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I'd like to slow down the little AC motor, which drives the mechanical controls on my washing machine (yes it's ancient but it works just fine). The wash cycle is a bit short, and I'd like to make it longer.

So, short of building a variable frequency inverter, I thought maybe I can slow down the motor by building a circuit which lets through only some AC cycles, something like this: 50% speed

50% speed

Of course the speed would oscillate up and down at a rate of 25Hz. Would that be a problem for the motor?

Thanks!

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    \$\begingroup\$ No, won't work. It would make more sense to simply interrupt the power to the timer motor for the amount of time by which you want to lengthen the wash cycle. \$\endgroup\$
    – Dave Tweed
    Commented Nov 20, 2023 at 19:47
  • \$\begingroup\$ i think something like that could work, but i would block it into say 5 complete waves, then a period of silence, then 5 more waves etc, to make sure the motor worked as expected. \$\endgroup\$
    – dandavis
    Commented Nov 20, 2023 at 21:21

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The concept of modulating the mains is sound, but a cycle or two at a time is probably not as the motor will constantly be in an ill-defined startup regime, rather than half speed.

If this is a typical slow geared controller, with relatively coarse event scheduling, you should consider longer duration on-off action, say every 5s. This is also easier to arrange with a simple SSR driven by a 0.1Hz square wave.

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  • \$\begingroup\$ Okay, I'll try that, thanks. It would appear I have to go with a mechanical relay though. The datasheets of the SSRs I had a look at specify a minimum load current of around 20mA. I don't know the exact power rating of the motor but I suspect the current draw is less than 20mA. \$\endgroup\$
    – merendo07
    Commented Nov 21, 2023 at 19:01

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