Here's an update. After considering all of the cheap SCR controller boards on eBay, I decided that it would be more involved than I had hoped because I would have to buy and populate an enclosure, since the boards were all too big to fit inside the popper housing, and then there was the heat dissipation problem. The much discussed Harbor Freight Router Speed Control had all the qualities I needed. And it was on sale for $19.99 and with the 20% OFF coupon it cost just $17.40 with the tax. What's great about it is it is a self-contained unit so there's nothing to build. It worked actually better than I had anticipated. I had read in the beer-making forums that people had to add a massive heatsink to the aluminum back-plate of the case, some even going so far as to mill a depression in the plate to better fit the heatsink. The first time I used it, I set the VAR control on maximum until first crack, about two minutes. It did get hot enough that I could only touch the back-plate with two fingers for two seconds. When I turned it down so the beans were barely swirling around, it was warm, not hot. The next time I put the switch on FULL until first crack and then switched over to VAR and turned it down until the beans were just barely swirling. This time the back-plate was barely warm the whole duration. So great, no need for a heatsink. I have to say that, even though the control also reduces the fan speed, the roast is slowed down enough so that it is much more controllable and much more even. So this is already a huge improvement. Phase one completed. Next I have to come up with a way to control the fan independently, using a minimalist, read that cheap and compact, approach. I'd prefer to have everything inside rather than have an external box with a separate wire. I'll report back on what I find.
There are numerous forum posts about this controller. People use it for controlling popcorn coffee roasters, beer brew kettle heating elements, even high power industrial lighting for video production, saving thousands of dollars off commercial controllers.
Here are two excellent posts about using it for coffee roasting: Ultimate Poppery II and Pumper - Home Roasting Hacking the Orville Redenbacher Hot Air Popper to Roast Coffee
Heh-heh, the 'mod', if you can call it that, took me as long as it took to go to the store, buy the unit, then go back there and exchange it because the one I got looked used. That's it. Just plug 'er in and go. :)
After using it several times, I decided the chip, which is a BTA26-600B A320 Triac, is getting too hot. This was designed to provide intermittent power to a router, not continuous power to a heating element. Even though I can replace this chip for $2 on eBay, I never want to overdrive a component like that so I decided to add a heatsink like the guys that use this for controlling heating elements for beer brewing and controlling industrial lighting. Mr P's 110v Harbor Freight controller duel element setup has a nice discussion about this. Here is a photo of his mod:
The heatsink will cost me more than a replacement chip and some work but I like to do things right the first time whenever I have the luxury of doing so. ;)
I decided there's no practical way to separate out the motor circuit and drive it internally so I will just slap a jack onto the shell and use a nice little 32V 750mA plug-in power supply from my trashed HP Piece-O-Crap® printer. That way I can use it on any popper.
OK, I finally got the heatsink from China and did the mod. I did an Instructable on it.
