Blaze King and Raspberry Pi

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b_collins

New Member
Dec 28, 2021
3
Cleveland, Ohio
I'm the new kid on the block and this is my first post. We purchased a Blaze King Chinook 20.2 late in the summer. We use it to heat a bathroom and a couple of bedrooms. Overall, we are very happy with the stove. We get great burn times. My only complaint has been that I have to fiddle with the fan once in a while particularly if the outside temperature changes drastically during the night. And I find that if I turn up the fan, I can pull enough heat out of the stove that I have to adjust the thermostat to keep the stove in the active range.

As a guy that is profoundly lazy, I put together a Raspberry Pi with a Max31856 thermocouple board, a K type thermocouple, a MCP9808 for ambiant temp, and a PCA9685 servo controller, 2 RC servos along with some software to make a Blaze King stove controller. I am using a 7" touch screen for a human interface.

I discovered early on that the flue temperatures fluctuate wildly as the Blaze King adjusts the airflow to maintain a constant or nearly constant burn rate. Instead, I sample the stove temp every 5 minutes to compute the rate that the stove temp is changing. If the stove temperature is decaying to the point where the combuster is in danger of falling out of the active zone, the thermostat is turned up slightly. Currently, the thermostat is only ajusted as needed but never more than once in a 15 minute period. Many times, the thermostat requires no adjustment for hours. The room temperature is maintained at the target temperature by modulating the fan speed. Only if the room temperature starts to decay relative to the target temperature and the fan speed is already at 100 percent, does the system intentionally turn up the thermostat.

I have some questions.

1. Has anyone else automated their Blaze King?
2. Are their any issues with running the stove near the bottom of the active zone during fall and spring?
3. Am I correct in assuming that it's more efficent to run a lower thermostat setting with a high fan speed than a low fan speed with a higher thermostat setting to maintain room temperature?
4. Does anyone know if all Blaze Kings have similar characteristics with respect to control operation. Our Chinook becomes very sensitive to changes in the thermostat as the thermostat is turned down. Is that true of other models?
5. Does anyone know if what the expected latency between thermostat adjustment and the reaction of the stove to the change?

Thanks,
Bruce

screen.png
 
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NorMi

Member
Nov 18, 2021
111
Northern LP, MI
Sorry I don't have any info on the BlazeKing questions, but I wanted to chime in and say nice job on the controller! Did you use VScode to write your controller and interface? I never used it if that's the case, but it looks cool whatever you used! Also, point 5 the question about latency looks like it got cut off on your list of questions.
 

b_collins

New Member
Dec 28, 2021
3
Cleveland, Ohio
Thanks for letting me know the last question got cut off.

The software is not done by long shot. I have a number of issues to address but I am getting there. As for the software, the back end is being written in python. I am using PyQT to manage the graphics. The physical graphics layout is done using Qt Designer. It's a pain to code but the screen can be re-arranged with Qt Designer in seconds without every having to change the underlying logic.
 

BKVP

Minister of Fire
I'm the new kid on the block and this is my first post. We purchased a Blaze King Chinook 20.2 late in the summer. We use it to heat a bathroom and a couple of bedrooms. Overall, we are very happy with the stove. We get great burn times. My only complaint has been that I have to fiddle with the fan once in a while particularly if the outside temperature changes drastically during the night. And I find that if I turn up the fan, I can pull enough heat out of the stove that I have to adjust the thermostat to keep the stove in the active range.

As a guy that is profoundly lazy, I put together a Raspberry Pi with a Max31856 thermocouple board, a K type thermocouple, a MCP9808 for ambiant temp, and a PCA9685 servo controller, 2 RC servos along with some software to make a Blaze King stove controller. I am using a 7" touch screen for a human interface.

I discovered early on that the flue temperatures fluctuate wildly as the Blaze King adjusts the airflow to maintain a constant or nearly constant burn rate. Instead, I sample the stove temp every 5 minutes to compute the rate that the stove temp is changing. If the stove temperature is decaying to the point where the combuster is in danger of falling out of the active zone, the thermostat is turned up slightly. Currently, the thermostat is only ajusted as needed but never more than once in a 15 minute period. Many times, the thermostat requires no adjustment for hours. The room temperature is maintained at the target temperature by modulating the fan speed. Only if the room temperature starts to decay relative to the target temperature and the fan speed is already at 100 percent, does the system intentionally turn up the thermostat.

I have some questions.

1. Has anyone else automated their Blaze King?
2. Are their any issues with running the stove near the bottom of the active zone during fall and spring?
3. Am I correct in assuming that it's more efficent to run a lower thermostat setting with a high fan speed than a low fan speed with a higher thermostat setting to maintain room temperature?
4. Does anyone know if all Blaze Kings have similar characteristics with respect to control operation. Our Chinook becomes very sensitive to changes in the thermostat as the thermostat is turned down. Is that true of other models?
5. Does anyone know if what the expected latency between thermostat adjustment and the reaction of the stove to the change?

Thanks,
Bruce

View attachment 289315
BKVP here,

When you turn the fans on, the air movement can induce a false (lower) reading on the cat thermometer. The more air, the more influence it has on the spring located under the gauge. I believe the manual makes reference to this in at least one location.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
#3: yes, correct.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,573
SE North Carolina
are you controlling blower speed and BK thermostat? are you measuring cat temp? If it were me I be using k type cat probe. I guess I would want to run a fixed blower speed for the burn as loud as I could without being intrusive, and adjust BK thermometer based on room temp with hi and low limits programmed on the cat temp.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
You day you use the stove to heat bedrooms and a bathroom.
Where is the stove located? In the US it is illegal to have a stove in a bedroom.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,712
Grande Prairie, Alberta, Canada
Why not pull the cat probe and add a K-type thermocouple for temp measurement there? Add another input to the Pi to read this probe and you have a guaranteed method to keep the cat from stalling and over firing. Still keep the logic as is for temp control, just add an if or elseif loop for a max min cat value.
 
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b_collins

New Member
Dec 28, 2021
3
Cleveland, Ohio
Thanks for all the replies. To answer some questions:
are you controlling blower speed and BK thermostat? are you measuring cat temp? If it were me I be using k type cat probe. I guess I would want to run a fixed blower speed for the burn as loud as I could without being intrusive, and adjust BK thermometer based on room temp with hi and low limits programmed on the cat temp.

The software changes both the thermostat and the fan speed. Currently, the software monitors the cat temp with a K type probe. The software will set the thermostat to maintain a temperature between 525 and 575 degrees. Anywhere in that range is acceptable. Once that temperature is reached, then the fan speed is modulated to maintain the room temperature at the target temperature. If the fan speed is 100 percent and the room temp starts to decay, then the only recourse is to turn up the thermostat. The software will turn up the thermostat slightly to increase the temp bracket by 25 degrees. So the new target for the cat probe is 550 to 600 degrees. In a nutshell the strategy is to maintain the room temp with the fan alone but when that the fan alone is unable to maintain the room temp, then the thermostat is turned up slightly. The fan speed is the primary tool to control the room temp, only when the fan is not sufficient to keep the room warm is the thermostat turned up.

On a related note. I took your suggestion. I do find the fan is intrusive at high speeds, particularly when I am trying to watch TV. So I added a TV mode check box. This limits the fan speed to a lower maximum level. At some point, I will also add a sleep timer that will allow the fan speed to resume to it's max setting.

Now with respect to this quote:
Where is the stove located? In the US it is illegal to have a stove in a bedroom.

I checked with the city, the state, my BK dealer and even my insurance carrier, none of them know anything about this. There are plenty of websites that advertise stoves that are suitable for bedrooms. This one comes to mind
https://www.efireplacestore.com/bedroom-approved-wood-burning-stoves.html

If it's illegal to have a stove in a bedroom, could you please supply the source? I am sure that it's illegal in some jurisdictions but I can find no evidence that it's illegal in Ohio.

I've attached a few more pictures. I discovered that the Thermostat and Fan Speed knobs were too small for my fat fingers so I made them larger. Also added the TV mode feature when in Hold Target Temperature Mode. The second picture is the inside of the case. There's a ambient temp sensor board, a yellow K type thermocouple plug, thermocouple amplifier and at 16 channel servo driver.

I have discovered that the thermostat knob is anything but linear. Moving from the 4 oclock to 6 oclock position has far less effect than movement from the 3 to 4 oclock position. Any movement north of the 3 oclock position has a dramatic effect on the stove. Is this normal? Along the same lines, is this true of all Blaze King Stoves? I'm sold on Blaze King and have plans to replace the current wood burner insert in the living room with a princess 29 this year.

As it stands now, it's not an issue to maintain a constant room temp. It is a big issue is that if initially there is a big difference between the room temp and the target temp. The software will overshoot the target by a wide margin and it will take several oscillations before things stabilize. There is a huge lag between changing the thermostat and any change in the room temperature. Now that the really code weather is here, I have an opportunity to log a ton of data. Then I will try to optimize the software algorithms.

2022-01-16-120200_800x480_scrot.png IMG_5701.JPG IMG_5706.JPG
 

stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
NFPA 211 does not allow stoves (solid fuel) in bedrooms. Most (all?) building codes adopt NFPA.
I thought "all" but maybe your location does not?
 
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stoveliker

Minister of Fire
Nov 17, 2019
6,313
Long Island NY
Regardless your manual explicitly states "do not install in a sleeping room". Case closed. If SHTF, you'll be liable.