Triac gate drive circuit

regarding objections to my zero voltage crossing circuit. Here is a gate drive circuit from "Power Electronics" by B.W. Williams. Note particularly the low voltage 10v circuit ground connection to the neutral of the mains. Highly dangerous and illegal according to some on this forum. No isolation between the low voltage and high voltage circuit.

You are correct, it is dangerous.

Do you have a question?

Often this sort of circuit would have to be entirely double-insulated as its live - for instance old light dimmer-switches would be like this.

These days opto-isolated triacs are available and would be the typical way to galvanically isolate the mains from a low-voltage circuit (observing clearance and creepage distances).

This is referring to the previous discussion here:

That topic was locked due to having reached an unproductive state. If this one goes the same direction, it will also be locked.

Thank you.

B.W. Williams is Professor of Electrical Engineering at an Edinburgh, Scotland university. Do you think he would put in a textbook for students of electrical engineering circuits that they are going to build that are dangerous.?
No question. I am using my circuit to cause an interrupt on a rising voltage on the Arduino board. No fizzled out parts on the board.
If you think its dangerous I suggest you stay right away from anything to do with mains voltages.

Connecting the Arduino to the power line is potentially dangerous! Especially if a human can touch it or if there is a possibility of accidently connecting the USB port to your computer with AC power connected, or if there are any other connections to the "outside world".

Is "V1" high voltage a.c. ('mains')?
How old is the textbook?

So? I do not know this B.W. Williams guy or whether he knows what he's talking about or not. I have no opinion about the guy either way.

See comment above. I have not seen his text book. Maybe in the text book it mentions the dangers associated with the circuit and how to mitigate those dangers, but I am speculating having not seen the book.

I don't 'think' it's dangerous, I know it's dangerous. I also know how to mitigate those dangers and use that circuit safely, or a different circuit safely. I have a similarly dangerous circuit in one of my projects, however I have taken appropriate precautions so that, while the circuit itself has dangers, no one is exposed to those dangers. If you cannot see the dangers or know how to mitigate them then I suggest you need to stay away from such circuits. I suggest relying on someone's title to keep you safe is in itself a dangerous practice, what will keep you safe is understanding the dangers of what you are doing and how to mitigate those dangers.

I'm not expecting the board to fizzle out, I am more concerned that YOU will fizzle out, or worse, someone innocent person who comes into contact with what you have built will fizzle out.

Further to the above, if you are using the circuit and the Arduino is connected to your computer via a USB cable, and if the computer is connected to the mains and earthed via the mains lead then I would expect the earth leakage protection on the mains circuit to trip. Not all computers are earthed, such as some laptops, but I would expect that a desk computer would be. If the computer is earthed and the earth leakage protection does not trip then I strongly suspect the wiring in the property is suspect and needs inspecting by a suitably qualified person.

If your GPO is wired incorrectly, that is Active and Neutral swapped. then your circuit reference or chassis would be at MAINS ACTIVE POTENTIAL!!!

I would be looking at safer transformer and/or opto-coupler type zero crossing detector circuits.

optocoupler zero crossing detector arduino

Much safer solutions.
Can you please tell us your electronics, programming, arduino, hardware experience?

Thanks... Tom... :grinning: :coffee: :coffee: :australia:
PS. What part of the world are you located?

who would be that silly to swap the Active and Neutral. Anybody likely to do that should have nothing to do with Mains voltages. 240v in Australia where I am located. The Yanks have opted for a safer lower voltage of 120v.
Yes my hardware experience. I have one of my circuits integrated into a silicon chip in a factory in South Australia. Don't ask me what products now use it. I wouldn't know. The circuit is one you would object to but unless somebody was going to take the trouble of reverse engineering the product and chip they would never know about the circuit.
I used a half wave power supply. At one half cycle of the mains the neutral was at 24v. In the next half it was ground. The zero crossing for phase control of the mains was picked up by connecting the neutral to comparators as the neutral changed from 0v to 24v and 24v to 0v.
Perhaps if you object so much to these types of circuits you should contact B.W.Williams who wrote the book "power electronics". Take up your argument with him. He is Professor of Electrical Engineering at a university in Edinburgh, Scotland.

The program is downloaded from a laptop to a Mega 328P microcontroller. So when the program is running the lap top is not even connected.


It happens, that is why in some parts of the world, including here in Australia, we have compliance and compulsory appliance testing.
I do PAT testing and it is surprising what you find.

It just takes an inexperienced individual to wire a plug wrong.
You can fix the wiring BUT not revive the body.

I am surprised as an Aussie with 240Vac, you have such an attitude to electrical safety.

Tom... :grinning: :+1: :coffee: :australia:
PS. Why just take the experience of "B.W.Williams" when many more are telling you the facts?
PPS. This book appears to be a theoretical teaching aid, you need to add a bit of common sense if you are going to implement it into the real world.

But they do, there is nothing you can do to stop them. You can however build circuits in such a way as to make it not matter if live and neutral are swapped. You should treat the neutral connection as if it were live.

Other possibilities that make the circuit dangerous:

  • The mains socket could be incorrectly wired.
  • The neutral could become disconnected due to a fault, making the only connection to the circuit the live, so making the whole circuit live.

The circuit can be made safe if you use it starting with the assumption that the whole thing and everything it is connected to is live and dangerous. That means at the very least enclosing it in such a way that no one can touch any part of it, or any part of anything electrically connected to it. Think of a simple light switch, in the back there are live wires that are dangerous to touch. At the front there is just plastic. The dangerous bits cannot be touched accidentally, you have to take the thing to bits to expose yourself to the parts that might kill you.

Note that it is not JUST this circuit that is dangerous, it is anything electrically connected to it, all must be treated as if they are or could become live.

Also, if you have earth leakage protection in your house wiring, and you should have earth leakage protection in your house wiring, then if the neutral comes into contact with anything earthed, such as the metal case of another electrical appliance, the the earth leakage device will (should) trip.

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