Originally Posted by
Terry Therneau
This is a motor that can do 1 HP continuously; modern motors are branded with the max HP, which is what they generate just as they stall out. A modern "2 HP" is likely closer to 1 HP continuous duty. (Different vendors stretch the truth by different amounts, though).
Terry Therneau
I'm afraid that's not true. Induction motors are rated honestly and really can deliver the nameplate HP continuously. So, to take your example, a modern 2HP motor will deliver a constant 2HP if you load it to that level, say to operate a fan.
The reason your motor does not stall out is that when you start to load it down, and slow down the RPMs, the starting circuit cuts in and provides some additional torque. [Added note: The starting circuit cuts in at about 70% of rated RPM. So for a 3450 motor, you'll have to stall the motor to about 2400 RPM in order to get the centrifugal switch to cut in.] However, the motor was not designed to operate that way and if you loaded the motor to that level continuously, you would burn up the motor from excess heat (because you're drawing excess current - beyond the rated current for the motor). The reason you get away with it is that you pull back when the motor starts to stall out so you limit the amount of heat generated in the motor. Then you probably allow the motor to run with no load for a while which allows the fan to cool down the motor. But whatever you do, the important thing is that you don't operate it continuously at that reduced RPM and you allow the motor to cool down.
So, no, your 1HP motor only delivers 1HP in normal continuous operation. A modern 2HP induction motor will deliver a constant 2HP in continuous operation and not overheat.
As a side note, Repulsion/induction motors have brushes which eventually wear out. Plus they have more parts which makes them more expensive. That's the real reason all the manufacturers moved away from repulsion/induction motors. Additionally, Repulsion/induction motors have high starting torque and that's generally not needed in woodworking tools because we start them unloaded.
The standard induction motor is much better suited to woodworking tools.
Mike
[A modern induction motor will not stall out at it's rated HP - it will operate just fine. Note that some modern induction motors have a service factor. That's the amount you can exceed the rated HP and the motor will increase in temperature by 10 degrees C. However, operating at that heat level will degrade the life of the motor. So if the service factor is 1.1, and you have a 2HP motor, you can operate the motor at 2.2HP and it will get 10 degrees hotter - and it's life will be degraded.]
[You're probably thinking of universal motors which are rated at their "stall HP"]
Last edited by Mike Henderson; 09-22-2016 at 11:27 AM.
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