120VAC TRIAC Dimmer - Page 1
Forum section: electronics / beginners

author: vidarr
author_rank: Frequent Contributor
timestamp: September 20, 2019, 01:57:24 pm
content: Can someone check my schematic. I built the circuit and it is not working. I am getting power to the "lamp", but it is not adjusting with the potentiometer. The pot is brand new (all the parts are new). I double checked it with a DMM. I went over the built circuit while looking at the schematic and everything is connected properly according to it. The connections are all good according to the DMM.I did not make that schematic. So, maybe the problem is that? IDKThe circuit I built does NOT include the 12k resistor shown in one of the schematics.Thanks

author: vidarr
author_rank: Frequent Contributor
timestamp: September 20, 2019, 05:13:05 pm
content: I built another circuit from scratch following the same schematic (but using the same potentiometer). I tested the output and it goes from 30V (all the way counterclockwise) to 42V (clockwise). This should be 0V to 120V right?edit:I retested the first circuit. It gives the same reading of 30V - 42V. So, this is a problem with the circuit design. The only common part is the potentiometer, which is brand new and tested.Checking other schematics online, many are similar to what I have. They all seem to be a little bit different though -- not any of them are the same.Maybe someone has a link to a schematic they Know is working?edit: I had the same problem with this circuit a while back and posted here. Back then, it had a bad potentiometer. Since then, I bought and changed out all the parts for new and still not working.Thanks

author: soldar
author_rank: Super Contributor
timestamp: September 20, 2019, 06:57:33 pm
content: With questions like this almost every time the schematic as shown is fine and there is an error in assembly that we cannot see.You need to double check that what you assembled is the same as what the schematic represents.

author: vidarr
author_rank: Frequent Contributor
timestamp: September 20, 2019, 07:44:22 pm
content: Yeah, I checked it many times. I built it twice from scratch -- I have TWO full circuits built based on the schematic and they both do the exact same thing.Both circuits built from the same schematic go from 30V with pot all the way counterclockwise, to 42V with the pot turned all the way clockwise.The schematic you attached has parts I don't think I have -- need to look. My plan was to take one of the circuits apart and build it based on another schematic I found. If I have the parts for the one you attached, I can try that.Is it possible that the schematic I am using is designed for 240V? I am in Brazil and we have 120V and 240V in our houses.

author: floobydust
author_rank: Super Contributor
timestamp: September 20, 2019, 08:30:01 pm
content: Check you have not mixed up triac MT1 and MT2 pins. What is your capacitor valueI do not know "1K400V"looks like u1K400V = 0.1uF each.It needs to be about 47nF with 500k potentiometer or 0.1uF with 250k potentiometer, with 120VAC.I have had troubles with chinese triacs and potentiometers not working well or lasting long. Check your potentiometer is not burnt.A better circuit adds a bridge rectifier to give "hysteresis free" or "no snapback" effect, like you see with lamp dimmers. It's also helps with inductive loads. The extra diodes discharge (reset) the firing delay capacitor every cycle.More can be found in figure AN1003.12 orTeccor App note AN1003This is the eBay circuit for the "4,000W SCR" dimmer.

author: soldar
author_rank: Super Contributor
timestamp: September 20, 2019, 08:35:59 pm
content: Quote from: vidarr on September 20, 2019, 05:13:05 pmThe schematic is good. It is pretty much the same found everywhere with minor variations.I would recommend you understand how it works so you can troubleshoot it.There have been many threads on the same circuit with the same problem: it doesn't work.You can do a search for triac dimmer power control etc.

author: soldar
author_rank: Super Contributor
timestamp: September 20, 2019, 08:44:24 pm
content: Hey, I thought I remembered doing this before! You're the same guy!https://www.eevblog.com/forum/beginners/ac-dimmer-circuit/You just abandoned and now you start all over again?

author: floobydust
author_rank: Super Contributor
timestamp: September 20, 2019, 08:50:45 pm
content: Yeah, that thread ended after he found the potentiometer was bad and needed to replace it.

author: vidarr
author_rank: Frequent Contributor
timestamp: September 20, 2019, 08:58:14 pm
content: Yeah, the potentiometer was bad and I stopped. I wrote above that I posted here about it before and where I left off. I put the project on hold because this is a hobby and I had other things to do. So, now I am back at it where I left off.I just finished unsoldering one of the circuits. I am going to try an alternate circuit I found online. I WANT to understand the circuit. I understand what all the components do individually. I understand how the TRIAC and DIAC work together. I do NOT understand why the capacitor(s) and resistor(s) are sized the way they are and why they are placed the way they are. I see so much variation in the circuit designs that I can't figure it out.

author: vidarr
author_rank: Frequent Contributor
timestamp: September 22, 2019, 05:59:44 pm
content: Quote from: floobydust on September 20, 2019, 08:30:01 pmI tried another schematic very similar to what I had tried and it did not work. Finally, in frustration, I copied a schematic from one of these Indian made, YouTube videos. Watching how they solder is hilarious. Anyway, my theory was if these guys could make this work, there is no way I wasn't going to succeed. I ended up making two of the Indian guys' circuits I found and they both worked. Go figure.So, I know my parts are good at least. I am going to try the schematic under: "Figure AN1003.9 Basic Diac-Triac Phase Control" in the link you posted. If that works, I will move on to the circuit with the bridge rectifier, as you suggested would be better. Thanks for the link to that "Phase Control Using Thyristors" PDF. That was very helpful.Thanks