AC motor control via "dimmers"

[les]

Hello.....
I was just at Home Depot trying looking for a quick fix
to a problem.
I need to slow down an AC fan motor (measured at 2.3 A full
speed/ 120V.) I was finding all ceiling fan controls are rated at
1.5 A. max. But then I found in the back some other lighting
controllers that were unusual. One was for low-voltage magnetic
and the other electronic transformer types. It connects to the AC
mains, and the magnetic load is downstream.
It seems to me that this controller rated at 5 A. might fit the bill.
Since the inductance/reactance is designed into this device, why couldn't
it work....? The motor type...don't know. However, it doesn't
use a starting cap.The windings are on the motor casing.
Comments please......Thank you.

Les

 

[Phil Allison]

"les"

I was just at Home Depot trying looking for a quick fix
to a problem.
I need to slow down an AC fan motor (measured at 2.3 A full
speed/ 120V.) I was finding all ceiling fan controls are rated at
1.5 A. max.

** Yep - ceiling fans have low powered motors.

But then I found in the back some other lighting
controllers that were unusual. One was for low-voltage magnetic
and the other electronic transformer types. It connects to the AC
mains, and the magnetic load is downstream.

** Yep - those are intended for use with 12 volt lighting set ups.

The dimmer can handle a transformer or electronic step-down device.

It seems to me that this controller rated at 5 A. might fit the bill.
Since the inductance/reactance is designed into this device, why couldn't
it work....? The motor type...don't know. However, it doesn't
use a starting cap.The windings are on the motor casing.
Comments please......Thank you.

** You have not stated the purpose clearly.

Is it an actual, air blowing FAN that you want to vary the speed of - or
just the motor out of one ?

Is it a domestic ( ie floor or pedestal ) fan - or something much worse.



....... Phil

 

[Chris]

Hello.....
I was just at Home Depot trying looking for a quick fix
to a problem.
I need to slow down an AC fan motor (measured at 2.3 A full
speed/ 120V.) I was finding all ceiling fan controls are rated at
1.5 A. max. But then I found in the back some other lighting
controllers that were unusual. One was for low-voltage magnetic
and the other electronic transformer types. It connects to the AC
mains, and the magnetic load is downstream.
It seems to me that this controller rated at 5 A. might fit the bill.
Since the inductance/reactance is designed into this device, why couldn't
it work....? The motor type...don't know. However, it doesn't
use a starting cap.The windings are on the motor casing.
Comments please......Thank you.

Les

Ceiling fans usually don't work very well with the standard triac-
based lamp dimmers, Les. But if you want to try, there are many
dimmers on the Home Depot website that can handle 600W (about 5A) at
120VAC. I'm sure some of them are in the store. You might want to
try one of those if you've got some spare time and don't mind taking
it back if it doesn't work well (probably).

If you want to get something that will work better, try the NuTone
Ventilation control switch Model 72W (Home Depot Internet/Catalog #
100490891). It's a little pricey at $53.18 ea., but has a different
type of circuit that will work better with the inductive load of a fan
motor. Call ahead to see if the store has it in stock.

Good luck
Chris

 

[les]

Thanks Chris, I'll look into your suggestion.
And Phil, the device is a whole house fan, 1600 cu. ft/min displacement,
hence the
large current draw. I want to slow it down to 33% if possible to cut down on
noise. Domestic made, though I don't know if the motor itself is from US.
I know Triacs are intended for resistive loads, so my eyes lite up when I
noticed
the claim that this "special dimmer" was intended for inductive loads. So
the next
question is what components are in this unusual dimmer, and would it suffice
in
my intended experiment........
I don't want to damage the windings in the motor by overheating.

Les

 

[Phil Allison]

"les"

And Phil, the device is a whole house fan, 1600 cu. ft/min displacement,
hence the
large current draw.

** Then it is not a fan motor designed for variable speed operation - like
all domestic and pedestal fans are.


I want to slow it down to 33% if possible to cut down on

noise.

** Using a triac dimmer will almost certainly make the fan motor buzz -
possibly quite loudly.

Domestic made, though I don't know if the motor itself is from US.
I know Triacs are intended for resistive loads, so my eyes lite up when I
noticed
the claim that this "special dimmer" was intended for inductive loads. So
the next
question is what components are in this unusual dimmer, and would it
suffice
in
my intended experiment........
I don't want to damage the windings in the motor by overheating.

** May I suggest using a Variac.

I use one with a small pedestal fan on hot nights to create a very light
breeze.

Totally silent.




........ Phil

 

[Tom2000]

Ceiling fans usually don't work very well with the standard triac-
based lamp dimmers, Les. But if you want to try, there are many
dimmers on the Home Depot website that can handle 600W (about 5A) at
120VAC. I'm sure some of them are in the store. You might want to
try one of those if you've got some spare time and don't mind taking
it back if it doesn't work well (probably).

If you want to get something that will work better, try the NuTone
Ventilation control switch Model 72W (Home Depot Internet/Catalog #
100490891). It's a little pricey at $53.18 ea., but has a different
type of circuit that will work better with the inductive load of a fan
motor. Call ahead to see if the store has it in stock.

Good luck
Chris

I've been doing some reading about motor speed control lately.

I've found that it's important to find out exactly what type of motor
you have before choosing a speed control.

Most common small devices such as fans, aquarium pumps, etc, are
powered by single phase shaded-pole induction motors. At 2.3 amps,
you might have one of these, but at that power level, you're in the
area where a more complex motor might do the job better. You need to
open the fan and take a look at the motor before you proceed.

If it's a shaded-pole motor, you need some sort of Volts/Hz speed
control, with a variable output frequency and the voltage reduced as
the frequency is reduced.

If the Nutone controller Chris mentioned will do the job, the off the
shelf solution is cheaper in terms of money and time than you'd invest
if you tried to build one. I couldn't find any specs on the device
with a quick Google search, so I don't know if it's suitable for your
app or not. You might email Nutone with the details of the fan you're
trying to control. (Their site is http://www.nutone.com )

I roughed out a Volts/Hz controller circuit as a discussion point on
this topic in another forum. I'm not sure it will work as designed,
but it will give you an idea of the sort of thing you'd have to build
if you decided to do the job yourself. You can find the schematic
here: http://www.mindspring.com/~tom2000/picaxe/VFContr.html

The microcontroller would set the switching frequency of the inverter,
from the motor's design frequency down to some lower level, as the
speed control pot is adjusted. As the frequency is reduced, the
voltage is also reduced linearly (V = freq * design V / design freq)
using the micro's PWM output and monitored by the micro's ADC input.

Note that this schematic is simply a talking point. I haven't
breadboarded it or, for that matter, even given it much thought. It
probably needs debugging.

If your fan doesn't use a single phased shaded-pole motor, your speed
control device might actually be simpler. When you know for sure what
sort of motor you're controlling, you might do some Googling.

Good luck with your project. When you've solved your problem, please
report your solution so the rest of us can learn from your experience.

Have fun!

Tom

 

[Jasen Betts]

Thanks Chris, I'll look into your suggestion.
And Phil, the device is a whole house fan, 1600 cu. ft/min displacement,
hence the
large current draw. I want to slow it down to 33% if possible to cut down on
noise. Domestic made, though I don't know if the motor itself is from US.
I know Triacs are intended for resistive loads, so my eyes lite up when I
noticed
the claim that this "special dimmer" was intended for inductive loads. So
the next
question is what components are in this unusual dimmer, and would it suffice
in
my intended experiment........
I don't want to damage the windings in the motor by overheating.

They make special "dimmers" for fans, these are different to the ones
intended for resistive, transformer, or electronic loads.

Bye.
Jasen

 

[les]

Tom....
I really appreciate your thorough analytical treatment.
I was suspecting this might involve controlling voltage and frequency
parameters,
but hoped it wouldn't require my own design or assembly.
I will definitely look over your suggested materials, and of course, I need
to determine the type of motor I have before proceeding further.
I'll check back with results when I dig thru the details.

Thanks to all !!
Les

 

[Bob]

Hello.....
I was just at Home Depot trying looking for a quick fix
to a problem.
I need to slow down an AC fan motor (measured at 2.3 A full
speed/ 120V.) I was finding all ceiling fan controls are rated at
1.5 A. max. But then I found in the back some other lighting
controllers that were unusual. One was for low-voltage magnetic
and the other electronic transformer types. It connects to the AC
mains, and the magnetic load is downstream.
It seems to me that this controller rated at 5 A. might fit the bill.
Since the inductance/reactance is designed into this device, why couldn't
it work....? The motor type...don't know. However, it doesn't
use a starting cap.The windings are on the motor casing.
Comments please......Thank you.

Les

Les,

Ya know, it's funny you should ask this. I just installed a GAF WHFS24M
(4500 CFM) attic fan that I got from Home Depot. It was way too loud even at
its low setting. I'll bet this is the same unit you have, eh?

I tried an X10 type lamp dimmer. It worked, but the dimmer got real hot at
certain settings and I wasn't sure whether it would harm the motor because
it doesn't feed the motor with a sine wave unless at full output. I think
my motor is a permanent split capacitor (PSC) type. There is a capacitor on
my motor. I'll post a picture of the motor label on
alt.binaries.schematics.electronic since it describes the capacitor.

Anyway, I ended up getting a variac at Fry's. It's the Philmore 48-1205 and
the Fry's p/n is 4638758. It's rated at 500VA and it costs $70. I feel
better about it since it alway drives the motor with a sinusoid.

The variac works extremely well. I can turn it down to 72 (out of 120) on
the dial and the fan sucks (which is a good thing, in this case) and with
minimal noise. I measured the current to be 1.3A @ knob = 72 and 2.4A when
it's plugged directly into the wall.

Bob

 

[les]

Bob....
Great timing on your part.
I have the smaller (1600 cu.ft/min model) but the current draw is almost the
same. As I said, I haven't inspected the motor type yet (as it's in the
ceiling already) and the included pamphlet could care less about technical
information.
The X10 idea: I'm surprised it just didn't crisp itself. I assume they use
Triacs
and could buzz loudly. The Variac idea has been bounced alot for this
purpose, but the only ones I've seen before are desk models with big
footprints. So, this Fry's device sounds VERY interesting.
And I assume it's a wall-mount type switch ( will fit typical electrical
wall box)....
Right?

I have a 2 and 4 year-old, and breadboarding is a thing of the past. That's
why I'm looking for turnkey devices, and go back to being a Dad.......
(although it's hard not to want to tinker around)

Thanks for this great suggestion.
Les

 

[Bob]

Bob....
Great timing on your part.
I have the smaller (1600 cu.ft/min model) but the current draw is almost
the
same. As I said, I haven't inspected the motor type yet (as it's in the
ceiling already) and the included pamphlet could care less about technical
information.
The X10 idea: I'm surprised it just didn't crisp itself. I assume they
use
Triacs
and could buzz loudly. The Variac idea has been bounced alot for this
purpose, but the only ones I've seen before are desk models with big
footprints. So, this Fry's device sounds VERY interesting.
And I assume it's a wall-mount type switch ( will fit typical electrical
wall box)....
Right?

I have a 2 and 4 year-old, and breadboarding is a thing of the past.
That's
why I'm looking for turnkey devices, and go back to being a Dad.......
(although it's hard not to want to tinker around)

Thanks for this great suggestion.
Les

Les,

Unfortunately, this variac is 5" high and its round section is 5" diameter.
I don't think that an autotransformer type of variac, with 500VA capacity,
could be any smaller.

Someone probably makes a smaller sinusoidal output switching type of
motor/voltage controller but I couldn't find one. I'm not saying that sine
waves are the only way to go, it's just what makes me feel "comfortable".

When your kids are older, remind them how much trouble they were when they
were this age, and how perfect you and I were. ;-D

Bob

 

[Ninja]

.... The Variac idea has been bounced alot for this
purpose, but the only ones I've seen before are desk models with big
footprints. ....

Variacs and fixed transformers are large and expensive. An inexpensive
alternative (if you don't need continuously variable speed) is to use
dropping resistors to lower the voltage. It could be just one (for fixed
speed operation) or several selectable ones.

Based on Bob's observation that 72 volts at 1.3 amps was about right in his
case, a 50 ohms 100 watt (allowing a safety factor on the power
rating)resistor might do the trick . I see that www.allelectronics.com has
50 ohm 220 watt resistors for $3.75. They also have 10 ohm 25 watt resistors
for $1 each. With five of these, you could try a wide range of
series/parallel combinations to find the speed you like best.

If you try this approach, keep in mind that the resistors will dissipate
about 70 watts of heat. You might mount them on a metal plate or heat sink
by the fan, where the air flow will give good convection cooling. I assume
that this is an attic fan, so appearance shouldn't be an issue.

 

[les]

Unfortunately, this variac is 5" high and its round section is 5" diameter.
I don't think that an autotransformer type of variac, with 500VA capacity,
could be any smaller.

Yes, I had that hunch the boys didn't come up with some miracle toroid to
cheat the huge dissipation factor. But it never ceases to amaze me what
new materials come forth.

Someone probably makes a smaller sinusoidal output switching type of
motor/voltage controller but I couldn't find one. I'm not saying that sine
waves are the only way to go, it's just what makes me feel "comfortable".

I agree here.

When your kids are older, remind them how much trouble they were when they
were this age, and how perfect you and I were. ;-D

ha-ha. but it's fun to see things thru "new eyes".

And in regards to Ninja, resistance is certainly fast and easy. I just hate
the
inefficiency. But it could work, and why bother with a resistor...how about
a
100 watt bulb in series for starters. Sure, in 3000 hours we need another
limiter, but hey, you get some light as well !!

Les

 

[Bob]

Yes, I had that hunch the boys didn't come up with some miracle toroid to
cheat the huge dissipation factor. But it never ceases to amaze me what
new materials come forth.


I agree here.


ha-ha. but it's fun to see things thru "new eyes".

And in regards to Ninja, resistance is certainly fast and easy. I just
hate
the
inefficiency. But it could work, and why bother with a resistor...how
about
a
100 watt bulb in series for starters. Sure, in 3000 hours we need another
limiter, but hey, you get some light as well !!

Les

I've used light bulbs as voltage droppers. It's not as stupid as it sounds.
In fact, you could keep a supply of different wattage bulbs and screw in the
one you want for the desired fan speed.

Bob

 

[HapticZ]

& with all these integrated power supplies that convert 120 ac to dc, then
reconvert thru a toroid system back to12/5/-12 volts,

they (the asians of course!) manufacture them for less than $5.00 each at
factory costs!

same basic approach, except forget to rectify the output and leave it
somewhat sinusoidal,

heck, even a wavetable might be used to drive some Hexfet bridge!

tear apart some of the UPS boxes, they do pretty much what we need.

heck, it might be worth it to build some kind of controller to fix this fan
speed issue, make sum money in the process too!



my uncle used to do welding with a 5 hp motor inline with the 120vac hot
wire and then to the weld rod holder.

ground the piece to weld and go at it.

kinda dicey as for safety, but the motor just spun up and kept the rod
current constant enough to weld effectively.

 

[Ninja]

But it could work, and why bother with a resistor...how about
a
100 watt bulb in series for starters. Sure, in 3000 hours we need another
limiter, but hey, you get some light as well !!

Yes, the light bulb technique was my first thought. In general, I like the
positive temperature coefficient as a safety device; It limits current on
short circuit to a lower level than a resistor would do.

But I wonder whether the PTC could cause start-up problems with a motor.
Don't they need a surge of current to get going?

Another concern is that a 100 watt bulb would drop the voltage far too much.
Don't you need to drop about 50 volts at 1.3 amps? A 300 watt bulb maybe (or
three 100w in parallel), but now you're talking about a specialty bulb (or
multiple bulbs in parallel). $ $ $

I suspect that resistors will turn out to be far less expensive than bulbs
and sockets. For local availability, though, light bulbs win hands down!

 

[Tom2000]

But I wonder whether the PTC could cause start-up problems with a motor.
Don't they need a surge of current to get going?

That's the nice part of speed controlling a fan. They don't have a
startup torque that must be overcome. They provide zero load at zero
rpm, then build as the speed builds.

Personally, I think the light bulb idea is brilliant, and should work
well.

Tom

 

[Marra]

Hello.....
I was just at Home Depot trying looking for a quick fix
to a problem.
I need to slow down an AC fan motor (measured at 2.3 A full
speed/ 120V.) I was finding all ceiling fan controls are rated at
1.5 A. max. But then I found in the back some other lighting
controllers that were unusual. One was for low-voltage magnetic
and the other electronic transformer types. It connects to the AC
mains, and the magnetic load is downstream.
It seems to me that this controller rated at 5 A. might fit the bill.
Since the inductance/reactance is designed into this device, why couldn't
it work....? The motor type...don't know. However, it doesn't
use a starting cap.The windings are on the motor casing.
Comments please......Thank you.

Les

I would have gone for a phase control.
Burst control could burn out the motor if uneven.
I would use a PIC to control the speed via a pot.

www.ckp-railways.talktalk.net/pcbcad21.htm

 

[HapticZ]

i use a 25 watt tungsten paralleled with my screw in "high efficiency
flourescents" in my rooms overheads with automatic IR switches
never had any trouble with starting the florescents after that.