HI guys
I have a project at my university where I need to heat air. For that matter, I utilize a heating element from a cheap hairdryer (1200W,220/230V). In the project I need to control how much this heating element heats up the air. Problem is that the heating element is connected directly to a wall socket powered with 230V/50Hz. How can I control the voltage input in the heating element using my arduino UNO (and therefore the amount of heat that produces) ??
By using an SSR ( Solid State Relay ). These can control mains devices on and off and are optically isolated so look just like an LED to an Arduino.
If you need to vary the heat output rather than switching it on or off, you need to use a circuit similar to a lamp dimmer. This turns the power on part way through the sine wave cycle. Bare in mind that the motor may not like being controlled so you may have to modify the hairdryer to separate the motor and element.
The dimmer can be connected to the arduino via a opto coupled triac. Google knows all so do a search.
Weedpharma
It is a heating element, the thermal time constant means there is little point in having proportional phase control. A simple on / off about five times a second will do fine.
Sounds like someone has been challenged to pop corn.
It is a chamber we design, in which a piece of cartilage will be tested for its mechanical properties. But hot air will flow through it during its working hours. Its not a closed system which I want to control. The idea is to have a temperature sensor inside the chamber to read the temp. Target value is 37C. I need precise control of that heating element to feed the chamber. SImply turning it on/off, doesnt mean that the feeding air temperature will flactuate too?
It depends on just how little fluctuation can be allowed.
As has been said, there is thermal momentum in the wire. But if the fan is blowing across the element then it will cool fairly quickly. So if on for five seconds and off for five seconds on a continuous flow you will get considerable fluctuation. That is why I mentioned the light dimmer (phase control) type of circuit.
Weedpharma
Five times a second, is not the same thing as each five seconds.
SImply turning it on/off, doesnt mean that the feeding air temperature will flactuate too?
No, because of the thermal time constant.
Even with proportional phase control yo are turning it on and off, it is just that it is being done every half cycle, so that is 100Hz or 120Hz depending on where you live.
However with something like a heater that is much faster than it need to be, so you can slow things down to just several times a second. The up side is that the electronics is way cheaper, the down side is nothing.
michinyon:
Five times a second, is not the same thing as each five seconds.
Sorry, my miss-read.
Weedpharma
You might be better off using a plain heater instead of a hair dryer. Google "strip heater", or "cartridge heater". A heater has a certain amount of thermal lag, due to mass. It takes several seconds to heat up or cool down. The hair dryer has a fan which creates a very rapidly changing environment, which isn't needed in this case. (It also slightly pressurizes the chamber, causing even more environmental changes instead of the steady-state that you are trying to achieve.) As stated by others, once you have a thermal mass, then the 1 second on/off/on/off time used with a standard solid state relay will work perfectly. A zero-crossing solid state relay will be electrically noise free. I would not use "phase angle AC control" because that generates electrically noise. Keep it simple, and it will work fine.
Some people would put the temperature measuring thermocouple in the air of the chamber. Some people would put the thermocouple directly on the surface of the product being tested. On the product is more correct for the type of work that you are trying to do.