Best way of controlling a heating element with an arduino

Projects General Guidance
1

SO I need to create a hotair source which blows air at around 250deg C. However, I should be able to vary the air temp between 150 to say like 250deg.

My plan is to measure the output air temp using an RTD. That part I think should not pose a problem.

But, What is the best way of switiching on and off the heating element?
I plan to use something like this: http://www.ebay.com/itm/220V-240V-250W-Replacement-Hot-Air-Gun-Heating-Element-/390396240677?pt=BI_Electrical_Equipment_Tools&hash=item5ae56de325#ht_1565wt_1037

Which I am guessing is capable of heating upto 250deg C.

I will be blowing air using a CPU fan which will then be heated by this.

So what's the best way of controlling this?

I thought of a solid state relay. Is this the best option or are there better methods?
I haven't thought yet weather to use fancy PWM or simply on-off but i will decide that later.

2

I thought of a solid state relay.

So did I.

Is this the best option

Yes.

I haven't thought yet weather to use fancy PWM or simply on-off but i will decide that later.

Decide it now. Simple on / of is all you need because the thermal time constant is long compared to the 50 or 60 times a second you can turn it on / off.

3

I thought of a solid state relay. Is this the best option or are there better methods?
I haven't thought yet weather to use fancy PWM or simply on-off but i will decide that later.

Most AC SSRs are only designed for on/off control. To try and control a AC voltage with PWM control requires direct access to the gate of a triac or back to back SCRs. Also you need a zero crossing detector measuring the input AC power so that the PWM timing can be sync'ed up with input AC timing. PWM control of AC is used for dimming circuits where you do require access to how much of the AC input waveform for each cycle is switched on to the load being controlled. But as GM said, controlling a heating element is much easier to just do with on/off control at a much slower switching rate then PWM uses.

Lefty

4

I have to agree, Solid State Relay

This is what is used in our Gas Chromatograph ovens.

I think a larger fan would be useful with maybe a simple speed control, this will help you get the temperature control 'dialed in'

5

I have used solid state relays on several large and small kin controllers and the Arduino works well. I don't know what fine control you need, but I use a thermocouple interfaced through an op amp back into the Arduino a/d and adjust the gain so that the max voltage in is 5.0 volts. The voltage is not linear but since all I need is a reproducible ramp, I just quantitate it the first time through and use the same values on subsequent runs.

One more thing... if you use a relay over speck it by at least 50%, the price difference doesn't make it worth while to be worried about burning them up. On the big guys I use both heat sinks and fan cooling.