Dimming AC without ZC

Hello all,

I concern is there any way to dim an AC lightbulb without detecting zero-cross? Because my home installment hasn't included 3 wire in light switch box on the wall, that why I can't use many examples available already and I would like to dim it with a triac and moc3021.

Thanks in advance.

why do you think you need 3 wires to detect zero crossing?

Juraj:
why do you think you need 3 wires to detect zero crossing?

Because all examples which I see uses natural and hot wire over bridge rectifier to deduct zc. But in my case there is only 2 wires exist.

and I would like to dim it with a triac and moc3021.

A TRIAC latches-on until current goes to zero (i.e. the next zero-crossing). So, a TRIAC always needs zero-crossing detection.

It's possible to dim with transistors or MOSFETs, but they only conduct in one direction so you either need a pair of complementary transistors/MOSFETs, plus the "support circuitry", or you can rectify the AC (which will work with regular incandescent bulbs).

Because all examples which I see uses natural and hot wire over bridge rectifier to deduct zc. But in my case there is only 2 wires exist

It can be done, but it's not "easy".

BTW - Most manual dimmers (which use TRIACs) only require 2-wires and the [u]X-10 dimmer switch[/u] only requires 2-wires.

Probably the bigger problem is that you need to power your circuit (including your Arduino or whatever is driving the opto-isolator). That also "can be done" without a neutral but most home automation switches do need a neutral. If you were planning on running additional wires into the switch box, you could add a neutral while you're at it.

There are several engineering & construction challenges in making a remote-switch that fits into a switch box, doesn't require re-wiring, works locally or remotely, and looks good. And, you probably can't build it for the price of an X-10 switch.

So... I always recommend choosing one of the existing home automation protocols and then BUY the controlled switches or outlets, and then you can build your own controller if you want to build something yourself.

DVDdoug:
A TRIAC latches-on until current goes to zero (i.e. the next zero-crossing).
It can be done, but it's not "easy".

BTW - Most manual dimmers only require 2-wires and the [u]X-10 dimmer switch[/u] only requires 2-wires.

Probably the bigger problem is that you need to power your circuit (including your Arduino or whatever is driving the opto-isolator). That also "can be done" without a neutral but most home automation switches do need a neutral. If you were planning on running additional wires into the switch box, you could add a neutral while you're at it.

There are several engineering & construction challenges in making a remote-switch that fits into a switch box, doesn't require re-wiring, works locally or remotely, and looks good. And, you probably can't build it for the price of an X-10 switch.

So... I always recommend choosing one of the existing home automation protocols and then BUY the controlled switches or outlets, and then you can build your own controller if you want to build something yourself.

Yes, there are many challenges but none of it harder nor expensive than running new cable in the wall.
Also, you may right about buying an existing product but I rather do it myself with components that I can get from local hobby stores than waiting for shipping.
I believe I have enough skill to do but lack of knowledge about controlling AC. And I am open to research and learn more. I appreciate it if you can provide me some resources which show me how can I do that.

and how do you want to power the controller?

I’m planning to put Nokia's old 1Ah lithium battery.

the

erkino:
I’m planning to put Nokia’s old 1Ah lithium battery.

the triac turns of at zero crossing. a current sensor could detect that and start the timer to turn the triac on at required period.

wait for zero current
wait required period
pulse triac in timer interrupt
repeat

Perhaps put the AC through a full wave rectifier to get DC.
Put an N-type FET on the ground side and the lamp on the +V.

Last step is get a 555 circuit to make PWM that can vary by pot/dial input to open and close the transistor gate. Turn the dial to vary what the bulb gets.

Only the rectifier, bulb and FET touch the current. This is beneath needing an Arduino, you need to make it wifi or IR-remote or IoT or something, maybe with a sensor other than dial.

Juraj:
the
the triac turns of at zero crossing. a current sensor could detect that and start the timer to turn the triac on at required period.

wait for zero current
wait required period
pulse triac in timer interrupt
repeat

It is a pretty clever trick but hard as you warn. I'll try to do it in the first opportunity.
Thanks a lot.

GoForSmoke:
Perhaps put the AC through a full wave rectifier to get DC.
Put an N-type FET on the ground side and the lamp on the +V.

Last step is get a 555 circuit to make PWM that can vary by pot/dial input to open and close the transistor gate. Turn the dial to vary what the bulb gets.

Only the rectifier, bulb and FET touch the current. This is beneath needing an Arduino, you need to make it wifi or IR-remote or IoT or something, maybe with a sensor other than dial.

I’m planning to use Arduino code running ESP8266. But can I connect serially a rectifier in the circuit? I don't think I can. There are only 2 wires.

erkino:
Hello all,

I concern is there any way to dim an AC lightbulb without detecting zero-cross? Because my home installment hasn't included 3 wire in light switch box on the wall, that why I can't use many examples available already and I would like to dim it with a triac and moc3021.

Thanks in advance.

I seem to remember triac being controlled via a pot and a diac, fairly simple circuit .
Can create noise on the line though.

Note in fig.6 the switch at the bottom is actually the active conductor(marking is incorrect).

It is necessary to use a pot which has a plastic shaft rather than the conventional splined metal, simply to eliminate getting booted if the pot fails in any way.

erkino:
Because all examples which I see uses natural and hot wire over bridge rectifier to deduct zc. But in my case there is only 2 wires exist.

That would be an electrical code violation in my country. Protective ground is never supposed to conduct current except in a fault condition.

What OP calls "natural" I think should be "neutral" rather than "ground/earth". Makes more sense in the context.

If the switch has two wire, I assume that is the live wire on one side, and the switch wire on the other. You should be able to do zero crossing on that, as the switched wire is actually the neutral, just that there's a light bulb in the way. Depending on the resistance that offers, zero crossing is still feasible.

Otherwise: two N-MOSFETs back to back, drains connected, and PWM. 960 Hz should be enough for smooth regulation of 50 or 60 Hz AC. This does require parts that can handle the AC peak voltage (325V for 220V AC), optical isolation of the gate (unless it's all very well packed in a box), and probably a gate driver to allow the devices to switch on and off fast - on the high voltage side of the isolation. Not a beginner's kind of project!

erkino:
It is a pretty clever trick but hard as you warn. I'll try to do it in the first opportunity.
Thanks a lot.

I’m planning to use Arduino code running ESP8266. But can I connect serially a rectifier in the circuit? I don't think I can. There are only 2 wires.

Maybe do some reading?

I use diodes to rectify and flatten Piezo disk signals. Rectifier you build needs parts rated to handle your AC load.

And once you have the rectified flow it is the FET that pulses the power.

You might want to use a transformer to get the AC volts <= 60V if you want to use cheap FETs.

Not much you can do (at the switch box) without a neutral line.
I've rewired many of these (lost count) ...

Part of the case for leading/trailing edge control (zero crossing), is to significantly reduce EMI/RFI emissions.

Back in the late 60s when triac dimmers first appeared, they had no ZC triggering.

The result was that every radio & TV within 100 metres was impacted with nasty mains interference.
In most locations now, it’s an offence to impose noise on the mains, or into the RF spectrum if it can be controlled.
First time it upsets anyone, you’ll get ‘told off’, the second time - a penalty.
If you interfere with public media or emergency transmissions it could bankrupt you.

If you manufactured a product, it would never get type approval - and worse, you’d be forced to recall or rectify all the sold items !

Just be careful.

what bothers me on this thread: who uses incandescent bulb in 2020 for other use then a terrarium heating or similar? Because only an incandescent bulb can be dimmed with a Triac
Yes, there are dimmable LED bulbs for AC, but there the DC part is dimmed based on sensing the AC dimming so doing a DIY dimming on AC side is not the right approach.

dlloyd:
Not much you can do (at the switch box) without a neutral line.
I've rewired many of these (lost count) ...

No need for neutral at the switch position.
If you use the correct approach for the circuit.
Clipsal units work in much the same manner, active and switch wire only.
see #10.
No need for any Arduino either.

Another example here, although they have the switch and (unnecessary fuse) in the wrong leg.
The top leg should be shown as neutral and the bottom wire should have the switch from the active line.

https://xtronic.org/circuit/dimmer-circuit-triac-tic-226/

No need for any Arduino either.

... or an electrical inspector either.

In the same situation as aarg, this wouldn't be approved for new installations (in Ontario) but might be OK for an existing repair or retrofit. Just saying there's very limited options available.