# RC Snubber design

#### Raj Kamal

Nov 3, 2017
4
I am trying to regulate the speed of fan using Triac BT136, triggered with MOC3021(OptoIsolator). Help me to figure out the values of R and C used as snubber across TRIAC.

#### Minder

Apr 24, 2015
3,425
A couple more.
The others are too large to upload, unfortunately.
M.

#### Attachments

• SnubberDesign.pdf
243.9 KB · Views: 56
• SnubberDesgTriacAN3008.pdf
1,010.1 KB · Views: 51

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,337
I would like to know the Coil (Inducatance and resistance value ) for the ceiling fan
How are we to know? You'll have tp measure if you really need to know. However, usually one does not have the exact load ratings when designing a dimmer circuit. Therefore typical values are assumed, e.g R=39 Ω, C=0.01 µF as in this example.

#### Raj Kamal

Nov 3, 2017
4
How are we to know? You'll have tp measure if you really need to know. However, usually one does not have the exact load ratings when designing a dimmer circuit. Therefore typical values are assumed, e.g R=39 Ω, C=0.01 µF as in this example.
It worked. Regulated the speed of fan using 47ohms resistance. But after few hours of operation, the resistance burn out. I used 1/4 watt resistance. Should I change the value to exactly 39ohms? Also, should i take 1/2 watt resistance?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,337
39 Ω or 47 Ω is not really relevant. YOu'd have to choose a really larger value, e.g. 150 Ω, to get a marked change in power dissipation. Obviously the power rating was insufficient.
Better use a 1 W resistor for some safety margin. Or use 2 or 3 times 47 Ω in series, each 1/2 W rated, toi distribute the power dissipation.

Note that without knowing the load details this can be only a rather general recommendation.

You work at your onw risk. Observe all necessary safety precautions to prevent any injury due to electric shock, fire from overheating etc.
This forum and its mambers can and will not take any responsibility for damages due to your design.

#### Raj Kamal

Nov 3, 2017
4
39 Ω or 47 Ω is not really relevant. YOu'd have to choose a really larger value, e.g. 150 Ω, to get a marked change in power dissipation. Obviously the power rating was insufficient.
Better use a 1 W resistor for some safety margin. Or use 2 or 3 times 47 Ω in series, each 1/2 W rated, toi distribute the power dissipation.

Note that without knowing the load details this can be only a rather general recommendation.

You work at your onw risk. Observe all necessary safety precautions to prevent any injury due to electric shock, fire from overheating etc.
This forum and its mambers can and will not take any responsibility for damages due to your design.
Can you comment on the capacitor value and the type of capacitor to be used? There in the pdf, whole analysis being done to get its value?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,337
I have no comment on the value. The type is preferably a film capacitor rated at more than the peak voltage of teh AC (e.g. RMS 230 V -> Peak 360 (incl. 10 % tolerance add on) -> 400 V capacitor, better 630 V).

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