Slowing down motor

Your motor is designed to work at only one (synchronous) speed determined by line frequency.

A VFD might work with a single phase motor (I've never tried it) but the easier solution is a Variable Speed Belt Drive. You shift the motor back and forth and the spring-loaded pulley in essence changes diameter to give variable speed operation. One source among many:

Good luck!

Carla

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I can see that I am probably going to have to run the motor straight into the gear reducer, and see how that rpm does. If it is unacceptable, then I will have to determine the acceptable rpm, and put an intermittent pulley assembly to drop the rpm down to a usable rpm. Which is what I was trying to avoid.

Steve

Some years back my sister tossed out an old exercise treadmill... I snapped it up for whatever hardware I could recover before re-scrapping.

It's speed control was accomplished by such a variable diameter pulley. If your not in a hurry, keep your eye out for one... in my 'hood' you see them out for collection several times a year. As always, YMMV.

Or... maybe you could cobble up some sort of step pulley arrangement as used by many drill presses and similar machinery.

Good luck!

Erik

You need to vary the frequency to change the speed of an AC induction motor - which requires a rather expensive variable frquency drive (VFD) - and generally speaking a 3 phase motor starts much better on a VFD than a single phase and produces better torque across the speed range.

Or get a DC motor and you can vary the speed by changing the voltage to the feild if it is shunt wound, or to the armature if it is PM.

1.5HP is right in the treadmill motor size range so they are quite readily available surplus - with PWM controllers.

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$25 But it WILL work.

Something like this:

Will work with any universal AC motor. On/Off/variable rocker switch, dial speed adjustment. Allows you to vary the speed of tools, or any brush type universal motor. Will not work on induction, shaded pole, soft/slow start, or brushless type motors.

Why not use a jack shaft and use up a second set of pulleys to get the speed that you want?

Do not bother to try a VFD on a single phase motor. It will not work very well.

Looking for a treadmill is a good idea. Some of them use DC motors to control the speed and some use variable speed pulleys. Either would work.

If you end up having to add a jack shaft , check laundry dryers. They usually use a jackshaft to slow the speed down.

You did not state the speed of the motor that you have. If it is a 3450 rpm motor, switching to a 1750 rpm motor would help.

Another idea is to check your lawn mower shop in your area. The axle of the rear end has about a 6 : 1 reduction and they are good for about the horse power you are using.

You might say where you are. Maybe someone here has a solution that would not involve expensive shipping.

Dan

You aren't the first person to want a variable speed AC motor. Look at the design of price-sensitive power tools, they have either a constant-speed AC motor and pulleys or a DC (sparks) motor with a variable voltage speed control. If there was a good way to slow down small single-phase AC motors you would see it everywhere.

You could buy a cheap used variable-speed drill with a bad cord or chuck to experiment with, to find the best speed range for a pulley speed reducer for your AC motor. jsw

The cheapest option is to replace the single phase motor with a 3 phase 1 HP motor and 115v variable frequency drive.

This will cost you roughly $200-250. You can sell your 1.5hp single phase to recoup some of the cost.

You can also make additional mechanical reduction, but this is more painful and cumbersome.

Of course, if you had access to a lot of motors and reducers, like if you were a scrapper, it would be a different story. But since you do not have such access, the above is my advice.

i

It will not work due to centrifugal capacitor switch.

Problem is safety. I want a direct drive into the main trommel shaft, or maybe one secondary shaft, so that it doesn't get all complicated with multiple spinning pulleys. This is going to be somewhat dangerous, and I want to keep it simple, and would rather have a spin dial to control rpm than have to change pulleys. Another thing, the operating speed of the motor is 1725 rpm, and I have to drop the trommel speed down to around 50 rpm. So I would have to have a HUGE pulley in a two pulley arrangement to come down to 50 rpm, or I would have to add an intermediary to reduce it down. Think I will go from motor to gear reduction, which will spin at about 72 rpm on output, then do another set of different sized pulleys to step that down a little, and call that good.

Steve

How about friction drive? Use the current motor & pulley to drive a powered bed. 4 pillow blocks, some 3/4" shaft and some 3/4" heater hose glued to the shaft. Couple the shafts with a pair of pulleys or sprockets and chain. Drive one shaft with your current motor.

Would give you about a 13 rpm rotation speed of the drum with the current motor and pulleys. Could easily be sped up by dropping the 14" pulley size. If you tossed a step pulley on the motor you would have a lot of adjustment.

On 12/25/2013 9:53 PM, Steve Bulicz wrote:> ... the operating > speed of the motor is 1725 rpm, and I have to drop the trommel speed > down to around 50 rpm. ...

Other suggestions about slowing down the motor (e.g., 3 phase & VFD) have this complication: you lose horsepower proportional to the speed drop. So a 1725 rpm 3 hp motor running at 50 rpm will only produce 1/12 hp! This is a matter of physics, not a technicality. I.e, unavoidable.

Mechanical slowings down (pulleys, gears) do not suffer this effect. They lose some hp, but not in a big way.

Bob

Let that gearbox and single pulley step-down get you into the neighborhood - If you can find an old Universal brush type motor (look for the nameplate specifying 120 Volts AC /or/ DC, then you can get a simple reactor motor speed control (think Sewing Machine, but heavier) and vary the motor speed down some. But Not Up, you'd need a stepped pulley or such to do that.

If that works and you plan to build this semi-permanently, go get a matching HP 1725-RPM 3-Phase Inverter Duty motor to run the drum drive, and a small Variable Frequency Drive to power it - if you don't have 3-phase power available make sure you get one that is rated to run on 120/240V single-phase input.

Then you can vary it down and up maybe 30% each way before you start getting in trouble. Major speed deviations may require a separate exterior cooling fan on the motor to make sure it doesn't cook itself

- the motor's own fan isn't turning fast enough.

Sometimes with a tumbling or polishing action you need to vary speed slightly to find the sweet spot where the abrasive is flowing and not fighting.

I don't think the pecans will all stick to the side of the drum at 71 rpm. If your bearing supports are stiff enough, you can likely run at this speed.

If you need a soft start and you're more of a mechanical guy, you could build in a centrifugal clutch.

Chris