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
ttdesign.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
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? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
That'd be me. Mine is fused (not slo-blow either) and it has never popped. Art
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?
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
"Tim Wescott"
** 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 ??** 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
China, of course. Where else do they make ceiling fans these days? :(
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
They may look like light dimmers, but they are probably something very different, as ceiling fans use induction motors.
Joe Gwinn
Such dimmers exist, and can be bought at Home Depot or your local lighting store. Look for a transformer-rated dimmer.
A fuse is always a good idea.
The part about transformer saturation causing a short circuit is exactly right.
Joe Gwinn
"Joe Gwinn"
** 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
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.
?-)
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. Again, there is a large patent literature.
Joe Gwinn
Stating the obvious, as usual.
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.
just
yIf you look on the internet at circuits for ceiling fan controls, you will find some are identical to light dimmers.
Dan
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
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
"Joe Gwinn"
** Blatant bullshit.** It works really well with fans.
** You need to check a real fan - f*****ad.
The motors are not like those use in bench grinders.
... Phil
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.