Motor speed control

I have this fan I use most of the summer months. It is older than I am
and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
horse two speed motor. That motor eventually burned up. It is now
powered by basically a washing machine motor at 1750 RPM.

The old motor was seven hundred something and eleven hundred something.


My basic idea here is to build a 1/2 voltage and 1/2 frequency
generator to power it at 1/2 it's normal RPM. Power transformers that
will rectify into 70-80 volt rails are out there. I can find them. Then
we are not talking about any class A amp stage here, switching
transistors, driven correctly should do the trick.Thirty hertz, sixty
volts. Would that be efficient ? I don't see why not. I could probably
even find a way to cut back the duty cycle for more savings.

See, I don't need this thing to do 1750 RPM, half that would be fine. I
could easily divide the line voltage and maybe even do it with discreet
components (IIRC how to build a flip flop). Of course now I am dating
myself. You might ignore me figuring I'll die soon, but I assure you I
will never get that lucky. I was meant to live.It is going to get hot,
I am not allowed to die.

Anyway, I used to use this fan in lieu of AC for a long time, only turn
the AC on once in a while since I had it. But that motor is too fast
for it. Looking for cheap and dirty.

My major concerns are starting torque (it has a centifugal start
switch) and if I do have to start it on 120V I will need protection
diodes. Also, should I put some inductance in the path ? or will the
motor windings takre care of that ? I know if I use any capacitance I
need to use inductance, but do I need any capacitance ?

I don't see any reason to screw around with waveshaping for a coil the
is going to turn a shaft, do you ?

T

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
>I have this fan I use most of the summer months. It is older than I am
> and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
> horse two speed motor. That motor eventually burned up. It is now
> powered by basically a washing machine motor at 1750 RPM.
>
> The old motor was seven hundred something and eleven hundred something.
>
>
> My basic idea here is to build a 1/2 voltage and 1/2 frequency
> generator to power it at 1/2 it's normal RPM. Power transformers that
> will rectify into 70-80 volt rails are out there. I can find them. Then
> we are not talking about any class A amp stage here, switching
> transistors, driven correctly should do the trick.Thirty hertz, sixty
> volts. Would that be efficient ? I don't see why not. I could probably
> even find a way to cut back the duty cycle for more savings.
>
> See, I don't need this thing to do 1750 RPM, half that would be fine. I
> could easily divide the line voltage and maybe even do it with discreet
> components (IIRC how to build a flip flop). Of course now I am dating
> myself. You might ignore me figuring I'll die soon, but I assure you I
> will never get that lucky. I was meant to live.It is going to get hot,
> I am not allowed to die.
>
> Anyway, I used to use this fan in lieu of AC for a long time, only turn
> the AC on once in a while since I had it. But that motor is too fast
> for it. Looking for cheap and dirty.
>
> My major concerns are starting torque (it has a centifugal start
> switch) and if I do have to start it on 120V I will need protection
> diodes. Also, should I put some inductance in the path ? or will the
> motor windings takre care of that ? I know if I use any capacitance I
> need to use inductance, but do I need any capacitance ?
>
> I don't see any reason to screw around with waveshaping for a coil the
> is going to turn a shaft, do you ?
>
> T
>
Can't you use a controller board culled from an old washing machine ? Might
be barking up the wrong tree, but over here, one motor drives all in a
washing machine, and its speed is controlled from virtually just turning
over to tumble the wash around, to full whack for spinning, all using a
simple triac cycle-chopper circuit. I wouldn't have thought that torque was
an issue with a fan blade set as a load ?

Arfa

On 5 Jun 2006 22:42:35 -0700, (E-Mail Removed) wrote:

>I have this fan I use most of the summer months. It is older than I am
>and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
>horse two speed motor. That motor eventually burned up. It is now
>powered by basically a washing machine motor at 1750 RPM.
>
>The old motor was seven hundred something and eleven hundred something.
>
>
>My basic idea here is to build a 1/2 voltage and 1/2 frequency
>generator to power it at 1/2 it's normal RPM. Power transformers that
>will rectify into 70-80 volt rails are out there. I can find them. Then
>we are not talking about any class A amp stage here, switching
>transistors, driven correctly should do the trick.Thirty hertz, sixty
>volts. Would that be efficient ? I don't see why not. I could probably
>even find a way to cut back the duty cycle for more savings.
>
>See, I don't need this thing to do 1750 RPM, half that would be fine. I
>could easily divide the line voltage and maybe even do it with discreet
>components (IIRC how to build a flip flop). Of course now I am dating
>myself. You might ignore me figuring I'll die soon, but I assure you I
>will never get that lucky. I was meant to live.It is going to get hot,
>I am not allowed to die.
>
>Anyway, I used to use this fan in lieu of AC for a long time, only turn
>the AC on once in a while since I had it. But that motor is too fast
>for it. Looking for cheap and dirty.
>
>My major concerns are starting torque (it has a centifugal start
>switch) and if I do have to start it on 120V I will need protection
>diodes. Also, should I put some inductance in the path ? or will the
>motor windings takre care of that ? I know if I use any capacitance I
>need to use inductance, but do I need any capacitance ?
>
>I don't see any reason to screw around with waveshaping for a coil the
>is going to turn a shaft, do you ?
>
>T
I'm no expert in variable frequency AC drives, but have used a few in
some applications . . .

First - if the motor is capacitor run or capacitor start it won't work
with a VFD - If you're lucky the capacitor will vent and leak all
over. It just won't work - that type of motor is unsuitable for your
app.. Capacitor start might work - after the cap is removed.

Straight induction motors can be used with VFD's, but even that isn't
a perfect application.

The ideal situation is to drive a three phase motor with a variable
frequency drive.

From reading between the lines I get the impression that you just
figure on halving the output speed, and figure there's some cheap easy
way to do it . . .

A transformer isn't necessary - decrease the voltage by keeping the
pulse width low. If you were to use a square wave you would be
dissipating more power than the RMS sine wave uses - a 70% duty cycle
square wave on each half cycle would be the equivalent of full power.

There will be some extra heat generated and some lost efficiency due
to the high frequency component in using a square wave - but it is
done all the time.

Pulse width and frequency track each other.

Fans don't require starting windings - but your motor almost
undoubtedly has a centrifugal switch in there that will be active
whenever the speed is below a rather high threshold (1/2 speed would
be too slow for the switch) - so you'd need to do some work inside
the motor or connection box if it has one.

I wanted a variable speed fan for my house and after checking the
options I settled on an array of 8" "Patriot" brushless DC fans
driven with a 6-48 VDC scr controlled power supply. Works well - but
a little loud at high speeds.

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(E-Mail Removed) writes:

> I have this fan I use most of the summer months. It is older than I am
> and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
> horse two speed motor. That motor eventually burned up. It is now
> powered by basically a washing machine motor at 1750 RPM.
>
> The old motor was seven hundred something and eleven hundred something.
>
>
> My basic idea here is to build a 1/2 voltage and 1/2 frequency
> generator to power it at 1/2 it's normal RPM. Power transformers that
> will rectify into 70-80 volt rails are out there. I can find them. Then
> we are not talking about any class A amp stage here, switching
> transistors, driven correctly should do the trick.Thirty hertz, sixty
> volts. Would that be efficient ? I don't see why not. I could probably
> even find a way to cut back the duty cycle for more savings.
>
> See, I don't need this thing to do 1750 RPM, half that would be fine. I
> could easily divide the line voltage and maybe even do it with discreet
> components (IIRC how to build a flip flop). Of course now I am dating
> myself. You might ignore me figuring I'll die soon, but I assure you I
> will never get that lucky. I was meant to live.It is going to get hot,
> I am not allowed to die.
>
> Anyway, I used to use this fan in lieu of AC for a long time, only turn
> the AC on once in a while since I had it. But that motor is too fast
> for it. Looking for cheap and dirty.
>
> My major concerns are starting torque (it has a centifugal start
> switch) and if I do have to start it on 120V I will need protection
> diodes. Also, should I put some inductance in the path ? or will the
> motor windings takre care of that ? I know if I use any capacitance I
> need to use inductance, but do I need any capacitance ?
>
> I don't see any reason to screw around with waveshaping for a coil the
> is going to turn a shaft, do you ?

A lot easier to just find a two speed motor surplus.

If you use a class A amp, anything you save on electricity to the fan
will go into the amp transistors. :-)

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Important: Anything sent to the email address in the message header above is
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some reading material on VFD's

http://www.findarticles.com/p/articl..._55817948/pg_3

describes method of using pulses to create a simulation of a sine wave
for the motor - pretty good article

Each cycle of the sine wave may be chopped into 20 or more on-off
pulses with widths simulating the voltage present during those phase
angles of the wave . . . Close to zero crossing the pulses are very
narrow becoming progressively wider as 90/180 degrees is reached, then
becoming more narrow at the next zero crossing. As frequency is
lowered all the pulses in each cycle can become narrower -
particularly with a fan load since the effort required falls off
rapidly as speed is lowered - no need for constant torque

That takes a fair amount of discrete logic or a programmable chip

If I were to attempt to design a vfd for a fan, I think I'd look to an
analog design to handle the pwm - be somewhat easier than using all
discrete logic.

http://en.wikipedia.org/wiki/Variable_Frequency_Drive Wickipedia's
dumbed down explanation.

You probably have one of those old Sears fans with the cast iron hubs
and steel blades. Built like a tank . . . My very OM was still using
the one I remember as a kid . . . . died about three years ago after
working for about 40 years with no maintenance.

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I think this one was going for around 40 years, or more, probably more.

I thank you all for the replies but it has become a moot point, the
replacement motor burned up today. I think going to 1750 on the drive
pulley did it. The load on such fan blades increases pretty much
exponentiall with RPM so I think it was just too much, even with the
bigger motor. It was noisy. I know the driven shaft bearings are loos
as a goose, but so what. We can make new ones.

I observed the fan and if it were the driven shaft bearings locking up
one side of the belt would've been tight.

Now that I think of it, this motor was not from a washing machine. Two
wires that is it. Even alot of motors from the 70s had at least two
speeds, to facilitat the gentle cycle. The old Kemores only switched
speeds for this, the transmission took care of the rest. This is more a
standard frame machinery motor. Perhaps it was from a VERY old furnace
that did not have speed control. The motor control consisted of a
temperature sensor in the plenum.

Regardless of what it was, I saw smoke. Brushes generally don't smoke
and they usually don't cause the lights to dim. When I heard the sound
change and the lights dim I looked at it, and that is how I know the
belt was not overstressed. The motor is gone.Unless there is a
possibility one of them dislodged and shorted to the frame, however
this unit is not grounded so if that caused the smoke the winding
insulation must be breached.

We have a pretty good sized fractional HP DC motor with a speed
control, but that is slated to go on one of the lathes.

I was just looking at the pitch of the blades on this thing, talk about
steep. I don't care about the fanshaft bearings, as long as they are
free. In fact, when the first motor went that's what I thought it was.
Then with the thing apart I saw that the friction was in the motor
shaft, not the driven shaft.

Now it just fired up again. It went off on thermal no doubt. I still
have to do something, I can't let this thing run unnattended. Thing
that bothers me is how soon it went off on thermal, maybe the driven
shaft bearings are locking up ?

Either way, driving it that fast is not a good idea. It is beyond
design limits. I still need options. The blade pitch on this thing is
awesome, it STARTS at about 45 degrees and the output edge is just
abnout paralell with the shaft ! When we put this motor in we ran it
outside in the yard, it threw a breeze over to the neighbors. It was
sitting on a chair and made the grass look like there was a windstorm.
Also being around 20" in diameter, with a mask, it moves some serious
air. As we have trees around here, I didn't have to use my AC even once
last year.

If I were to install the same type of motor, which I might, I really
need to reread all your responses. I only skimmed them because of the
smoke I saw today, but I will read them in depth and get back to you.

The cheapest way is just get another of what I got. Even if I have to
setup my own start relay, start it at full then go to the duty cycle
control or whatever. If I don't push it so hard it should last, and,
the way it's running now you can't light a match in here. That's nice
when it is in the 90s, but right now it is too much.

I have people coming over soon, and I am glad the thing simply works at
the moment. Later I will read everything and get back to you.

One respondant mentioned duty cycle. I kind like that, don't bother
rectifying anything. Just use an SCR. I could trigger it from a single
stage flip flop then to get the 30 Hertz. Heck I could even do 20 Hertz
with flip flops, and just cut the duty cycle accordingly.

JURB

Arfa Daily wrote:
> <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) ups.com...
>
>>I have this fan I use most of the summer months. It is older than I am
>>and is a Sears. NOT a Sears-Roebuck. It was powered by I think a 1/6
>>horse two speed motor. That motor eventually burned up. It is now
>>powered by basically a washing machine motor at 1750 RPM.
>>
>>The old motor was seven hundred something and eleven hundred something.
>>
>>
>>My basic idea here is to build a 1/2 voltage and 1/2 frequency
>>generator to power it at 1/2 it's normal RPM. Power transformers that
>>will rectify into 70-80 volt rails are out there. I can find them. Then
>>we are not talking about any class A amp stage here, switching
>>transistors, driven correctly should do the trick.Thirty hertz, sixty
>>volts. Would that be efficient ? I don't see why not. I could probably
>>even find a way to cut back the duty cycle for more savings.
>>
>>See, I don't need this thing to do 1750 RPM, half that would be fine. I
>>could easily divide the line voltage and maybe even do it with discreet
>>components (IIRC how to build a flip flop). Of course now I am dating
>>myself. You might ignore me figuring I'll die soon, but I assure you I
>>will never get that lucky. I was meant to live.It is going to get hot,
>>I am not allowed to die.
>>
>>Anyway, I used to use this fan in lieu of AC for a long time, only turn
>>the AC on once in a while since I had it. But that motor is too fast
>>for it. Looking for cheap and dirty.
>>
>>My major concerns are starting torque (it has a centifugal start
>>switch) and if I do have to start it on 120V I will need protection
>>diodes. Also, should I put some inductance in the path ? or will the
>>motor windings takre care of that ? I know if I use any capacitance I
>>need to use inductance, but do I need any capacitance ?
>>
>>I don't see any reason to screw around with waveshaping for a coil the
>>is going to turn a shaft, do you ?
>>
>>T
>>
>
> Can't you use a controller board culled from an old washing machine ? Might
> be barking up the wrong tree, but over here, one motor drives all in a
> washing machine, and its speed is controlled from virtually just turning
> over to tumble the wash around, to full whack for spinning, all using a
> simple triac cycle-chopper circuit. I wouldn't have thought that torque was
> an issue with a fan blade set as a load ?
>
> Arfa
>
>


It sounds like it's an induction motor from a North American washing
machine, unlike the universal motors used in European machines, these
are usually two speed with a centrifugal starting switch, they can't be
made variable speed easily.

>
> If I were to install the same type of motor, which I might, I really
> need to reread all your responses. I only skimmed them because of the
> smoke I saw today, but I will read them in depth and get back to you.
>
> The cheapest way is just get another of what I got. Even if I have to
> setup my own start relay, start it at full then go to the duty cycle
> control or whatever. If I don't push it so hard it should last, and,
> the way it's running now you can't light a match in here. That's nice
> when it is in the 90s, but right now it is too much.
>
> I have people coming over soon, and I am glad the thing simply works at
> the moment. Later I will read everything and get back to you.
>
> One respondant mentioned duty cycle. I kind like that, don't bother
> rectifying anything. Just use an SCR. I could trigger it from a single
> stage flip flop then to get the 30 Hertz. Heck I could even do 20 Hertz
> with flip flops, and just cut the duty cycle accordingly.
>
> JURB
>


Ok so I guess this was a brush motor, how about a surplus treadmill
motor? They're small, quite powerful, and easily controlled.

> (E-Mail Removed)rote

>
> Now it just fired up again. It went off on thermal no doubt.
stil
> have to do something, I can't let this thing run unnattended. Thin
> that bothers me is how soon it went off on thermal, maybe th
drive
> shaft bearings are locking up
>
> One respondant mentioned duty cycle. I kind like that, don't bothe
> rectifying anything. Just use an SCR. I could trigger it from
singl
> stage flip flop then to get the 30 Hertz. Heck I could even do 2
Hert
> with flip flops, and just cut the duty cycle accordingly.

Okay I'm new here but if anyone knows induction motors here, it seerm
to be me. If this is the same kind of fan I am thinking of that i
often used as a portable windstorm for low-budget movies, what yo
are proposing to do is a good way to burn up a brand-new motor. Wha
noone here seems to know is that the stator core contstruction i
specifically designed for the frequency response, using a variabl
frequency power supply, or a variac with such a fan is a sure way t
cause a meltdown. You do not "cog" or run an inductio
motor on a "duty cycle" other than an on and off period
Induction motors do not respond to SCR switching like a DC moto
does

The thermal is blowing on the motor because you are overloading it
The formula for fans is as follows

Cu. ft. air per minute x water guage pressure (in.
HP = _______________________________________
6,350 x % efficienc

where approx efficiency of a propeller-type fans is as low as 35

Points about driving fans to remember
The volume of air delivered by a fan varies directly with the fa
spee
The pressure produced by a fan varies as a square of the fan spee
The HP of a fan varies as the cube of the fan spee

To replace an 1100 rpm motor with a 1750 rpm motor will require twic
the horsepower. If this fan is pulley-driven, you need to adjus
pulley sizes to accomodate your speed requirements. a 20" fa
blade sounds like nothing more than the typical box fan

Alternately you can try to be a bit more creative and try to repai
the fault in the motor, or even rewind it. If you can't manage this
just get a new motor. I like the idea of using the treadmill motor
as if you are brilliant enough to strip it's speed control as well
you will have a fully-variable fan out of it, and treadmill motor
are rated at least 1 horsepower. Just be sure that if you get th
opportunity to strip a treadmill, that you take ALL of it'
electronics and electrical, most importantly all parts of the spee
control including the slider pot on it's console for spee
adjustment. If you can remove the flywheel from the motor (if no
set-screwed it is threaded on), do so and use a pulley that will fit
I would suggest grinding a flat or keyway into the shaft (keep meta
dust out of a permanent magnet motor), and then being sure not t
exceed 1800 RPM on a 20" fan blade or you will have quite a mes
on your hands..

Anytime you want to replace a motor that has burnt out, always chec
for binding in the driven side first, then for binding in the moto
itself. Belt pressure should ideally be at just barely above th
point where slippage occurs, but it seems lack of actual care for th
motor is what caused the burnout in the first place because either
bearing went dry and gummed-up, or the motor got loaded up with dus
and debris and overheated as a result of the insulating layer o
crud. Try a bi-annual maintenance schedule next time....

For this application, the ideal motor is a Permanent Split-Capacito
motor (capacitor start/capacitor run with the same capacitor). Thi
is the same type of motor used in 14" or so desktop fans and i
always accompanied by a low-valued capacitor that is constantl
energized. The PSC motor is essentially a two-phase motor adapted fo
single-phase, and the ideal as a fan motor. This motor is als
switchless so there is no switch to maintain. Find yourself
japanese-made washing-machine and you will likely have a perfec
motor for it...

Any questions adress me directly or PM m

> (E-Mail Removed)rote

>
> Now it just fired up again. It went off on thermal no doubt.
stil
> have to do something, I can't let this thing run unnattended. Thin
> that bothers me is how soon it went off on thermal, maybe th
drive
> shaft bearings are locking up
>
> One respondant mentioned duty cycle. I kind like that, don't bothe
> rectifying anything. Just use an SCR. I could trigger it from
singl
> stage flip flop then to get the 30 Hertz. Heck I could even do 2
Hert
> with flip flops, and just cut the duty cycle accordingly.

Okay I'm new here but if anyone knows induction motors here, it seerm
to be me. If this is the same kind of fan I am thinking of that i
often used as a portable windstorm for low-budget movies, what yo
are proposing to do is a good way to burn up a brand-new motor. Wha
noone here seems to know is that the stator core contstruction i
specifically designed for the frequency response, using a variabl
frequency power supply, or a variac with such a fan is a sure way t
cause a meltdown. You do not "cog" or run an inductio
motor on a "duty cycle" other than an on and off period
Induction motors do not respond to SCR switching like a DC moto
does

The thermal is blowing on the motor because you are overloading it
The formula for fans is as follows

Cu. ft. air per minute x water guage pressure (in.
HP = _______________________________________
6,350 x % efficienc

where approx efficiency of a propeller-type fans is as low as 35

Points about driving fans to remember
The volume of air delivered by a fan varies directly with the fa
spee
The pressure produced by a fan varies as a square of the fan spee
The HP of a fan varies as the cube of the fan spee

To replace an 1100 rpm motor with a 1750 rpm motor will require twic
the horsepower. If this fan is pulley-driven, you need to adjus
pulley sizes to accomodate your speed requirements. a 20" fa
blade sounds like nothing more than the typical box fan

Alternately you can try to be a bit more creative and try to repai
the fault in the motor, or even rewind it. If you can't manage this
just get a new motor. I like the idea of using the treadmill motor
as if you are brilliant enough to strip it's speed control as well
you will have a fully-variable fan out of it, and treadmill motor
are rated at least 1 horsepower. Just be sure that if you get th
opportunity to strip a treadmill, that you take ALL of it'
electronics and electrical, most importantly all parts of the spee
control including the slider pot on it's console for spee
adjustment. If you can remove the flywheel from the motor (if no
set-screwed it is threaded on), do so and use a pulley that will fit
I would suggest grinding a flat or keyway into the shaft (keep meta
dust out of a permanent magnet motor), and then being sure not t
exceed 1800 RPM on a 20" fan blade or you will have quite a mes
on your hands..

Anytime you want to replace a motor that has burnt out, always chec
for binding in the driven side first, then for binding in the moto
itself. Belt pressure should ideally be at just barely above th
point where slippage occurs, but it seems lack of actual care for th
motor is what caused the burnout in the first place because either
bearing went dry and gummed-up, or the motor got loaded up with dus
and debris and overheated as a result of the insulating layer o
crud. Try a bi-annual maintenance schedule next time....

For this application, the ideal motor is a Permanent Split-Capacito
motor (capacitor start/capacitor run with the same capacitor). Thi
is the same type of motor used in 14" or so desktop fans and i
always accompanied by a low-valued capacitor that is constantl
energized. The PSC motor is essentially a two-phase motor adapted fo
single-phase, and the ideal as a fan motor. This motor is als
switchless so there is no switch to maintain. Find yourself
japanese-made washing-machine and you will likely have a perfec
motor for it...

Any questions adress me directly or PM m