Rewind single phase motor for 3-phase

[Circlotron]

The normal common-as-dirt single phase (actually split phase) induction motor that has been fitted to washing machines since the beginning of time, do they have the right amount of stator slots so that they can be rewound for 3-phase? What about capacitor run motors? And what about cap start / cap run motors that are commonly on small air compressors? Could they be converted also?

[Benta]

Single-phase motors are actually two-phase motors, the second phase offset 90 degrees by the cap. Whether the pole number is divisible by 3 is a question of opening up the motor and counting.

[SeanB]

Generally yes, but your pole number will change, and thus the speed and torque as well. However in most cases the stator stack for single phase and 3 phase motors are identical in the same frame size and series from any manufacturer, though the running speed for them will be different. only difference is that you will have to remove centrifugal start mechanisms and split capacitor for the 3 phase variant, but there will be generally a 6 bolt terminal block in the housing. Small motors, typically under 500W, will run cooler as 3 phase as well, especially at low load.

[Zero999]

That's news to me. I thought most washing machine motors are still brushed and Google image search seems to confirm this. I've seen some which appear to be induction motors, although it isn't clear whether they're two or three phase.

Another thing you might want to consider is, if it's an induction motor, it's likely to be run at a higher frequency, than the mains, so you'll need to use an inverter.

[Circlotron]

In Australia at least, for many decades top loading domestic washing machines had 1/3 hp 4 pole split phase induction motors. The only front loading machine I ever played with had a brush motor. The last top loader we bought twenty years ago and the current front loader both have permanent magnet synchronous motors driven by an inverter.

The reason I ask about a conversion is that I have a small 3 phase variable frequency inverter that is just looking for a motor to play with. Doing something practical is secondary.

[Stray Electron]

Single-phase motors are actually two-phase motors, the second phase offset 90 degrees by the cap.

  It's only shifted by 90 degrees in theory and with absolutely no load on it.   In the real world, the phase shift was be less than 90 degrees but still enough to make the run start and run in the desired direction.  Until the cap dries out and loses it's capacity and then the motor stalls and overheats.

   FWIW the newish washers in this county (US) have MANY phases feed into them and are controlled by a BUNCH of electronics.  I took the coils out of two of them recently for the copper windings and I think I counted 27 poles in the windings and numerous inputs. I got about 500 feet of good 15 or 16 ga varnish covered copper wire out of each one.  The wire will make a GOOD antenna or a decent Tesla coil :-)

[AlfBaz]

It would probably be cheaper to buy a small 3 phase motor than to pay to have one rewound.
Keep in mind that sourcing a 3 phase 240V motor might prove a little difficult compared to 415. The latter would be fine but at a much reduced torque
 
It's not a trivial thing to rewind a motor if you've never done it before and value your time.
Cutting the connections and rewiring for 3 phase might have been an option also but I'm fairly certain the coil placements within the stator would be all wrong if starting out with split single phase motor.

Please let me know what you end up doing, especially if your inverter generates 3 phase 240. I've been steadily chugging along with my own 3ph VVVF drive (purely for shits and giggles) and will have to go down this road in the very near future

[Stray Electron]

   I agree with Alf.  In a lot of motors the windings are pressed together in a very large press and the entire winding is then bent in a press so that it will fit the curve of the motor housing. Then they're usually sealed in epoxy so getting them apart is nearly impossible.  Here in the US, 3 phase motors are rare outside of large industry and used 3 phase motors and equipment using them are dirt cheap.   

[AlfBaz]

In a lot of motors the windings are pressed together in a very large press and the entire winding is then bent in a press so that it will fit the curve of the motor housing.

I worked in a motor rewind shop for a number of years, I wasn't a winder but no presses were involved.
We had adjustable jigs to wind the coils but the simplest method is a slab of timber with nails or screws to wind the coils on. They are then fed into the slots a few wires at a time with the coil projections either end bashed with a plastic hammer to get them into the desired shape. Once done lace the ends with resi-glass tape, bake, dip in varnish and rebake

Larger (greater than a couple of hundred kW) used formed coils (coils made up of copper section). They got those made externally although we made our own for DC armatures

[james_s]

That's news to me. I thought most washing machine motors are still brushed and Google image search seems to confirm this. I've seen some which appear to be induction motors, although it isn't clear whether they're two or three phase.

Another thing you might want to consider is, if it's an induction motor, it's likely to be run at a higher frequency, than the mains, so you'll need to use an inverter.

This varies by region. In North America washing machines traditionally used single phase induction motors with a mechanical transmission. Things have changed in recent years though, most front loaders use switched reluctance or brushless DC motors and the regional differences are gradually disappearing.

[Zero999]

It would probably be cheaper to buy a small 3 phase motor than to pay to have one rewound.
Keep in mind that sourcing a 3 phase 240V motor might prove a little difficult compared to 415. The latter would be fine but at a much reduced torque

I thought most three phase AC motors will run off either 240V or 415V, depending on whether they're configured in delta, giving 240V, or star (also known as Y)  giving 415V.

[Circlotron]

I thought most three phase AC motors will run off either 240V or 415V, depending on whether they're configured in delta, giving 240V, or star (also known as Y)  giving 415V.

The ones I have seen, only up to 1 or 2kW are 240V delta, 415V star.
Decent size motors are 415V delta.

[Kalin]

Here in Canada at least there are a few suppliers who sell 3 phase motors down to small numbers like 1 HP for very little money. I think the list price for a WEG TEFC 1HP 1750rpm cast iron frame is like 450$ CAD. Which considering what your are getting is unbelievably low. I install alot of their motors for work and I am always impressed with the quality.

Sent from my SM-G930W8 using Tapatalk

[Zero999]

I thought most three phase AC motors will run off either 240V or 415V, depending on whether they're configured in delta, giving 240V, or star (also known as Y)  giving 415V.

The ones I have seen, only up to 1 or 2kW are 240V delta, 415V star.
Decent size motors are 415V delta.

To be honest, I haven't work with larger motors than that. At my last job I worked with relatively small motors, on conveyor belts and filling machines. In your previous post you talked about a ¹/₃HP motor so it shouldn't be a problem.

[james_s]

If you're willing to go with used or surplus motors they can be had much more cheaply. This was especially true back before VFDs became cheap and readily available, few people wanted small 3 phase motors.

[AlfBaz]

Here you go, found one on evilbay for cheap
https://www.ebay.com.au/itm/Bonfiglioli-Electric-Motor-240-Volt-3-Phase-1330-RPM-0-18-Kw-Model-BN63BA/202241250739?epid=27010932251&hash=item2f168495b3:g:qfQAAOSwm3paJ4Ss

[duak]

Here's some food for thought, years ago I ran across a Leeson FHP series AC inverter that claims to be able to drive single or three phase induction motors.   see http://www.leeson.com/TechnicalInformation/pdf/FHPSeriesChassisMountVSpeedDrives.pdf

If you look in the above document on pages 28 & 29 you should see how to use it with a single phase motor both with and without a phase shift capacitor.
I have one of these inverters but it has an LV power supply problem so I haven't been able to try it out.  I did try another brand 1 hp inverter with a capacitor run motor without the capacitor and it does indeed work.

I recall analyzing a two phase motor driven by a 3 phase inverter with the winding common connection direct to one of the phases and, if memory serves, the voltages on the phases are 60 degrees apart relative to the common connection.  While not the desired 90 degrees it should be good enough to be useful.

If the common connection's voltage swing is reduced the angle between the other two phases is increased.  I believe 87% of the other two will give a net 90 degrees.  If one was building their own inverter it should be possible to have the voltage on the common phase reduced by reducing the PWM duty cycle variation but it can be done with transformers.  Look up Scott-T connection and imagine using a tap on the non-center tapped transformer to reduce the common phase voltage. 

I'll bet there will be a fair ripple voltage at the motor run frequency on the DC link supply due to the unbalanced load currents pumping the DC voltage up.  ie., when the two winding currents are negative, these currents have to go back into the inverter and are pushed back into the DC supply capacitor causing its voltage to rise.

As an aside, I used a washing machine motor many years ago on a small drill press.  I got two speeds plus forward and reverse.  I wonder if the motor was wound for a Dahlander or consequent pole connection.  ie., switchable number of poles.  I gave it away so I'll never know.

Best o' luck,

[james_s]

It might be a fun project to try rewinding a motor even if it's not hugely practical to do so. You might even end up with a better motor, a lot of those cheap appliance motors are wound with aluminum wire, at least they were for a while.