Vari-speed control

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grizzled gizzard

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Aug 31, 2010
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Just wondering if it is feasible to use something like a variable speed control, generally regarded as "(wood) router speed controllers" for 15-20 amp tools, on a 1x30 (3amps) belt grinder, or an ordinary 6" grinder, For some reason I don't see people doing this. Why is this?
 
Something like this came up in another thread a while back. Long story short, the variable speed controllers to which you're referring are made for DC motors (motor is plugged into AC, but is internally rectified for DC operation). The motor requires less internal windings for DC operation, which allows the motor (and the tool) to be smaller and lighter (portable). These are the types of motors found in routers, portable electric drills, portable sanders, etc. The motors used in bench grinders are generally AC-only (although there are exceptions). When a speed controller made for a DC motor is used as such on an AC-only motor, bad things happen (smoke, fire, blown breakers, etc.). There are variable-speed controllers made for AC motors, but they are more complex and much more expensive.

Edited to add:
Here's the thread to which I was referring, from a while back:

http://www.bladeforums.com/forums/showthread.php?p=8479571
 
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So on brushless AC motors you have to use a VFD, but on AC/DC brushed motors you can use a cheap little voltage regulator? Basically, brushless-VFD, brushes-volt reg.?

Thanks a bunch for the help and the link and all. Much appreciated.
 
grizzled gizzard said:
So on brushless AC motors you have to use a VFD, but on AC/DC brushed motors you can use a cheap little voltage regulator? Basically, brushless-VFD, brushes-volt reg.?
Click to expand...


So far as I understand it, that's what it comes down to, in a nutshell.

As always, if you still aren't sure what works with your gear, get in touch with the manufacturer (of your grinder) and ask 'em what can/can't be used to vary the speed of your specific tool. The makers of the variable speed controllers oughta' know too. But, they might tell you anything in order to make a sale of their product. I'd take whatever they'd tell you with a grain of salt. Better safe than sorry... ;)

Good luck. :thumbup:
 
I have one of those router speed controllers. I also made a hacked one out of a rotary dimmer switch and a power strip. It works fine with my Skil 3x18 belt sander, which I use inverted, clamped in a vise, as a bench sander, I can get to a rather low speed without a major dropoff in torque so the motor does not bind. I tried it with my Ryobi bench grinder and it does not work well at all, it will turn the wheels at a lower speed, but there's almost no torque behind them, it's almost like you shut the unit off. The wheels will stop with very light pressure. I'm sure it would damage it as well, so I don't use it.
 
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