How to choose opto-triac and triac? - Page 1
Forum section: electronics / beginners

author: PinheadBE
author_rank: Regular Contributor
timestamp: February 01, 2016, 10:07:46 am
content: Hi,I'm in the process of identifying parts for a module for a hobby project.From a logic level, I have to command relays and other solenoids on a 60 VAC line. (No typo: it is sixty volts, indeed)To do that, I want a good isolation between the AC and DC lines, and thus, I'll use an opto-triac that will then trigger a common triac.Since I'm dealing with all highly inductive loads, I have 3 questions:1. - Is there a point in choosing an opto-triac with an integrated Zero-Cross Detection. Intuitively, I would say no, because of the phase shifting, but what is your opinion?2. - Which one is better: a snubberless triac or a "regular" triac with an external snubber? In that case, how can I choose the values of the C and R ?3. - I have plenty of current available on the 60 VAC line, so, is there a point in choosing a sensitive gate triac, or, on the contrary, should it be better to have a higher gate current to avoid potential noise or latching or whatever problem would possibly occur with (too) sensitive gates ?Any information welcome.Thanks to all, and have a nice day!

author: PinheadBE
author_rank: Regular Contributor
timestamp: February 04, 2016, 09:26:27 am
content: Hi,Is there really no one that can help me ?thanks

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 04, 2016, 09:48:43 am
content: You seem to be in the wrong area. Beginners only here...Lol

author: PinheadBE
author_rank: Regular Contributor
timestamp: February 04, 2016, 11:04:47 am
content: Really?I was under the impression that my question was "newbie-ish" .....

author: wraper
author_rank: Unknown
timestamp: February 04, 2016, 11:52:49 am
content: Quote from: PinheadBE on February 01, 2016, 10:07:46 am1. - yes, Without zero crossing you'll much more likely will have false triggering, optotriacs without a zero crossing have lower voltage rating too. What do you mean by the phase shifting, why would you want it?2. - snubberless triac is not a replacement for a snubber. It is just more robust to false triggering. For highly inductive load I would advice to use both snubberless triac and a snubber + MOV.2. - you don't need a sensitive gate. Just choose the value of current limiting resistors properly to don't exceed a max peak current of the optotriac (much easier to do this wrong without a zero-crossing).http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00003865.pdfas you can see on page 13, they use snubberless triac, snubber + MOV.

author: wraper
author_rank: Unknown
timestamp: February 04, 2016, 12:00:12 pm
content: Another question is, why do you need those relays at all if already using the triacs?

author: PinheadBE
author_rank: Regular Contributor
timestamp: February 04, 2016, 01:04:49 pm
content: Thank you, that is a very comprehensive answerI will carefully read that application note.The reason I need that kind of arrangement (opto-triac + triac + relays) is because the relays are the original relays, AC powered, in an old Electro-mechanical pinball.I'm in the process of making the game a bit more fun by adding new rules and new effects. Therefore, a micro-controller will be used to activate some of these relays that perform some basic tasks like adding a point, adding a bonus and so on.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: February 04, 2016, 05:38:40 pm
content: Triacs like to fail to a short. If the duty cycle of the solenoids in particular is low, then they will overheat because the shorted triac won't turn off.It's more complicated, but you may want to add a main triac to control power to everything you are adding, along with a readback circuit to verify proper operation.

author: PinheadBE
author_rank: Regular Contributor
timestamp: February 04, 2016, 06:52:13 pm
content: I will use super-over-sized triacs, like BT139's (16 A - 800 V) while most of the relays to switch use no more than 1 A at 30 VAC. And indeed, most of them will be clicking at a low duty cycle.I take good note that the failure mode of triacs is to go shorted (I didn't know that), and indeed, a feedback of some sort could be usefull in some cases. Probably a simple AC optocoupler, such as PC814 would do the job. I have plenty in my binsThanks for those very usefull information