let me preface this by saying I don't know the details on how the fec auger gets feedback from the temperature system (if at all). but here's something I've observed that I think answers the questions asked before about temps spiking while cooking.
I was using some mequite pellets- these were rather long pellets, an inch or so typically. Everything was running along and I decided to switch to hickory towards the end of the cook. I poored these into the hopper on top of the remaining mesquite.
The first observation was that the hickory pellets were small (more like pellets) kinda like rabbit poo. An hour or so later I noticed the temps climbed a bit. I'd say the low 200 setting (225? was running about 265 whereas before it was running 240ish. I noticed the auger was now feeding the rabbit pellets.
So my thought is that the smaller pellets feed more efficiently. The big pellets clog the auger screw a bit and so less material is actually delivered per time increment. With smaller pellets each turn of the auger delivers more fuel.
So there it is. This is a no-brainer if there is not open loop communication between the auger and the temp systems. If the auger speed is constantly adjusted via the temp feedback (on top of the control knob's setting) then this hypothesis looses some credibility.
For those noticing temperature fluctuations during cooking that aren't due to the weather or other obvious thing.. have you examined the pellets you're feeding? are they the same size as what you started with? are they the same manufacturer (pellet density differences could also account for this).
okay enough over-nerdifying bbq. what can I say, there's a launch on sunday and the brain is still in bbq mode!
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