, which is gratifying. I've actually measured the spindle speed from 5 Hz to 120 Hz and with that pair of pulleys the spindle speed seems to be exactly half of the driving frequency. 5 Hz (ie 300 / min) gives a spindle speed of 150 rpm. 120 Hz gives a spindle speed of 3,600 rpm. In theory I should be able to run from 6.7 rpm (1st pair of pulleys, in back gear at 5 Hz) all the way up to 5,520 rpm (4th pair of pulleys, in direct drive at 120 Hz).

When I first rewired the motor, I found that it didn't seem to like going above 70 Hz - from the way that it started heating up and consuming current, I assumed that the motor was reaching saturation. Now that it's mounted on the machine in the correct orientation, it seems much more content. Maybe it simply didn't like lying on its side and running hot: in any event, the current it draws is only 1.5 A at 120 Hz so it seems to be happy enough the way that it's set up.

Once the rewiring is finished, my first project is to make a tramming device with a pair of clocks mounted in a block of aluminium. It dawns on me, however, that if I'm going to trust the tramming device, it has to be properly square, and so I'm going to have to tram the mill the old fashioned way first! After the tramming device, I'm going to have a go at making a quick-change tool post and some tool holders for my modified Myford/Drummond lathe. I'm quite chuffed at the moment: this month's _Model Engineer_ has an article by Alan Hearsum, all about the way he built up my lathe from parts and modified the spindle. A sort of fame-by-proxy, if you will. I'm a dog with _three tails _now.

Kind wishes,

Nick


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## RJSakowski (Mar 18, 2017)

Nick Hacking said:


> ............It dawns on me, however, that if I'm going to trust the tramming device, it has to be properly square, and so............Nick


You don't have to be concerned with having the tramming tool perfectly square.  Just zero the indicators at the same spot on your vise or table.  In order to hit the same spot, they will have to be the same distance out from the spindle axis though.


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## Nick Hacking (Nov 12, 2017)

A quick update, in case anyone is really interested.

The low-voltage control circuits that I improvised and the conversion of the anglepoise lamp to use a 12V LED have now been running without any issues for more than six months.

The motor continues to run well at 240V from the VFD although its sometimes "sticks" on start up. I don't think that the alterations to the case geometry that I caused by slitting the case open have done the motor any favours: I should really pop the top cap off the motor housing and look at the bearing again. I may end up having to put a substitute motor in, one day, but this is going to involve grafting the end of the long shaft onto the new motor. Someone _has_ posted a thread about doing this (with success) but for now, I'm happy to simply feed the machine a new bearing race every few months.

The X-feed stalled a while back, immediately melting the Chinese 240-120V autotransformer, so that's now in the scrap bin and I'm using a big, external transformer rated at about 1KW. It's over-kill, but it was cheap, it works, and with the transformer sitting on the floor behind the mill, it's hard to notice the difference.

All in all, the conversion from 415/480V 3-phase to 240V single phase has been a success. The machine can fairly rip through metal with the right cutter, I'm now definitely the weak link in my home manufacturing set up.

Kind wishes,

Nick


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## markba633csi (Nov 12, 2017)

Good deal Nick, reading this thread with interest. Glad you got it sorted
Mark S.


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## Nick Hacking (Dec 29, 2017)

Thanks, Mark but all is now woe, death and destruction.

I was out in the workshop this afternoon, hiding from the family (in the UK we have a holiday period between Christmas and New Year when many people take time off) and milling away like a demon, all pleased with my powerful Bridgeport and my fancy powered X-axis. I was making a toolpost for my old Sheldon lathe, as it happens... anyway, all of a sudden, the mill stopped and the VFD said "E GF" which I took to mean "error: ground fault" so I lifted off the motor and stripped it down, fully expecting to find that with the heat my insulation tape had softened, allowing the sharp edge of one of my solder joints to contact the case.

Sadly, even with all of my connexions pulled well free of anything, there is now a low resistance between one of the coils and the case. I think the poor old thing is toast.

Firstly, I'm going to see if I can find a 3-phase motor with a shaft of 3/4" diameter and 4" stick-out. If that draws a blank, things may get more complicated. Blast: just when things were going well and I'd started to get a feel for the machine. C'est la vie.

Kind wishes,

Nick


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## markba633csi (Dec 29, 2017)

Sorry to hear that, sometimes old motors' windings insulation breaks down when subjected to the spiky waveforms that VFDs generate, hence the
modern term "inverter rated" motor
Mark


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## Nick Hacking (Dec 29, 2017)

Thanks again, Mark. That might explain it.
At least I got a few months use out of the motor, and leaned a good deal about wiring 3-phase motors, thanks to the good folk here.

Kind wishes,

Nick


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## markba633csi (Dec 29, 2017)

Your experience got me thinking that line filter chokes in each of the three legs between the VFD and the motor might be a good idea for 
older motors- they would have to be high current chokes >10 amp but I don't know how much inductance would be required. 
Mark


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## Nick Hacking (Dec 29, 2017)

markba633csi said:


> Your experience got me thinking that line filter chokes in each of the three legs between the VFD and the motor might be a good idea for
> older motors- they would have to be high current chokes >10 amp but I don't know how much inductance would be required.
> Mark



Maybe we should ask Henry?
(Sorry: too many Christmas cracker jokes recently)

Nick


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## markba633csi (Dec 29, 2017)

HO HO HO!   (or maybe we should ask his dwarf helper Micro-Henry) HAR HAR


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## Nick Hacking (Jan 3, 2018)

Yes, sorry about that.
Now that I'm back at work and stone-cold sober, I can hardly believe that I thought it was funny.
So, we shall not mention his niece: Millicent.

[fx: tumbleweed]

I found a replacement Bridgeport motor on Amazon! Hurrah! Sadly £1,300 including import duty and delivery. That's about $1,750 US and since I only paid £2,000 for the whole mill, it seems a bit steep. Fortunately, I've found a three-phase motor from a UK company which is "VFD rated" at only £150, delivered. I'll have to hack the spindle about and do some work on the mounting - but that shouldn't be beyond me. I don't think that I even need to bother mounting the whole 4-step pulley stack: I never shifted the belt once when the motor was working, I used my VFD to vary the speed. 

God-willing, the motor should be here in a few days and when I get around to fitting it, I'll post an update.

Happy New Year.

Nick


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## markba633csi (Jan 3, 2018)

That's funny my Moms name is Millicent 
good luck with the motor retrofit
Mark


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## Nick Hacking (Feb 4, 2018)

The new motor is in!

It was more of a fiddle than I'd imagined.

Yet again, I simply could _not_ get the pulley stack off the shaft of the old motor, despite heat, cold, levers, gear pullers and (eventually) extreme violence. In the end, I had to cut the shaft of the old motor off: the part I really needed to keep being the base plate (to mate to the Bridgeport's head). That took a full day.

The next problem was that the motor I'd bought had a 1" diameter shaft, 1.5" long. I needed a 3.5" long shaft to take a pulley with an id of 3/4". I ended up making an adapter out of a length of 2" diameter steel. Turning that down, drilling through it and boring it out took the best part of another day. At least I got to use my 10" Sheldon lathe for a project.

Adapting the new motor's base plate was easy (angle grinder) as was cutting out the holder for the bearing on the old base plate and drilling it to fit the new motor. I would have used my Bridgeport but, of course...  so, I had to resort to drilling free-hand and it went surprisingly well.

With the new motor in place, it became obvious that I'd made the shaft just a tad too long. My pulley wheel was catching on the final drive to the mill's spindle. Whereas the old motor was a squat, fat thing, my new motor is thinner and longer. This matters because my workshop has quite a low ceiling and the new motor just about touches the roof spar. Lifting up the motor to put a spacer washer underneath proved to be quite tricky.

The electricity was a doddle. The motor came with clear instructions (in the connexion box) for choosing either Wye or Delta and my only niggle was swapping wires to get it to run in the desired direction.

I used my hand-held rev counter and I seem to be getting about 39 rpm per Hz. I mean that at 60Hz I have a spindle speed of 2,340 rpm; at 80 - 3,120; at 30 - 1,170. I think it will be useful for the jobs that I'll be asking of it.

My only problem now is that the belt is a bit slack, even with the tension set to maximum. Under load the spindle has a tendency to stall while the motor keeps spinning. I think the solution is to fit a slightly smaller belt. Or, maybe, a new standard sized belt that hasn't stretched with years of use. Does any one know the dimensions of the standard belt? That would be useful...

Onwards and upwards!

Kind wishes,

Nick


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## Nick Hacking (Feb 4, 2018)

Here we go: the internet can be useful at times!
Bridgeport BP 11192101 V-Belt, 34-5/8" Length x 1/2" Width


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## British Steel (Feb 4, 2018)

markba633csi said:


> Your experience got me thinking that line filter chokes in each of the three legs between the VFD and the motor might be a good idea for
> older motors- they would have to be high current chokes >10 amp but I don't know how much inductance would be required.
> Mark



Load  (not line) chokes are usually specified by %, e.g. 3%, 5%. This is the percentage of line voltage dropped at full load amps so e.g a 5% choke will drop 12v on a 240v supply - 3% is typical for VFD/ motor protection, 5% if it's an irreplaceable item. 
To get inductance from voltage drop and full load current at operating frequency the voltage drop divided by current gives the inductive impedance (Z), Z = 2 pi x frequency x inductance, rearranging that Z divided by (2 x pi. x frequency) = inductance - expect it to be in the millihenries.

Mine worked out at around 10 - 15 mH for a 6.5A full load current at 415v so...

I built a set on three identical 24v lighting/control transformer cores with the windings stripped, the E and I laminations rearranged to all-Es and all-Is separated by a PTFE shim and a hundred and some turns of 1.5 sq.mm emamelled wire in the original coil bobbin, they measure about 12 mH and appear to work so far...

Understand that the impedance increases with the frequency so a choke that drops e.g. 12v at 60 Hz drops substantially more at the harmonics of the VFD switching frequency (some kHz stretching to some 10s2or 100s of KHz) which make up the fast rising / falling edges that a VFD generates and which break down insulation in older motors, the current and voltage downstream of the chokes will be much closer to a sinewave (although a knobbly one).

Hope that helps, rather than confuses, YMMV etc.

Dave H. (the other one)


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## markba633csi (Feb 4, 2018)

Great information there Steel, I see you've been knocking about with electrons for a bit
Mark


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## Nick Hacking (Feb 10, 2018)

Every day I learn something new.

An A33 belt is *not* 33 inches long, it's 35 inches long. If one wishes to buy a 33 inch belt, one should order an A31.

Obviously  http://crossbelts.com/conventional/avbeltsizes.html

Now waiting for yet another belt delivery from eBay.....

Kind wishes,

Nick


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## amuller (Feb 10, 2018)

Wow, you have been put through the wringer on this Bridgeport motor.  You should not need line reactors with inverter-rated motors, and the general experience with backyard shop use seems to be OK without them even on old motors.  Obviously your experience was different.  Don't know if discarded treadmills are common where you are, but they very often have a choke in them for smoothing the DC motor operation from a "chopper" type drive.  Maybe the primary winding of a microwave oven transformer would work?  Obviously you'd need three quite similar chokes.  I don't see this being a two-speed motor.  Are you sure the original switch isn't just for manual wye-delta starting?


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## Nick Hacking (Feb 18, 2018)

Thanks,

The original motor was, in fact, wired for two speed operation on 415 V. Strictly, I suppose, four speed (two forwards and two reverse).

I wouldn't try to draw too many conclusions about using old three phase motors with modern VFDs from my experience. I sliced the outer case of the motor with an angle grinder, cut the wires to the windings and re-wired it to make it run on 240 V. Frankly, I think I was lucky to get a year out of it.

The new motor is "inverter rated" and I'm not going to bother with chokes and filters: I suppose it might have helped with the old motor, but we will never know. All I can say with any confidence is that my old, hacked-about motor suddenly started giving me ground-fault errors on the VFD and these disappeared when I fitted the new motor. It seems that something bad happened to the windings, but it was as likely to be me as the voltage spikes from the VFD.

Anyway, for the record, with a belt of the correct size the machine is now running smoothly again and I can carry on learning the basics of running a milling machine. I'm very grateful to everyone here who has given me advice: no-one has (yet) suggested that I might be an idiot.

Kind wishes,

Nick


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