Woodstove controller help!

[Titantornado]

Hello to anyone reading this.  Been quite a long time since I posted anything here at Otherpower.  Since the last time, I've moved off grid.  Today's question is about attaining better control over my woodstove.  I've discovered the wonderful, affordable world of PID controllers, but I can't figure out how to integrate it into the stove.

Here's what I want to do.  I want to install an actuator onto the factory air damper. (my stove is fitted with an outdoor air intake, so installing a sepsrate damper would be possible, but would like to avoid that for safety concerns)  The stove is small and requires loading in the middle of the night.  I want to be able to load with the damper open, and be able to go back to bed, and have the controller trim the air damper when the stove comes up to temp.  It would also help to run the stove when I'm not right there to tend it, like when a stubborn burning piece of wood could use more air, or to tame down a flare up when the wood shifts.

I've stepped out a few times, only to come back to a stove that was running way too hot, so I really dpn't like to leave it unless I can have the damper closed now, but that sometimes leads to a smothered fire. 

So if someone can help me with integrating a PID controller to an actuator, preferably using 12v, it would be appreciated. 

[bart]

   From an HVAC background all the PID controllers that we've used/come across output 0-10 vdc, 2-10 vdc, or 4-20 milli amp.
 For a source on damper actuator  try KELE, Grainger. or source one from your local HVAC parts store.
   

[Titantornado]

Ah!  So actuators would function as "position determined by voltage"?  If so, that makes this whole thing make more sense to me.

[bart]

   Sounds right to me. Normally 10 vdc is full open, 0 vdc (or 2 vdc) is full closed. Can buy ones with a reversing switch or program it the other way. Some actuators are available that are spring return closed/open, depending on usage. Most are 24 vac or vdc powered and the control signal is your 0-10 vdc.  Don't know about 12 powered vdc ones.
   Some are just 24 v powered open to whatever criteria and powered is removed to hold that position. All types of flavors.
Careful what you select.

[Titantornado]

Nice!   Yes, the 12v controllers I've been eyeballing are 0-10v output.  Thanks for the insight.  It's all making more sense to me how the components function and work together.  I'll tell ya, if I get this figured out, I'm going to enjoy a much better night's sleep! (and less stress worrying if I leave with the damper partly open) I like the sound of a spring return close to act as a fail-safe.

Makes me wonder why wood stoves don't come configured this way?

[bart]

   If you don't mind me asking, what brand controller are you using ?

[Mary B]

Creosote buildup might be a concern. Wood pellet stoves operate in a similar manner but they control the amount of air entering the burn pot along with the amount of fuel.

[thirteen]

I have a older Blaze King stove and have a manuel thermosat which works fine. It will open up and close depending on the setting. I've never had a problem with any build up  or major problems with it. i have had to clean it up twice in 14 years it got squeaky. They do not carry the same type of controler for the fire and have gone to a better one, but you might look into several other types. Less electricity used less wiring. 13

[Titantornado]

Following up on questions and comments:

I don't have a controller yet. (if that question was directed at me)  I'm still trying to figure all this stuff out.

Creosote buildup is not a concern.  I want the controller to hold a temperature above creosote depositing temps, but also prevent overheating as well.  If anything, there will be less creosote buildup with a controller, than without.  Ideally, I'd like to see the stove operate in a 400 to 450 degree range. (damper full open below 400 and full closed above 450)

Yea, I know Blaze King has the bimetal thermostat.  I plan on installing a Blaze King when I get the house built.  I see no way to adapt the Blaze King's thermostat to my wood stove.

So anyhow, it appears I'm looking for a temp controller with a 12v supply voltage and an analog output.  Whether that is PID or not, I don't know. (I'm still trying to get my mind wrapped around this stuff)  What I am trying to avoid is s "bang-bang" open/close or on/off controller. 

[ChrisOlson]

Why would you want to put an electric actuator controller on a wood stove?  Isn't that a failure just waiting to happen?  Personally I wouldn't trust that setup any further than I could see it, to make sure it's still working.

Why don't you put one of these on it instead?



We have a Daka 621 125,000 BTU central forced air furnace with that type damper on it.  It's the only heat we have in the house.

It maintains a perfect 500 degree stack temp as long as the firebox has enough wood in it.  I can run the stack anywhere from about 250 degrees up to 800-900 degrees by just setting that damper knob, and it maintains it perfectly - without need for any electronics or electrical stuff - which on a wood stove is like scary.

You can order Daka's damper unit for their smaller furnaces here:
http://store.dakacorp.com/product_p/%28170%2932100.htm
--
Chris

[Titantornado]

OK you have peaked my interest.  From your photo, or any photos on the web of it, I can't determine how it functions.  I wonder if it can be adapted to fit my 6" double wall stovepipe, and function correctly.

If it can, it would certainly be easier than trying to put together the electric system components.  Though, I'm not fearful of combining electrics with the stove.  The only piece exposed to any significant heat would be the thermocouple. (which they are intended for)

[Titantornado]

I just found a youtube video discussing that auto damper, and can see that it won' t work for me.  From what I can gather, it mounts over an air inlet opening on the firebox, and opens and closes against it.  You threw me when you mentioned stack temperature, and I assumed it was some sort of flue damper.

So it uses inside air to feed the firebox, and my stove is closed (outside air intake) to meet mobile home standards. If I could even come up with a way to mount it, it wouldn't meet mobike home standards, and surely violate my insurance policy.

[Crispy]

A flue damper will not give you the kind of regulation of your firebox you are looking for. Dampers will limit the amount of air feeding the fire to a degree but are really meant to slow the draft enough to lower some heat loss up the chimney. My stove will still go thermonuclear on me with a full load and the damper closed once the load gets burning good. Regulating the incoming air supply is the only way to get the results you are looking for.

I assume the device Chris suggested regulates the air feed into the firebox and is controlled by a thermocouple in the flue pipe. That would be exactly what you need and you should be able to find a way to "plumb" it into your outdoor air supply.

[Crispy]

The device in the link below has a programmable wireless thermostat and battery back up. It is modular, allowing for controls for blower fan speeds as well. Not sure of the pricing though. Looks like it may not be cheap........

http://www.inveninc.com/Images-Products/SmartStove-InformationSheet.pdf

[ChrisOlson]

I don't know that they even recommend installing flue dampers anymore, especially on EPA approved furnaces or stoves.  Regulation of the air supply to the firebox is pretty much the standard way to control burn and stack temp.

We have a stack temp monitor on our furnace because it has a catalytic recombustor in it that burns all the smoke so all we get out the stack is water vapor, CO₂ and some trace gasses.  The recombustor "lights" at around 450 degrees and that stack temp has to be maintained to keep it going, so I usually run the stack at around 500.  If the outside temp is not cold enough but we need heat in the house, then I'll open the bypass on the recombustor and close the auto-draft down so the fire burns cooler and slower.
--
Chris

[Crispy]

Chris,  Do you have anything that's low tech? 

Not related, but I thought I'd throw this out there since it is a safety issue. I cleaned chimneys years ago and was called to a friends house filled with smoke one day. Turns out he had been using that stuff you throw on the fire to "clean" your chimney. It works, to a degree, but if you have any kind of obstruction like a damper or a 90 degree elbow in your flue the creosote falls off and can accumulate to the degree that it blocks your flue.

Not good, especially if it happens at night and your smoke detector decides not to work.

[ChrisOlson]

Chris,  Do you have anything that's low tech? 

I still use a wedge and maul to split wood   

Our furnace is new enough that it has the secondary burn chamber in it with a catalyst.  It works REALLY good too.  Takes half the wood for the same amount of heat.  There's a lot of heat in the particulates in the smoke.  The core of the catalytic recombustor runs at like 1,600 degrees when it's burning the gasses and particulates in the smoke.
--
Chris

[Titantornado]

I agree about not regulating with a flue damper.  I'd really like to just have a system that works the existing air damper.  Seems the best way in case you ever had to get your insurance company involved. (what's the difference if I position the damper, or a mechanical device does it?) 

[DamonHD]

That's a trick question, I know, but your insurer's lawyer will tell you after they refuse the payout on your place burning down that you'd never have opened it up to max like that while no one was around to watch...  %-P

Rgds

Damon

[Crispy]

Chris,  Do you have anything that's low tech? 

I still use a wedge and maul to split wood   

That's low tech for sure, but efficient since the wood warms you twice that way 

Titan,

Can you post some pics of your setup? We may be able to offer more options if we can see what you have to work with.

 

(what's the difference if I position the damper, or a mechanical device does it?) 

Weren't you looking for something automated so you could set it and leave without worrying the stove would get too hot? By damper, you mean the fresh air intake right? Just want to make sure we are both talking about the same things. Damper usually means in the flue and the fresh air intake would be "draft" control.

I've seen draft controls that bolt to the stove door in place of the manual draft cap. Nothing more than a small box with one side of the box being a hinged flap that was opened and closed by a small servo and thermocouple with an adjustable thermostat. It should be easy to incorporate something like that into your outside air intake pipe.