I would like to convert (I don't know what is the right term) an incoming AC 220v to a DC 50v, and trigger the on and off using PWM.
I am confused : shall I use a Triac? a MOSFET? a MOTOR CONTROL module?
I can take care of the programming side, but I am not sure about the physical side...
thank you!
A power supply does that.
Why PWM? What's the load of your circuit?
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You can't use a triac with DC source
Is it for MOTOR CONTROL module? Most of Motor drivers accept the control PWM with low voltage, ie 3-5v, so you probably do not need switching off and on entire 50v
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I suggest that you study how switching power supplies work, and use the concept to transform 220VAC into 50VDC.
Ex:
https://www.circuitbasics.com/what-is-a-switch-mode-power-supply/
To transform 50VDC into PWM I suggest using the LM555 IC and a MOSFET coupled to it.
Ex:
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Hi, @sfynx_2019
Welcome to the forum.
Can you tell us the overall purpose of your project?
What are you aiming to do with the 50Vdc?
Thanks.. Tom... 
wow, I wasn't expecting so many reactions so quickly. this is an amazing forum!
ok, it's a bit tricky case perhaps :
I have a heating paint with graphene in it. It heats up when I apply current in it. AC or DC, doesn't matter actually.
I tried with a 12v current, it heats up a bit, but not enough.
So I would like to apply something like 50v to heat up a terrarium, but I need to modulate the current, therefore the temperature between day and night.
that's why I am looking for a solution to convert the AC220v to a switchable/variable DC voltage, that I can control with an arduino
You better use heating mats with strong isolation against electric hazard.
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What is the resistance of the graphene heater?
What is its power rating in Watts?
You need these figures to see what power requirements you need, not just 50V.
Thanks... Tom...
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How is the paint related to the terrarium?
I'm sure you can buy a heater, or heating element, for a terrarium.
Generally, low voltage needs to be isolated from lethal line voltage. That means a transformer. Transformers are AC, but DC power supplies are built with transformers.
Anything over 50V is considered dangerous by the regulatory agencies in most countries.
A "high power" transformer or power supply, which you'll need for significant heat, won't be cheap.
There are lots of commercial heating pads, electric blankets, etc., that work directly from the power line. So you can probably modify something like that, but it has to be insulated (and
I assume protected from moisture/water).
Heat is directly related to wattage. A heater is easy to build with one or more resistors. Typically, you'd use power resistors something like this (I'm just showing that for the picture... I'm not recommending that particular resistor).
Wattage is calculated as Power (Watts = Voltage x Current). But from Ohm's Law you can also derive Power = Voltage Squared / Resistance.
You should leave a good safety margin and use resistors rated for about double the calculated wattage. Multiple resistors can be used in series or parallel or series-parallel to share the wattage and spread-out the heat. (You can look-up series & parallel resistance to calculate the total.)
Temperature control - Temperature doesn't change instantly and virtually all heating/cooling systems work by simply switching on & off. I'm sure you've noticed that your home furnace works that way. i.e., the heat comes-on when you're below the target temperature and off when you are above. (Usually with some small hysteresis or "dead zone" so it doesn't switch on & off several times per second.)
The simplest way to control it is with a relay. A relay is an electrically-controlled and electrically-isolated switch. The Arduino can't directly power a relay coil, but there are "relay boards" with a built-in driver circuit.
Or, there are solid-state relays that can be directly-controlled from the Arduino. Just make sure to get one that's rated to switch AC or DC, whatever you are using, because they are generally not interchangeable.
If you are switching AC power, this "industrial type" of solid state relay is easy to wire-up and mount.
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Resistance : 3.5ohm
power consumption : 56W/h
but it also depends on the size of the final surface... here, it is for 0.72sqm. Which is more than enough
a relay. a relay is what I need! fantastic! I am going to check if I can find whatever I need and get back to you! (because most probably I will need some help!)
thank you all!
thank you tom!
what is the difference between a relay and a mosfet tho?
Hi,
Using your figures.
12V supply to 3.5R.
Power = (V x V) / R = (12 x 12) / 3.5 = 41W
You are almost at maximum power with 12V.
If you use 50V
Power = (V x V) / R = (50 x 50) / 3.5 = 714W.
You will overload the 56W heater.
If 41W is not capable of KEEPING the temperature correct, then you need a better heater.
How long did you wait and see if the 12V could get the system to target temperature.
Have you insulated the base of the terrarium?
Tom...
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I did a test again today and it seems like you are right, with enough layers of the graphene paint, it works nicely
I was also using a bare conductive paint to wire it, but using a copper tape seems to work better.
So, what shall I use to turn it on and off with an arduino? is using a relay still the right solution?
A mosfet would certainly be a good choice here (if you stay at 12V... or maybe 24V. 50V is in the danger zone...).
Using a mosfet, your arduino will share ground with your heater. A relay will need replacement after somany switches. A mosfet could also control your heater via pwm. So it is not just on/off like with the relay. This may be an advantage since you are not heating a big mass of water that would bring a large heat buffer. Pwm control would prevent overshoot and undershoot. With on off control you would need to set a dead zone of around 1 deg.C in order to prevent the relay from continuous switching.
Also, you will hear the click of the relay. If it is in your sleeping room, that may be annoying.
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thank you for your reply!
I ordered a 24v mosfet, so I am going to try that with my setup and see how it goes
indeed, the click sound can be irritating after a while
I can't wait to test it!
This might come in handy.
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Hope you got a logic level MOSFET that can be triggered by your MCU's output voltage and handle your Amp draw.
