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Pit-Boss 820D: Temperature Controller

Discussion in 'Pellet Smokers' started by banjo, Jun 6, 2018.

  1. banjo

    banjo Fire Starter

    NOTE: THIS THREAD HAS BEEN REPLACED BY THIS THREAD, WHICH HAS ALL 8 P SETTINGS CHARTED: https://www.smokingmeatforums.com/threads/temp-time-charts-p0-p7-for-my-pit-boss-820d.276325/

    NOTE: There is a temperature chart at bottom.

    I've taken a break from my other items I had posted last month, in order to take an in-depth look at the Pit-Boss 820D Temperature Controller. I intend to finish up those posts (regarding PID controllers) soon.

    A month or so back, a friend and I each purchased this model smoker. We were both disappointed in the temperature controller that came with the unit.

    I wanted to get a feel for what was going on, so I wanted to instrument the smoker with four (4) thermocouples, and two (2) relays.

    The thermocouples (type K, using Max31855 thermocouple amplifiers) would monitor temperatures at the following locations:
    • Combustion Chamber
    • Location in center of grill where meat usually is place first; as more meat is added, it typically is added left and right of the center.
    • The current location where the Pit-Boss 820D has their RTD temperature sensor (left front of smoke chamber)
    • Outside air temperature
    The two (2) 120vac relays were used to monitor (one each):
    • Auger motor
    • Fan motor
    Using a Raspberry Pi 3 (RPi), I wrote a C++ program to monitor these different devices (six total), at a 1-second interval, and to store that on the RPi. I streamed this across the network so that I could monitor all six values while performing the tests. The total tests took around six (6) hours, so a lot of data at 1 second for 6 devices.

    The test consisted of multiple segments, with each segment being associated with a single P setting (P0 - P7) or setpoint temperature (200, 225, 250, 300, 350) setting.Each segment had a time interval of at least 15 minutes, and some went to 40 minutes (I was sometime occupied and didn't get to switch the setting at the same times).

    I used Pit-Boss Pro Blend pellets for the test.

    I ran into a problem during the test of setting P7. While doing the setpoint temperature test for P7, the fire went out. Monitoring the augur state (on/off) and combustion chamber temperatures (which was falling), it was apparent that the fire had gone out, but more pellets were being feed to the combustion chamber. I let it go on for a while to see if it would re-light itself, but it did not. I set the smoker control unit to 'Off', then unplugged it to stop the feed, then removed the diffuser (the newer type, that is a curved plate the full length of the smoke chamber), and noted the combustion chamber was full of pellets, and they had just started falling into the floor area of the smoker. I dug all of the built-up pellets out, and restarted the smoker at P7. This ran away for a while with a high temperature. This will show up on the details for test P7.

    The test data is too unwieldy for a single post, as is the inclusion of the full data. Therefore, I have produced a chart picture of type png, which is readily viewable on most browsers.

    Below is the chart for the test of P0. The P0 setting does not use any temperature setpoints; it just sets the ratio of auger on/off. With higher P values, the off duration becomes longer, so higher P values will result in lower low-end temperatures and bigger temperature swings. The P0 setting has the highest ratio of on-to-off values, and so has the lowest temperature swings.

    I intend to list here each test as I get the unwieldy data into a single test, then produce the chart.
    Last edited: Jun 8, 2018
  2. G-Rod

    G-Rod Fire Starter

    Looks like some great info/data here. Is there any chance you can reupload the chart so it is bigger. I'm having a time reading the small print. Appreciate you sharing this research!
  3. banjo

    banjo Fire Starter

    G-Rod, I'll have a look at the LibreOffice Calc program to see if that's possible; it filled my screen when I did it. It will be tomorrow before I can do that.

    In the meantime, try doing Ctrl + on your computer several times, until you get it large enough to read. Another trick I sometimes do is to right click on a photo, then select 'open in new tab', then enlarge that tab as big as I need.
    G-Rod likes this.
  4. banjo

    banjo Fire Starter

    G-Rod, it appears the forum scales the pictures so it will fit on the page, so that's the best I can give you, so you'll have to 'enlarge' it with the suggestions above.