According to Amazon.com, who I guess is just repeating info from the manufacturer:
“The Porter Cable C2002-WK is an oil-free 1.5 HP running pancake-style air compressor. The induction motor provides longer life and better performance. This motor has replaceable brushes for that will help extended life motor even further.”
What kind of motor is this? I would think a 1.5 HP motor on a compressor for home use would be a split phase induction motor or possibly a capacitor start induction motor to handle higher torque so it can start on a compression stroke.
None of these would have brushes. In fact, I think the point of a brush motor on small items that run on line power is to get higher HP in a smaller package because motor RPMs are higher, and on a compressor that would mean speed reduction, pulleys or a gearbox. That’s the last thing they’d want to add. If they add that, why not just use a durable old-fashioned piston pump with an oiled crankcase, like industrial machines up to maybe 20 or 50 HP would use?
There is a type of AC induction motor the “wound rotor” motor that uses slip rings: AC motor - Wikipedia, but I wouldn’t think it would be used in a compressor.
I know about pancake motors and have used them since the mid 70’s. They are great for their torque to angular momentum ratio and so they accelerate very well. Since they have little induction, they don’t arc much around the brushes, either. As I recall, they are made, or at least were first made, using printed circuit board methods, and therefore one of the companies that popularized them is called Printed Motors Inc. or PMI for short.
They aren’t induction motors.
Beowulff is right about induction motors with wound rotors. I think there are several kinds, actually. But Beowulff is also right about them being an unlikely choice for a small compressor.
One of the customer comments at Amazon said it runs at 1700, not 3600, rpm. Induction motors running on 60 Hz have synchronous speeds of 3600 or an integer fraction such as 1800, 1200, and so forth, depending on how many poles (2, 4, and so forth) they wind it with. They actually run at somewhat less than the synchronous rate so that currents are generated in the rotor to magnetize it, usually. This reduction is called “slip” (not to be confused with “slip rings”, which are like commutators only without a switching funciton). If they are used as generators on a power grid, they run at a slightly greater speed. It is common in big polyphase motors to wind the rotor to create poles without slip, and to use slip rings to power the windings, and such motors run at the synchronous speed. The most efficient electric motors made (AFAIK) are these synchronous induction motors, and I discussed a 1000 hp one powering a compressor with somebody who was repairing it (hammering the chopsticks into place). But these motors are a pain to run because they must first be brought up to speed with a pony motor or by shorting the rotor windings to make it work with slip at first (which I think is hard to do with salient pole rotors). Nobody’s going to sell a portable compressor to consumers with one of these.