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Thread: Post your HeaterMeter graphs

  1. #21
    TVWBB Honor Circle Bryan Mayland's Avatar
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    I think that has a lot to do with it, the fact that I have a BGE. I've also had like 4 years to dial in my PID values. The new PID info dialog (press P on the home page when logged in) helped a lot this time.

  2. #22
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    John, Nice to see you built the "air burner" and it is working out for you. It's really a very simple concept, but getting the air distributed more evenly under the coals is a big help in getting your coals to burn eventy.

    If I had built your unit I would have gone a bit bigger (if it will fit) and added a cross member in the middle. I would have also gone with the holes on the top instead of bottom. I have the holes on top on mine and have never had any problem with ash or anything, the air will push it out if any gets in there. The thing I like about the holes on top is the little jets of air blow directly on the coals and this stokes them better, specially during the initial fire up. I can start my fire with just a little piece of paper set ablaze with a lighter, the jets of air assure the fire wont go out even if it just starts out smoldering.....

    At any rate, it's awesome to see you build one of these, makes me feel like I contributed something to the community..... Happy Smoking!

  3. #23
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    Bryan, that graph looks awesome! Did I read it right, that you were running both the fan and servo and let the fan blow all the time? I guess your BGE must need a lot more air flow than my Fauxmado if that is the case.... At any rate, that looks like about as perfect as it gets. I know when I got my first graph that looked like that I was really "stoked"....

    Thanks for the tip about hitting P to get the PID info dialog display, I had done that by accident one time and wondered what the hell I had done! LOL I still find PID tuning to be very mysterious and haven't quite got a feel for it yet. Could you possibly give an estimate of the operating range for each parameter? I have a hard time deciding how much I should alter the numbers, and it takes so much time to let the pit react and figure out what your change has done... My cheapo smoker works like magic with the default PID settings, but this Fauxmado is really tricky, I would really like to learn to dial in the PID settings for this thing cause I know it needs a lot of tweaking....

  4. #24
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Yeah both at the same time. My fan has gotten somewhat gunky inside over the years I guess so my min fan speed is 25% to make sure it turns on. With your fan installed on the servo but off you can maintain 250F? I was worried about it needing >80% servo just to keep the temperature up. My fan is duct taped on for now though so maybe that causes extra restriction or something.

    As for the PID value ranges, you definitely don't want anything close to 100 as that would mean the output would be pretty much on/off all the time.

    P - Here's the easiest place to start. Think about what the acceptable temperature range is for operation. At what point of the pit temperature dropping do you want BWOOP BWOOP giver 'er all she's got, Captain! Divide 100 by that number. That's going to set the lower limit on the P value. For a setpoint 225F with a lower temperature limit of 215, P = 100/(225-215) = 10. That's your ballpark. The faster your grill can change temperatures by changing the output value, the smaller this number should be. In my graph the P was 3 because the blower can really turn things around quickly in there. With just the servo, if I opened it fully it would still take a long time before anything actually happened. Fast response, low P. Slow response, high P.

    I - This is where the PID status window on the home screen can really help. Subtract your setpoint from the current temperature, multiply by that by your I constant and that is added to the I value on the pid status window every second. If you have a I of 1 and the temperature is off by 5 degrees, it will add 5% output every second. Because this can compound so fast, you want a pretty small number. The value again depends on the response time of your grill, faster response, lower I (I think, not 100% sure on this one). The easiest thing to do is watch the I value i the PID status as the temperature swings back and forth across the setpoint. It shouldn't have wild swings from like -25% to 25%. The I term's job is to figure out exactly how much output it takes to maintain your setpoint. The value should roughly be the same as the yellow "average blower speed" pip on the blower speed bar on the home screen. Your P value needs to be set at least close before you can tune this, and the value I think should be 0.1 or less always.

    D - Again the PID status will help here. Your D constant is multiplied by the value dT shows on the status window. dT is the change in temperature over the last minute or so. You want to set your D high enough that you can see the output reversing as your temperature is changing. If you're at the bottom of a temperature swing and the temperature is starting to rise, you should see dT getting larger and the D status subtracting % from the output trying to prevent overshoot. If you set it too high you'll see the output stop before it gets to the setpoint, or the fan turn too early and prevent the grill from cooling to the setpoint. The way to logically think of a good value for this is to ask "If I'm at 223F, setpoint 225F, ad the temperature has come up 1 degree in the past minute, how much do I want to throttle back the output to prevent overshoot?". Like the I constant, this number is proportional to the P constant. Probably best to keep this under 20 unless you're having serious overshoot problems, and that's probably created by the P or I constants being too high.

  5. #25
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    Quote Originally Posted by RalphTrimble View Post
    John, Nice to see you built the "air burner" and it is working out for you. It's really a very simple concept, but getting the air distributed more evenly under the coals is a big help in getting your coals to burn eventy.

    If I had built your unit I would have gone a bit bigger (if it will fit) and added a cross member in the middle. I would have also gone with the holes on the top instead of bottom. I have the holes on top on mine and have never had any problem with ash or anything, the air will push it out if any gets in there. The thing I like about the holes on top is the little jets of air blow directly on the coals and this stokes them better, specially during the initial fire up. I can start my fire with just a little piece of paper set ablaze with a lighter, the jets of air assure the fire wont go out even if it just starts out smoldering.....

    At any rate, it's awesome to see you build one of these, makes me feel like I contributed something to the community..... Happy Smoking!
    Ralph, thanks! I can always flip it over!


    22.5" WSM, 22.5" OTG

  6. #26
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    Thanks a bunch for taking the time to post that Bryan, I think I have a much better idea how to go about PID tuning now. I'm sure I will read it a dozen times over before it has all sunk into my (semi) thick skull...

    So far I've not been altering the PID values in much smaller amounts than your post suggests may be appropriate, and haven't had the PID display onscreen to help me figure this out. I was gonna take a day off from the Fauxmado but I just got another blower I want to try out (15CFM) and want to experiment with this new information at hand, so I think I'll go and pick up a chicken or something that doesn't need to cook forever (cause I got a late start here today) and give her a go...

    I did pizza's the last couple days with a new 25CFM fan, it did a lot better than the stock blower getting up to pizza oven temperatures, but at this point the 3/4" copper tube is limiting the flow a bit much so the fan whistles like crazy and still isn't quite delivering the air I need. I'm hoping this 15CFM fan is a bit quieter and plan on adding a second 3/4" tube to my grill adapter to double the air delivery volume for high heat pizza cooks.

    On my Fauxmado grill with an undampered 3/4" input tube attached to the stock HM fan the pit will overshoot set points below 300 degrees reliably (LOL), it tends to want to settle in the upper 300's, so I have to damper down the input to keep the temps in check. The volume of the 3/4" copper is roughly equal to the opening of the stock HM fan, I have to reduce that down quite a bit to hold temps in the low 200's. That is why I was surprised you weren't getting enough draft through the fan on your BGE. Not sure if it's because your fan is gunked up and restricting flow, or my FauxMado is leaking somewhere and stoking a bit on it's own... prob my grill leaking... I haven't inspected it in a while and have done a lot of super hot pizza cooks, since its pretty new still it may have opened up somewhere from all that heat, I'll have to give it a once over (and cleaning) and make sure things are still nice and tight...

    Thanks again for the very helpful info above, and all your work on the Heater Meter....

  7. #27
    TVWBB Guru Steve_M's Avatar
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    Bryan,

    What BPID settings did you find worked best on your BGE when you were running with just the fan? (ie: no servo in the mix at all)

    I'm looking for a baseline BPID to use with my kamado joe, which is about the same size as the large BGE.

  8. #28
    TVWBB Honor Circle Bryan Mayland's Avatar
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    The HeaterMeter defaults (BPID): 4, 3, 0.005, 5.

  9. #29
    TVWBB Guru Steve_M's Avatar
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    Not a great start to the first non test use of the HM on the Kamado Joe.

    Used 1 weber lighter cube, placed on the indirect plate, closed the lid and let the HM go to town.

    BPID are defaults ( 4, 3, 0.005, 5 )
    Fan is set to defaults ( Min 10, Max 100 )



    I've got the top daisy wheel just open a crack, just enough to ensure that smoke doesn't get trapped inside.

    I'm limiting the natural convection via the fan with some tape, but it's only marginally helping.

    I can see myself being a good candidate for the servo driven damper.


  10. #30
    TVWBB Guru Steve_M's Avatar
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    It took about 45 minutes for the overshoot in temperature to come back down to 225. The HM has been holding a pretty steady 225 for about 3 hours now. I opted to let this be a dry run rather instead of an actual cook. Pretty pleased with the way it's holding temps and I'll let it chug away overnight.


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