Thread: Easy variable speed controller?

That device is designed to control the speed of a brush or universal motor. Most grinders are induction motors and their speed is controlled by the frequency of the supply.

Originally Posted by Bohdan

That device is designed to control the speed of a brush or universal motor. Most grinders are induction motors and their speed is controlled by the frequency of the supply.

Not only that, but even on a universal motor they have a very limited speed/usable power range. The work OK on lightweight things like fans and cake mixers but when anything has a load applied they are nearly useless.

Thanks Bodhan and Bob. Sounds like it's not right for me.

Jaycar do a kit for induction motors up to 1.5 kW

Speed Control Kit for Induction Motors | Jaycar Electronics

NB. See the note that it does not work on motors with a centrifugal switch

That was discontinued years ago. I doubt you will find one.

My two cents worth, be cautious with the use of speed controls
The design of the tool includes cooling the appliance with its internal fan.
Fans and air flow observe a square law, that is half the speed quarter the air flow.

If any one is running three phase equipment, I have a bunch of small 3phase VSDs I can sell.

No, they won’t convert single phase to 3 phase.

pm me.

Originally Posted by NCArcher

That was discontinued years ago. I doubt you will find one.

Maybe this one?

K6032 - Silicon Chip Magazine 1.5kW Induction Motor Speed Controller Kit - Altronics

$$$$ though

Originally Posted by dinosour

My two cents worth, be cautious with the use of speed controls
The design of the tool includes cooling the appliance with its internal fan.
Fans and air flow observe a square law, that is half the speed quarter the air flow.

I agree about the cooling issues but flow and fan speed are normally directly proportional
eg see Understanding the Basic Fan Laws - Axair Fans

For most fans with unrestricted flow the First law of fans applies eg
"Volumetric flow rate (V, m³/hr) varies directly proportional to the ratio of the rotational speed (RPM) of the impeller.

Maybe you are getting mixed up with teh 2nd or 3rd Laws fro fans?
Fan pressure varies according to the square of the rotational speed.
Power requirements varies according to the cube of the rotational speed.

Originally Posted by Lappa

Maybe this one?

K6032 - Silicon Chip Magazine 1.5kW Induction Motor Speed Controller Kit - Altronics

$$$$ though

Thanks Lappa. Probably cheaper to buy a slow grinder And putting together a kit, I wouldn't be sure where to begin