Help with a washing machine motor.

[richard.cs]

When you say 1400 rpm, do you mean on the motor (not the washing machine drum)?

That's quite a low speed. You could achieve that in shunt connected mode and not need to use feedback (in shunt mode the motor will tend to run at constant-speed like a permanent-magnet motor, in series mode it tends to run at constant-power and overspeeds at low loads).

In the shunt arrangement the field winding is put in parallel with the brushes, possibly with a resistor or some electronics to limit the field current. I would be inclined to connect a 100 W tungsten lamp in series with the field, and then connect that to the mains input, and the brushes also to the mains input. Then wind it up slowly on a variac (or a large light dimmer if you don't have a variac) and see what speed you get. Find the size lightbulb that gives you the speed you want, and then you can replace it with some simple electronics to regulate the field winding.

Of course if you really want constant 1400 rpm, then you would be better off with a 4-pole induction motor. The main advantage of a universal motor is that they can spin faster than synchronous speed, and thereby achieve high power in a small space. If you don't want to go fast then it's a relatively poor choice.

[Zero999]

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When you say 1400 rpm, do you mean on the motor (not the washing machine drum)?

That's quite a low speed. You could achieve that in shunt connected mode and not need to use feedback (in shunt mode the motor will tend to run at constant-speed like a permanent-magnet motor, in series mode it tends to run at constant-power and overspeeds at low loads).

In the shunt arrangement the field winding is put in parallel with the brushes, possibly with a resistor or some electronics to limit the field current. I would be inclined to connect a 100 W tungsten lamp in series with the field, and then connect that to the mains input, and the brushes also to the mains input. Then wind it up slowly on a variac (or a large light dimmer if you don't have a variac) and see what speed you get. Find the size lightbulb that gives you the speed you want, and then you can replace it with some simple electronics to regulate the field winding.

Of course if you really want constant 1400 rpm, then you would be better off with a 4-pole induction motor. The main advantage of a universal motor is that they can spin faster than synchronous speed, and thereby achieve high power in a small space. If you don't want to go fast then it's a relatively poor choice.

Consider, using a belt or gears, to reduce the speed.

A small transformer, around 24V to 50V, could be used, to run the motor in shunt mode. Something, like a current monitoring relay, is a good idea, to cut the power to the armature and prevent overheating/speeding, if the field winding/transformer/wiring fails, for whatever reason.

[amyk]

In the shunt arrangement the field winding is put in parallel with the brushes, possibly with a resistor or some electronics to limit the field current. I would be inclined to connect a 100 W tungsten lamp in series with the field, and then connect that to the mains input, and the brushes also to the mains input. Then wind it up slowly on a variac (or a large light dimmer if you don't have a variac) and see what speed you get. Find the size lightbulb that gives you the speed you want, and then you can replace it with some simple electronics to regulate the field winding.

Note that reducing the field current will increase the speed of a shunt-wound motor.

Also, field windings for shunt operation will have finer wire and more turns than for series; attempting to use the latter in the former configuration can lead to the release of magic smoke...

[Benta]

It's possible, but risky to try shunt mode. A couple of points to be aware of:
- the windings on universal motors have very low resistance. You'll need some kind of current limiting for the fiels coils, and decrease the voltage to the armature (the brushes).
- the motor will no longer run on AC, but only DC.

[richard.cs]

My understanding is that shunt operation is an intended and supported mode in at least some washing machines, but probably not without some current limiting on the field winding. I have certainly used the motors in shunt on lower voltage DC, though it of course makes sense to measure winding impedances and/or bring it up slowly whilst watching current if trying to do this from full mains voltage.

It will remain an AC/DC motor in shunt mode so long as your method of limiting the field winding current keeps the correct phase relationship. A resistive ballast will do this (hence the tungsten lamp suggestion), as will a PWM-based electronic solution.

[Miyuki]

The Post Apocalyptic Inventor had made a few videos on reusing washing machine motors:

I never realized how insanely fast this thing must run to reach 1000+RPM on the drum 
That gearing ratio is huge

[Benta]

My understanding is that shunt operation is an intended and supported mode in at least some washing machines, but probably not without some current limiting on the field winding. I have certainly used the motors in shunt on lower voltage DC, though it of course makes sense to measure winding impedances and/or bring it up slowly whilst watching current if trying to do this from full mains voltage.

It will remain an AC/DC motor in shunt mode so long as your method of limiting the field winding current keeps the correct phase relationship. A resistive ballast will do this (hence the tungsten lamp suggestion), as will a PWM-based electronic solution.

I've never seen shunt operation, but there may be some rare washing machines that use it. Normally, if there are two field windings they are either serial or parallel for speed or torque, but still wired in series with the armature.

Concerning shunt operation on AC: yes it can be done but power and torque will not be good. The problem is, that field and armature timing will be different to universal mode, where timing is "forced" by the series connection.

The video posted by NiHaoMike is really good, by the way, and touches on all the points raised in this thread.

[amyk]

The Post Apocalyptic Inventor had made a few videos on reusing washing machine motors:

I never realized how insanely fast this thing must run to reach 1000+RPM on the drum 
That gearing ratio is huge

That motor is insanely loud too, sounds more like a vacuum cleaner than a washing machine to me... are universal motors and the additional circuitry needed to control their speed going to cost less or more than an induction motor?

[avitsur]

Hi to all,
I'm amazed by the amount of info given here and I would like to thank each and every one of you. now to work.

[james_s]

Again, don't forget the tacho feedback. It's necessary.

Why? I have loads of devices powered by universal motors, none of them have tacho feedback. It's needed by the washing machine to regulate the speed under widely varying loads but it shouldn't be necessary to run the motor.

[james_s]

That motor is insanely loud too, sounds more like a vacuum cleaner than a washing machine to me... are universal motors and the additional circuitry needed to control their speed going to cost less or more than an induction motor?

They're not really all that loud when installed inside the washer. Universal motors have been pretty standard on European washing machines for decades, they're used because it's easy to control the speed and the washers are front loaders and don't have a transmission like American washers have. It's really only in North America that induction motors are the norm, in top load washers with an agitator. Most modern washers I've seen have switched reluctance motors, I'm pretty sure some have BLDC and I suspect that will eventually be used in pretty much everything.

[Siwastaja]

Where's "here"?
Must be an interesting place. Personally, I've never seen a washing machine with an induction motor.

I have seen one, in an apartment building I lived in while studying, it was an old "industrial" machine, with three-phase supply. Likely has two windings, high-speed (likely 2 poles per phase) and low-speed (more poles). The obvious downsides of the induction motor, despite dual windings, is large size and lowish spinning speed, because the speed choices (for 50Hz) would be, for example, 600 and 3000 rpm. There was a separate machine for spinning the laundry afterwards, also used an induction motor but now geared for high RPM. That did a great job.

People often forget mains frequency driven induction motors are very crappy, practically useless for all other purposes except constant-speed near the rated speed. This feature also makes "starting" them awkward.

A VFD (inverter) fixes this fundamental problem. But a brushed motor does the same in a simple way (it's a mechanical "variable frequency drive"), and brushed motors can actually be very good if constructed well.

So being able to generate acceptable torque with acceptable efficiency at any RPM is one reason to use brushed motors (against fixed frequency AC motors), but another one is miniaturization, they can run with higher internal frequency, higher RPM, and thus, less iron. This is specifically why they are used in vacuum cleaners, compare the 1kW vacuum cleaner universal motor with an 1kW induction motor, the weight difference is like 0.5kg vs. 5kg! The exact same thing why 400Hz AC motors are much smaller for the power than 50 or 60Hz motors.

[james_s]

American washing machines always had induction motors, the only time I ever saw anything else was a couple of different European washing machines people had imported, the cute little  front loaders that are common there were totally foreign here, no stores ever sold them and most considered them to be far too small.

There were only 2 or 3 different companies that actually built them and they didn't really change at all on the inside from the 1950s up into at least the early 2000's when front loaders like the Maytag Neptune started to gain traction. The only real difference between a 1960 washer and a 1990 washer is the cosmetic skin, a nice thing about this is you can still buy most of the parts for even the very old ones. The induction motors are very reliable, I've never seen a washing machine motor fail. They have a mechanical transmission that is used to select between back and forth agitation and the high speed spin cycle. Shifting is accomplished by the oscillating mechanism referred to as a wigwag, it oscillates whenever the motor is running and carries a pair of solenoids that pull or push on a pair of sliding shift levers depending on which solenoid is engaged. About the only thing that ever goes wrong with these things is the seal on the agitator shaft and occasionally a wire breaks to the wigwag.

[Benta]

Again, don't forget the tacho feedback. It's necessary.

Why? I have loads of devices powered by universal motors, none of them have tacho feedback. It's needed by the washing machine to regulate the speed under widely varying loads but it shouldn't be necessary to run the motor.

Did you even bother watching the video posted by NiHaoMike? Apparently not. It shows the issue perfectly, including the runaway behaviour of the motor. But OK, 17 minutes is a strain on attention span.
No worries, the interesting part is between 1:00 and 9:30.

[james_s]

No, I don't like watching videos, I'm busy and usually multitasking. It isn't a matter of attention span, it's simply not wanting to spend 17 minutes on something that could be conveyed in 10 seconds. Either way I've run lots of universal motors without tach feedback. If it runs away then run it at a lower voltage or make sure you keep a load on it.

[Benta]

Didn't you just post two videos? 44 minutes and 30 minutes.
Keep riding your hobby horse, but you're NOT helping the OP here.

US washing machines are not relevant, sorry.

The only thing we can probably agree on is, that US appliances are significantly different to European ones. That's fine. Let's leave it at that.

Cheers.

[Siwastaja]

No, I don't like watching videos, I'm busy and usually multitasking. It isn't a matter of attention span, it's simply not wanting to spend 17 minutes on something that could be conveyed in 10 seconds.

I explained the speed runaway issue and the two possible solutions (feedback or a suitable (not any) mechanical load) also in my first post in this thread, it takes maybe 1 minute to read.

[james_s]

Didn't you just post two videos? 44 minutes and 30 minutes.
Keep riding your hobby horse, but you're NOT helping the OP here.

US washing machines are not relevant, sorry.

The only thing we can probably agree on is, that US appliances are significantly different to European ones. That's fine. Let's leave it at that.

Cheers.

Somebody said they had never seen an induction motor in a washing machine so after looking for a diagram and not finding one I found a couple of videos. You don't have to sit there and watch the entire cycle for 44 minutes, glancing at it for a few seconds shows you everything necessary to understand how the machines work. If you don't think it's relevant then ignore it.

[amyk]

I guess some people are just a little too eager to show how their country's appliances are better.

No, I don't like watching videos, I'm busy and usually multitasking. It isn't a matter of attention span, it's simply not wanting to spend 17 minutes on something that could be conveyed in 10 seconds.

I explained the speed runaway issue and the two possible solutions (feedback or a suitable (not any) mechanical load) also in my first post in this thread, it takes maybe 1 minute to read.

The washing machines that use them have a really huge ratio between the drum and the motor, 10:1 or more, and spins are >1000RPM, so >10kRPM is normal and not at all stressful for these relatively small motors. The guy in that video was just scared of turning it up all the way, he didn't even let it reach 10k!

It doesn't look like it's easy to damage one by overspeed anyway; here's a video of one running full speed and then even faster(!) by field weakening (which is definitely very hard on the brushes and commutator):

[eblc1388]

Checking my circuits collection I have found the following universal motor control circuit with speed feedback. The source is, unfortunately not known.




 

[avitsur]

eblc1388, thanx for the circuit diagram. I would like to ask two questions - 1. is it for 230Vac mains supply?  2. how do you control the direction of the rotation?

[Zero999]

eblc1388, thanx for the circuit diagram. I would like to ask two questions - 1. is it for 230Vac mains supply?  2. how do you control the direction of the rotation?

1) The supply voltage will depend on the motor's rating.

2) Reverse the connections to the brushes, to change the rotation.

3) This is not a beginner friendly circuit.