It would help to post the exact current requirements and type of heating element(s) you are using, and what material are you heating?

 

Bug13,

Look in the allaboutcircuits eBook for a reveiw of how an SCR works,
http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

It turns on when the trigger is above threshold voltage and turns off ONLY when supply voltage drops to zero. That means you need one switch to turn on the device (a momentary push of the on-switch will keep the device on forever). The only way it will turn off will be if the main power is interupted so you need a second swith to turn it off. An AC circuit drops to zero every cycle by itself so you need to essentially keep some sort of voltage on the trigger all the time to keep the power on the motor or anything else you control.

If you want a dimmer or a power control for a motor in an AC circuit, you can add a capacitor (see eBook referenced above) to delay the trigger each AC cycle. This becomes phase control (a sort of zero crossing sensing each cycle) that delays when the power will be started for the rest of the AC cycle.

Now you can think about how it is important to time your DC microcontroller switching with the AC phase so you can consistantly hit each AC sine wave at the same phase for consistant power control.

 

You can construct your own SSR using the MOC optosolator's as in Post 3
along with a properly rated Triac. See Page 7 Bottom for circuits examples.
A Triac will control the full AC cycle.
SCR's only work on 1/2 the cycle, so 2 are required to do the same job as one Triac.

That being said, Heed the warnings from me and others regarding 240 VAC. You should have a Technician/Electrician help with the line voltage side of things unless you are thoroughly familiar with the pertinent electrical codes and working with High voltage AC.

 

It would help to post the exact current requirements and type of heating element(s) you are using, and what material are you heating?

These are the heating elements I will be using, and I am planing built a reflow soldering toaster oven.

It will be 1400W, 240VAC

there is another post here about the reflow soldering toaster oven

 

That being said, Heed the warnings from me and others regarding 240 VAC. You should have a Technician/Electrician help with the line voltage side of things unless you are thoroughly familiar with the pertinent electrical codes and working with High voltage AC.

I do know a couple of electricians, or I can get my project coordinator to look at it before I do anything silly. (or I can get a certificate myself, it's one of the requirement for next year's study)

Thanks others and your kindly warnings, it's really appreciated

 

Here's a SSR Rated for 25amps @240vac:

http://www.alliedelec.com/search/pr...gclid=CMqvlubCqbQCFYVFMgodGiQAXw#tab=overview

 

I do know a couple of electricians, or I can get my project coordinator to look at it before I do anything silly. (or I can get a certificate myself, it's one of the requirement for next year's study)

Excellent.

If you decide to build an SSR Using Triac/Opt here's an example Triac:
http://www.nxp.com/documents/data_sheet/BTA312B-600CT.pdf

 

http://www.opto22.com/site/pr_details.aspx?cid=4&item=240D10

is this one good enough for 1400W, 240VAC? this is the only one I can find locally and seasonally price

 

1400w at 240 volts calculates to 5.83 amps,
So looks good.