Thread: Spindle / router / trimmer

A question for question 1 - What is the smallest induction motor anyone knows about?

The smallest induction motor I can think of is probably the one inside my hand blender!

The reason why induction motors aren't often used in portable power tools is the fact that their design allows fairly high speed but rather low torque, especially on start up. Brushed motors have considerably higher torque in a smaller package. The only hand held power tool I can think of in my shed with an induction motor is my heat gun. Table saws, jointers, dust extractors and drill presses usually have induction motors but these are obviously able to mount such physically large items.

Also, induction motors are pretty much single speed. You can only change their speed by altering the phase frequency.

Thanks Chief, good explanation

Induction motors in Aus (50HZ mains) have a theoretical max speed of 3000RPM, (50 cycles per second x 60 seconds per minute). However in order to produce usable power, they must have 'slip' a reduction from theoretical synchronous speed that produces torque. Hence typical max specified speed is in the range of 2800 to 2880 RPM depending on the designed slip of the motor.

Other variations with more winding poles have lower speeds like 1500 RPM synchronous (1400 to 1440 RPM) for 4 pole motors and 1000RPM synchronous (typically 960 RPM rated). These speeds are way to slow for effective direct drive of router bits.

For 60Hz mains the basic numbers are 3600 RPM synchronous less slip for about 3450 RPM rated, or half or one third for multipole designs.

Re heat guns, I have been inside a couple of heat guns and a few hair driers, and the fan motors that I have met there were low voltage permag motors connected across the +/- terminals of a bridge rectifier connected in series with the heater element. May be different for heat guns with some sort of thermostat control. but the basic ones are that basic.

Originally Posted by malb

Induction motors in Aus (50HZ mains) have a theoretical max speed of 3000RPM, (50 cycles per second x 60 seconds per minute). However in order to produce usable power, they must have 'slip' a reduction from theoretical synchronous speed that produces torque. Hence typical max specified speed is in the range of 2800 to 2880 RPM depending on the designed slip of the motor.

Other variations with more winding poles have lower speeds like 1500 RPM synchronous (1400 to 1440 RPM) for 4 pole motors and 1000RPM synchronous (typically 960 RPM rated). These speeds are way to slow for effective direct drive of router bits.

For 60Hz mains the basic numbers are 3600 RPM synchronous less slip for about 3450 RPM rated, or half or one third for multipole designs.

Re heat guns, I have been inside a couple of heat guns and a few hair driers, and the fan motors that I have met there were low voltage permag motors connected across the +/- terminals of a bridge rectifier connected in series with the heater element. May be different for heat guns with some sort of thermostat control. but the basic ones are that basic.

Basically from the above, I gather that a portable router using an induction motor, is not now, nor probably ever will be available.
I appreciate your detailed response, and certainly puts paid to any more internet searches on the subject.

Are CNC spindle motors - induction type motors?
(yes I know these are a tad more expensive )

Not sure what you mean by CNC spindle motors; if you are refering to the motors which move the machinery around from one position to another then these are usually DC stepper motors.

Spindle motors use a variety of different technologies, some are high frequency induction motors driven by variable frequency inverters. This gives them significantly higher synchronous sprreds as they are not limited to 50/60 Hz mains frequency. However the motors need to be specially designed to reduce losses in windings and core materials etc.
Other options are DC universal (brushed) motors with extensive driver electronics and feedback systems to set and regulate speed, torque, acceleration, deceleration etc.

Both of these are essentially expensive options compared to a mains voltage brushed motor with a speed regulion module attached, as with the better current generation routers.

Yes, I did check out come spindle motors along the lines of :
SKF Linear Motion United Kingdom
But I am sure that they are out of the "hobby" price range , and I doubt they would be very suitable for hand-held operation.

I suspect that freehanding those 7.5KW spindle motors would be a good way to get sent into orbit. I have seen a 5HP 3 phase jump of a bench and migrate about 10m accross the floor when started unloaded without appropriate restraint.

Why are you seeking a non brushed router/spindle motor?

only supposedly for the peace and quiet of a brushless motor

Noise is a function of operating speed rather whether they are brushed/brushless. For example, the old generic domestic sewing machine motor is typically a brushed motor, 150W, about 2500RPM and almost whisper quiet. Three horse router motor is damned noisy, but running 10 times faster and at 15 times the power. Portable saws and drills typically 5000 to 8000 RPM brushed motor, most of the noise is the gear drive sytem. Dusty. any size always noisy because of the amount of air they move, but the induction motor on its own is fairly quiet,