Arduino Space Heater - switching large AC current (~12.5a @ 120v)

Hello all,

Got a new project in the works where I'm going to use a Ardunio to control a heating element in a DIY space heater. Don't worry, I won't be running this experiment unsupervised - I know this is a major fire hazard.

So basically it's going to be just like one you'd buy at the store. It will be composed of a nichrome heating element, fan, enclosure, thermostat, and a relay of sorts.

The only part I haven't figured out is the device that will switch the current to the heating element.

Should I use a mechanical relay, or a solid state one? I'm thinking 1500 watts will do the trick. That's 12.5a @ 120v. Probably need some sort of safety margin in there too.

What would you recommend for the relay?

Thanks!!! -M

Edit:

http://www.amazon.com/40A-SSR-Solid-State-Relay/dp/B005KPIX9A/ref=sr_1_2?s=hi&ie=UTF8&qid=1388217499&sr=1-2&keywords=solid+state+relay

what do you think of this? looks like others are using it to switch large currents for heaters too. plus 40a gives me lots of over head- might not even need a heat sink.

Hi, M, that sort of current could be switched by a relay, but constant switching will probably cause failure later on and arching will certainly cause pitting of the contacts and electrical interference. Another solution that is probably safer and easier is to use a SSR, or Solid State Relay, most have logic level input, ie 3 to 30V input volts will turn it on, ideal for arduino output, and with a resistive load it should work like a dream. Try your supplier or Google it, there are many shapes and sizes out there that will do the job.

Tom.... :)

For some of the installations that we have done, we use an interposing relay to control a contactor. The relay has a small coil that can be controlled easily by a ULN2803 on an output on your Arduino. Cheap chip designed for controlling relay’s. Then the relay can handle the contactor and the contactor, depending on what you buy, can handle the amperage as high as you like.

I am a sparky by trade and pretty new to electronics, but this is how we control up to 6.6 Kv motors at work from a 5 volt PLC output.

There are many MOSFET's rated for far more than your current/voltage requirement.

Mark

Thanks for the replies. As Tom said if I went with a mechanical relay I'd probably get arcing and need some kind of snubbing circuit. So in the case I'm going to go with SSR I found on Amazon first. Not cost effective like other options, but not needing amplification of the Arduino's logic output is a plus. Also isn't a SSR just a huge MOSFET inside?

M_Faraday: As Tom said if I went with a mechanical relay I'd probably get arcing and need some kind of snubbing circuit.

That's why they make the contactors specially for this purpose.

M_Faraday: Also isn't a SSR just a huge MOSFET inside?

A Triac actually, plus an opto-isolator.

But hey, it does the job (if the ratings say so), buy it!