HM keeps overshooting and then fire dies and needs to be relit at 225.


 

JasonL

TVWBB Member
How does the Akron have it's coal. Is it on a grate of some kind and the damper below, like a weber. Or do you have them on the bottom of the Akron. I would do a minion method of lighting the coals. You shouldn't have to push the coals to one side of the smoker.

Yea on a grate with the lower vent below that
 

RalphTrimble

TVWBB Diamond Member
I started up a dry run cook a bit ago on the Akorn so I can share some details and examples of the concepts I mentioned above. My HM config currently is as shown below:

HM_CONFIG.jpg


This is my dual purpose setup that can handle both low and slow and high heat cooks without tweaking the HM settings between the two. As you can see I have the duty split between the servo damper and fan at 50%, it is damper only up to 50%, the fan kicks in at 50% and ramps to its MAX value at 100%. For low and slow, during the cook the HM output stays below 50% and the fan never runs. For high heat cooks the HM output runs past 50% so the damper opens up fully and the fan stokes and controls the fire, the damper functions only to tamp down overshoot.

I start the fire differently depending on the target temp for the cook...

If I were doing high heat I would put a large load of lump coal in the burn pan and light 1 weber starter cube (or two if I was impatient) under the center of the pile. I would let the fire burn with the lid open until the white smoke from the weber cubes as subsided and quite a bit longer if I were shooting really high like for pizza, or close the lid sooner if I where shooting for steaks or roasting etc. Getting to know your grill and how much fire it takes to achieve various temps is important, I think it's a good idea to learn the grill with a few manual cooks before you add the HM to the mix, this makes things easier to suss out when you are setting up your HM rig.

I've found in general with the HM the more the blower has to work to achieve the target temp the more forgiving it is to things like PID settings, vent settings, fire size etc... and therefore high temps are easier to nail than low and slow, and low and slow is easier to nail with a small crack in the top vent and the fan blowing. The damper only low and slow cook would be the most difficult to nail but IMHO it is the best method from the cooking perspective, because cool air isn't being forced into the pit causing more fuel to burn and smoke to roll around the pit a while before it gets pushed out the cracked open top vent. With damper only convection control the top and bottom vents are opened more evenly and there is less air flow overall, so less drying of food, less fuel burned, and smoke moves more freely out of the pit making the smoke around your food fresher.

Here is a screen shot from the test run I just fired up:
HMGRAPH.jpg


For the above low and slow startup I put 1/2 a weber starter cube under a small pile of lump coal, just about enough to cover the bottom of the Akorn burn grate then pushed into a pile over the starter cube. I let it burn with the lid open until the white smoke from the starter cube was gone and I could see a small section of coals glowing at the bottom of the pile, then closed the lid with the top vent set so just the dimples were open. I set the vent tight like this because at this point the fan is blowing 100% and when the fan is blowing you want to keep the top vent open only a slight bit.

As you can see in the graph, while the HM is at 100% the temp rose rapidly, but as the temp approached the 250F setpoint these PID settings told the HM to back down the output which allowed the pit to settle nicely at 250F. When the temp settled at 250F the HM output was riding at roughly 50%, so the damper is sitting wide open and with the top vent just cracked to the dimples, the HM will eventually make the fan kick in to maintain the setpoint. I dont want this to happen because I want to use the damper only for this cook so I open the top vent to about 1 of 5 to allow convection air flow to get started. The first small bump in temp is right after I opened the top vent to 1, as you can see the pit held the setpoint nicely with the HM output just under 50%, this means I built the appropriate size fire to maintain the target temp with convection flow. I let it roll a while like that as an example, you can see the temp has a slight downward trend and the damper is nearly fully open (HM output near 50%), this shows the fire needs more air flow, but the top vent is close to where it needs to be at the 1 of 5 position. (which I already know from experience with this grill) For a real cook I would have opened the top vent to about 1.5 and put the food on the gill at the same time instead, after the lid mode timer expired the pit would have settled on the setpoint and the ballast of the cool food would helped keep the HM system stable.

Instead for this test cook I moved the top vent open to a 2 of 5 position just before you see the second bump in temp and the longer period of overshoot. This kinda shows the negative side of the convection flow control and PID settings that react sooner but in a less aggressive fashion. You can see even though the temp overshot about 10F the HM kept the output in the teens leaving the damper open about a third, which made the pit temp fall more slowly back down to the target, but it lands nicely right where you want to be with the damper opened about a third of the way and plenty of room to stoke or choke the fire.

On the other side of the coin, if I were using the blower to control the pit with the top vent only open a crack I could use faster and more aggressive PID settings which would close the damper right when the target temp is achieved. This would cause a more rapid temp bloom and higher overshoot temps that would fall quicker back to the target temp, at which point the fan would kick back in and land the pit on the target temp quicker. It is easier to control this kind of setup and it will generally hold the target temp a bit more accurately, say +/- 1F as opposed to +/- 3-5F with convection control, but the blower method will cause more air flow, more fuel consumption and leave smoke in the pit for a longer period of time.

So it comes down to priorities how you decide to run your pit, your experience with your grill and managing a pit may play a role in this decision. If you have solid technique and experience with the grill the damper only method might be good for you, if you just want easy control you are probably better off setting the blower and damper to run the full range with the top vent barely open.

Speaking of skills and technique, John brings up a good point about coal configuration re: minion method etc... This is something I did when I was less experienced with the HM on my Akorn, it did make things easier for me control by limiting the amount of coals that can be lit at once. I used what I call the "ring O fire" method, using a mesh ring I made in the middle and coals in a circle around the outside. This config will burn a really long time and the fire can never really get too big, another nice thing is you can place your wood chucks at strategic spots to control the smoke during the cook. Here is a pic of that configuration:
RingOfFire.jpg


Hope this info was usefull and not too boring to read....
 

JasonL

TVWBB Member
This was super helpful, I'm going to give these suggestions a shot once I have some free time to do another dry run. Appreciate how detailed instructions!!

I started up a dry run cook a bit ago on the Akorn so I can share some details and examples of the concepts I mentioned above. My HM config currently is as shown below:

HM_CONFIG.jpg


This is my dual purpose setup that can handle both low and slow and high heat cooks without tweaking the HM settings between the two. As you can see I have the duty split between the servo damper and fan at 50%, it is damper only up to 50%, the fan kicks in at 50% and ramps to its MAX value at 100%. For low and slow, during the cook the HM output stays below 50% and the fan never runs. For high heat cooks the HM output runs past 50% so the damper opens up fully and the fan stokes and controls the fire, the damper functions only to tamp down overshoot.

I start the fire differently depending on the target temp for the cook...

If I were doing high heat I would put a large load of lump coal in the burn pan and light 1 weber starter cube (or two if I was impatient) under the center of the pile. I would let the fire burn with the lid open until the white smoke from the weber cubes as subsided and quite a bit longer if I were shooting really high like for pizza, or close the lid sooner if I where shooting for steaks or roasting etc. Getting to know your grill and how much fire it takes to achieve various temps is important, I think it's a good idea to learn the grill with a few manual cooks before you add the HM to the mix, this makes things easier to suss out when you are setting up your HM rig.

I've found in general with the HM the more the blower has to work to achieve the target temp the more forgiving it is to things like PID settings, vent settings, fire size etc... and therefore high temps are easier to nail than low and slow, and low and slow is easier to nail with a small crack in the top vent and the fan blowing. The damper only low and slow cook would be the most difficult to nail but IMHO it is the best method from the cooking perspective, because cool air isn't being forced into the pit causing more fuel to burn and smoke to roll around the pit a while before it gets pushed out the cracked open top vent. With damper only convection control the top and bottom vents are opened more evenly and there is less air flow overall, so less drying of food, less fuel burned, and smoke moves more freely out of the pit making the smoke around your food fresher.

Here is a screen shot from the test run I just fired up:
HMGRAPH.jpg


For the above low and slow startup I put 1/2 a weber starter cube under a small pile of lump coal, just about enough to cover the bottom of the Akorn burn grate then pushed into a pile over the starter cube. I let it burn with the lid open until the white smoke from the starter cube was gone and I could see a small section of coals glowing at the bottom of the pile, then closed the lid with the top vent set so just the dimples were open. I set the vent tight like this because at this point the fan is blowing 100% and when the fan is blowing you want to keep the top vent open only a slight bit.

As you can see in the graph, while the HM is at 100% the temp rose rapidly, but as the temp approached the 250F setpoint these PID settings told the HM to back down the output which allowed the pit to settle nicely at 250F. When the temp settled at 250F the HM output was riding at roughly 50%, so the damper is sitting wide open and with the top vent just cracked to the dimples, the HM will eventually make the fan kick in to maintain the setpoint. I dont want this to happen because I want to use the damper only for this cook so I open the top vent to about 1 of 5 to allow convection air flow to get started. The first small bump in temp is right after I opened the top vent to 1, as you can see the pit held the setpoint nicely with the HM output just under 50%, this means I built the appropriate size fire to maintain the target temp with convection flow. I let it roll a while like that as an example, you can see the temp has a slight downward trend and the damper is nearly fully open (HM output near 50%), this shows the fire needs more air flow, but the top vent is close to where it needs to be at the 1 of 5 position. (which I already know from experience with this grill) For a real cook I would have opened the top vent to about 1.5 and put the food on the gill at the same time instead, after the lid mode timer expired the pit would have settled on the setpoint and the ballast of the cool food would helped keep the HM system stable.

Instead for this test cook I moved the top vent open to a 2 of 5 position just before you see the second bump in temp and the longer period of overshoot. This kinda shows the negative side of the convection flow control and PID settings that react sooner but in a less aggressive fashion. You can see even though the temp overshot about 10F the HM kept the output in the teens leaving the damper open about a third, which made the pit temp fall more slowly back down to the target, but it lands nicely right where you want to be with the damper opened about a third of the way and plenty of room to stoke or choke the fire.

On the other side of the coin, if I were using the blower to control the pit with the top vent only open a crack I could use faster and more aggressive PID settings which would close the damper right when the target temp is achieved. This would cause a more rapid temp bloom and higher overshoot temps that would fall quicker back to the target temp, at which point the fan would kick back in and land the pit on the target temp quicker. It is easier to control this kind of setup and it will generally hold the target temp a bit more accurately, say +/- 1F as opposed to +/- 3-5F with convection control, but the blower method will cause more air flow, more fuel consumption and leave smoke in the pit for a longer period of time.

So it comes down to priorities how you decide to run your pit, your experience with your grill and managing a pit may play a role in this decision. If you have solid technique and experience with the grill the damper only method might be good for you, if you just want easy control you are probably better off setting the blower and damper to run the full range with the top vent barely open.

Speaking of skills and technique, John brings up a good point about coal configuration re: minion method etc... This is something I did when I was less experienced with the HM on my Akorn, it did make things easier for me control by limiting the amount of coals that can be lit at once. I used what I call the "ring O fire" method, using a mesh ring I made in the middle and coals in a circle around the outside. This config will burn a really long time and the fire can never really get too big, another nice thing is you can place your wood chucks at strategic spots to control the smoke during the cook. Here is a pic of that configuration:
RingOfFire.jpg


Hope this info was usefull and not too boring to read....
 

JasonL

TVWBB Member
tried again with your settings but am not having much luck.

http://imgur.com/a/p6ne1

The thing I dont really understand is why is my fan % still so high even as it approaches the target temperature (even now, its over the target temp and still has the fan at > 0%). I went with a volcano (center clear open) and I put a cotton ball in the middle and put 1 piece of lump on top of it. i dont think the fire started too big because you can see how slowly the temperature is creeping up. This is with your settings that you posted above.

EDIT: this is with the top vent open a bit past the dimples. I was going to wait for it stabilize before I opened the top vent more but that hasnt happened yet.
 
Last edited:

RalphTrimble

TVWBB Diamond Member
What kind of pit do you have, and where is your pit probe located?
Your attached graph shows it taking about 45 mins heating up to 250F? Unless I read that wrong or you have some kind of monster pit that is way out of whack. The HM is reading the amount and rate of temp change and reacting to that, as you can see in my test cook the pit landed on its target temp in about 15 minutes, so the HM is responding differently to that rapid rate of change in my pit as opposed to the slow rate of change in yours.
I used alcohol soaked cotton balls for a short while, moved away from them because I didn't like the burning cotton in my grill after the alcohol had burned away. Hard for me to say at this point how much heat they are supplying to the fire compared to the weber starting cube I am using (or half a starter cube for a low and slow). Half a starter cube burns only a few minutes and then it is completely gone, leaving a few lit coals behind. A box of a couple dozen cubes is only a couple bucks, so you might give them a try... maybe the cotton balls burn cooler and longer?
 

JasonL

TVWBB Member
SDAl1XY.jpg


Akorn so same as you. Yea it took like 45min to get up to temp. The pit probe is grate level above the diffuser.

Edit: near the end I was playing with the top vent. When it was close to 225 I opened the vent a bit then it shot up. I closed it a bit but it dropped too much now so I opened up a little more

Edit: I do put the diffuser + grate and close the lid almost immediately after I put the cotton ball. Maybe I need to let it get the fire going a bit more before I close it up to allow it to get a bit hotter before I cut off the airflow by closing the lid.
 
Last edited:

JasonL

TVWBB Member
aZXpji0.png

Here's with the settings changed a bit and turning on the fan at min 5% (+ p is at like 3.1 instead of the 1.4 you had). A bit hard to see but the graph craziness around 10;:30pm was because my fire looked like it was dying since the fan was running but the temp kept dropping to like 190 degrees. I took a look at the fire and tried restarting it, but looks like there was still some lump already lit anyways. I let the fire stoke a bit with the lid open before I put back on the diffuser and lid. Top lid is cracked barely past the dimples.
 
Last edited:

JasonL

TVWBB Member
7YkiIXl.png

Was curious how it would respond to a different temp so upped it to 250. What should I take from this? It wasn't stable at 250 even though it did well at 225. Should I have opened the top vent a bit more whenever I want to up the temperature until it gets stable?
 

Andrew-Dollins

TVWBB Member
Jason this is probably one of the hardest grill to control. I have one and let's face it once you overshoot you might as well throw a bag of ice on the grill to cool it off. So the key to setting this one up is low proportial values like 1.0-3.0 high derivitaves of 4.0-8.0. You need a nice tight seal on the bottom ash catcher, and the side vent. I use a BBQ-gruru with a highly modified fan case I will post a link to it when I get to my big computer. It was derived from Mr. Trimbles excellent roto damper fan case design. The key here is no air leaks, a mouse farts on your coals and you will quickly overtemp. I keep the fan off until 5% - 10% and use the servo full open at 1%. Your servo will actually be enough to control the temps, once the grill stabilizes. You will see some time the fan kick on but I believe that occurs as you fire moves from piece of lump to piece of lump. One other important piece of advice the top damper is going to be your rough temp control ONLY open it to the moons, or a little past you will hear the fan speed up as you close it once the pitch goes up close it a little more. And most importantly NO FANS over 5.0 cfm unless you know what your doing, do not even let a 10 cfm run at full speed!!! You will blow out your coals out or over temp faster than a hog eating slop. Remember the acorn is in my opinion the hardest grill to control since it does not blead heat easily and you do not want to blast it with air when under temp. This grill does not need much fire to heat up and is super efficient. Get this running correctly and you can grill briskets without even thinking about it. You can load it with lump and grill up to 40 hours without even thinking about more lump.
 

Andy Snider

TVWBB Fan
Jason this is probably one of the hardest grill to control. I have one and let's face it once you overshoot you might as well throw a bag of ice on the grill to cool it off. So the key to setting this one up is low proportial values like 1.0-3.0 high derivitaves of 4.0-8.0. You need a nice tight seal on the bottom ash catcher, and the side vent. I use a BBQ-gruru with a highly modified fan case I will post a link to it when I get to my big computer. It was derived from Mr. Trimbles excellent roto damper fan case design. The key here is no air leaks, a mouse farts on your coals and you will quickly overtemp. I keep the fan off until 5% - 10% and use the servo full open at 1%. Your servo will actually be enough to control the temps, once the grill stabilizes. You will see some time the fan kick on but I believe that occurs as you fire moves from piece of lump to piece of lump. One other important piece of advice the top damper is going to be your rough temp control ONLY open it to the moons, or a little past you will hear the fan speed up as you close it once the pitch goes up close it a little more. And most importantly NO FANS over 5.0 cfm unless you know what your doing, do not even let a 10 cfm run at full speed!!! You will blow out your coals out or over temp faster than a hog eating slop. Remember the acorn is in my opinion the hardest grill to control since it does not blead heat easily and you do not want to blast it with air when under temp. This grill does not need much fire to heat up and is super efficient. Get this running correctly and you can grill briskets without even thinking about it. You can load it with lump and grill up to 40 hours without even thinking about more lump.

I have a big steel keg, which might be even more insulated, and this is solid advice for these types of grills. You need to seal up the bottom vent - I use AL duct tape. DO NOT OVERSHOOT. REPEAT, DO NOT OVERSHOOT.
 

JasonL

TVWBB Member
thanks for the suggestion guys. I've done a few test burns and I've gotten it a bit more dialed in but still working on getting my settings correct. I've gone with starting a fire with a cotton ball, letting it get going a bit before i close the lid, and then keeping the top damper somewhere between 1/2 to fully open. Once it gets within 50 degrees or whatever my desired temperature is, I close to damper to somewhere around the dimples on the CGK depending on the temp. Once it gets to the target temperature, I start playing around with the top damper until the temperature is able to stabilize with the fan going between 10-30%. This has worked decently for me (did chicken wings a couple nights ago, starting at 250, followed by 375, and 2 rib plate racks last weekend at 285).

I do still need to work on my lump charcoal placement though, I dont think I've figured out how to do that too well just yet. Alot of people have suggested just dumping large amounts of lump into the bottom up to the difuser tabs, but I've found that to be difficult for the HM to control the temperatures (I think because the airflow is pretty poor from bottom through all the lump to where the fire actually is). I've also tried leaving a small 2-3" hole in the middle, though I've also had the fire die on me when I was smoking the rib plate racks 1/2 way through.
 

Dan Francis

TVWBB Fan
Wow, open lid, close lid, adjust damper, place charcoal. Really? Why bother with a controller if you are doing all that. You are way over thinking this or something. 4 pages of problems that nobody else has, should be dump in charcoal. light fire, turn on heatermeter. Been doing that over two years.
 

JasonL

TVWBB Member
Not sure what your point is? I obviously am having the issues and some people are being more than helpful (hint, you're not one of them) in giving me suggestions on how to solve.


Wow, open lid, close lid, adjust damper, place charcoal. Really? Why bother with a controller if you are doing all that. You are way over thinking this or something. 4 pages of problems that nobody else has, should be dump in charcoal. light fire, turn on heatermeter. Been doing that over two years.
 

Andrew-Dollins

TVWBB Member
Have you tested your probe in boiling water? Also google the temp water boils at in your location. I only had a flame out once and that was because my cable was not connected to the fan. I never had a problem with the hm, ever! Yes it took a bit to tune and control overshoot. One other thing to try is set your temp to 250, and cook there it is not a rocket 250 is going to still make great food.
 

JasonL

TVWBB Member
Yea I actually did last week because I was confused why my rib plates were reporting so high so quickly. 1 was 214 and 1 was at 215 so off a couple degrees but generally pretty good. On the last flameout, it liked it overshot a bit and then turned off the fan waiting for the temperature to come down. It started blowing the fan once it got close to the temp but the temperature never rose. The fire must have died before and the blowing just cooled it down even quicker.

Have you tested your probe in boiling water? Also google the temp water boils at in your location. I only had a flame out once and that was because my cable was not connected to the fan. I never had a problem with the hm, ever! Yes it took a bit to tune and control overshoot. One other thing to try is set your temp to 250, and cook there it is not a rocket 250 is going to still make great food.
 

JasonL

TVWBB Member
dx08Qdw.jpg
. How should I read into this? Doing a brisket and started out pretty well but slowly temps have started fluxating with a much wider range...
 

WBegg

TVWBB Pro
Might want to think about a fan/damper that has a little more 1:1 reaction to PIDs such as the MicroDamper or the Adapt-a-Damper. or any number of Tom Koles designs. It really does make a big difference when comparing damper profiles but not so much in design, but in ease of adjusting PID settings.

Too, it's how you lite the fire. Lite low, and let the HM do the rest. That's what it's there for.
 

JasonL

TVWBB Member
Interesting. Didn't think too much re: the different designs on the dampers but will keep that into consideration. MAinly though it seemed pretty dialed in for a few hours but progressively just got worse and worse. Wasn't sure how to read into thay
 

 

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