Bench Grinder Speed Control Mod?

[DIY_Guy79]

Hey guys, I have an old Buffalo(made in Taiwan) bench grinder. Nothing fancy. Got it from my mother in law. But bearings were bad in it, currently waiting for a new set to arrive in the mail. And was gonna put some fresh paint on it.

Thinking about adding a Pot in for speed control as a nice little mod/upgrade while I've got it torn apart. If Im thinking right, I just need to add the pot on the hot side in series after the switch, right? Not sure if this is going to end up melting itself or causing a fire with extended resistance from the pot after extended periods, though or not?

If not, could someone point me to a wiring diagram/schematic or maybe draw one to add the speed control in?

Thanks.

 

[exmaxima1]

Speed control won't work on that grinder.

 

[Onefastgsx]

I dont know why it would or would not work on your particular model. But I've been using a router variable speed control box from harbor freight on my Delta bench grinder for 3 or 4 years.
I just always make sure to start it with the control on high speed, then adjust as necessary. Never had an issue

 

[seber]

Routers use universal motors. They can use a pot for speed control. Bench grinders use induction motors. Speed can only be controlled by frequency. Using a pot will burn it up in short order.

 

[Wyoming09]

I was thinking of doing this very thing. You guys may have just saved me a grinder. Thanks!

 

[dogdog]

Routers use universal motors. They can use a pot for speed control. Bench grinders use induction motors. Speed can only be controlled by frequency. Using a pot will burn it up in short order.

Most of them are not POTs the pot on the grinder actually controls the SCR/Triac type controller like the ones inside your good old fashion incandescent lights... the HF ones posted is an triac type controller... you can find plenty of those on Ebay... few popular utuber have review them and give them a thumbs up... for the circuit, but not the casing...

It should work fine for non-torque demanding motors like the grinder... There are plenty of youtube videos shows how these circuit operates... Just keep in mind low torque application...

ebay is flooded with them "AC motor speed control..."

 

[6PTsocket]

Dogdog is correct. They use triac controllers for commercial cieling fans, too and they are not universal motors, either. Home fans, which are also not brushed(universal) motors usually get 3 or 4 speeds by putting different value capacitors in series with the motor for all but the top speed. If anybody is looking for a really solid triac controller, MLCS makes a standard and a heavy duty model. The HD model is far superior in construction and design to the one from HF. Baldor 2 speed bench grinders actually have 2 sets of motor windings for HI and LO. The far cheaper Eastwood 2 speed loses half the horsepower on LO. I have not opened mine up to see how they did it.

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[exmaxima1]

Dogdog is correct. They use triac controllers for commercial cieling fans, too and they are not universal motors, either. Home fans, which are also not brushed(universal) motors usually get 3 or 4 speeds by putting different value capacitors in series with the motor for all but the top speed. If anybody is looking for a really solid triac controller, MLCS makes a standard and a heavy duty model. The HD model is far superior in construction and design to the one from HF. Baldor 2 speed bench grinders actually have 2 sets of motor windings for HI and LO. The far cheaper Eastwood 2 speed loses half the horsepower on LO. I have not opened mine up to see how they did it.

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I'd bet that grinder has a start winding (unlike a fan) and will burn up in short order when used with a speed control. Shaded pole induction motors, and even some split capacitor designs can work with a speed control---but not split phase or cap start where the start winding is switched out during spool up..

 

[Onefastgsx]

Routers use universal motors. They can use a pot for speed control. Bench grinders use induction motors. Speed can only be controlled by frequency. Using a pot will burn it up in short order.

So you're saying the controller I've been controlling my grinders speed with for 3 years isn't actually doing anything at all?

 

[6PTsocket]

I'd bet that grinder has a start winding (unlike a fan) and will burn up in short order when used with a speed control. Shaded pole induction motors, and even some split capacitor designs can work with a speed control---but not split phase or cap start where the start winding is switched out during spool up..

I can never seem to keep all those flavors of AC induction motors sorted out and it always sends me back to Google for a refresher course.

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[Rabid Badger]

AC motors are touchy. Making one capable of variable speed adds a fair bit of complexity that manufacturers don't bother with in a fixed-speed device.

In other words, if it was easy (and smart) everyone would be doing it.

 

[6PTsocket]

As the OP pointed out, he had to start at full speed. Loss of torque, especially starting torque can be a problem. This is the reason it is not done that way commercially. He found a work around and got enough power at lower speed to do what he wanted to do.Not every home brew solution is perfect but if it gets the job done and you know the limitations it is a good idea. Thanks for posting.

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