Slowing down motor

[Steve Bulicz]

I have a 1.5 hp motor that I have running on a vee belt pulley, turning
a 16" dia. x 3' long trommel of sorts to dehull pecans. I have a gear
reduction motor, with a reduction of 24:1. Right now, I have the
trommel hooked up to a 1725 rpm motor with a 1.5" dia pulley, then a 14"
pulley. I hooked it up today, and it nearly took off across the shop.
I don't want to really want to use the gear reduction drive, as I
compute that if I hook it up straight through, I will end up at about 71
rpm on the trommel, kinda fast sounding, but wouldn't know unless I hook
it up and run it. It needs to spin just fast enough so that all the
nuts keep tumbling, and not go to one side of the cage like a blanket in
a washing machine spin cycle. So, I wanted to hook up a rheostat.
Tried a dimmer, forget that. Looked at variable voltage controls, and
they are from $20 to $2,000. What do I need to put in line on this
motor to be able to regulate its speed? It is a big heavy motor, and it
has two covers on top, I think cap starts. Look like the old bulbous
things on a 55 Chevy starter, but two of them.

Want to keep it simple. I could get another gear reduction, but that
would have to be a miracle, as I won't pay retail. Don't want a series
of pullies, would rather have electrical controller. I need some
control, as the hopper will be loaded with different poundages of nuts,
and different shapes which will change tumbling characteristics.

Help appreciated.

[Carla Fong]

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:
<http://www.lovejoy-inc.com/products/variable-speed-drives.aspx>

Good luck!

Carla

Interestingly, the two states which require no license to carry
(firearms), Vermont and Alaska, have not had any problems due to this
liberal approach. Equally curious is that Washington, D.C., where not
only concealed carry but any firearms ownership is illegal, has one of
the highest rates of violent crime.

[Steve Bulicz]

On 12/24/2013 9:52 PM, Carla Fong wrote:

>
> 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:
> <http://www.lovejoy-inc.com/products/variable-speed-drives.aspx>
>
> Good luck!
>
> Carla

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

[Erik]

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

[cl...@snyder.on.ca]

On Tue, 24 Dec 2013 21:32:13 -0700, Steve Bulicz <snu...@hemlock.net>
wrote:

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.

[cl...@snyder.on.ca]

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.

[F. George McDuffee]

On Tue, 24 Dec 2013 21:18:30 -0800, Erik <sp...@this.com>
wrote:

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

============
see

http://www.wttool.com/index/page/category/category_id/15990/

http://www.wttool.com/index/page/category/category_id/21687/


--
Unka' George

"Gold is the money of kings,
silver is the money of gentlemen,
barter is the money of peasants,
but debt is the money of slaves"

-Norm Franz, "Money and Wealth in the New Millenium"

[Gunner Asch]

On Tue, 24 Dec 2013 20:52:56 -0800, Carla Fong
<carla_...@97381.com> wrote:

Only 3ph motors work on a VFD.

That being said...3ph motors are dirt cheap, particularly in the
1.5-3hp range. There are a number of VFDs out there that are designed
to input SINGLE PHASE and output 3ph..so not having 3ph is not an
issue.

Id strongly suggest going up a full hp or more when using a vfd and
running at slow rpms. Example...if your motor is 1.5 hp..install a 3hp
VFD at minimum, so your motor doesnt bog down the VFD.

A 3h p VFD can be had on Ebay for less than $100 and new ones are
about $200-225 from DrivesDirect etc etc

One can pick up a 3ph 3hp motor for $25-50 easily enough.

Gunner

>
>Interestingly, the two states which require no license to carry
>(firearms), Vermont and Alaska, have not had any problems due to this
>liberal approach. Equally curious is that Washington, D.C., where not
>only concealed carry but any firearms ownership is illegal, has one of
>the highest rates of violent crime.
>

--
"Owning a sailboat is like marrying a nymphomaniac. You don�t want to do that
but it is great if your best friend does. That way you get all the benefits without any of the upkeep"

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[Gunner Asch]

On Tue, 24 Dec 2013 21:58:04 -0700, Steve Bulicz <snu...@hemlock.net>
wrote:

I do..do have a variable speed drive in a can..NOS..Ill have to see if
I can find it and see what the ratios are. I figure its worth $300
plus shipping if you want a mechanical method.

They sell on Ebay for over a grand.

As I stated earlier...do a search on Ebay for "3hp vfd" and they are
showing up as new..for $149 and used ones are less..but they are not
mechanical.

Gunner

[Richard]

$25 But it WILL work.

Something like this:

http://www.ebay.com/bhp/variable-speed-motor-controller

http://www.turbineproducts.com/servlet/Detail?no=30

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.

[John B.]

On Tue, 24 Dec 2013 21:32:13 -0700, Steve Bulicz <snu...@hemlock.net>
wrote:

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

John B.

[dca...@krl.org]

On Wednesday, December 25, 2013 12:18:30 AM UTC-5, Erik wrote:


> > A VFD might work with a single phase motor (I've never tried it)
>
> >
>

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

[Jim Wilkins]

"Steve Bulicz" <snu...@hemlock.net> wrote in message
news:l9dn4j$q5g$1...@speranza.aioe.org...
>...> Want to keep it simple. I could get another gear reduction, but

>that would have to be a miracle, as I won't pay retail. Don't want a
>series of pullies, would rather have electrical controller. I need
>some control, as the hopper will be loaded with different poundages
>of nuts, and different shapes which will change tumbling
>characteristics.
>
> Help appreciated.

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

[Ignoramus5946]

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

[Ignoramus5946]

On 2013-12-25, Carla Fong <carla_...@97381.com> wrote:
>
> A VFD might work with a single phase motor (I've never tried it) but the

It will not work due to centrifugal capacitor switch.

[Steve Bulicz]

>>> 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:
>>> <http://www.lovejoy-inc.com/products/variable-speed-drives.aspx>

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

[Steve W.]

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.

--
Steve W.

[Gunner Asch]

On Wed, 25 Dec 2013 19:53:39 -0700, Steve Bulicz <snu...@hemlock.net>
wrote:

>

So you want a VFD .

Quick, simple and easy.

[Bob Engelhardt]

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

[Gunner Asch]

You lose the horsepower if you match the VFD to the motor. If you
DOUBLE the size of the VFD..you loose very little if any power.

[Bob Engelhardt]

On 12/26/2013 9:43 PM, Gunner Asch wrote:
You lose the horsepower if you match the VFD to the motor. If you
> DOUBLE the size of the VFD..you loose very little if any power.

I don't think so ... horsepower is torque x rpm; torque is proportional
to current; current is limited by motor windings.

Bob

[et...@whidbey.com]

What Bob says is true. Induction motors are designed to work at a
certain frequency and voltage. If the frequency is increased then the
voltage should be increased too in order for the motor to have the
same torque. This results in the motor developing more horsepower as
the speed increases. However, most VFDs will not increase the voltage
along with the frequency. This means that when the motor is running
faster it will have less torque and instead will have a constant power
output. The VFD will also not reduce the voltage when it lowers the
frequency because this would result in a loss of torque. So as the
frequency drops the voltage still stays the same. This results in
motors operating slower than the nameplate rating becoming constant
torque machines and motors operating above the nameplate rating
becoming constant HP machines.
Eric

[Richard]

Slowing down? wouldn't that be a lower RPM?

[Ned Simmons]

On Fri, 27 Dec 2013 09:49:15 -0800, et...@whidbey.com wrote:

>On Fri, 27 Dec 2013 09:23:30 -0500, Bob Engelhardt
><BobEng...@comcast.net> wrote:
>
>>On 12/26/2013 9:43 PM, Gunner Asch wrote:
>> You lose the horsepower if you match the VFD to the motor. If you
>>> DOUBLE the size of the VFD..you loose very little if any power.
>>
>>I don't think so ... horsepower is torque x rpm; torque is proportional
>>to current; current is limited by motor windings.
>>
>>Bob
>What Bob says is true. Induction motors are designed to work at a
>certain frequency and voltage. If the frequency is increased then the
>voltage should be increased too in order for the motor to have the
>same torque. This results in the motor developing more horsepower as
>the speed increases. However, most VFDs will not increase the voltage
>along with the frequency.

All VFDs adjust voltage along with frequency. In fact, the simplest
open loop VFDs are often referred to as V/Hz (volts per hertz) drives
to reflect the fact that they maintain a constant ratio between
voltage and frequency, as opposed to the more complicated schemes used
by closed loop drives.

>This means that when the motor is running
>faster it will have less torque and instead will have a constant power
>output.

Generally speaking, with a VFD, torque is constant from close to zero
up to base speed. HP is constant above base speed.

>The VFD will also not reduce the voltage when it lowers the
>frequency because this would result in a loss of torque. So as the
>frequency drops the voltage still stays the same.

The winding current will rise and the motor will overheat if the
voltage is not reduced along with frequency.

>This results in
>motors operating slower than the nameplate rating becoming constant
>torque machines and motors operating above the nameplate rating
>becoming constant HP machines.

Bob was right when he said the torque is a function of current. The
voltage is reduced to control the current, and thus the heating, of
the motor. The constant torque is a consequence of the need to limit
current.


--
Ned Simmons

[Gunner Asch]

True indeed. That being said...I make my money fixing VFD run machine
tools and most have zero gearing with a VFD doing the hard work.

So perhaps in calcs it may not work..in the real world..it most
certainly does.

One could simply make one pulley larger than the other so the works
are turning at 75 rmp..but the motor is turning 150-300-600-1200 rpm

What ever you are happy with.

[Jim Wilkins]

"Ned Simmons" <ne...@nedsim.com> wrote in message
news:p3mrb91vc7fiij97b...@4ax.com...

Here's why that is true:
http://en.wikipedia.org/wiki/Counter-electromotive_force
The spinning motor acts as a generator, producing a voltage that rises
with RPM and opposes the input. The current the motor draws depends on
the difference between the applied and internally generated voltages,
so as the motor slows down it pulls more current, which can become
enough to overheat the windings unless the applied voltage is also
reduced.

Conversely as the motor speeds up and its internally generated voltage
rises, it draws less power from the line until it's taking only as
much as it needs to overcome friction and its load.

If anyone disagrees with this oversimplification, feel free to post a
nontechnical explanation of phase shift.
jsw

[Bruce L. Bergman (munged human readable)]

On Wed, 25 Dec 2013 19:53:39 -0700, Steve Bulicz <snu...@hemlock.net>
wrote:

>

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.

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[Christopher Tidy]

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