Soild State relay can control the speed?

Hi Everybody,

I like to know CNC shield and GRBL can control speed rpm of my trimmer router by soild state relay?



A SSR can just switch on and off but not adjust the voltage. Therefore you’ll need a MosFET or something like that I think.

You usually use a triac to reduce the speed of a router. They actually only reduce the power of the motor, so you don’t get flat rpms. To control the rpms, you really need a pid speed controller.

This soild state relay has triac inside, it said 3-32v input. if I need add Potentiometer to adjust voltage from 0v to 3v control input for IR LED to let control triac in solid state relay, that will be work?

I don’t understand what you’re asking.

Sorry for my bad english,

I just ask, if good idea to connection varible resistor to solid state relay input to help control speed the motor?

I show you picture of oval drawing that where can I connect to solid state drive.

No. That won’t work. That input is looking for any voltage over 3V. If it detects it, the output will be completely on.

So have you experience build AC motor control circuit?,

may you can give me an introduction to step for build circuit with Triac.

Building a motor controller for AC is quite different than for DC.
Unlike a DC motor, changing the voltage does not affect the speed.
Unlike a DC motor, changing the duty cycle with PWM does not control the speed predictably.
You need what is called a zero-crossing circuit. This is usually in the form of an optoisolator on a chip. Basically it triggers when the AC waveform crosses 0V, which signals to your circuit when the wave is starting. You can then choose (using a microcontroller, 555 timer, or whatever) how much of the waveform to send to the motor, and when to cut it off by triggering a TRIAC. This is called phase angle control. This is how AC light dimmers and fan speed controllers work.


Here is a good video explaining the basics. This is not a circuit for beginners, because it uses mains power.


Thank you for explain clear about how triac work and different between AC and DC.

I decided brought new 2000watts AC motor speed controller which is triac included on circuit board that made by factory.

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it cost just $2.80

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Let us know how it works!