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+-- Thread: Can you change the rpm of an electric motor? (/showthread.php?tid=7359770)
Can you change the rpm of an electric motor? - stoppy - 12-29-2020
Have a 3450 rpm grinder that I would like to slow to 1725. Can you do this? If yes, how?
RE: Can you change the rpm of an electric motor? - fredhargis - 12-29-2020
While I'm certain there is some magic somewhere that will do this, the basic answer is NO. Some 3 phase motors can be slowed down with VFD, and I think certain single phase motors can be as well. But I'd bet your grinder isn't one of them.
RE: Can you change the rpm of an electric motor? - Flat Lander - 12-29-2020
If your motor has brushes, probably not, you could use the Harbor Freight router speed control. If it's a induction motor you're pretty much out of luck.
RE: Can you change the rpm of an electric motor? - TDKPE - 12-29-2020
As a general rule, no. But there are exceptions, specifically shaded-pole motors. Like the little motors in table fans and such. If the grinder is small, it may actually have a shaded-pole motor (no start winding at all), and therefore it may be possible to control its speed. But that's a big 'if'. A 6" grinder may in fact use a shaded-pole motor, though I've never ripped one open and don't know for fact either way. Might also be PSC motor, like ceiling fans, which may be amenable to a speed control. Bigger grinders aren't likely to have such motors, though.
You can buy an 8" slow speed grinder for a little over $100. No risk, either, as opposed to investing in a speed control that may or may not do what you want. I have an 8" slow speed grinder with no name on it, which I use primarily for lathe tools and it's been great for that.
RE: Can you change the rpm of an electric motor? - Timberwolf - 12-29-2020
(12-29-2020, 12:59 AM)stoppy Wrote: Have a 3450 rpm grinder that I would like to slow to 1725. Can you do this? If yes, how?
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I don't know what you intend to do with it Jim but have you considered using six inch wheels on the 8" grinder"...That will make grinding less aggressive due to the slower "RIM" speed, but the smaller wheel diameter may not work well if you intend to grind longer material...One thing I do to offset the smaller wheel diameter is "bevel" the face of the wheel very slightly which provides clearance for the larger motor diameter when grinding longer objects...But I am pretty sure the wheel manufacturer does not recommend this..
RE: Can you change the rpm of an electric motor? - Bob Vaughan - 12-29-2020
(12-29-2020, 12:59 AM)stoppy Wrote: Have a 3450 rpm grinder that I would like to slow to 1725. Can you do this? If yes, how?
While single phase grinders have various starting devices, the fundamental speeds are determined by the windings surrounding the motor. A 3450 rpm motor will have two sets of windings and a 1750 rpm motor will have four sets of windings.
There are some two speed grinders on the market but they have switching devices that will go from 1750 to 3450 but I believe that the motor must have four sets of windings to start out.
I guess the short answer is NO, it can't be done if the grinder motor is a single phase 3450 rpm induction motor.
Baldor makes some really smooth 1725 rpm grinders. Consider one of them as replacement.