What makes an older Wascomat whistle as it spins up/down?

[superocd]

Was just thinking about the old Wascomats and how they sounded like jet engines. The spindown sound has me particularly puzzled. The newer Wascomats plus the other kinds of commercial machines aren't nearly as dramatic yet they spin faster. Why do these older Wascomats whistle/sound like jet engines?

Here's what I'm talking about (see link):

 

[launderess]

Don't know about revving up, but screeching sound as spin ends likely is caused by belt being stopped instead of coasting down.

My Miele will do this if one stops spin cycle by advancing timer past a certain point. Say if timer stops spin cycle, but while drum is still spinning timer moves over to "pulse/fluff" portion. There is a loud screech as drum quickly stops, then all is quiet as it starts to tumble to and fro to fluff wash.

At one point thought this would harm the belt, but once when Miele repair tech was working on Big Bertha and put an abrupt end to spin it made same sound. Asked if doing so harmed the machine, and was told "no". That "Miele used commercial quality belts on these washers. In fact copy of service manual have for W770 says same thing, that washers have high quality commercial belts and stopping spin quickly (as say part of diagostic testing by a tech), won't cause harm.

For the record every front loading washer I've used or seen at laundromats makes that same screeching sound as machine stops spinning.

 

[gizmo]

I can't give you a precise technical explanation, but it is a function of the change from 1 speed winding to another speed winding in a 2 speed induction motor.

I think it is something like this: When the washer is tumbling, the motor is turning at slow speed and the drum turning at the corresponding speed.

When the spin winding is engaged in the motor, initially the motor is still turning at wash speed, and there is a surge of electric current to accelerate the rotor till the speed matches the design speed of the fast winding. It is NOT belt slipping, is is a squeal from the motor when the rotor is not turning at the synchronous speed for the energized winding. Once the rotor  reaches the correct speed, the scream stops. It's the same for ramping up speed to spin and reducing speed back from spin to tumble.

Domestic machines tend to coast back to tumble speed, but I guess in a commercial installation, every minute counts, so it engages the tumble winding to slow the drum after spin.

[this post was last edited: 2/4/2021-06:57]

 

[cam2s]

I will agree with Gizmo about the older motors and the shift in windings. The sudden and dramatic change in speed is what makes them have that distinctive whirring noise. As the machines get heavy use the belts can start to slip under the sudden load changes too and add the noise. Almost all newer commercial machines use an induction motor driven by a variable frequency drive. The VFD slowly ramps the motor up and down instead of suddenly changing speeds. While not as dramatic this practice saves wear and tear on parts and draws less power.

 

[revvinkevin]

Just to add my two cents, I agree with Cam and Gizmo above. When the machine is slowing the drum from spin, that is dynamic braking, as explained above uses the motor to slow the drum down. My Kenmore He5t and Miele front load washers also do this at times, depending on the cycle, but it’s not nearly as pronounced or loud as the commercial machine above!

Kevin