[OP]
Member
I am replacing the motor on my Parks 12 inch planer. I can go with either a 3450 rpm or a 1725 rpm. I just have to use the right pulley. Is there any reason one should use one motor over the other? Or are they equivalent? I was going to go with a 2 hp and wire for 220. Thoughts?
Member
You need to determine the correct speed of the cutters, and then adjust the pulley sizes to get it right with whichever motor you choose. but be careful. There may not be enough room for the pulley size change needed to use a motor with double the speed of the original motor. I might use a motor with a little more horsepower than the original motor, but I WOULD NOT try to come up with a way to use a motor that runs twice as fast as the original motor. The motor itself isn't the problem. It's what it would take to reduce the speed to the correct speed for the tool that I would try to avoid, because of the need for a very small pulley on the motor and a very large pulley on the tool, which likely won't fit the guards, etc. Change the horsepower a little, but don't try to go with a motor that turns twice as fast as the original motor. It just gets too messy.
Charley
[OP]
Member
Here is what the manual says
manual.jpg
So I am guessing it doesn't matter between the two RPMs?
[OP]
Member
So I suppose my question is.... is there something inherently better about the 1725 over the 3450 (or the 3450 over the 1725) in certain applications or are they equivalent, other than the rpm.
Contributor
HP is RPM times torque times a constant. So a 1725 RPM motor has to generate twice the torque to provide the same HP as a 3450 RPM motor, which means that a 1725 motor will be physically larger than a 3450 motor for the same HP.
[A 3450 RPM motor is a 2 pole motor. A 1725 motor is a 4 pole motor. If you had an 8 pole motor, it would run at 862.5 RPM and would be even larger for the same HP.]
Note that all these RPM speeds are under full load. At light load, the 3450 will run close to (less than) 3600 RPM, and the 1725 RPM will run close to 1800 RPM. As you load the motor, the slip increases until you reach full load which is where the specification is given. A 3450 RPM motor can never run 3600 RPM because there must always be some slip for the motor to operate. They make synchronous motors that can run 3600 RPM (for example) but those are special purpose.
Mike
Last edited by Mike Henderson; 09-20-2016 at 8:23 PM.
Go into the world and do well. But more importantly, go into the world and do good.
Member
No. With the obvious exception of direct drive applications the two are equivalent. With the right pulley your planer will never know the difference.Originally Posted by Mark R Webster
Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.
Contributor
In general a low speed motor costs more to purchase and is bigger/heaver. But a low speed motor may be a little quieter, not an issue on a planner. The low speed motor will use a smaller pulley which may be easier to fit into the machine. The high speed motor may be smaller and easier to fit into the machine even with it's bigger pulley.
Bill D.
[OP]
Member
Thanks for all the info guys!!
Contributor
Guys,
It seems to me that a 2 HP 1725 rpm motor operating through the 7" pulley will deliver half the torque of a 2 HP 3450 rpm motor operating through a 3.5" pulley. If a 3450 rpm motor is smaller and cheaper for a given HP it would seem to be the better choice, if maximum torque is an issue in the application.
Doug
Contributor
No, the 1725 motor will have twice the torque for the same HP as a 3450 motor. So if you use pulleys to double the speed with the 1725 motor, you will cut the torque in half at the tool - it will be the same as the 3450 motor.
There's no free lunch. If the tool is to run at the same RPMs, it doesn't matter which motor you use - you'll have exactly the same HP and torque at the working edge.
The only difference is that the 1725 motor will be physically larger.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
[OP]
Member
Good info thanks Mike.
Contributor
Mike,
My physics terminology is rusty. I meant the force exerted would be halved. If the force exerted at the end of a 7" lever was the same as the force exerted at the end of a 3.5" lever, there would indeed be a "free lunch".
Doug
[OP]
Member
My physics it rusty as well ;-) thanks
Member
I agree with Mike. I use Newtonian physics fairly often.
[OP]
Member
My physics is about 40+ years rusty and fading fast.
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