Angle grinder speed reduction

It works just fine with no harm to either the grinder or the speed control. I used just that setup to clean the tiles on my pool for years. The speed will bog down as the load increases but so will the router. Art

This should work fine as long as the angle grinder uses a universal (brush type) motor. And the grinder draws no more than 15A.

Not with an angle grinder. But it works fine for other universal motors.

Could also use a variac.

The problem as I understand it is that a series wound universal brush motor does not produce a back emf that can be usefully interpreted electronically and so unlike with a PM brush motor where I/R comp can be used for speed regulation, a universal brush motor is still very likely going to overspeed, and then bog down when a load is put to it.

That said, at least he will be able to limit his free-wheel rpm down to something that more reasonably suits his application.

True. Although the torque with the variac is lower at all but full rpm's vs the SCR speed controller circuit. Art

I used a variac to slow down the drill I used to mix the mortar when I did the tile job in my bathroom (you don't want to mix the mortar too fast or it gets air bubbles). The drill would definitely slow down when I put the paddle in the mortar mix, so I had to adjust the variac to give a no load speed a bit higher than what I needed as a working speed, which worked out fine.

Jon

Thanks everyone for their replies. I ended up with a Makita variable speed grinder. I hope it will be worth the extra $$$.

Michael Koblic, Campbell River, BC

I've had good luck driving universal-wound motors with a fullwave rectifier bridge driven by a variac. Universal motors prefer DC.

Joe Gwinn