i need to turn on washer motor , how to turn on at zero crossing with bt 137 triac, is zero crossing essential ? do triacs (bt137 etc) automatically turn on at zero crossing?
if not how to measure zero crossing with 817? (i don't have mc3041).
i need to know the when the zero crossing happens and turn on the triac in code.
(also the motor turns on a thousand times so i really need it)
i watched and read lot of tutorials still not sure how to obtain zero cross with 817.
(i know SSR is the right option, and also know There are TRIAC-driver with zero-crossing built-in availabe . )
The triac does not do zero crossing detection. I would suggest looking at solid state relays (SSRs) They include the isolation for the control signal and can be zero crossing or random depending on the unit. They are (usually) cheaper and a lot easier then do it yourself.
I believe zero crossing is "helpful" for motors (inductive loads) and it may reduce switching noise on the power line.
There are TRIAC-driver opto-isolators with zero-crossing built-in. This means the TRIAC will switch on at the next zero-crossing after the LED inside the opto-isolator is turned on (as long as the LED is still held-on when the zero-crossing happens).
And there are similar opto-isolators without the zero-crossing limitation that will turn-on instantly.
If you are controlling AC power with a TRAIC and an Arduino, you MUST isolate the lethal voltage from the Arduino (and yourself, and your computer's USB port, etc.) anyway.
A TRIAC will ALWAYS switch-OFF at a zero crossing because TRIACs latch-on until current drops to zero.
A standard light dimmer works by switching a TRIAC on part-way through the AC half-cycle (non-zero crossing) and then it stays-on until the end of the half-cycle.
Zero crossing is not necessary but helps reduce EMI. You state: " i need to know the when the zero crossing happens and turn on the triac in code. (also the motor turns on a thousand times so i really need it) i watched and read lot of tutorials still not sure how to obtain zero cross with 817".
I have included a sample picture of solid state relays, they are not expensive and much safer then building it yourself. As far as your motor turning on 1000 times I do not believe it unless I am under the wrong assumption. I am assuming it is an AC motor that will be powered from the mains which would be 50/60 Hz. You can turn on the triac but it will not turn off until the current drops below its holding current. Once on it stays on. The Triac will communicate and turn off each time the AC power crosses zero so you can turn it on a maximum of 2x the line frequency. It will fire again once the voltage passes zero and if properly driven stay on until the current falls below the holding current. In my opinion you should not try to build this yourself, from your question I feel you do not have enough resources in this area.
SSR's are also the "right" way to do it as they are safety certified! You should NEVER connect ANYTHING to the mains that is not already safety certified.
When talking about inductive loads, there are two zero crossings, voltage and current, so if power is cut off when voltage is at zero, current may still be many degrees positive or negative, hence the noise generated.
I have fair knowledge in electronics and arduino, i work as a electronics repairmen, but this is my first question in a forum, i know SSR is the right option, and also know There are TRIAC-driver with zero-crossing built-in availabe . but ssr is expensive or need to by in bulk and wait for more than a month , same goes with mc3041 as i pointed in question. and also i have around 6 triacs to operate (planning to add more) , so the circuit will become bulkier and expensive.
But if i use one 817 to read zero crossing and operate all the triacs in code it will be easier
Here is a link that explains what is going on. and how to implement a triac. You indicate you are competent and know how to work with mains power. Triac Principles and Circuits — Part 1 | Nuts & Volts Magazine
Changing the contact to an optocoupler in figure 8 will get you close to what you want.
