Controlling AC with arduino

I need to controll AC for a project with arduinos PWM. Im thinking of using this module as dimmer. The electronics I need to drive is with a little bit of odd inputvoltage 60VAC and I want to dim this voltage between 0-60VAC.

Would i be enough to controll the above module with PWM and feed the input of the module with 60VAC instead of 220VAC?

Alternatively, would i achieve the same thing if I am simply just limiting the dimmering not going to high with the PWM and stopping at 60 VAC out?

Hi,
If you look at the page you linked to, there is a github URL to an Arduino library that has most of the information you will need.
It even includes how to connect it to the controller.
It should be able to control 60Vac supply.

Tom... :slight_smile:

There's a LOT wrong with the "embedded" version.

Not enough clearance between the AC tracks. Resistors with too low voltage rating. Not enough clearance between high and low voltage sides (that cut in the PCB is just for show). A snubber using a ceramic cap which no way has enough voltage rating. That I see from looking at the images. Avoid this one. The version with through hole components appears pretty badly designed as well, suspected insufficient clearance between the AC tracks. Can't see it well enough, but can see enough to put it in the "suspected scary" category.

AC is led through two 120k resistors in parallel (effectively 60k - at 60V that's 1 mA of current, 1.42 mA peak). Barely enough for the ZC optocoupler to function. This is an issue you may run into. Other than that, it will be able to switch 60V AC.

Will the device you are feeding the 0 - 60 VAC to be able to stand the chopped up AC voltage?
Paul

FYI - A standard (TRIAC-based) AC dimmer doesn't use regular PWM. When a TRIAC is turned-on it latches-on until current drops to zero. With AC that's the next AC zero-crossing. For example, you find the zero-crossing and delay. If you trigger the TRIAC at 90 degrees (1/4 of a cycle past the zero-crossing) it stays-on 'till 180 degrees (the next zero crossing). If you repeat that for the negative half-cycle the power is on half of the time and the light is dimmed.

Paul_KD7HB:
Will the device you are feeding the 0 - 60 VAC to be able to stand the chopped up AC voltage?
Paul

Not sure to be honest. I need to give it a try.
I guess this one would be enough for my purpose in 60 vac
Dimmer module 5A

The other are only types for higher voltage and current right Dimmer HL 16A-600V and Dimmer 8A-400V and Dimmer HL 24A-600V

The specs on the glass are:

Driving voltage 65±5 volts AC
Current less than 20 mA/ft2(215 mA/m²)
Power less than 0.5watt/ft2(5 watt/m²)

It appears that you’re attempting to drive a Polyvision LCD privacy glass (please correct me if I’m wrong…)

If this is the case I don’t think your scheme will work and it could be dangerous.

The glass is rated for 65VAC but dimmers usually work in the time domain; they delay the turn on after a zero-crossing by some amount to reduce the time the load sees current but they aren’t guaranteed to reduce the voltage. So while the RMS power delivered to the load is reduced (giving a dimming effect on, say, lights), the full 230Vac output could still be there.

LCDs typically require a square wave that (in this case) is 65Vp-p above and below GND.

Please don’t connect dimmed-AC to your panel. You could damage it or get hurt.

Blackfin:
It appears that you're attempting to drive a Polyvision LCD privacy glass (please correct me if I'm wrong...)

that is correct :slight_smile:

Blackfin:
The glass is rated for 65VAC but dimmers usually work in the time domain; they delay the turn on after a zero-crossing by some amount to reduce the time the load sees current but they aren't guaranteed to reduce the voltage. So while the RMS power delivered to the load is reduced (giving a dimming effect on, say, lights), the full 230Vac output could still be there.

im using a transformer in between so the voltage I am feeding the dimmer with is 60vac. So the maximum output of the dimmer would be 60vac. So I guess the worst thing that could happen is that nothing happens? I mean that it still will be 60 volt and it wont dim?

So when you are saying that 230Vac output still could be there it could not be more than 60Vac right since that is all I am feeding the dimmer with.

It is a bit of experiment though since I want to find a way to dim them with PWM.

acroscene:
that is correct :slight_smile:
im using a transformator in between so the voltage I am feeding the dimmer with is 60vac. So I guess the maximum output of the dimmer would be 60vac. So I guess the worst thing that could happen is that nothing happens? I mean that it still will be 60 volt and it wont dim?

So I guess when you are saying that 230Vac output still could be there it could not be more than 60Vac right since that is all I am feeding the dimmer with.

It is a bit of experiment though since I want to find a way to dim them with PWM.

Be careful. The 230vac wall outlet is going to be Vrms; the peak voltage could be +/- 325V; a 65Vac transformer might give ~60Vac RMS but its peaks will be higher (like 85V). And it would be unregulated... And 60Vac is still hazardous.

Your panel is likely going to want a signal that goes from +30V to -30V in a square wave. Assuming you could safely transform your AC source down to those voltages it'll still be a sine wave; will the panel be happy with a sinusoid or will the segments act weird?

If what you really want is create a variable square wave of sorts, it is probably much easier to rectify the AC output (or use a 60V DC power supply which also takes care of the ripple and so), then use an H-bridge to create the waveform you want.

If you need +/-30V then maybe you can do this by connecting two 30V power supplies in series, if you can't find a dual power supply (which are indeed rare).

Hm. Another idea I had was to use mosfets for dimming say 12 v dc with pwm and then use an inverter for converting it from DC to 60VAC. Would this actually be a better approach?

No. :roll_eyes:

What you have to do now is take a very good read of the datasheet of this mysterious thing you’re trying to operate, and figure out exactly what voltages, currents and waveforms (block/sine; duty cycle; frequency) it expects to see to do what you want it to do.

When you have that information we can talk about how to generate this waveform.

Hi,
Can I suggest you get to the manufacturers to see if you can actually control the amount of crystal alignment to control the transparancy?
I have looked at about 6 videos of "Polyvision LCD privacy glass" and they all go straight from "transparent" to "opaque", never fade slowly.

If you read the specs, it takes 100ms to change from one state to the other.

Tom... :slight_smile:

We have acutally managed to dim the LCDs with a cheap light dimmer and using resistors taking down the voltage from 230 vac. This might not be the best solution and a bit risky but it works for now. But we want something more safe indeed

But the conclusion is that the LCDs works for dimmering.
However the LCD have burned when we are controlling the dimmer with low inputvalues. My guess is that it is because the waveform are getting more intense than the LCD can handle? So it works as long as the waveform is long enough but with shorter waveform the LCD burns. Could that be a correct assumption?

Regarding the specs, it is not easy to get more information from a seller at aliexpress than the information on the page itself.

Most LCDs require a symmetrical AC voltage to drive them and are damaged if there is any net DC component.

For a single element, a series capacitor will generally prevent any net DC component.

Okej, so my assumption was wrong than maybe :slight_smile:

So just if I understood you right. The LCD needs a symmetrical waveform from the AC voltage and are damaged then of course if there are no. But what happens in the lower inputvalues from the dimmer. Does it change the waveform so it is getting closer to DC? And putting a capacitor in between can prevent this?

The capacitor does not change the waveform to any great degree, but prevents any net DC current flowing.

Ok, thanks. Last question. How do I pick the right capacitor then for blocking DC?
The specs is:

Driving voltage 65±5 volts AC, 50/60 Hz
Current less than 20 mA/ft2(215 mA/m²)
Power less than 0.5watt/ft2(5 watt/m²)

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