Dimmer Question

[S'mise]

Not an expert on dimmers but it probably flashes because the electronics in the dimmer can not handle the square wave the upstream dimmers sends out. So it tries to work until the power supply decays and the light goes off, then the caps charge after the load (light) goes off so it goes back on again. What we used to call a "jack-off" circuit. lol

 

[Brady Electric]

Dimmer Question

You can only have one dimmer on each light. If you have two three way switches and one four way on a kitchen light you can put a three way dimmer in place of one of the three way switches the rest have to stay as they are. Same goes on ceiling fans, you can only use a fan dimmer on one switch. Semper Fi.

 

[macmikeman]

Sometimes little things like the subject of this thread highlight the obvious.... next time READ the directions supplied with whatever device you are installing when you are unfamiliar with that particular device, be it a simple three way dimmer, or the slave on a multilocation type dimmer.

 

[brantmacga]

You can only have one dimmer on each light. If you have two three way switches and one four way on a kitchen light you can put a three way dimmer in place of one of the three way switches the rest have to stay as they are. Same goes on ceiling fans, you can only use a fan dimmer on one switch. Semper Fi.

i'm not sure if you are talking about a specific type of dimmer, but multi-location dimmers and fan speed switches are available, although expensive.

http://www.lutron.com/maestro/?s=17000&t=17200 <<< Dimmers - 10 location dimming.

http://www.lutron.com/maestro/maestrofan.asp?s=17000&t=17200 << Fans - 3 location switching.

Leviton also makes multi-location dimming and fan speed switches in their acenti line of devices.

 

[Brady Electric]

Dimmers

Dimmers

I use leveiton dimmers. I am not talking about multi purpose dimmers they are two expensive. The person that said always read the instructions is correct no matter what kind you use. I also use lutron dimmers which are about $20 each and I don't have any customer that want to pay more than that. It just makes sense to dim at one location and not be comfused. Just my opinion and trying to be helpful after 35 years in the bussiness. Semper Fi.

 

[brantmacga]

i wasn't trying to knock your opinion; from the context of your post i assumed that you were unaware of multi-location dimming and fan switching. i just wanted you to know such things exist in case you were ever in need of such a device.

 

[coulter]

... but it probably flashes because the electronics in the dimmer can not handle the ....

I don't know. Last time I saw this, it was the flux capacitors resonating with the E-field inductors. It caused a VLFI oscilation.

carl

 

[jaylectricity]

Sparky -

I don't think anybody is going to know. You're asking why a piece of equipment operated in a undefined manner after it was connected and operated in a fashion not known to the mfg or us.

carl

I have only read up until this post #17 or #18 whichever this was.
I think the first feasible answer was the second or third post that talked about delaying one half of the sine wave. So if two dimmers are trying to do that, there will eventually be a cycle where both dimmers agree, and apparently that happens at a speed of 1 Hz(once per second). Hence the light actually glowing for a flash every second.

That being said, I always thought dimmers worked on a resistance principle. As in: As you turn the dimmer down, more and more resistance is applied to the load. That, to me explains why dimmers get warm and why they have a wattage limit.

Any thoughts?

 

[LarryFine]

. . . I always thought dimmers worked on a resistance principle. As in: As you turn the dimmer down, more and more resistance is applied to the load. That, to me explains why dimmers get warm and why they have a wattage limit.

No, a 600w variable resistor would be about as big as a 1-pound coffee can. The dimmer's potentiometer (variable resistor) simply controls a timing circuit. The heat is more like that from an audio amplifier.

A dimmer works by using a bi-directional solid-state device called a triac; basically an SCR that conducts in both directions. Once triggered into conduction, an SCR continues to conduct until the current halts.

On AC, the zero-voltage crossing accomplished this twice per cycle. The adjustment knob or slider works by delaying the trigger time during each half cycle, and then the triac conducts for the remainder of that half cycle.

The persistance of the hot filament averages out the power over time, so you usually don't see any flicker. After all, we're still talking about 120 pulses of current per second.

What I believe happens with two dimmers in series is that the timing circuitry of each dimmer charges more slowly, so it takes many cycles to reach the triac's triggering point, rather than a fraction of a cycle.

Also, since both dimmers' triacs are effectively in series, the load will only be energized when both triacs are triggered, which obviously happens once per second or so. It's based on the circuit expecting steady full voltage.

 

[S'mise]

Very funny coulter, the flux capacitors much reach 6 jigawatts. Laryfine explained it better than I. Many people believe that they are just big resistors jayletricity but they just trim the top (and bottom) portion of the sine wave into a square wave. Like Laryfine said:” the timing circuitry of each dimmer charges more slowly, so it takes many cycles to reach the triac's triggering point, rather than a fraction of a cycle." So, if it can’t charge at the proper rate the circuit charges until it can fire the triac and then decays as soon as the load is switched on. AKA "Flashing light"

Originally Posted by coulter
Sparky -I don't think anybody is going to know. You're asking why a piece of equipment operated in a undefined manner after it was connected and operated in a fashion not known to the mfg or us.

I never underestimate the knowledge of this forum, to question why something works is not just a sign of intelligence it's how we learn.

 

[LarryFine]

. . . but they just trim the top (and bottom) portion of the sine wave into a square wave.

Not exactly. It more that the voltage stays at zero until triggered, then the rest of the half cycle is the remainder of the sine wave. Here's a waveform of a dimmer around half-brightness:

 

[S'mise]

Ah yes, I stand corrected. I have never seen a waveform of it. A o-scope tells a thousand words!

 

[blue spark]

Thanks Larry! One of those "learn something new everyday" type things. Except here it's something I install every other day and thought I knew how it worked. Now I just have to re-read 10 more times to see if I really understand it:grin:

 

[jaylectricity]

No, a 600w variable resistor would be about as big as a 1-pound coffee can.

So what kind of switchplate would that require? haha...

Thanks, your post was most informative.

 

[coulter]

Here is what I am saying about we don't know how it was connected. First, I don't know too much about 3-way dimmers, and my quick look showed two generic types. If these don't fit, the rest of the post doesn't count.

Thirty years ago, they were using inverse parallel SCRs, Twenty years ago they went to triacs. I don't know what they are using now. Could be they are using a turn-on/turn-off device like a hexfet (inverse parallel) , SCS, GTO (inverse parallel). Could be phase angle fired any-of-the-above or pulse modulated on the last three.

The top picture looks like a non-starter - the current is going the wrong direction through the power element.

Door #2 (marked "Picture ?) could give some current to the bulb.

So, anybody know:
1. What is the generic type - or if maybe neither of these is correct?
2. What the connection was?
3. Are any of the mfgs using a pulse modulated output?

Going to need to understand the guts to do any good.

Carl

 

[LarryFine]

A 3-way dimmer is simply a dimmer with a 3-way (SPDT) switch between one dimmer wire and the pair of travelers. Your drawings with a dimmer at either 3-way is correct; the 3-way dimmer simply has the switch built in.

They still use triacs. Next time you have the opportunity, open a defective dimmer. You'll find the triac (typically a TO-66 case) riveted to the front plate for heat-sinking. Hexfets are usually used on DC with PWM drivers.

 

[coulter]

...They still use triacs. ...

Larry -
Seem like when I was fooling with this stuff 20 years ago, I recall some articles using inverse, parallel SCSs and using multiple pulses per half cycle. So nobody has gone to that in commercial/residential equipment?

...Hexfets are usually used on DC with PWM drivers.

Doesn't suprise me, but I haven't seen any. Most of the stuff I see are PWM VFDs with GTOs - Not that I could look at the outside and tell the difference - except some of the GTOs are the size of a hockey puck.

The only reason I thought the mfgs might have gone to a multiple pulse per half cycle is to get rid of the low level flicker inherent with phase-angle triggered devices operating at near off. Probably not an area of my expertise (mildly )

carl

 

[coulter]

... Your drawings with a dimmer at either 3-way is correct; ...

Larry -
Well that's good. However, the dimmers were connected in a manner unknown to anyone except possiply the OP. And unless we know that, it isn't likely we can deduce why the two devices operated in the manner they did.

carl