"regular" dimmer switches and transformers

[Tim Wescott]

I've heard over and over again that dimmer switches don't like inductive
loads, but in the background of that is the occasional refrain "oh, it's
not so bad".

I've never analyzed the usual dimmer switch circuit but -- what would
happen if you connected a dimmer switch to a transformer that had a
resistive load on it? Would you just not have full range, would the
switch or the transformer burn up, what?

I could make use of a dimmer switch into a transformer with a resistive
load on the secondary; hence my questions.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

[Jamie]

Tim Wescott wrote:

> I've heard over and over again that dimmer switches don't like inductive
> loads, but in the background of that is the occasional refrain "oh, it's
> not so bad".
>
> I've never analyzed the usual dimmer switch circuit but -- what would
> happen if you connected a dimmer switch to a transformer that had a
> resistive load on it? Would you just not have full range, would the
> switch or the transformer burn up, what?
>
> I could make use of a dimmer switch into a transformer with a resistive
> load on the secondary; hence my questions.
>

Some dimmers are rheostats, which should not pose a problem, the others
are thyristors (triacs) which generally do not have much in the way to
suppress the collapse at unexpected events. Of course there are the
auto transformers but I don't think you're referring to those.

All I can say is, yes, it'll work because we have some applications
like that however, the secondary side gets rectified to a DC buss. Other
than that, it produces a rather saw tooth type of wave, more or less,
depending where the phase angle is.

You do need to add some snubbers for the unexpected collapse of mag
field out of control.

I wouldn't be using it for mission critical systems!


Jamie

[Artemus]

"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:zvCdnXGNrfdHRBvM...@giganews.com...

It works for me. I use a regular dimmer on my hot wire cutter.
The dimmer feeds a MOT on which I have replaced the secondary with
about 10T of 12ga. That goes to a piece of piano wire which does
the cutting. Been using it for over 10 years with no problems.
Art

[Tim Wescott]

By coincidence, the application I'm asking about is a hot wire cutter.
Whadaya know.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

[Joe Gwinn]

In article <zvCdnXGNrfdHRBvM...@giganews.com>, Tim Wescott

<t...@seemywebsite.com> wrote:

> I've heard over and over again that dimmer switches don't like inductive
> loads, but in the background of that is the occasional refrain "oh, it's
> not so bad".
>
> I've never analyzed the usual dimmer switch circuit but -- what would
> happen if you connected a dimmer switch to a transformer that had a
> resistive load on it? Would you just not have full range, would the
> switch or the transformer burn up, what?
>
> I could make use of a dimmer switch into a transformer with a resistive
> load on the secondary; hence my questions.

Some thyristor dimmers are built to drive transformers, some are not.
The issue is maintaining DC balance in the transformer, to avoid
saturating the transformer core.

Lutron has a number of models that are intended to dim low-voltage
light strings (like under-cabinet lights) through a step-down
transformer.

If you are interested in the technical details, look up the patents
listed on the box or the instructions, or do a patent search for
patents assigned to Lutron.

Joe Gwinn

[Jasen Betts]

On 2013-05-05, Tim Wescott <t...@seemywebsite.com> wrote:
> I've heard over and over again that dimmer switches don't like inductive
> loads, but in the background of that is the occasional refrain "oh, it's
> not so bad".
>
> I've never analyzed the usual dimmer switch circuit but -- what would
> happen if you connected a dimmer switch to a transformer that had a
> resistive load on it? Would you just not have full range, would the
> switch or the transformer burn up, what?

yes!

> I could make use of a dimmer switch into a transformer with a resistive
> load on the secondary; hence my questions.

get one that's designed for inductive loads.

--
⚂⚃ 100% natural

--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---

[Jim Thompson]

On 6 May 2013 05:52:43 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:

>On 2013-05-05, Tim Wescott <t...@seemywebsite.com> wrote:
>> I've heard over and over again that dimmer switches don't like inductive
>> loads, but in the background of that is the occasional refrain "oh, it's
>> not so bad".
>>
>> I've never analyzed the usual dimmer switch circuit but -- what would
>> happen if you connected a dimmer switch to a transformer that had a
>> resistive load on it? Would you just not have full range, would the
>> switch or the transformer burn up, what?
>
>yes!
>
>> I could make use of a dimmer switch into a transformer with a resistive
>> load on the secondary; hence my questions.
>
>get one that's designed for inductive loads.

Or roll your own. I found, back in my discotheque days, that I could
dim neon displays via the transformer, by feeding the transformer
integer cycles of AC... used a TRIAC, feed a few full cycles,
dead-time, feed a few full cycles.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

[Tim Wescott]

On Mon, 06 May 2013 08:15:41 -0700, Jim Thompson wrote:

> On 6 May 2013 05:52:43 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:
>
>>On 2013-05-05, Tim Wescott <t...@seemywebsite.com> wrote:
>>> I've heard over and over again that dimmer switches don't like
>>> inductive loads, but in the background of that is the occasional
>>> refrain "oh, it's not so bad".
>>>
>>> I've never analyzed the usual dimmer switch circuit but -- what would
>>> happen if you connected a dimmer switch to a transformer that had a
>>> resistive load on it? Would you just not have full range, would the
>>> switch or the transformer burn up, what?
>>
>>yes!
>>
>>> I could make use of a dimmer switch into a transformer with a
>>> resistive load on the secondary; hence my questions.
>>
>>get one that's designed for inductive loads.
>
> Or roll your own. I found, back in my discotheque days, that I could
> dim neon displays via the transformer, by feeding the transformer
> integer cycles of AC... used a TRIAC, feed a few full cycles, dead-time,
> feed a few full cycles.

I was hoping to find out if a dimmer switch from Home Depot and a
transformer from Radio Shack would fulfill the need.

I'm gonna try it, and see if anything gets hot or lets out magic smoke.

[Jim Thompson]

On Mon, 06 May 2013 11:38:42 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:

>On Mon, 06 May 2013 08:15:41 -0700, Jim Thompson wrote:
>
>> On 6 May 2013 05:52:43 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:
>>
>>>On 2013-05-05, Tim Wescott <t...@seemywebsite.com> wrote:
>>>> I've heard over and over again that dimmer switches don't like
>>>> inductive loads, but in the background of that is the occasional
>>>> refrain "oh, it's not so bad".
>>>>
>>>> I've never analyzed the usual dimmer switch circuit but -- what would
>>>> happen if you connected a dimmer switch to a transformer that had a
>>>> resistive load on it? Would you just not have full range, would the
>>>> switch or the transformer burn up, what?
>>>
>>>yes!
>>>
>>>> I could make use of a dimmer switch into a transformer with a
>>>> resistive load on the secondary; hence my questions.
>>>
>>>get one that's designed for inductive loads.
>>
>> Or roll your own. I found, back in my discotheque days, that I could
>> dim neon displays via the transformer, by feeding the transformer
>> integer cycles of AC... used a TRIAC, feed a few full cycles, dead-time,
>> feed a few full cycles.
>
>I was hoping to find out if a dimmer switch from Home Depot and a
>transformer from Radio Shack would fulfill the need.
>
>I'm gonna try it, and see if anything gets hot or lets out magic smoke.

As long as the ultimate load is resistive and the dimmer generates a
symmetric waveform it should work. For my neon situation, that didn't
work, because the neon tube didn't always strike, and I smoked more
than few transformers before I caught on >:-}

My discotheque days were fun, but probably why I now need to wear
hearing aids :-( I still like the music from the disco era... my wife
hates it ;-)

[amdx]

How often do you need to make an adjustment?
Do you cut Styrofoam only?
Is it set it and forget it?
I'm thinking about a plus or minus 10% is about all the
variance you would need.
Anybody want to argue? :-) oh, I mean I'm here to learn!
Mikek
Mikek

[amdx]

On 5/5/2013 8:41 PM, Artemus wrote:

[Jeff Liebermann]

On Sun, 05 May 2013 17:14:50 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:

>I've heard over and over again that dimmer switches don't like inductive
>loads, but in the background of that is the occasional refrain "oh, it's
>not so bad".
>
>I've never analyzed the usual dimmer switch circuit but -- what would
>happen if you connected a dimmer switch to a transformer that had a
>resistive load on it? Would you just not have full range, would the
>switch or the transformer burn up, what?
>
>I could make use of a dimmer switch into a transformer with a resistive
>load on the secondary; hence my questions.

Once upon a time, I was stuck on a holiday weekend trying to patch
together some assembly line equipment. One problem was a small AC
spot welder, that I had fabricated from a disemboweled Weller
soldering gun. It worked too well and would blast holes instead of
welding. I needed a way to reduce the voltage. I had an auto
transformer, which worked, but I didn't want to leave it on the
production line. So, I "borrowed" a handy light dimmer from someone's
office wall, and wired it to the spot welder. Much to my amazement,
it worked. Well, it worked for about 5 minutes or about 30 welds,
when the dimmer overheated and exploded (no fuse). I don't recall the
brand or type. I temporarily wired some random resistors to a switch
in series with the xformer on the 117VAC side. Temporarily lasted
about 6 years.

Lessons learned:
1. If the transformer load is resistive, a dimmer should work.
2. Ignore the maximum rated load, and it will not work for very long.
3. Nothing useful can be accomplished on a holiday weekend.
4. If it works, it's permanent.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Tim Wescott]

My understanding is that it depends on the length of wire, the width of
the styrofoam you're going to cut, and the speed that you draw the wire
through the foam.

But -- I haven't actually cut any foam that's made its way into a model,
so I'm hardly an expert. I'm just regurgitating things I've read.

[amdx]

Ya #4 happens, in the 70's while driving my VW bug home from the
beach, the motor quit. I found the wire to the coil had shorted
somewhere and burned off a bunch of insulation. I carefully rerouted the
wire and found the Bug started. I drove the last couple hours home and
promptly forgot about it. Wasn't reminded again until I was selling the
bug to my auto shop teacher, he opened the motor cover and noticed the
burned wire immediately. "what the heck is this!" I then explained what
happen 3 months ago. He bought the car.
Mikek
>

[amdx]

I'm sure the length of wire matters, do you plan on having a variable
length wire? My point, poorly conveyed, was once you have a fixed hot
wire cutter, I don't think you vary the current much. but if you have a
design for a variable length wire, that would be kinda cool.
I think!
Mikek

[Artemus]

"Tim Wescott" <t...@seemywebsite.com> wrote in message

news:OO-dnTwxtc96mRXM...@giganews.com...

The length and guage of the wire determine it's resistance. The forcing
voltage gives you watts/unit length so the thickness of the foam isn't a
big factor for that. Thickness will effect the force you need to feed the foam
for a fixed cutting speed. Faster cutting speeds need higher watts input.
Don't forget the cutting wire's length will change as it's temp varies from
no cutting to cutting.
Art

[Tim Wescott]

Well, I've never had a building board yet that, sooner or later, wasn't
too small for the next project. I'm sure that wing cutting bows are the
same.

Foam comes in different densities, and as you get better you'll cut
faster (or smoother, or both). So even if you never changed bows, you'd
still need to change the setting at some point.

[Artemus]

"amdx" <am...@knology.net> wrote in message
news:7c4ec$5187fc94$18d66b6a$95...@KNOLOGY.NET...

I cut styrofoam and foam rubber. The rubber requires a higher setting for
the same cutting speed. It's pretty much set and forget but it's much nicer
to twist a knob to get the initial setting than to fiddle with adjusting cutting
wire length.
Art
length

[Jim Thompson]

On Mon, 06 May 2013 14:30:47 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:

When I last built such a creature, used for Plexiglass bending, I used
NiCr in a slotted Bakelite fixture, spring-loaded to keep it taut as
it heated.

[lang...@fonz.dk]

remember I guy I worked with he had an old car, Opel I think, the
ground strap
to engine block would corrode and break eventually melting the clutch
cable that
became the only ground for the starter

the quick fix was ten alligator test leads, worked for many years an
never fixed


-Lasse

[Jeff Liebermann]

On Mon, 06 May 2013 14:38:16 -0500, amdx <am...@knology.net> wrote:

>(...) Wasn't reminded again until I was selling the

>bug to my auto shop teacher, he opened the motor cover and noticed the
>burned wire immediately. "what the heck is this!" I then explained what
>happen 3 months ago. He bought the car.
> Mikek

That's a different lesson:
5. Never sell a used car to a friend. I've made this mistake twice
and had to endure endless complaints, denunciations as me being a
crook, and pleas for repair advice. If my present vehicle ever needs
to be sold, I'll break it down to parts before I sell it to anyone
whom I value as a friend.

[Jasen Betts]

On 2013-05-06, Artemus <bo...@invalid.org> wrote:

>> How often do you need to make an adjustment?
>> Do you cut Styrofoam only?
>> Is it set it and forget it?
>> I'm thinking about a plus or minus 10% is about all the
>> variance you would need.
>> Anybody want to argue? :-) oh, I mean I'm here to learn!
>> Mikek
>
> I cut styrofoam and foam rubber. The rubber requires a higher setting for
> the same cutting speed. It's pretty much set and forget but it's much nicer
> to twist a knob to get the initial setting than to fiddle with adjusting cutting
> wire length.
> Art
> length

My cutter uses salvaged nichrome wire (from a 5A heating coil)
to adjust the heat I just change taps on the replacement secondary of
the repurposed MOT i use to run it

[Michael A. Terrell]

Jamie wrote:
> >
> Some dimmers are rheostats,


Maybe 50 year old theatrical dimmers, but some of those were banks of
Variacs to reduce the waste heat & fire hazard.

[whit3rd]

On Monday, May 6, 2013 9:38:42 AM UTC-7, Tim Wescott wrote:
> On Mon, 06 May 2013 08:15:41 -0700, Jim Thompson wrote:
>
>
>

> > On 6 May 2013 05:52:43 GMT, Jasen Betts wrote:

>
> >
>
> >>On 2013-05-05, Tim Wescott wrote:
>
> >>> I've heard over and over again that dimmer switches don't like

> >>> inductive loads

The issue, being that inductors for AC input will burn up if fed DC.

> I was hoping to find out if a dimmer switch from Home Depot and a
> transformer from Radio Shack would fulfill the need.
>
> I'm gonna try it, and see if anything gets hot or lets out magic smoke.

USE A FUSE.

The dimmer switch uses a Quadrac (a triac with an integral trigger diode).
The trigger is NOT accurately symmetric.

If you omit the fuse, it's a race to see if the dimmer switch burns, or
if the transformer gets carbonized. A short circuit related
to transformer saturation is nearly certain.

[dca...@krl.org]

On May 5, 6:14 pm, Tim Wescott <t...@seemywebsite.com> wrote:
> I've heard over and over again that dimmer switches don't like inductive
> loads, but in the background of that is the occasional refrain "oh, it's
> not so bad".
>

Don't you have an oscilloscope? A few minutes looking at actual
operation of a dimmer will beat all the advice you get here.


I have used a dimmer with a transformer with no problem, but can not
guarantee your dimmer is the same as mine. A transformer will tolerate
a little unbalance in the voltage applied to it.

Dan

[dca...@krl.org]

On May 6, 12:38 pm, Tim Wescott <t...@seemywebsite.com> wrote:


>
> I was hoping to find out if a dimmer switch from Home Depot and a
> transformer from Radio Shack would fulfill the need.
>

> Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com

Check to see if there is a Habbitat for Humanity store near you. The
last dimmer I bought at the local HHFH store cost me a buck.
Sometimes they have some heavy duty ones for more money. While you
are at it, see if they have all the stuff needed to make a short
extension cord with a dimmer controlling the output. Handy for
keeping a soldering iron warm and then turning it on full when
soldering.


Dan

[Tim Wescott]

That comes after hearing at least one person say "I did it and it worked
fine".

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

[Artemus]

"Tim Wescott" <t...@seemywebsite.com> wrote in message

news:UfudnVRY78VhPxTM...@giganews.com...

> On Tue, 07 May 2013 17:28:12 -0700, dca...@krl.org wrote:
>
>> On May 5, 6:14 pm, Tim Wescott <t...@seemywebsite.com> wrote:
>>> I've heard over and over again that dimmer switches don't like
>>> inductive loads, but in the background of that is the occasional
>>> refrain "oh, it's not so bad".
>>>
>> Don't you have an oscilloscope? A few minutes looking at actual
>> operation of a dimmer will beat all the advice you get here.
>>
>>
>> I have used a dimmer with a transformer with no problem, but can not
>> guarantee your dimmer is the same as mine. A transformer will tolerate a
>> little unbalance in the voltage applied to it.
>
> That comes after hearing at least one person say "I did it and it worked
> fine".
>

That'd be me. Mine is fused (not slo-blow either) and it has never
popped.
Art

[Michael A. Terrell]

"dca...@krl.org" wrote:

>
> Tim Wescott wrote:
> >
> > I was hoping to find out if a dimmer switch from Home Depot and a
> > transformer from Radio Shack would fulfill the need.
> >

> Check to see if there is a Habbitat for Humanity store near you. The
> last dimmer I bought at the local HHFH store cost me a buck.
> Sometimes they have some heavy duty ones for more money. While you
> are at it, see if they have all the stuff needed to make a short
> extension cord with a dimmer controlling the output. Handy for
> keeping a soldering iron warm and then turning it on full when
> soldering.

They make variable speed controls for ceiling fans that look just
like light dimmers.

[Spehro Pefhany]

Cool, but where would you find a ceiling fan that looks like that?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[Phil Allison]

"Tim Wescott"

>
> I was hoping to find out if a dimmer switch from Home Depot and a
> transformer from Radio Shack would fulfill the need.
>

** What is the resistance of your hot wire ?

I bet is it very low, like under 1 ohm.

How much power does it need to do the job ?

10W, 20W, 50 W or 100W ??

> I'm gonna try it, and see if anything gets hot or lets out magic smoke.

** Transformers running on reduced primary voltage LOSE power rating PLUS
if the wave form is chopped the rms current value goes way up. So the
tranny may have to be oversize.

Triac dimmers come in many versions, but the cheapest "two wire" kind will
not like a tolerate load that has a significant phase angle - more than 20
degrees is a worry.

A low cost, "split bobbin" transformer operating into overload is a prize
example of the above - leakage reactance is in series with the load and the
phase angle can reach 45 degrees. The result is that at some settings on
the dimmer, there will be mis-triggering and a large DC component applied to
the tranny.

It will growl loudly in protest - then let out smoke.

A 50 watt or more tranny will likely take out the triac if this happens too.


.... Phil

[Michael A. Terrell]

Spehro Pefhany wrote:
>
> On Tue, 07 May 2013 23:26:56 -0400, the renowned "Michael A. Terrell"
> <mike.t...@earthlink.net> wrote:
>
> >
> >"dca...@krl.org" wrote:
> >>
> >> Tim Wescott wrote:
> >> >
> >> > I was hoping to find out if a dimmer switch from Home Depot and a
> >> > transformer from Radio Shack would fulfill the need.
> >> >
> >> Check to see if there is a Habbitat for Humanity store near you. The
> >> last dimmer I bought at the local HHFH store cost me a buck.
> >> Sometimes they have some heavy duty ones for more money. While you
> >> are at it, see if they have all the stuff needed to make a short
> >> extension cord with a dimmer controlling the output. Handy for
> >> keeping a soldering iron warm and then turning it on full when
> >> soldering.
> >
> >
> > They make variable speed controls for ceiling fans that look just
> >like light dimmers.
>
> Cool, but where would you find a ceiling fan that looks like that?

China, of course. Where else do they make ceiling fans these days?
:(

[Tim Wescott]

You are as wise as you are helpful and tolerant, Phil.

The fact that the thing flows less than two amps on 12 volts should give
you a hint about your tolerance and helpfulness level...

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

[Phil Allison]

"Tim Wescott"

Phil Allison wrote:
>
>>
>>> I was hoping to find out if a dimmer switch from Home Depot and a
>>> transformer from Radio Shack would fulfill the need.
>>>
>>>
>> ** What is the resistance of your hot wire ?
>>
>> I bet is it very low, like under 1 ohm.
>>
>> How much power does it need to do the job ?
>>
>> 10W, 20W, 50 W or 100W ??
>>
>>
>>> I'm gonna try it, and see if anything gets hot or lets out magic smoke.
>>
>> ** Transformers running on reduced primary voltage LOSE power rating
>> PLUS if the wave form is chopped the rms current value goes way up.
>> So the tranny may have to be oversize.
>>
>> Triac dimmers come in many versions, but the cheapest "two wire" kind
>> will not like a tolerate load that has a significant phase angle - more
>> than 20 degrees is a worry.
>>
>> A low cost, "split bobbin" transformer operating into overload is a
>> prize example of the above - leakage reactance is in series with the
>> load and the phase angle can reach 45 degrees. The result is that at
>> some settings on the dimmer, there will be mis-triggering and a large DC
>> component applied to the tranny.
>>
>> It will growl loudly in protest - then let out smoke.
>>
>> A 50 watt or more tranny will likely take out the triac if this happens
>> too.
>>

> You are as wise as you are helpful and tolerant, Phil.
>

** While you are nothing but a total smartarse.


> The fact that the thing flows less than two amps on 12 volts ....


** Too late now to supply the essential details that were previously left
missing by YOU.

Fucking idiot.

[Joe Gwinn]

In article <2uidnSgNpL6WWxTM...@earthlink.com>, Michael A.

They may look like light dimmers, but they are probably something very
different, as ceiling fans use induction motors.

Joe Gwinn

[Joe Gwinn]

In article <8353c463-5a75-4bf7...@googlegroups.com>,

whit3rd <whi...@gmail.com> wrote:

> On Monday, May 6, 2013 9:38:42 AM UTC-7, Tim Wescott wrote:
> > On Mon, 06 May 2013 08:15:41 -0700, Jim Thompson wrote:
> >
> >
> >
> > > On 6 May 2013 05:52:43 GMT, Jasen Betts wrote:
> >
> > >
> >
> > >>On 2013-05-05, Tim Wescott wrote:
> >
> > >>> I've heard over and over again that dimmer switches don't like
>
> > >>> inductive loads
>
> The issue, being that inductors for AC input will burn up if fed DC.
>
> > I was hoping to find out if a dimmer switch from Home Depot and a
> > transformer from Radio Shack would fulfill the need.

Such dimmers exist, and can be bought at Home Depot or your local
lighting store. Look for a transformer-rated dimmer.

> > I'm gonna try it, and see if anything gets hot or lets out magic smoke.
>
> USE A FUSE.
>
> The dimmer switch uses a Quadrac (a triac with an integral trigger diode).
> The trigger is NOT accurately symmetric.
>
> If you omit the fuse, it's a race to see if the dimmer switch burns, or
> if the transformer gets carbonized. A short circuit related
> to transformer saturation is nearly certain.

A fuse is always a good idea.

The part about transformer saturation causing a short circuit is
exactly right.

Joe Gwinn

[Phil Allison]

"Joe Gwinn"

>
>> They make variable speed controls for ceiling fans that look just
>> like light dimmers.
>
> They may look like light dimmers, but they are probably something very
> different, as ceiling fans use induction motors.

** Triac dimmers can vary the speed of induction motors as used in fans just
fine.

There will need to be a suitable RC snubber across the triac and buzzing
noise may be an issue.


... Phil

[josephkk]

On Sun, 05 May 2013 17:14:50 -0500, Tim Wescott <t...@seemywebsite.com>

wrote:

>I've heard over and over again that dimmer switches don't like inductive

>loads, but in the background of that is the occasional refrain "oh, it's
>not so bad".
>

>I've never analyzed the usual dimmer switch circuit but -- what would
>happen if you connected a dimmer switch to a transformer that had a
>resistive load on it? Would you just not have full range, would the
>switch or the transformer burn up, what?
>
>I could make use of a dimmer switch into a transformer with a resistive
>load on the secondary; hence my questions.

Well, IME you can dim a fluorescent with a standard (triac type) dimmer,
it just doesn't work so well. And that is a fairly inductive load, and
the lamp itself is horribly non-linear. That must have been about 45
years ago when triacs were kind of new. A transformer with a resistive
load should look somewhat resistive.

?-)

[Michael A. Terrell]

Joe Gwinn wrote:

>
> Michael A. Terrell wrote:
> >
> > They make variable speed controls for ceiling fans that look just
> > like light dimmers.
>
> They may look like light dimmers, but they are probably something very
> different, as ceiling fans use induction motors.

DUH!!!

I was talking about them being made to fit in an outlet box, in place
of a standard light switch.


The "Tim Taylor" ceiling fan used a Chevy 283 engine, and the Amish
have fans that run from compressed air. Neither of those will work with
a light dimmer, so what's your point?

[Joe Gwinn]

In article <vqadnRHvt5KtYBPM...@earthlink.com>, Michael A.

To warn people not to lump them together:

Induction motors do not behave like resistors driven through a
transformer. Again, there is a large patent literature.

Joe Gwinn

[Michael A. Terrell]

Joe Gwinn wrote:
>
> Michael A. Terrell wrote:
> >
> > DUH!!!
> >
> > I was talking about them being made to fit in an outlet box, in place
> > of a standard light switch.
> >
> > The "Tim Taylor" ceiling fan used a Chevy 283 engine, and the Amish
> > have fans that run from compressed air. Neither of those will work with
> > a light dimmer, so what's your point?
>
> To warn people not to lump them together:
>
> Induction motors do not behave like resistors driven through a
> transformer.

Stating the obvious, as usual.

> Again, there is a large patent literature.

What good will warnings do? Idiots will find a way to do things
wrong, no matter how large or verbose the warning. Like idiot
newscasters insisting on setting up ENG vans under power lines, and
being electrocuted in spite of multiple warning labels on the van,
antenna and doors.

[dca...@krl.org]

On May 12, 11:46 am, Joe Gwinn <joegw...@comcast.net> wrote:

> > > Michael A. Terrell wrote:
>
> > > >    They make variable speed controls for ceiling fans that look just
> > > > like light dimmers.
>
> > > They may look like light dimmers, but they are probably something very
> > > different, as ceiling fans use induction motors.
>

> To warn people not to lump them together:
>

> Joe Gwinn

If you look on the internet at circuits for ceiling fan controls, you
will find some are identical to light dimmers.


Dan

[Joe Gwinn]

In article
<e8a77359-9a05-4ea1...@g9g2000vbl.googlegroups.com>,

And many that are not.

One can control the speed of an induction motor with a variac as well.
It sorta works. But the motor is fighting you - it wants to run at a
bit below synchronous speed, which depends on supply frequency more
than supply voltage.

Joe Gwinn

[Jamie]

Yes and the fans have a short life.

Caps burn up, wire hot, etc...

Many of cheap fan design depends on air passing over the motor in the
hopes the hopes of cooling it down.

We have an application where we operate a 220 volt single phase cap
run motor (not start) at 120 volts. We do this to obtain RPM but low
torque. It works fine but we are using a rather standard sinusoidal
power source.

Jamie

[Phil Allison]

"Joe Gwinn"
>
>> If you look on the internet at circuits for ceiling fan controls, you
>> will find some are identical to light dimmers.
>
> And many that are not.

** Blatant bullshit.

> One can control the speed of an induction motor with a variac as well.
> It sorta works.

** It works really well with fans.

> But the motor is fighting you - it wants to run at a
> bit below synchronous speed, which depends on supply frequency more
> than supply voltage.

** You need to check a real fan - fuckhead.

The motors are not like those use in bench grinders.



... Phil

[dave]

On 05/12/2013 11:50 PM, Phil Allison wrote:
>
> "Joe Gwinn"
>>
>>> If you look on the internet at circuits for ceiling fan controls, you
>>> will find some are identical to light dimmers.
>>
>> And many that are not.
>
> ** Blatant bullshit.
>
>
>> One can control the speed of an induction motor with a variac as well.
>> It sorta works.
>

A sine wave oscillator and a audio power amp will work better...