Combustion Fan Control

Good day!

I need your assistance to create a controller for my home heating system.

This device will control a 12 Volt brushless DC air induction fan on a wood-fired boiler.
A K-type thermocouple is installed in the chimney flue; it measures the temperature of the exhaust gasses.
The goal is to maintain a temperature of 450 degrees Fahrenheit (programmable) in the flue when the fan is operating.
At present, I have a PID controlling the fan, but it offers no modulation. The PID works, but it is too choppy.

The operating parameters would be:
Below 400 degrees F, the 12 Volt DC induction fan would operate at 100%.
Between 400 F and 450 F, the speed of the fan would be reduced from 100% to 10% in a linear fashion.
Temperatures above 450 F would maintain a fan speed of 10% (or whatever the minimum speed of the fan is.)
I have tried several sketches (unsuccessfully) and watched many, many YouTube videos. Just can’t seem to get all the pieces to work together.
The 12-Volt fan (Model BFB1012EH) draws about 3 Amps.
Any suggestions/assistance would be greatly appreciated!

Is this a repeat post of this request from a few weeks back when someone asked the same questions ?

You can’t mess with these things and risk creating CO , or forcing products back into a room by changing the back pressure on the burner .

Possibly. If its a repeat I created, I do apologize. But I would still appreciate the help.

As I said don’t do it ...

You must know if you’ve asked this before ???
Anyhow ...

It won’t control the temperature anyway , just the volume of hot products - it is dangerous project .
Changing the back pressure on the burner could easily force combustion products into the house and kill someone.

Abandon this and do something else

I have tried several sketches (unsuccessfully) and watched many, many YouTube videos. Just can't seem to get all the pieces to work together.

What works and what doesn't work???

Can you read the temperature? Can you control the fan speed?

Hammy...

This is not a dangerous project.

This device would be used in conjunction with the boiler's master digital controller which, maintains a selected water temperature (172 degrees F). Not only will the master controller prevent an over-temperature condition, I have an additional aquastat in series with the master controller as a fail-safe.

I have radiant floor heating, but maintain the higher temps to prevent the boiler from sweating inside the firebox. The heated boiler water has to be tempered before it is pumped through the floor.

Back pressure? If you are talking about the combustion air, there are two fans; one fan supplies regulated combustion air, the second is a draft inducer mounted on the chimney. I can't describe the entire system in a couple paragraphs. All I can say is I have used it eight full heating seasons with no safety issues. In addition, the boiler is located in a building away from my house.

I have a manual pwm module that I using in series with the PID ; it works just the way I want, but I'd rather not be there to make adjustments 24/7.

Instead of being critical, how about working with me to create the control system? I will give you full credit!

DVDdoug

I tried to adapt this YouTuber's sketch, but when I download and try to verify the code it fails:

Several YouTube postings have Arduino setups for kilns, but they use SSRs which is what the PID uses.
Other fan / temperature control setups use sensors that can't tolerate the higher temps.

The manual PWM fan control (mentioned earlier) works great except I have to be there full-time to make adjustments. I have found that if I start to throttle back the fan speed at 400 F, then keep slowing the fan speed I can maintain the 450 F quite easily.

I have been working on this boiler for 3 years now. I have the mechanical issues resolved; the last piece of the puzzle is to get the fan PWM control figured out. I'm good with iron/steel, not so much with C++.

I tried to adapt this YouTuber’s sketch, but when I download and try to verify the code it fails:
PID temperature controller DIY Arduino - YouTube

Several YouTube postings have Arduino setups for kilns, but they use SSRs which is what the PID uses.

I wouldn’t recommend copying someone else, unless…

A - You are exactly-duplicating and building what someone else built.

Or, B - You fully understand what’s being done so you can modify it.

The manual PWM fan control (mentioned earlier) works great except I have to be there full-time to make adjustments. I have found that if I start to throttle back the fan speed at 400 F,

OK. the output is done!

Next work on the input. I guess you already, so you’ll need a thermocouple amplifier. Connect the amplifier to an analog input and read it. (You don’t have to worry about calculating temperature until you’re sure you’re getting a reading that’s proportional to temperature.)

After you can read temperature, you can “connect” the input & output with software… if-statements and maybe a map() function to control the fan.


the speed of the fan would be reduced from 100% to 10% in a linear fashion.

Just FYI - That kind of thing can be difficult to control because it might constantly “hunt” for the correct speed. It’s generally better to have a limited number of speed-steps.

And some hysteresis is a good idea. For example, a normal furnace set for 70 degrees will come-on at 69 (or 69.5) degrees and then stay-on 'till the temperature gets to 71 (or 70.5) degrees. Then after it shuts off it won’t come on again until the temperature falls back to 69 degrees.

DVDdoug:

Thanks for the reply!

LOL...if I knew how to "correctly" modify an existing sketch, I wouldn't be here.

I was able to successfully replicate Robojax setup:
http://robojax.com/learn/arduino/?vid=robojax-max6675-thermo

Unfortunately, that project uses a relay; which operates the fan similarly to the PID.
Robojax sketches usually work well for me.

You say: "After you can read temperature, you can "connect" the input & output with software... if-statements and maybe a map() function to control the fan. "

The above is the black hole for me. I have tried using bits and pieces from other sketches; sometimes a line-at-a-time.

If I can do this without the PID, that is fine with me. I just need to modulate the fan speed based on the flue temp.

I understand about "hysteresis". The master digital controller has 2 degrees F hysteresis between the setpoint and actual actuation for some functions.

Hopefully, we can continue this discussion? Thanks!