voyageur505 wrote:Hey Allon, Could you please expand on your PID'd iRoast?
I picked up a used one recently, the original three stage version, and after about 2 dozen roasts I have bumped up against it's limitations. The programmability is an illusion, it does what it wants to do. However, think the hardware is more robust than the corn poppers and it should be a good candidate for manual or PID control. I like the visibility of the roast in the glass bowl.
For starters, I thought I would just add a switch to the main heater that I could toggle to prevent the iRoast from running away. But I was wondering if interrupting the heater while the under power would damage the electronics driving the heater. Any thoughts on that?
I haven't tried to map out the circuit yet, have you (or anyone) found a schematic for it?
Thanks...
Yeah, I have a 5-stage one, and you're right, the programmability is a complete illusion.
There are two circuit boards, one is a relay board which handles the high power, and the other contains a custom microprocessor IC, user interface, and sensor input.
I took wire cutters to mine. You can have the circuit boards, if you want to play with them
My initial improvement, which gave me SOME control was to exhaust the iRoast to the outside through a dryer vent hose; I added a 12V fan to draw the air out. The fan speed is controlled by a 24V variable speed power supply (haven't burnt the fan out yet).
For my next improvement, I removed all the electronics from the iRoast. I wired the fan directly to a power cord (the clear one) and both heaters in parallel to another power cord (the black one). The box you see has its own line cord that plugs into the wall. The duplex outlet has had the tabs removed from it which splits it into two independently controlled outlets. The top outlet is controlled by the dimmer, and controls the iRoast fan speed. The bottom outlet is controlled by a solid state relay (mounted to the bottom of the metal quad-box for heat sink purposes). The SSR is controlled by the PID. The PID reads the temperature from a type K thermocouple plugged into the front of the box; the thermocouple (naked) is snaked into the bottom of the roasting chamber, smashed under the rubber seal.
The PID itself is a 24V model, so there's a transformer inside the box. In any case, I lucked out and scored this PID cheap. It is an Omron E5CK-T. The T is important - without the T, it just maintains a temperature; with the T, it is programmable, with 4 programs of up to 8 steps of ramp.
My usual load is 160g. I drop the beans into the chamber, turn the exhaust fan to 12V and turn on the iRoast fan to get a little bit of agitation. Then I select the program (and/or customize it) and start the roast. I may occasionally change the fan speed to keep the agitation about right, or if the heater can't quite keep up with the program/bean load. When the program finishes, I boost both fans to full for cooling, until it gets down to around 110-115 degrees (it seems to cool with diminishing efficiency around there). Then I dump the beans back into my scale tray (I remove the lid and dump the whole iRoast upside down without removing the chamber. This keeps my thermocouple in about the same spot, and doesn't overly stress the cable). I throw four used Mazzer burrs in with the beans to help soak up the heat.
After 30 minutes of running the exhaust fan, the roaster is ready for another batch. If I go again too soon, the beans roast a bit darker.
I should get a picture of the inside of the box. I used a plastic terminal strip to wire it up, splitting power between the transformer for the PID, the dimmer, and the SSR.
This box would work just fine with any other roaster that has split wiring and draws less than 18A (the SSR rating). So if the iRoast dies, I'll use a split-wired popcorn popper with the same unit until I get another one.
by voyageur505 on Thu Jul 21, 2011 11:59 am 
