Originally Posted by DaveOmak
At 5300', you have exceeded the limit for oxygen in the air... Try legs on the AMNPS and maybe a small fan..... or use the AMNTS... give Todd a call... He'll take care of you...
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- 1932 Shawnee Road, Eagan MN 55122-1032
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Thanks! I really do appreciate the suggestions and offers of help.
I'm not unhappy with the AMNPS. It's really the best thing ever for my MES-40. And 99% of the time, it's been working just dandy for me.
I set the unit on the metal bars that run across the smoker like this:
So that keeps it elevated two or three inches above the drip pan on the bottom.
I also run with the chip hopper completely removed and the sliding drawer open partway as shown. And, of course, the damper at the top of the smoker is always fully open. Also, I never use the water tray thing.
And almost always, I get complete burning of whatever amount of chips I use. So it has worked very well for me.
BUT. It's usually very dry around here. But lately, we've had more humidity here than normal. And it's actually rained a few times right when I was doing some smoking, or just beforehand. And that pushes the humidity way up, of course.
So with regard to how humidity affects the burning of the pellets, what I've observed has been that even starting with dried pellets, an hour or two into the burn, when it's very humid here, the pellets will go out. So it seems that the pellets absorb moisture from the incoming ambient air over time, and when their moisture level reaches a a certain threshold, the combination of moisture and lower air density at this elevation is just too much to allow them to continue to burn.
As an experiment last night, even though the nuts I was smoking were already done, and had gotten a really very pleasant amount of smoke (the pecan halves are fantastic!) I stuck my "magnetic fan" directly over the inlet hole and fired it up.
With it positioned directly over the inlet, it forces a lot of air through the smoker, so I adjusted the top vent damper to half open. There was still a nice breeze blowing up out of the smoker that you can feel easily with your hand. I wanted plenty of airflow, but not so much that it would prevent the heating element from being able to keep the smoker up to temperature. I watched it for a while and was satisfied that the heater was cycling off every now and then, telling me that the smoker's control, at least, thought that the temperature at its probe was where it wanted to be.
Interestingly, with the forced air flow, there is actually very little hysteresis in the temperature control. It'll cycle off when the temperature is at the setpoint, and cycle back on only a couple of degrees below the setpoint. So that gave me a glimpse into the operation of the controller that I normally don't get. Without the fan forced air flow, the unit cycles farther up and down due to the heat capacity of the heating element creating a lot of overshoot. But I digress! :)
With the fan forced operation running, with the vent at half open, I was getting a good plume of smoke out the top, and I figured, if anything, the pellets might burn way too fast and burn themselves out far faster than we'd really like. So I went back to work for a couple of hours, and when I came back, expected to find all of the pellets burned. But in fact, what happened was the row that was burning (which was about 7/8ths of the way down the first row) burned down around the corner and started back up the middle row, and got about 1/8th of the way into the middle row, and then went out.
So even with the forced air, it went out. But again, it was quite humid and cool out. Probably about 65°, and really muggy feeling (of course, muggy to someone in Wyoming is a relative thing since humidities are often in the single digits here)!
I think I had too much air flow, actually. For real smoking, it would've been far too much air through the smoker. But theoretically, I could throttle the top vent and achieve any air flow I want. And I may play with that. But for the purposes of getting the pellets to burn, massively excess airflow didn't help in this case. The humidity and air density here were just too much for it, I think.
One of the things that plays a HUGE part in wildland fire behavior is humidity. You wouldn't think it'd be a big deal, but it really is. When fighting a fire, people pray for the humidity to go up even just a little bit. And at night, the relative humidity usually does go up. And that's why fires are often said to "lay down" at night. The burning slows tremendously. In fact, this recent pulse of humidity that has caused me to have these two pellet burning failures also has allowed firefighters to finally gain the upper hand on several of the large forest fires burning around the state. So that's fantastic!
And I've had these failures at night, too, when the relative humidity has been highest.
So I think it's interesting to realize that humidity really has a large effect on how things will burn. In firefighting, they refer to different kinds of dead plant fuels based on their diameters. And of course, the smaller the diameter of the dead wood or grass, the faster it absorbs and releases moisture. And the small stuff is also the best "kindling". So humidity affects its moisture content rapidly, and that has a very quick effect.
The wood pellets are made of compressed sawdust sort of stuff. And that helps them burn, of course. But it also makes them very susceptible to absorbing or releasing moisture based on the ambient humidity. So I think that even though I started off with oven-dried pellets, the high humidity has been moistening them fairly quickly of late. And when they're moist, they just don't want to burn at this elevation because, as you've said, oxygen levels are right at the limit.
I'm curious as to why the tube-shaped smoke generator would work better. It seems like it'd be about the same. But maybe using sawdust rather than the pellets would help. But then, I've got a nice stockpile of pellets. Maybe I should grind some of them up into the dust and give that a try. I'll need another good high-humidity night, and maybe test the dust side by side with the pellets to see if it works better.
Another thing might be to set things up so that the pellet burner sits above or at least more directly in the air-stream coming off of the heating element so that that heat drives the moisture out of the pellets constantly. Maybe I've created a dead-zone in my smoker with the foil I have above the AMNPS as a drip shield. I've seen posts where people add some stovepipe inside of the smoker to direct the incoming air towards the smoke generator. I may have to play with that because it'd be easy to do and simple.
But really, for me, the main reason for even posting about this was because I'd seen this thread about humidity affecting things. And based on my experience of late, and then thinking about it with respect to wildland fire behavior, it all makes sense. So thought I'd chime in with my experiences.
Since the system I have now has worked so well for a number of years, I haven't been motivated to alter it. But if it's going to continue to be wet whenever I get in the mood for some smoking, then I'm gonna have to tinker some more! But then, I love tinkering. :)
I think the AMNPS is a dandy product. As I've said, it's made all the difference in the world to how my MES works. The MES was more or less useless as it came because the chips wouldn't burn unless the heating element was cycled on, and that, of course, is (and should be) determined by the heat demand of the system. The smoke generation needs to be independent of the heating system.
So don't take these posts as customer complaints. I'm just interested in all of this and found the humidity angle quite appropriate for what I've run into the last few times out.
As with anything, I will take this as a challenge because I figure the right modifications may make my pellets burn despite high humidity and elevation! There has to be a way!
Maybe we need a segment on the forums for "high altitude smoking".