Automated Airflow

[CampHamp]

I was tired of fiddling with the damper on my Jotul F600 (Firelight), so I automated it using a motor and a micro-controller. I have no desire to produce and sell this, but just like to automate repetitive tasks around the house and learn new stuff!

The logic allows for different modes:

• "Manual" - control lever with the app's slider bar
• "Standard" - get up to temp, limit air flow and pat down gradually until new load
• "Overnight" - up to min temp then close air way down
• "Room Temp" - keep room at a target temp
• "Stove Temp" - keep stove at a target temp

I've posted some pics of the user interface (made with "Blynk") which connects over WiFi to the controller (an ESP8266 - the mess of wires!) and the lever attached to a "stepper" motor which gives precise lever movement. There are also two temp sensors - one on top of the stove and one for the room temp.

It decides airflow changes based on the difference between current and target temps (stove and room, depending on mode) and, just as important, it considers the temp change rate. This allows for a "soft landing" instead of spiking above/below targets (which happened at first).

Also, it seems that the airflow rate is not proportional to the lever position. For example, the change from 1-20% open seems to produce a greater effect on the combustion than 80-100%. So, I wrote a function to translates desired airflow change to a lever position by weighting the lower increments.

I think there is added efficiency in the middle 3 modes, because it fires over 380F on start-up (which seems to burn all the fumes) and the secondary burn carries temp for a good wile after tightening-up. Also, if the Room Temp calls for a stove temp of 340 to 380, it will round up to help limit smoldering. However, the greatest benefit is I don't need to attend it - the system does what I would do if I paid attention to it.

It's a prototype (i.e. ugly-looking) for now. The motor will live under the stove next year (instead of duct-taped to the cat condo!), by routing the draw cord with a tiny pulley. I'll probably glue-gun the electronics together and put into a plastic box at a safe distance. I control the primary airflow now, but might try dampening the general intake port to compare that technique and to improve aesthetics.

I've lurked for a while, but this is my first post. I expect if anyone likes this stuff besides me, they would hang out on this forum!

 

[begreen]

That's pretty slick. Thanks for posting. Now about the automatic wood loader...

 

[jebatty]

Very cool ... or hot, depending on perspective. How about some more info on the stepper motor, micro-controller, and programming?

 

[CenterTree]

I bet the cat is p*ssed.

 

[CampHamp]

OK. Here is more info on those pieces...

The Stepper Motor


Stepper motors can be moved forward and backwards in tiny increments and can hold a position against force. Above is the one I am using. It's about a 2in cube. They need their own power source and are connected to the control board through a purpose-build card like this:

At the top-right, you can see the "step" and "direction" pins. A simple pulse to the step pin causes this to move the motor 1.8 degrees.

A smaller motor with gearing would be quieter and draw less power. I will swap one in when it arrives from China.

The Micro-Controller

Here is where the program lives. There is a technology movement called "Internet of Things" (IoT), which is driving all the appliances and lights in your home to be connected and controlled with intelligence. This little baby is the engine behind that movement! The main chip (left side) is the size of your thumbnail. It has an antenna and built-in logic that allows easy programming; just give it your WiFi login and it's on the Internet. Besides that key built-in, it can run custom programs and has lots of input pins for connecting to sensors (like to read temps or step the motor). That's a USB port on the right to connect to a PC to upload your code.

Programming
The program is written in a language called "C++" which is mostly English with special characters that punctuate logical commands and loops. The free program (with example programs and push-button uploading) where you write the custom program is called "Arduino IDE". It runs on a PC or Mac.

This part of the solution can be learned by anyone. If you have the patience to start off with simple example programs that turn LED lights on and off, you're half way there! Be warned that your friends will call you a "nerd" if they hear you trying this.

Cost
The technology is super cheap. The micro-controller is $3, the sensors and other bits are less! Just amazing to me. The motor shown was $8 (used on EBay) but the $2 one to replace it will be better.

 

[Highbeam]

nerd!

I expect regulations will one day force this level of control onto solid fuel burners.

 

[fishki]

I bet the cat is p*ssed.

I saw that

 

[firefighterjake]

While I personally like the no frills, simple stove that can be operated without any electronics I suspect the are many folks who would like or benefit from this. OP you should share this with Jotul and see if they have any interest.

 

[EatenByLimestone]

Nerd +1, lol!


But I'm sure some would love this on their stoves. It would be nice to be able to load a stove and forget about it. I could do that with the Century as it was almost too small to overfire. If it increased output through efficiency and increased burn time I can't see a bad side to making it an option!

 

[brenndatomu]

NICE!
Might hafta adapt this idea to the ole Tundra wood furnace...'twould be the last piece of the automation puzzle! Been wanting to do something like this, just didn't take the time to figure out what I would need to control the stepper motor...been thinkin we need more nerds interested in wood heating!

 

[jetsam]

I've seen one commercial electronic thermostatic wood stove on the market, but I haven't seen anyone actually review one yet.
(broken link removed to http://www.quadrafire.com/Products/Adventure-III-Wood-Stove.aspx)
(broken link removed to http://www.quadrafire.com/Products/Adventure-III-Wood-Stove.aspx)

That is a neat retrofit.

 

[brenndatomu]

I've seen one commercial electronic thermostatic wood stove on the market, but I haven't seen anyone actually review one yet.
(broken link removed to http://www.quadrafire.com/Products/Adventure-III-Wood-Stove.aspx)

That is a neat retrofit.

That's probably just a motorized damper controlled by a tstat, like a wood furnace...full open or full closed. I doubt the damper is actually being held open/closed in increments like what @CampHamp has done. Nice option though!

 

[Trex83]

nerd!

I expect regulations will one day force this level of control onto solid fuel burners.

Already is.
Just imagine how you can reach Step 2 NSPS for hydronic heaters (with cordwood, not cribwood testing). Cant do it without a lambda sensor which controls primary and secondary air...

 

[Trex83]

While I personally like the no frills, simple stove that can be operated without any electronics I suspect the are many folks who would like or benefit from this. OP you should share this with Jotul and see if they have any interest.

I've already mentioned something in the same lines to the lead designer at SBI. Too complicated, would add too much cost and lots of user are afraid of electronics (and their potential repairs down the line).
If the installer does a good job of adjusting the equipment and making sure you dont have too much draft, then it shouldn't be a problem (and crack).
I've installed a lambda sensor to monitor the excess air in the exhaust of my sister's now belated Tundra I a couple of years back. Yes it did crack, she got her money back no problem.

It was well over 200% excess air. So there is room for improvement to measure stack temps, internal pressure and control the air input. An arduino is well suited for that. One of the analog input pins on the micro controller can read the output of a lambda sensor 0-10 Vdc or 1-10 Vdc.

Enjoy!

 

[HoosierHillJack]

I already have automated air on my wonderwood stove with its high tech bimetallic thermostat damper. Haha

If you wanted to go no electronics the bimetallic system works well my only complaint is that the damper will flutter and make noise when its near the temperature limit on the dial. You could make a double redundant system in case of power failure.

 

[begreen]

my only complaint is that the damper will flutter and make noise when its near the temperature limit on the dial

Our old Resolute's thermostatic damper had that issue too. When the flap was almost closed sometimes it would tap like a nervous granny. A small magnet on the edge of the air flapper stopped the problem.