Snubber component types for a triac-controlled dimmer

Thread Starter

electrophile

Joined Aug 30, 2013
167
What kind of capacitors and resistors would be used for a snubber in a triac controlled dimmer that would typically control say ceiling fans. For the resistor would a 1W carbon composition be sufficient? Also the local hardware store recommended these two types of capacitors. One of them has an AC voltage rating (275V) while the other has a DC voltage rating (630V). Which of these would be appropriate? (images attached).
 

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Alec_t

Joined Sep 17, 2013
14,280
The cap should be an X2 rated one (which the one in the first pic is).
Without knowing the dimmer spec/characteristics I can't comment on the resistor, except to say that it needs to be rated for the mains voltage you have.
 

takao21203

Joined Apr 28, 2012
3,702
Dont use the DC capacitor by all means.
The x2 parts are approved for mains connection.

0.1uF is for very small watts, 220nf or 0.47 is better for a dimmer.
 

Thread Starter

electrophile

Joined Aug 30, 2013
167
@takao21203 Thanks! That helps.

@Alec_t The dimmer is supposed to dim/speed control incandescent lamps and ceiling fans working with AC mains voltage. The lamps are rated for not more than 100W and the ceiling fan no more than 75W.
 
What kind of capacitors and resistors would be used for a snubber in a triac controlled dimmer that would typically control say ceiling fans. For the resistor would a 1W carbon composition be sufficient? Also the local hardware store recommended these two types of capacitors. One of them has an AC voltage rating (275V) while the other has a DC voltage rating (630V). Which of these would be appropriate? (images attached).
hello dear, Have U made the circuit for celing FAN dimmer . WOULD U please share with me, I also trying to make a fan dimmer
 

Ian0

Joined Aug 7, 2020
9,680
You will also need an inductor. You stand no chance of passing EMC regulations without.
The capacitors must class-X.
 

DickCappels

Joined Aug 21, 2008
10,152
Every time I have tried to "dim" a fan with a triac, I got an annoying acoustic buzz.

The only methods I could find to slow down a fan without the annoying buzz is to use a step-down transformer (Variac in fact) or a motor run capacitor in series with the fan. The capacitor value was found experimentally.

Oh, and one other method, and that was to drop every-other powerline cycle. it was quiet alright, but it killed the thermal fuses in two floor fans before I figured it out.

Using a transformer or a series dropping capacitor eliminates the need for a snubber.
 

Ian0

Joined Aug 7, 2020
9,680
Oh, and one other method, and that was to drop every-other powerline cycle. it was quiet alright, but it killed the thermal fuses in two floor fans before I figured it out.
Used to use that method with disco lighting - it was called “shimmer dim”. It reduced the lamp life horribly, and quickly ruined transformers for low-voltage lamps.
I wonder if it would work using every third half-cycle?

Fans have induction motors which like to run at (line speed - slip). By reducing the power you reduce the torque and increase the slip. Eventually you reduce it so much it stops. It’s not the best way of speed-controlling an induction motor, but it can be effective.

P.S. My iPad upgraded today, and QUOTE and REPLY no longer work. Anyone else found that?
 

DickCappels

Joined Aug 21, 2008
10,152
Now on Mac OS 10.13.6 running Firefox I had the same problem but a Firefox update may have fixed it. Quote and Reply worked but it took many clicks.
 

Alec_t

Joined Sep 17, 2013
14,280
The only methods I could find to slow down a fan without the annoying buzz is to use a step-down transformer (Variac in fact) or a motor run capacitor in series with the fan. The capacitor value was found experimentally.
Years ago I tried the series capacitor idea on a pump. The pump speed was indeed reduced, but the pump life thereafter was short. I did an autopsy and found signs of arcing having occurred inside. My guess is that the capacitor and pump inductance happened to resonate at the mains frequency, or a harmonic, and generated very high voltages. So, something to be wary of.
 
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DickCappels

Joined Aug 21, 2008
10,152
Maybe one lesson here is that if an approach to solving a problem seems unusual or surprising (not commonly used) there may be a good reason.
 
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