Motor speed control

Guest
Hi,
I Like to use ola motor (AEG 112g 63) from Elektrolux washmachine. Do
somebody know shematic for wiring motor and shematic for seed control?
Krešimir
 
<ZZactly@aol.com> wrote in message
news:1149572555.852288.95160@y43g2000cwc.googlegroups.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
Click to expand...
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, ZZactly@aol.com 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
Click to expand...
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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ZZactly@aol.com 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 ?
Click to expand...
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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some reading material on VFD's

http://www.findarticles.com/p/articles/mi_m0BPR/is_8_16/ai_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:
ZZactly@aol.com> wrote in message
news:1149572555.852288.95160@y43g2000cwc.googlegroups.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
Click to expand...

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
Click to expand...

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


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 ?

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

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 fan
speed
The pressure produced by a fan varies as a square of the fan speed
The HP of a fan varies as the cube of the fan speed

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

Alternately you can try to be a bit more creative and try to repair
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 motors
are rated at least 1 horsepower. Just be sure that if you get the
opportunity to strip a treadmill, that you take ALL of it's
electronics and electrical, most importantly all parts of the speed
control including the slider pot on it's console for speed
adjustment. If you can remove the flywheel from the motor (if not
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 metal
dust out of a permanent magnet motor), and then being sure not to
exceed 1800 RPM on a 20" fan blade or you will have quite a mess
on your hands...

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

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

Any questions adress me directly or PM me
 
ZZactly@aol.comwrote:


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 ?

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

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 fan
speed
The pressure produced by a fan varies as a square of the fan speed
The HP of a fan varies as the cube of the fan speed

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

Alternately you can try to be a bit more creative and try to repair
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 motors
are rated at least 1 horsepower. Just be sure that if you get the
opportunity to strip a treadmill, that you take ALL of it's
electronics and electrical, most importantly all parts of the speed
control including the slider pot on it's console for speed
adjustment. If you can remove the flywheel from the motor (if not
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 metal
dust out of a permanent magnet motor), and then being sure not to
exceed 1800 RPM on a 20" fan blade or you will have quite a mess
on your hands...

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

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

Any questions adress me directly or PM me
 
On 6 Jun 2006 18:21:19 -0700, ZZactly@aol.com wrote:

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.
Click to expand...
A BELT drive fan? The sears I was talking about was direct drive . .
.. Why not just change the size of the pulley, or put an adjustable
speed pulley in - that's a low cost easy solution even if you to
change the belt size.

I used the words duty cycle, but as an analogy to make a distinction
between RMS and square wave power consumption, and again in making an
ersatz sine wave for a VFD.

You can't just cut down the duty cycle or use SCR/Triac type
controllers for FHP Induction motors. They overheat, unless the
pulses approximate a sine wave - the two efficient ways are with
stepped voltages (usually six levels, plus and minus - and relatively
complicated to pull off) or varying the widths of several pulses for
each half cycle of the sine wave (still relatively complicated IMHO -
but better than dealing with voltage levels)

Then there's that pesky starting winding - you're driving a fan. A
fan (unless it is seriously broken) turns freely with no real
resistance (unlike wash machines with transmissions seals and gears to
get moving, compressors, or most anything else . . .) until the fan
gets up to speed - torque required tracks shaft speed.

Run the motor at half speed and the starting winding will kick back in
even if you start it at full speed.

DC brush, or "universal" AC/DC motors are ideal for speed control
applications - but the longevity of the brushes is a limiting factor
and one reason they are seldom used to drive fans. (also noisy,
create sparks and ozone, radio interference)

We had this centrifuge at work - big one horse brush type motor with a
variable transformer to change the speed. Probably dated back to the
40's. The transformer burned out one day and they wanted $400 for a
new one. I went to Grainger's and got a high power lamp dimmer for
$20 - no problems.

A VFD drive that uses single phase power and drives a three phase
motor is probably the ideal if cost is less important than longevity,
excellent speed control, and efficiency.

Plenty of appliance repair/junk dealers around with two speed wash
machine motors - and a new one might cost $50- $70.


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I agree much with Default, yet there is one general rule for any
induction motor: They are not variable speed. You can select
different speeds based upon the wound poles, but to cause the motor
to slip excessively is not an operable condition. The only way to
safely adjust the speed of any induction motor (aside from
shaded-pole) is to reduce frequency and voltage amplitude on a
measured scale. Shaded-pole motrs are horribly inefficient, but more
tolerant of moderate overloads.

Once the stator field loses grip on the squirrel-cage, the losses are
converted to heat in the stator as a result of decreased
inductive-reluctance in the stator, which results in increased
current. The heat will be turned on the resistive value of the
windings rather than the inductive properties that normally control
the current, and hence it will overheat, meaning the motor will lose
it's inductive properties and become closer to an unwound length of
wire to the line current....

If you are intending on varying the speed other than preset values for
an induction motor that are avaliable, you best either use a DC power
motor driven by SCR's such as a treadmill motor, or a brushless DC
motor, which is phenomenally-more expensive and rarely worth the
project.

My enthusiastic advice here is to either repair or replace the motor,
or convert yourself to DC. Then and only then will a
duty-cycle/amplitude modulation be useful for adjusting the speed.

In any case I advise anyone to get speed controllers from discarded
treadmills, they are the diamonds in the rough for anyone working
with anything DC-compatible, replacing the lab variac for DC
applications. Just be sure to salvage or at least know the pot
(varistor, not weed ya goofball) value for it, as guessing can be
hazardous to the controller. I now have one rated 28 amps DC
145+V-out, detuned to work on a standard 115VAC circuit at 15
amps...The motors couldn't be any more ideal for any application
anyway, so grab those too!

Gold I tells ya....gold....grab them like they are the last power
supply on Earth, because most of the cost is in these parts anyway...
 
"Electromotive Guru" <Prometheuspb@gmail-dot-com.no-spam.invalid> wrote in
message news:449b44e7$1$70924$892e7fe2@authen.yellow.readfreenews.net...
I agree much with Default, yet there is one general rule for any
induction motor: They are not variable speed. You can select
different speeds based upon the wound poles, but to cause the motor
to slip excessively is not an operable condition. The only way to
safely adjust the speed of any induction motor (aside from
shaded-pole) is to reduce frequency and voltage amplitude on a
measured scale.
Click to expand...
Am I right in thinking the RMS voltage should be proportional to the
frequency when this is done?
 
"mc" <look@www.ai.uga.edu.for.address> wrote in message
news:qIJmg.5160$w84.320@bignews4.bellsouth.net...
"Electromotive Guru" <Prometheuspb@gmail-dot-com.no-spam.invalid> wrote in
message news:449b44e7$1$70924$892e7fe2@authen.yellow.readfreenews.net...
I agree much with Default, yet there is one general rule for any
induction motor: They are not variable speed. You can select
different speeds based upon the wound poles, but to cause the motor
to slip excessively is not an operable condition. The only way to
safely adjust the speed of any induction motor (aside from
shaded-pole) is to reduce frequency and voltage amplitude on a
measured scale.

Am I right in thinking the RMS voltage should be proportional to the
frequency when this is done?

Yes, the voltage and frequency are usually reduced. To vary the speed of AC
Click to expand...
motors a device called an inverter is used. Internally it will convert the
AC to a DC voltage and then convert it back to an AC type of voltage that
the frequency and voltage are matched to the motor load. I say AC type
because most of them do not put out a sine wave but odd looking waveforms.
Some use several steps in the output to step up to the maximum voltage and
then back down to 0 and then the same for the negative half cycle. We use
some where I work that put out a very odd waveform and normal volt and amp
meters will not work correctly on them. They use something called a
carrier wave that is operating at from around 5 to 15 kiloHz. No where the
normal 60 Hz or less you would normally think of in the US.

Here is a link to the type I am thinking of.

http://www.yaskawa.com/site/products.nsf/products/Industrial%20AC%20Drives~J7.html
 
mcwrote:
Am I right in thinking the RMS voltage should be proportional to the
Click to expand...

frequency when this is done?
Click to expand...
Yes, it should be, however the formula for this varies by the motor
itself and it's physical construction. What you need to do if you
intend to try this is to carefully watch current as you alter the
frequency, however there is only so far you can go before the
reactance of the stator core breaks down and the stator fails to
respond proportionally because magnetic saturation has a sort-of
flywheel effect....yes, electrons have mass too....

As mentioned before, only a switchless motor will respond to any
resonable degree because most induction motors are not meant to vary
their speeds. When you lower the frequency, you affect the magnetic
flux of each laminate in the stator and rotor cores, as well as
overall efficiency and it's power factor. Lower-frequency motors have
thicker plates because they can respond to the lower frequency and
saturate more slowly.

The best way to perform this is to find yourself a 400Hz induction
motor (see aircraft service) made to run at a comparable speed as
what you are replacing, and then work from there. Be sure to find the
highest service factor for this motor that you can find, 1.35 is an
ideal, with class H insulation (preferably class B rise with class
F-H insulation)...

While it may be entertaining to try varying the speed of an induction
motor, it is far from preferred practice. If you really want to vary
speed while taking advantage of the non-contact design of an
induction motor, go find a synchronous/stepper motor to run from, as
this will respond exactly as you would want it to up to a much wider
range than the standard induction motor, the more phases the better.
If you really wanna get trick, use a Hall-Effect motor/circuit,
alhough a bit excessive for a simple fan....

Still above and beyond is the use of a DC power motor. Brush
replacement is not nearly the factor that many think it is, as proper
maintenance/operation can provide over a decade of service. If brushes
are that much a biog deal, opt for a brushless DC motor...

If ya wanna try something fun, take an alternator and short it's
rotor's slip-rings and run it as a low-impedance 3-phase induction
motor after you remove all the DC components from the circuit. Over
80 amps is usually wound delta, so keep his in mind...

Whatever you do, best of luck to ya, but I still strongly recommend
the DC power motor, like the treadmill motor.
 
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