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Electronic Wood Stove Control

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by ControlFreak, Jan 25, 2008.

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  1. RedRanger

    RedRanger New Member

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    Gadgets are not meant for stoves or inserts. They malfunction, there goes your house.!!!!!!!!

    Right now I`m thinking of greenhouses, where the vents open or close depending on the heat and humidity,Sometimes They Fail!!

    Never,never would I trust one of these things. I want to be able to leave my home knowing the manual controls I use have set the insert to minimum burn,will stay that way. When I go to bed at night, same thing. Don`t want to be tossing and turning wondering if this new gadget is going to malfunction and leave everything "wide open"?

    Maybe you can sell this to the inexperienced wood burners, but not to the rest of that are still (partially sane) :coolhmm:

    Some of you experienced wood burners may disagree? But remember, I said that those of us that are at least Partially Sane, would never,ever even give this product a -second nod...

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  2. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Well, that did it. I have just got to have one now. ;-)
  3. ControlFreak

    ControlFreak Feeling the Heat

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    Hi Sonnyinbc,
    Thank you so much for your candid feedback. Every bit of feedback we get is valuable, even feedback that's not favorable. Reliability will be a key area of focus.
    Dan
  4. ControlFreak

    ControlFreak Feeling the Heat

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    To address a lot of the questions and comments posted here, here’s some info:

    I began heating with wood in 1996 with a Napoleon 1401. After about 6 years, I became very tired of constantly having to monitor the draft setting in order to have a nice clean fire without overheating the stove. It bugs me if the fire is smoking up the glass in the door, and worse, when I forget to check it and come back too late and the fire is so hot that the draft control can't even slow it down.

    A pellet stove is not an option. It's just not a real fire, and I don't want to be tied to a pellet supplier. So this is the closest thing to the convenience of a pellet stove, but still having the cost advantage and beauty of a real wood fire.
    In 2004 the development began for SmartStove. Between then and now, we have gone through many revisions of the product to get to where we have a reliable and reasonably fault-tolerant control system today. For the past three winters, I have run my Napoleon stove with various prototypes, experimenting and learning what works, and what doesn’t. As the system runs, it logs the operation so data can be downloaded and performance can be examined at the end of the fire. I have logged many fires and tuned the controls so it now runs the stove better than I ever did.

    The product was developed with these considerations and requirements:
    1. Safety. #1. It MUST be failsafe when AC power drops. Must never fail with draft wide open.
    2. Reliability. It must never fail, but if something does go wrong, like an open door, it should warn the user.
    3. Functionality. It must work perfectly --- always. Otherwise it’s useless.
    4. Cost. It must be affordable, or nobody will buy it.
    5. Flexibility. It must be configurable for many stove applications.
    6. Adaptability. It must be able to self-adapt to various draft configurations.

    Dan
  5. ControlFreak

    ControlFreak Feeling the Heat

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    To respond directly to some of the comments:

    "I want mine on a remote control. Sometimes I damper it down to quickly and would like to open the air inlet from the comfort of my couch." That's what this fixes. It will be dampered down just right.

    "Im curious , How would one install the actuator and thermo probes in an existing stove?" We are targeting OEM installations for new stoves.
    "Or are you primarily looking at integrating it in at the stove factory?" Yes.
    "and how much would this unit cost?" This is one area of study. It needs to as inexpensive as we can make it, but also reliable.

    "I am a guy with a pretty severe walkiing disability and spend most of my time on the kitchen level and the stove is on the lower level." This is perfect for you.

    "There has been a lot of talk about integration between different appliances in a “modern” home—why not include the woodstove?" Maybe some day.

    "I like to adjust mine, but, atleast I know if the wife is at home by herself or if my father-inlaw comes over than its operating like its supposed too." Initially, there was a auto "override" for the draft control to enable manual control. It was eliminated since it was never needed, and there was concern that it would be accidently put into manual mode and overheat the stove.

    "How would it function on stoves with a bypass damper?" SmartStove has the capability to drive two actuators to accomodate stoves like the Quads that have two controls.

    "And again, cost is a big factor…" It sure is. I think that this has been an inhibiting factor.

    "Also, lots of stove owners like to futz with the controls." We will be sure to install special "futz" features. Acutally, there is a configuration menu where tinkerers can tweak settings. We'll make sure we put in some special settings just for the futzers.

    "Yes, you’ll have to tinker with it to make it work properly, and it may never deliver 100% of what it promises." Yes that's what normally happens. Frankly, this by far exceeded my expectations when it was first working. I'm pretty spoiled by it now.

    "If it had USB..." We have considered this. It very well might be there by the time we get to mass production. I used to download operating data that's logged throughout the fire while checking things out.

    "Well, that did it. I have just got to have one now." Eventually you will.
  6. begreen

    begreen Mooderator Staff Member

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    I'm sure you looked at this but I was referring to stoves like the Quadrafire Isle Royale, downdraft stoves like the Lopi Leyden, VC non-cats and the VC cat stoves. These are fairly stout bypass controls, not just an air damper. I'm having a hard time imagining how one would put a servo on this. It would require a fair amount of leverage and I would think that the stove is too hot there to attach a motor to.
  7. tkirk22

    tkirk22 New Member

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    Enough marketing...here are some of my questions:

    Will it fail safely if I was to cut any one sensor or any combination of sensors?
    How about if those sensors are shorted or they receive some external low voltage?
    What happens if any of the 3 wires to the air inlet servo fail?
    Will it fail safely if a power surge takes out the micro controller but not the servo circuit?

    Please don't get me wrong. I do like the idea. However I also like the idea of children having computers BUT only as long as the computer is not considered the child's babysitter.

    I would also like to put my vote in for you to send a test unit to Corie.
  8. ControlFreak

    ControlFreak Feeling the Heat

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    Controls that require a great deal of power will be a problem that has to be fixed. You're right. A servo isn't going to drive these.
  9. ControlFreak

    ControlFreak Feeling the Heat

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    Wow, good questions. Now you're talking about doing Failure Mode and Effect Analysis. That's not done yet. We are fail-safe for the most common failure: AC power. We do have feedback from the draft control so if something hangs up the draft and it doesn't move, the controller can see that it's stuck.
  10. TruePatriot

    TruePatriot New Member

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    Dan,

    Crap!

    I just lost a 6,000 character post because I bumped into the "character limit Gremlin." You know, where you type ONE CHARACTER TOO MANY AND THE WHOLE POST DISAPPEARS! Arrgghhh!!!!! (It may happen when hitting "Backspace" while at the char. limit--not sure).

    In short, I refused to buy any steel, NC stove that doesn't offer thermostatic control of the PRIMARY (and possibly secondary) air supply, other than the Englander 30-NC. I've studed the steel-plate, non-cat stove market extensively, for too many years, and the Englander 30-NC is meeting or exceeding all performance measures of the $2,200-3,000+ stove market, at 1/3 to 1/6 the price (if you get one at 50% off at Lowes, as I just did), against even such formiddable models as the Quad 5700.

    IOW, if I can't have thermo-control of the PRIMARY intake air, for $3,000.+, then why would I spend such money, when the Englander 30-NC meets or exceeds the perfomance of such $3,000/+ stoves, at 1/3 the price? (Or 1/6, if purchased at a 50% discount.).

    Thermostatic control is the single biggest feature I seek, after materials choice.

    In 2007, I contacted every major steel stove mfr. and asked if they were going to offer thermo control. Quad mumbled "maybe, since we have our ACC system on the market," but the only serious response I got was from Mike at Englander, saying he would forward my suggestion to "the slide-rule types" (my term, not his). I felt the other mfrs. were just blowing me off--though I felt Quad might have been serious, but I doubt it. I do believe Mike has passed my concerns up the channel, and we shall see if they respond as I hope they will. If they do, my second stove will be an Englander as well!

    I know PE offers thermo control of the SECONDARY air intake, but feel that is too little to accomplish what I, and now YOU, would like to see, i.e., full thermo-control, where one could select a rate of burn, load the stove, and forget it, knowing it's metering the air necessary for complete, efficient combustion at the output level selected by the operator.

    I know Blaze King offers thermo control, but don't want a cat stove. I also know some cast iron stoves offer thermo control (Quad's Island Royale, possibly?) but again, I don't want any cat, or cast, stoves. (No offense to such owners--it's just that I'm l-a-z-y, and don't like replacing cats or furnace cement. Welded, plate steel stoves make me feel more confident about their integrity than stoves bolted together with furnace cement, but that is my personal preference. I only mention it here because I want Dan to offer his electronic system to OEM's of plate steel, welded stoves, so I can buy one! LOL)

    But to recap: I put off spending $3,000+ on a stove that lacks even the bimetallic intake air control that even some of the smoke dragons of the '70's had.

    If the Englander hadn't been available at 1/3 the price of the Quad 5700, I would have bought NO stove. So when the Englander 30-NC became availbable for 50% off, or ONE-SIXTH the price of the Quad 5700, but with comparable performance and superior emissions, I bit. But I'm determined to wait to spend $3,000. for a "pretty" stove until thermostatic control of the primary intake air is available. And, when that is offered, I will buy the new stove and move the 30-NC to my cottage.

    Re: the concerns I share with others about a failure leading to a runaway stove, please address this: I feel the electronic servo should pull against an extension spring that is contantly trying to close the draft, similar to how, on a garden tractor engine, the operator opens the throttle against a governor that is contantly trying to close the throttle. I see this as a common-sense approach to avoiding a failure that results in a runaway.

    I would be into the electronic control's additional features of "logging," remote control and particularly, OVER-FIRE ALERTS and low-fuel alerts, IF I FELT THE FAIL SAFE MODE WOULD RESULT IN A CLOSED DRAFT, and if the stove could be run MANUALLY in case of extended blackouts.

    Sorry I can't write more, and sorry for the mistakes and poor writing--as I say, I was one character away from a well-groomed post, answering all of your Q's, when *POOF!* it was gone. I forgot to write it in Word first and post it here, and having been burned like this too many times in the past (sorry, Craig, but it happens to me, too often--I know, I'm a "wordy **** :lol: ) I'm just too frustrated to rewrite the whole thing.

    I seriously hope you pull this off, Dan. If for no other reason that it should spur the OEM's to get off their asses and offer the same thing, so we can have the same convenience enjoyed by pellet stove owners, for cryin' out loud! It's about FORTY YEARS OVERDUE, since it was offered in the '70's, right?

    I would also be interested in a retrofit kit for the Englander NC-30, Quad 5700, etc..., IF you could offer strong assurances that Homeowners carriers and code enforcements' concerns could be met, especially without risking denial of coverage should the woodstove (for any reason, not necessarily involving your system) be cited as the cause to a house fire (knock on wood three times.) And I have to tell you that, as an attorney, I think that will be an uphill battle, in terms of a retrofit that won't make the carriers underwriters jump right out of their trees in an effort to say "NO" to covering such a mod. Perhaps if a licensed professional HVAC guy/gal did the modification, that would help, but I don't know. I didn't practice in the area of products liability, however, so value my .02 accordingly, on this last point.

    I truly wish you the best of luck in pulling this off!

    And yes, to sharp the sharp-witted like BB, I realize this post is as long as the one I lost--it's just more rambling and disorganized. ;-P

    Thanks again.
  11. ControlFreak

    ControlFreak Feeling the Heat

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    TruePatriot,
    Your insight is priceless!

    "I seriously hope you pull this off, Dan."

    I will pull this off. It's just a matter of time.

    "I would be into the electronic control’s additional features of “logging,”

    Take a look at the attachment. This data was collected two years ago. This is a plot of a typical fire. One thing that has always surprised me is how the temp measurement always drops off significantly after about 2-3 hours into the burn. For a long time I questioned the measurement. You'd never expect to see this from watching the fire. Anyway, I download these frequently to see how the night's burn went and whether the code is doing what I expect.

    Dan

    Attached Files:

  12. begreen

    begreen Mooderator Staff Member

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    Dan, what stove was this tested on? Is the draft spike at the end due to opening up the air control fully to burn off coals? I'm surprised to see no corresponding rise in stove top temp.
  13. begreen

    begreen Mooderator Staff Member

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    My understanding is that PE's EBT controls primary and secondary air. This is only on the Summit/T6 models. VC stoves have thermostatic damper on the secondary. To my knowledge, the Isle Royale does not.

    I've only had a thermostatically dampered stove once, the original VC Resolute, but I agree, it was really nice to have and worked well. I too hope Dan succeeds with this endeavor and in prodding other manufacturer's to incorporate thermostatic control. To be fair though, John Gulland does not. He would be a good one to setup with a test unit.
  14. Woodrat

    Woodrat New Member

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    Question-- Do you know WHY not????

    Woodrat
  15. begreen

    begreen Mooderator Staff Member

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    Good question. I don't remember him going into much detail during the interview with Craig. Seems like a good topic for him to expand on in the next one.
  16. TruePatriot

    TruePatriot New Member

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    Dan,

    Thank you for this:
    I don't hear that nearly enough--lol. Can you tell my g.f.?

    And seriously, there is a pretty serious discussion of thermostatic control shaping up in a (unfortunately, highjacked?) thread over here, regarding PE's increasinly-mysterious (IMO) "EBT" system: http://www.hearth.com/econtent/index.php/forums/viewthread/14507/P0/

    If nothing else, it will provide further confirmation for you of the great deal of interest in having thermostatic control of the woodburning experience which, to me, is the primary benefit of the electronic control you posit.

    Enjoy,

    Peter
  17. begreen

    begreen Mooderator Staff Member

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    One thought came to me was that modern stoves seem to thermostatically damper the secondary air. The old Resolute dampered the primary air. This seems more useful. After the wood gases are burnt off and the wood is in the hot coal stage, why would it need secondary air?
  18. Woodrat

    Woodrat New Member

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    [quote author="ControlFreak" date="1201494957"] We are targeting OEM installations for new stoves.
    "Or are you primarily looking at integrating it in at the stove factory?" Yes.


    Let me preface this by saying that I’m not a technophobe by any stretch. The fact still remains, however, that having FIRE in your home is like living with an “800 lb gorilla”-you have to be 100% certain you’re in control!
    I can understand why you would be interested in getting manufacturers to offer your system, as opposed to marketing it to existing stove owners and I wish you success with that approach. Hope that you can also realize that contrary to popular opinion around here there is a large well-established base of woodheat enthusiasts out here in the “real world” who have needs and concerns that do not necessarily translate into buying new stoves that are starting to approach prices that could have purchased a decent car not too long ago.

    #1 If you can address the needs of people like: steam man
    “I do think most stove nuts here would like some kind of remote monitor option possibly to alert for problems and time to fill the stove. “

    #2 And the concerns of people like: sonnyinbc "Gadgets are not meant for stoves or inserts. They malfunction, there goes your house.!!!!!!!!
    Right now I’m thinking of greenhouses, where the vents open or close depending on the heat and humidity,Sometimes They Fail!!
    Never,never would I trust one of these things. I want to be able to leave my home knowing the manual controls I use have set the insert to minimum burn,will stay that way. When I go to bed at night, same thing. Don`t want to be tossing and turning wondering if this new gadget is going to malfunction and leave everything “wide open”?
    Maybe you can sell this to the inexperienced wood burners, but not to the rest of that are still (partially sane) 
    Some of you experienced wood burners may disagree? But remember, I said that those of us that are at least Partially Sane, would never,ever even give this product a -second nod…"

    #3 As well as capturing the attention and interest of people like: sixminus1“The thought of “automating” a wood fire is a little scary, but as you said—if it’s well-tested, and can be completely shut down to allow full manual control when necessary, I think it would be a very cool thing to have.
    A stove with this feature would require the same diligence as bringing fire into your home in the first place—try it out, keep an eye on it, and make absolutely sure that it does what you expect. Don’t leave it alone until you trust it, and even then, don’t completely trust it. It would also require the same type of learning curve that everyone on this forum had with computers (and stoves)—how to use it properly. It’s a tool, it’s a human invention (thus, it’s imperfect), it’s potentially dangerous, and everyone’s mileage will vary. Hey, that’s life.”

    If you can do all of the above-- you'll have a hit!

    I realize that that your main focus will be the number (3) group, I’m just saying that may be enough people in groups 1&2;to keep in mind. If features of your system could be marketed a “stand-alone” items (maybe designed as you have them to be interconnected later) That might even be a way to gain entry to the existing stove market and get manufacturers’ attention at the same time. Am I making any sense---or just babbling?

    Best wishes---Woodrat
  19. kellog

    kellog New Member

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    Control Freak,

    Let me first say that I hope you are wildly successful with your product. The idea of automatic control of a wood stove is not new but I think it has not been given a good chance to be successful. Bimetalics are not good enough. Even the PE EBT system which takes bimetalics one step further with a clever mechanical mechanism is not near perfect (http://www.chimneysweeponline.com/hoebt.htm).

    I have a very standardized way of running my stove that I think could be automated easily with electronic controls and do a much better job than I do while saving me the drudgery and time.

    Of course, without question, all the safety concerns need to be addressed (failsafe damper closing, over temp alarm, etc.).

    Don’t forget a coal burning step at the end of the cycle (wide open air).

    My stove is catalytic and has a primary air control on both sides, a bypass and a damper. That’s a lot of controls. I don’t think you want to control that system. Likely it is best to work with an OEM so you can optimize the system and minimize the controls required.

    Please stick with it and I wish you the best of luck.
  20. EddyKilowatt

    EddyKilowatt Member

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    Dan -

    I'll join the others and wish you good luck in developing and selling your product. I have long thought that a simple control system is a no-brainer for something as unstable as a chimney-drafted fire, and have wondered why this feature has practically vanished from modern wood stoves. I would love to see it re-appear. (Ben Franklin would not be pleased that we have made so little progress!)

    That said, I also have to agree with the comments that getting something reliable and fail-safe enough to be safety certified to control fire inside people's homes is going to be a long row to hoe.

    I'm an electrical engineer myself, and not an evening passes where I don't watch my stove burn and think about automatic control of the draft. Thermocouples and PICs and servos cross my mind -- they are what I work with -- but for me there is just too much dissonance between 3.3V power supplies and USB ports on the one hand, and cast iron and firebrick on the other.

    I myself would be happy if stoves just had what TruePatriot describes, a single control that maintains the burn rate at a chosen setpoint over the course of a burn. That is the inner loop of any control system, and for me it would be plenty. My gut feel says (contrary to my EE roots) that a simple mechanical system, that controls draft based on flue temp, would do the job -- whether based on bimetal flex or pneumatic pressure or wax-pellet expansion (like a car thermostat) or whatever sort of heat sensor and damper actuator. A simple one-variable mechanical system with a bare minimum of moving parts, that anyone can understand by looking at for sixty seconds. I think there's a strong need to adhere to K.I.S.S. both for safety reasons and in order to relate to the woodburner culture that exists today.

    But still, I think it is great that you have pursued this and are provoking these discussions. *Somebody* has to move the industry forward in the areas of performance, safety, and emissions, and it is guys like you who will do it. Keep up the good work and let us know how it is going!

    Eddy
  21. KeithO

    KeithO Minister of Fire

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    Much as I hate saying this, the easiest way to obtain the failsafe reliability needed would be to add a forced draft blower. Basically, the connection between draft fan and stove would be so restrictive that there would be no way that the stove could overheat if the draft fan wasn't powered. Now a simple thermal switch can be added (or 2 in series for redundancy) which cut power to the draft fan if the stove temperature exceeds a pre-determined setpoint. This setpoint would be higher than the software would allow, thus the failsafe would activate for circumstances where either the controller is toast or something on the sensing side has driven the system towards overfire. This system can be set up with latching relays so that once tripped, it cannot reset by itself (requires powering down and back up again after the stove has cooled).

    On startup, the forced draft would operate at maximum power. At this operating point the blower will be relatively noisy, but it would be tolerable for the short time it takes to establish a hot fire and is particularly useful at a time when the chimney draft is relatively weak. As the fire gets established, the control system compares the desired heat output (maybe on a 1-20 scale) and regulates draft to stabilize the burn temperature. With an established fire, the chimney will power the draft to a large extent so the power requirement to the draft blower will be reduced, making it run much quieter. Speed sensing on the draft blower will be required. Most woodstove users appreciate the peace and quiet of their stove operation, compared to the drone of pellet/corn stoves.

    As the fuel burns low, it may be sensible to have a user option to choose NOT to completely burn the coals, but to coast into "standby" mode instead, so that it makes re-starting the fire less problematic.

    As I said in the beginning, any cause for an overfire results in the draft system being disabled. If someone breaks the glass in the door, you're on your own. Same as what we have today with manual controls.
  22. kellog

    kellog New Member

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    I second Eddykilowatt’s last paragraph. If someone didn’t work to improve stoves we would still be using Ben Franklin’s original design.

    We now have controlled air intake stoves with secondary burn and some with catalytic elements, some with bimetallic assisted controls, etc. Our EPA stoves burn much less wood in an environmentally better way. If we don’t get better, BI types will continue to hound us. Look at the OWB political issues. We need to move forward and Controlfreak is one who is trying to help us. His unit may or may not be the answer but at least he is doing something. Keep up the good work Dan.

    If you do what you always did, you get what you always got.
  23. ControlFreak

    ControlFreak Feeling the Heat

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    More comments:
    "What stove was this tested on? Is the draft spike at the end due to opening up the air control fully to burn off coals? I’m surprised to see no corresponding rise in stove top temp."
    This is a Napoleon 1401.
    The change in the draft setting at the end is preparing for the next fire. Obviously by this point, the draft control no longer has any effect on the amount of heat produced, probably because there's only a deep coal bed and the draft is much reduced to where the air restriction no longer has much of an effect.

    As for the issue of safety: Most of us here fly in planes, and every time we take off, we consider what would happen with a major failure. I know I do. Yet most of us accept the risk and fly anyway. We all run the risk of having our house burn down because we have automated furnaces in our basement. The risks are kept in check with redundancy and fail-safe mechanisms. This is a problem that can be addressed with wood stoves, but it will never be perfect, just like your furnace. We speak of risks of fire, but how many people out there continue to use old smoky stoves that line their chimneys with combustible fuel just waiting for enough heat to ignite it? What causes chimney fires? Crappy stoves combined with human error. What's more common, human error or a control system failure? The system has never failed and when we have lost AC power it has shut down the stove as designed (before battery backup). For me, my stove haven't overheated in the last 3 years since running this system. I overheated it several times per year before using it. It's not out of the question to load up a stove with the draft wide open and then get an emergency phone call and forget the stove. I'll take the automation with an over-temperature alarm and a smoke detector sitting on the mantle above the stove. We all choose our balance between convenience and risk. I think this is safer as it is now and it will be made even better with the help of all you guys.

    Comments?
  24. Gooserider

    Gooserider Mod Emeritus

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    I think that the overheating risks are being overstated - yes over-firing your stove might damage it, but part of the entire UL certification process was to establish safe clearances in the event of an over-fire... Thus I would consider it unlikely that you would burn the house down in the even of a failure of the control system - or at least no more likey than if the HUMAN control system failed.

    I would second the earlier suggestions / requests for a nice display equipped, multi-sensor (ideally) temp monitor to start with - preferably with a way to connect to a PC for data logging and possibly remote monitoring. I'd prefer an ethernet connection, but...

    I'd also like to get controllers that would work with my current stove, a VC Encore Cat. This has a draft control on one side (thermostatic primary) and automated thermostatic secondary, and a "binary" bypass damper with a fairly stiff action.

    I wouldn't try to do a servo on the bypass, but it might work well with a linear actuator, or possibly some sort of geared motor with a spring trip, and a micro switch on each end to control the motor and signal the "state" to the controller. (which could sound an alarm if unable to set the damper to the desired state)

    The primary and secondary dampers could either be switched to servo control, or left as thermostatic, with the possible ability to do a short term "full air" over ride to get a fire started, or char in a fresh load.

    Gooserider
  25. tkirk22

    tkirk22 New Member

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    Nov 20, 2007
    Messages:
    299
    Loc:
    VA Mountains
    I think some kind of auto control would be great on a wood stove but I just don't have the confidence to toss in a full load of wood with the air open to full and leave the house. A wood stove is a different beast than my oil burner with a nozzle that mechanically limits it's maximum output.

    If I'm going to be home then I would certainly love to have the stove managed for me.

    The unit you are designing is for OEMs. Have you thought about something for the rest of us? Possibly something in the form of a DIY kit that the more advanced user could solder and install himself. That would limit the liability and also give you a good base of testers using different stoves. There seems to be a good amount of mechanically minder people here.

    A few guys have mentioned a temp logger in this thread. Making something like that would be relatively easy and be a good way to get the company name out.

    I was thinking about making such a board for my own use but I decided to go a different/easier way for my one-shot logger. Anyway, I'll tell you how I was thinking about making it in case you or someone else here wants to do it. Note: I am not an EE so take the following for what it's worth.

    Start with a DS2762 chip. It's cheap, they have free samples, it will read a thermocouple, it has a built in chip temperature sensor, and it has some built-in memory. There is also an alarm function on the chip that may be interesting but I haven't looked into that. Anyway, run the chip input through a multiplexer to read 4 thermocouples. Now use a small cheap micro controller to drive the multiplexer, read the thermocouples, and upload the temps back onto the DS2762 chip's memory. Run 2 wires out of the box to a $26 USB 'dongle' on a PC. Those same 2 wire also power the box. From there on out it's software. With 4 thermocouples and 2 power wires the biggest part of the unit would be the wire connector. I think it could be built the size of a cardboard matchbox (or 2).

    I am working on a setup similar to what I outlined above but it's hooked up to an $80 dollar micro computer using a USB 'dongle' and it uses off the shelf components. The stove thermocouple is being read by a DS2760 chip with type K thermocouple wire. (graphs below) For you eagle eyes out there, It's not hooked to a stove yet. I had the thermocouple measuring my computers heatsink at first and later switched it to measure my beer temperature. Then later is was measuring ice water. The stove thermocouple is not compensating for the chip temperature yet so it's is about 20 degrees off on the graph. Oh yea, the basement/office temp is accurate and it is that !@#$%^&* cold. The other graph is logging radiation clicks in my basement. That's the main reason I started working on a logger.

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