This afternoon when I was home for lunch I ran the Arduino control touching a light bulb plugged into the heater output. It tracked the heat pretty closely until it got up around 300 degrees. It overshot by about 10-20 degrees initially and then once it caught up it was pretty close the rest of the way pulsing the power as necessary. After it neared 300 degrees it couldn’t keep up and started lagging. At that point I left the fan running at full speed for the duration of a normal roast.
This evening I went out and plugged in the heater. The heater is a totally different monster! It tracks but it OBVIOUSLY needs the PID calibrated until it works better. At low fan when the heater dies down it has a massive swing in temperature going under and then back over again. It appears to only do ok at the lower temperatures and then is all over the place at the higher temperatures. What is noteworthy is that it DOES track the same “slop” drift around the target temperature all the way up. The drop/gain on the % power is simply too drastic and needs to be adjusted to flatten out more.
For giggles I’m throwing out for view a test graph as it ran (no beans) for a few minutes once with low fan and another with higher fan. I have the heat maxed at 80% power in the program so that I don’t burn anything up accidentally until I’m sure it can run like it should.
First Arduino Roast Controller test with heater connected
In the lower graph it shows a low fan vs a higher fan setting. The middle one is a heat amount that actually gets reduced to 80% in the code during testing. The green in the top graph is the target while the red is the actual temperature reading. Both tests were run with the roasting chamber left empty. I’ll try adjusting the PID settings a little bit to smooth it out to have smaller sweeps and then start loading some old green coffee in to test it with a “load” and see how much that stops the swing.
Now that the heat is able to be completely shut off this helps the temperature drop a lot faster. It’s my guess this would be better for the roaster overall to completely drop the temperature of the coils before turning it off while it cools the beans. I’ve set the system so that the cooling requires the probe to reach a low temperature before turning off so the coffee beans should be quite cooled before it shuts down by itself.