Stoker Overshoot Probelm....could StokerLog manual fan control help?


 
K

KeithG

TVWBB Fan
First, let me start by saying that I only have 5 cooks under my belt using the Stoker and StokerLog. And I don't do comps....just personal use at home. But on a couple of cooks, I have had overshoot problems....both from coming up to the desired temp and also getting the temp down to the desired temp. Basically I am getting very big overshoots when the fan runs a long time getting the temp up, then shuts off once it reaches the setpoint. Big overshoot, then big undershoot since the fan doesn't come on until it goes below setpoint.

I have had very good success controlling the overshoot on the last cook by manually controlling the temp setpoints to gradually ease the temp up (or down) to the desired temp. For example, yesterday I did 2 chickens and wanted to achieve 350*. My initial temp was 400 and first set the pit temp to 385, let the fan come on a couple of times to stabilize the falling temp, then lowered the pit temp to 375. Let the fan cycle a couple of times, then lowered to 365, then to 350. This worked great. I have also done this when raising my temp since my temps usually start out around 200 when the food goes in and then I ramp up to 210, then 220, then 230 and settling in around 250. Going up I stop the fan from running for a couple of mintues before bumping up the temp.

Am I missing something in how the Stoker works to avoid these big overshoots? On one overnight cook where I just let the Stoker do its thing, there were a series of about 6 overshoots where the temp would overshoot by 20* and then undershoot by 20* for about 4 cycles, then on the last couple they got smaller until it finally settled into its normal 3-5* variance.

One thing that I was thinking to help was if there was a way to manually toggle the fan operation (turn on or turn off), so that you could manually control the air flow without keeping on changing the temp setpoint. What this will allow you to do is interrupt the big transient to feed some air (if temp is coming down too fast) or stop the fan (if temp is going to rise too fast). Basically being able to click a fan override button to cycle on or off.

BTW, these overshoot problems are using a 5cfm fan and my WSM is pretty well sealed so no extra air is causing this.

Anyone else seeing this? I know it is better to try to get my temp about right once it is assembled but with all the factors (like the wife not having the chickens ready in time) then the temps can easily get about 50* off and that is when the overshoots happen if I let the Stoker do its thing.

Thanks for any help and sorry for the long winded post.
Kg
 
I don't own a Stoker but how is your top vent set on the WSM? With my CyberQ I have it only open 1/3 of the way.

I left it wide open one day and over shot the temp by 25 degrees but the fire was self drafting.
 
Above 300 vent wide open.250-275 went1/4 to 3/4 depending on weather. 200 vent almost closed or closed depending on air leakage form WSM.One other thing. with cooks above 300 no water in the pan and I wouldn't use a heat sink like a clay saucer.
 
Above 300 vent wide open.250-275 went1/4 to 3/4 depending on weather. 200 vent almost closed or closed depending on air leakage form WSM.One other thing. with cooks above 300 no water in the pan and I wouldn't use a heat sink like a clay saucer.
Click to expand...

The vent is open for 350* cooks. For my 235-250* cooks, my vent is about 1/3-1/2. I don't use water and I use a clay saucer. But the saucer is not causing the overshoot and I have no problem getting the temp up with the saucer in. So the saucer is not the problem....the problem is the over and undershoot, which would actually be worse without the saucer.

Thanks
Kg
 
I think stoker has a hard time adapting to the million different conditions it sees with all the different smokers and fire conditions.

I too have seen destructive overshoots where the fan will stop too long causing the fire to almost go off.

I really like your trick to avoid it by not giving too high a target for stoker to try to reach in one step. I will add a mode in the future to ramp up the temp in stokerlog as you are doing.

For now, you can automate it just the same using timed cooking. Simply set two separate targets separated by X minutes.
 
Thanks Amir. Yes I agree that I think the fire is going out too much when the fan is not running for such a long period during an overshoot. Then the fan has to run a lot because it does not come on until below the setpoint and the undershoot is steep, taking a lot of air to relight the coals.

I will take a closer look at the time cook feature. I appreciate the help and consideration for a ramp up mode. I really think this will help so much because if I ramp up (or down) to the desired temp in steps, the Stoker is then rock steady for as long as you have charcoal.

Thanks again.
Kg
 
As we continue to do things like insulate our smokers/pits, add heat holding mass (fire bricks, clay saucers, heavy plate steel), or when we raise/lower pit temps where overshoot/ undershoot can occur, the need becomes greater to have the fan "Bellow" to keep the fire alive as the temps settled down. For example this "Keep Alive" feature would cycle the fan say on 15 seconds off 85 seconds with both times changable by the user. This would be a background subroutine that restarts after every on cycle of the fan.

(Pellet grills cycle the auger feed system as the ”pilot light”. On the Traeger Pellet Grill the auger run time is set to 15 seconds, the off time is changeable by the user with a low value of 55 seconds. During temp ramp up the temp controller uses a step cycle to ramp up to temps.)
 
That's such a great idea, Amir!

Thanks.

Originally posted by Amir:
I think stoker has a hard time adapting to the million different conditions it sees with all the different smokers and fire conditions.

I too have seen destructive overshoots where the fan will stop too long causing the fire to almost go off.

I really like your trick to avoid it by not giving too high a target for stoker to try to reach in one step. I will add a mode in the future to ramp up the temp in stokerlog as you are doing.

For now, you can automate it just the same using timed cooking. Simply set two separate targets separated by X minutes.
Click to expand...
 
I'm currently battling this same problem - wild temp swings on my WSM - and find it quite aggravating. I thought that it might be because the fan (5 cfm) wasn't big enough to stoke the fire properly during the initial short duration fan pulses.

I tried a 10 cfm fan figuring that it would deliver more air to the fire on these short pulses and would maintain temp. I found that a 10 cfm fan on the small WSM actually provides so much air that it drives the temp down each time it turns on. Turning the fan off manually, I would get a huge temp spike as the fire heated all of this "fresh air."

Interesting part is that on my Klose the Stoker maintains a flat temp line - no temp spikes at all - and the short duration fan pulses are spread out. FWIW, there are no air leaks on that pit and the fire always stays lit. The fire on my WSM frequently goes out - part of what is causing the temp oscillations.
 
Sorry, but I don't have permissions that allow me to post a graph.

The top vent was open about 1/4, all others are closed. Temp was set to 245.

During the test today, I set the temp to 230. The Stoker brought it up to temp fine, temp settled, I opened lid to simulate a mopping event, closed the lid and temp settled in again. I brought the temp up to 245, temp settled, I opened the lid again, the Stoker brought the temp back. Within 30 minutes, temps started varying up and down. These oscillations grew until they were 50 degrees peak to valley. It didn't matter what I did to the vent or program (manual intervention to temp settings), I could not get the oscillations to stop. If I manually set the temp to the peak of the temp swing, the Stoker couldn't maintain stability. Once the fan pulsed, the temp would drop, causing the fan to go on even longer on the next pulse, driving temps lower until the fire finally caught up, only to overshoot up to 280 degrees.
 
I'm only guessing....

The Stokers algorithm read the moping events as massive temp drops and tried to predict future temp drops, hence the overshoot then the oscillations.

Try this: On StokerLog disable lid open detection. Before opening the lid on the WSM, pause the blower using the Stoker. It will come back on after 5 minutes. Let us know what happens.
 
Thanks for the response.

I had the lid open box checked on the first mopping event. Stoker Log did not detect lid open until 15 minutes later. At that point, Stoker Log (rel. 5) lost connection. Upon restart of Stoker Log, it stabilized the temp. I unchecked lid open and brought the pit to 245 (from 230), so the second mopping event did not use the lid open feature.

Incidentally, I've had the problem with my WSM regardless of version of Stoker Log and firmware. I've been battling this problem for awhile and have changed both multiple times. Again, I do not see this on my Klose with the same set up.

I'll try more testing today.
 
I tried the trick earlier in this thread of setting my target lower when I first fired the stoker and then bumped it to where I wanted it to be. That worked a lot better than one step process!

So at some point I will add this logic to stokerlog. For now, stokerlog does NOT control how stoker manages the temp. So any issues are unrelated to stoker other than using the obsolete lidopen feature (use the version 6 of stoker and simply power cycle the stoker when you open the lid)
 
I understand. Stokerlog's only involvement is to be report what I would not otherwise be able to see.

I know that the problem is with the WSM. It is a combination of how the Stoker reacts to/maintains the fire, the top vent position and the amount of air leakage. I'm just trying to figure out how to set it to get rid of/minimize the fluctuations.

The stoker has no problem bringing the temp up and settling. Today, I did not open the lid at all. The temp came up and settled for about 30 to 45 minutes. Then, the temp slowly evolved into huge oscillations. Looking at the fan pulses, I see them start out as uniformly spaced with short durations. As time progresses, the pulses begin to bunch up with longer and longer periods between groups. The fan pulse duration starts to extend, which is when the temp oscillations begin.

I'm still playing with the top vent to see if I can get the swings to settle.
 
Wonderful, the day a Stoker shows up on my doorstep I log in and find that most people have serious problems with it on a WSM! I swear I have been reading this forum for over a year and besides some internet connectivity issues the thing was portrayed as bullet-proof. Oh well, how disappointing. Dan
 
Dan, there is no widespread problem on WSM. There are many happy users. Give it a try and don't be disappointed
icon_smile.gif
. We will be here to help!
 
+1 Most people I know are happy with their Stoker, including me.

It works flawlessly on my Klose. I'm simply having problems with it on my WSM, which means that there is nothing wrong with the Stoker, just my WSM. I suspect it to be airleaks.

I bought my WSM used and did too good of a job cleaning it when I got it. It looked like new but had no cooking residue to seal the various joints, some of which leak slightly.

I'll kick the WSM to the curb before I get rid of my Stoker.
 
I did not mean to imply anything negative about the Stoker or the WSM which I like very much. Just that this is the first mention that the combo of the two may not be the best. I am not buying a different smoker. My WSM is rock solid on holding temps with just the vents, I am just a bit of a gadget-head and was looking forward to managing pit temp and monitoring food temps all in one unit. However, Harry Soo is sold on the Stoker/WSM combo so I am hoping for the best with my WSM. Dan
 
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