Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Pellet stove controllers ?

Status
Not open for further replies.

stugguls

New Member
What I know about electronics I could put in a thimble but have decided to learn enough to get me by. This post is probably premature also, as I need to open some more books, but someone here might give me some direction?

I dink around with out of production pellet stoves a bit and have adapted boards from manufactures still in production to stoves that are not. They usually work fine , but involves considerable expense as the manufactures are proud of their electronics. If the boards were made in China, they would be 5 bucks, but run anywhere from 160-350 without the harness which is another 60 bucks. Most of these boards can be repaired, but some need changing to allow modification of design flaws of the original applications or voltage changes etc.

What my ambitions are at this point is to build a simple board just consisting of a stoker control that would run the auger. This would require a timer, the correct relays with a duty cycle that would hold up to firing every few seconds and learning how the timers are plumbed. Different boards use different timers. One board sitting on my desk in front of me uses a 556 dual timer ( two 555 timers in one enclosure). Why 2 timers, maybe to shorten the firing time, I don’t know? Another board sitting here appears also to have two timers if those are actually timers I am looking at? The working board with the 556 timer is simply constructed and controls more functions than the other board ( which is toasted) and looks like someone's combination pizza. I guess there is something to be said about simplicity in design?

Where do I go from here? First I need to learn how to identify all the components on the boards, timers, relays etc? I know some basics, but a lot of this stuff looks foreign to me.

Possibly someone on this forum knows about timers relays etc and their application and can point me in the right direction?

Thanks for your time,

JB
 
Ideally, the auger motor should be controlled by a temperature monitoring circuit. Simply having a timer circuit to control the motor won't keep the stove's temp stable. A monitoring circuit with a small range for temperature adjustability (manually via a pot) is best. Since pellets burn at varying rates depending upon their composition, % moisture, and size, a timer circuit on the auger motor could have the ashpot either overflowing with pellets or underfilled. An even better circuit would also feature a sensor to monitor temps in the room to adjust the fan motor accordingly. If you don't get burn temps in their proper ranges, you end up with inefficiency, poor combustion and "klinkers", and possibly too high temps that can damage stove internals depending upon the quality of metals/castings used. Flue temps also should be considered for long term reliability and fire safety.

I would suggest that you go at this VERY METHODICALLY and WITH CAUTION. You can set yourself up for costly failures. Perhaps you can hook up with a local pellet stove dealer and their serviceman for some guidance.
 
Last edited:
I have retrofited several of these stoves with other boards, still keeping all saftey snaps in place and even adding some that should have been stock. I am very familiar with the stoves. All augers in these stoves run off a simple constant speed timing circuit and most have trim controls for fine tuning for different mfg fuels. These machines are not hi tech but all have high, low limit snaps for safety. Your timer and auger rpms are matched. There are no controls that automatically adjust auger speed when burning. On low with a 1rpm auger the timer runs about 3.5 seconds on and off, on high the one time is longer and the combustion fan comes up a bit, that's it and mostly they run fine. I used an ac422 timer on one machine as an experiment and it worked fine, but are expensive and have no duty cycle on the relay side. It is not the correct component for the application. Buiding a stoker control is very doable for someone that understands the timers and relays used. One stove in particular used just a stoker timer to run the stove, snaps for saftey, high and low limits etc.
 
It sounds like your goal is to design your own control board. Is that the case?

I'd start with a large piece of paper or a software equivalent so that you can make a block diagram of your system. You might first sketch out the pellet stove - what goes in - what goes out - and what you might control. Is it an auger only? What about dampers - inlet or outlet - to control air?

If the things you might control are the auger and possibly a damper then you need to describe what inputs or information is needed. Is the control based on the demand for heat - that might be indicated by room temperature? Is there a minimum flue temperature (to prevent any buildup on the chimney)? Is there a maximum flue temp?

For the auger control - would you expect the auger to simply run or not run - or would the auger speed rate be variable? What kind of power does the auger need.

I hope you see where I am going with this. It's a lot of detail but it's necessary, in my opinion, for you to design your system. I don't know if your design is to be limited to one kind of stove - or if your plan is to design a universal controller - adaptable to other kinds of pellet stoves.

Now with all of this said - you need to keep in mind that pellet stove control systems are part of a rather hazardous and risky installation. I would expect there to be regulations that require some kind of certification of safe operation - possibly UL, CSA, ETL or other entities.

Seems like a fun project. I might try something like this for my own stove but I would not assume the risk for a product like this without doing a lot more homework and protecting myself from the liability.
 
No offence, but you are making this awfully complicated, but do raise some good questions.The reason I am doing this is that I have rentals that run some of these stoves and I use them as well. I have been keeping them running for many years even though the mfg is out of business. Saftey is always a concern and most pellet stoves are riddled with many safety or limit snaps and even a exhaust backpressure switch. These are all wired in series with the auger motor. If just about any part of the stove gets too hot, guess what, the auger stops. but the combustion and circulation fans stay running. I have added additional snaps to stoves where I thought the factory was remis.

Yes the timer should have multiple speeds as well as the combustion fan and circulation fan. This has been accomplished a bunch of diferent ways. The first stoves had a stoker control which was a timer that used a potentiometer to vary auger speed. Then there were two other controls to run the fans and of course there was a combustion air control. There were no stops on the controls so it was easy to over fire or underfire the stoves. Overfiring the stove and it quit same with under firing. Due to the combustion characteristics of wood pellets they will run and stay burning within a broad range of settings, and anyone with half a wit can do just fine with the old controls, which I happen to like the best. I dont think you could get one of these things to start a fire unless the single snap on the hopper box stuck closed. I usually install redundant snaps on the stoves I use. I have never heard of a hopper starting fire on a top loader auger which is what I use. Some of the earlier bottom loaders had some burn backs.

As far as designing a system is concerned I just need a stoker control which is a timer that will run between 2seconds on and 6 seconds on and varying off times also. All the other saftey features that came with the stove will still be wired in. setting up fan controls is a no brainer. There is a electronics club site in the uk I ran into last night (http://www.kpsec.freeuk.com/) that uses the 555 timer in some of their projects and has some limited information about the devise. Their timing starts with one minute, I need 2 seconds minimun which can be achieved. One of my pellet stove controllers here has two 555's integtrated into a 14 pole# 556.( 555 is 7 poles) I don't know the reason for the dual timers and was hoping someone could explain the way these things work.

Anyway for now I am using a card from Whitfield's cascade model for keeping another good unit running. It is a bare minimum of a card with only 2 speeds but will work with the stove i am working on which is a positive pressure unit, which I don't think anyone makes any more?...JB
 
Ok, now I think I understand - you are looking for help with a portion of the control system - specifically the timer control for the auger.

It would help if you'd describe the expected operation of the auger. You've already said "on" between 2 and 6 seconds - and you said varying off times. What is the range of "off" times and how do they relate to the "on" times? The next question - what is it that will cause the on or off times to vary? Is it a varying voltage from a temperature sensor - manual input from the user via a potentiometer?

It is clear that you have a good understanding of how the pellet stoves work. The people who might help you are likely to be experienced in other things and they may not know what you know. That's pretty normal and we all struggle thru this stuff. You teach us about pellet stoves - we teach you what we know, as best we can. What I am trying to extract from you is information that will provide a common place for us to begin.

Eventually someone will say this - that a PIC or other microcontroller might be perfect for this application. There is an investment in learning to use PICs- I've not made the investment yet. Clearly other manufacturers are using 555s or 556s - IC timers. There are probably other ways to do it too. The PIC (or other microcontroller) has the advantage of being easily reprogrammed. You can do whatever it is that's being done with the timers and probably much more. Once you've got the program - replication is relatively easy. With that said, you need to work with technology that you understand and if you are comfortable with hard wired ICs then you'll probably want to go in that direction.
 
stevez said:
It is clear that you have a good understanding of how the pellet stoves work. The people who might help you are likely to be experienced in other things and they may not know what you know. That's pretty normal and we all struggle thru this stuff. You teach us about pellet stoves - we teach you what we know, as best we can. What I am trying to extract from you is information that will provide a common place for us to begin.
precisely my thoughts. I've seen quite a few posts on other boards about broken whitfield (sp?) controllers and frankly couldn't make heads nor tails of the the request. So, please provide a Pellet-101 minicourse!
Eventually someone will say this - that a PIC or other microcontroller might be perfect for this application. There is an investment in learning to use PICs- I've not made the investment yet. Clearly other manufacturers are using 555s or 556s - IC timers. There are probably other ways to do it too. The PIC (or other microcontroller) has the advantage of being easily reprogrammed. You can do whatever it is that's being done with the timers and probably much more. Once you've got the program - replication is relatively easy. With that said, you need to work with technology that you understand and if you are comfortable with hard wired ICs then you'll probably want to go in that direction.

OK, I'll say it. A microcontroller is a great way to approach this. Yes, there is a learning curve but there are advantages well beyond reprogramming. Foremost is that you can create one controller that supports multiple stoves. And you can select the model via switches. It also can have different profiles for different modes of operation for different times of the day, week or what ever. One thing that uCs give you is the ability to monitor the operation of your system (via a PC) which is priceless for debugging your system (ie knowing what happened).
 
stugguls said:
Saftey is always a concern and most pellet stoves are riddled with many safety or limit snaps and even a exhaust backpressure switch. These are all wired in series with the auger motor. If just about any part of the stove gets too hot, guess what, the auger stops. but the combustion and circulation fans stay running.
The combustion fan needs to remain operational until the sensor dictates a cooler, safe temp to turn off that motor. Otherwise smoke would likely back up into the room through the minute air gap between glass & door. The combustion chamber needs to remain under positive pressure until the remaining burn-pot fuel is spent. I don't know if you're familiar with Jamestown brand stoves but their control boards are quite complete in design for various safety parameters. The high end Whitfields also incorporate similar. The cheapo stoves sold in home DIY centers and farm supply stores (like New Englander) tend to skimp on the details that sets one stove apart from another.
 
It would help if you'd describe the expected operation of the auger.

I HAVE USED THE WHITFIELD BOARD FROM THEIR CASCADE MODEL FOR RETRO FITTING STOVES NO LONGER BEING MADE. ON LOW SETTING THE AUGER IS ON 1.9 AND OFF 4.2 SECONDS HI 1.9 ON AND 2.O OFF. THE TIMER CAN BE TRIMMED WITH A POTENTIOMETER / VARIABLE RESISTOR OR SOME TURNEY THINGIE. TO THE FOLLOWING PARAMETERS LOW=1.6-4.5 ON HIGH=1.6-4.5 ON ALSO kEEPING IN MIND THE OFF TIMES ARE DIFFERENT BETWEEN HI AND LO. JUST GOT THIS INF OUT OF ONE OF THEIR MANUALS.

MANY OLDER STOVES USE THE 556 DUAL 555 CHIP. I HAVE JUST ORDERED ANOTHER WHITFIELD CASCADE CARD AND WILL LOOK AT THE CHIP WHEN I GET IT AND TRY TO INDENTIFY. I SUSPECT THE NEWER STOVES USE NEWER TECHNOLOGY, BUT FROM WHAT I AM READING THE 555 IS A PRETTY COOL CHIP, CHECK THIS OUT
https://www.electronics-tutorials.com/devices/555.htm THE TIMING IS ONLY PART OF THE PROBLEM AS THERE IS A RELAY CONNECTED TO THE TIMER THAT TRANSFERS LINE VOLTAGE TO THE AUGER MOTOR .5 AMP +/- AND THIS THING CYCLES EVERY 4 SECONDS OR SO. 3600X24=86400 DEVIDED BY 4= 21,600 TIMES THE RELAY CONTACTS IN A 24HR BURN ON HI. CAN YOU EVEN IMAGINE THE DUTY CYCLE OF THESE COMPONENTS? AN ATC 422 REPEAT CYCLE TIMER WITH INTEGRATED RELAY IS AVAILABLE , WOULD WORK BUT NO DUTY CYCLE, TRASH IN A COUPLE MONTHS. I HAVE A GLO KING USING A 556 THAT HAS RUN FOR 15 YEARS ON THE SAME CARD EXCEPT I HAD TO REPLACE THE START BUTTON. FROM WHAT i AM READING THE 555 NEEDS A CAPACITOR AND SOME OTHER GOODIES WIRED INTO THE LOOP TO MAKE IT FIRE, DIFFERENT GOODIES DIFFERENT FIRING TIMES AND DUTY CYCLES DEPENDING ON HOW IT IS PLUMBED SEE THE WEB SITE ABOVE.

THIS IS PRETTY AMBITOUS PROJECT I AM SEEING NOW AND NOT NECESSARY TO DO PERIOD, BUT A CHALLANGE AND MIGHT BE FUN. i CAN BUY CARDS ALL DAY FOR 160 BUCKS, DON'T MAKE A LIVING DOING THIS, JUST PLAY.

jb

- and you said varying off times. What is the range of "off" times and how do they relate to the "on" times? The next question - what is it that will cause the on or off times to vary? Is it a varying voltage from a temperature sensor - manual input from the user via a potentiometer?
 
My previous home had a Whitfield Cascade stove!!!! I never gave any thought to duty cycle of relays or other components but I can assure you that the stove performed flawlessly from Feb. 1999 right up to May 2005 when I sold the home.... and I'm assuming that it still is working good. That model was their entry model and albeit was fabricated out of too much stamped steel for a stove, amazingly it help up just fine. Would I buy another one like it? No.... I like iron castings when it comes to wood burning stoves and vehicle engines/transmissions/axles.
 
Pellet Stove Controllers

Did you ever get anywhere with this? I'm considering a similar project, perhaps we could collaberate?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top