View Full Version : Connecting a Thyristor to a BS2PX?

01-28-2010, 01:39 AM
I'm building a kiln controller to replace a bespoke one I had purchased which has stopped working. I'm using a BS2PX and A BOE. I have a DS1302 and a DS2760 hooked up and running for time and temperature, now I need to be able to switch the power to the kiln on and off. The kiln is 240 V AC and as much as 30 A. The old kiln controller used a Thyristor for the switching (see attached images).

I know little about electronic circuits, how should I hook up this thyristor to be switched by the stamp? The old one had an opto-isolator between the thyristor and the controller, do I need that with the stamp? The old opto-isolator was an MOC3043. Could I use an MOC3022 (I have a source for those)? What else is needed in the circuit to hook it up?


01-28-2010, 01:53 AM

Have you researched using a Triac? There are a number of options available, and with the use of the Opto chip, you could turn it on and off with relative ease. Most have a high voltage range and good current rating; I'm using a 600V 16A to control some stuff in my house and have a opto chip to protect the I/O; works like a charm.

If you do a Google search you can get a listing for triacs that can switch that type of load. Digikey has a part that looks like it might be a place to start. Here is a link for your review.



Joshua Donelson
www.parallax.com (http://www.parallax.com)

01-28-2010, 09:23 PM
I am an electronics newbie, but at least according to Wikipedia a triac *is* a thyristor. But whether I use the part I have or the one you mention Joshua (which certainly looks like it would do the job), what I need help with is connecting it safely to be triggered by the BS2PX. It sounds like the opto is a good idea, do I just hook that straight up to one of the stamp's pins? Or do I need a resistor in between? How big of a resistor?


01-28-2010, 10:26 PM
The device you show is not a triac but a set of back-to-back SCR's which function as a triac. Both triac and SCR's are thyristors. Whereas the triac has one gate connection your device has one for each element. When you re-use the thyristor block, make sure your new triggering scheme triggers the elements correctly.The opto is definiely a good and safer idea.

You don't say whether the heating is on-off or proportional, but a simpler solution for you is a good solid state relay which will incorporate all the gating and opto-isolation within one module. Pick a 240v 30 A (or greater) for the load side and apply 5 volts from the Stamp to the opto in the relay.


Tom Sisk