My Homemade PC-Based "Coal Trol" and Stoker Control Theory

I am in the process of designing a PC-based control system for my newly acquired (used) Harman Magnum. I know for a couple hundred dollars I could buy a real CoalTrol, but I enjoy the challenge and satisfaction I will (hopefully) get when it is completed and fully working, plus I have ideas for extra features that aren't available on the coaltrol -- such as the ability to automatically adjust the stove output according to outdoor temperature, check the stove status, house temperature, and set the temperature remotely, and email reminders for refilling, cleaning, and periodic maintenance, etc. BUT, since this is my first experience with a coal stove I am still learning about the best way to control it.

Currently, I have the feed shaft turned all the way for maximum stroke and I control the coal feed rate by turning the feed motor on/off in proportion to the amount of heat I want the stove to generate. I also control the combustion blower to vary the amount of time it runs when not asking for 100% output. I haven't actually used the original Harman controller that's on the stove (I know, shame on me ), but my understanding of how it works (from reading the manual) is that it's full-on (combustion blower and feed motor) when the thermostat is calling for heat, but when the thermostat is at or above the setting, it goes into a pilot mode which turns the feed & combustion blower on for an adjustable period of time and then off for an adjustable period of time. If I'm wrong, please correct me.

Now my question is, does the CoalTrol work like a more refined version of the Harman controller? I know it says it can hold the temperature more consistently by controlling the stove more precisely and that it is programmable for different temps at different times. But does it still just use the same two modes of operation as the Harman controller, i.e. ON and Pilot? Or does it vary the feed frequency and/or combustion fan based on the heat output requirements? If that is the case, how does it gauge the heat output requirements? By "learning"?

I welcome any and all discussion

WissaMan

Combustion blower runs all the time, the feed rate and convection blowers varies depending on temp setpoint. ( I know there's a lot more involved, but the Coaltrol guys would have to explain it - Read the Coaltrol Section, there was explainations of various things). You wouldn't want to vary it too much, since you could loose the fire if you slow the combustion blower down too much, you have to have maintain a certain amount of airflow to properly maintain a good fire on Idle/Pilot mode, then if's it too low, it takes longer for it to come back up to temperature. I know some of the older units did vary the Feed/Combustion with a rheostat, many update those units with a 24/7 combustion for better burns.

My Coaltrol on my Leisure Line Hyfire maintains about 1 Degree within the room setpoint.

My keystoker has the standard stock controls (Thermostat and timer box) and does a very efficient job at idle or calling for heat.

I'll have to check out that Coal Trol section -- I didn't realize there was a whole forum dedicated to it!

I don't actually control the speed of any of the blowers, I just cycle them on and off. Currently, I decrease the frequency that the combustion blower cycles as I decrease the coal feed rate. My goal is to reduce the coal usage as much as possible while in pilot mode and reduce the amount of heat that gets pushed up the chimney while running at a medium setting. I won't be sure how effective it is at the latter until I attach a thermal probe (which I have on order) but I can say in pilot mode it uses hardly any coal--I wouldn't be surprised if it could go a week on a refill.

I have found that running it at ~40% is about the minimum before I start to get unburnt coal along the edges. I plan on using the thermal probe to let the controller adjust the pilot mode dynamically, as well as control the distribution blower and also as a safety to cut the coal feed and combustion blowers if the temp drops too low (fire out from a power failure or run out of coal)

As I work on this I'll post my results and see if they are anything to write home about...

As a retired mainframe computer consultant, I briefly toyed with what would be needed to control the stove with an ‘intelligence’ that I could figure out, eg, program it myself, rather than in someone elses’ PROM chip (Coaltrol).

But after some thought, I figured it’ll be a whole lot easier to simply purchase a Coaltrol rather than go nuts trying this, or trying that, or trying whatever to make it work. Of course, all the trial and error period, including lost fires, and, perhaps damaged electronic equipment, the bottom line is it would be FAR easier and much less frustration to “plug it in, and it works” with a Coaltrol.

Some things to consider….

Lets assume you’re using an older PC, Windows 2000 or something similar. So the cost for the box is zero. Believe it or not, I’m thinking I’d be much happier using DOS and PC Assembler for such a project. I still have a 20 meg (yes, MEG!) hard drive with DOS 6.0 on it laying around somewhere...I booted my 3.2 ghz box with it a couple years ago and I couldn’t read the screen with a simple DIR command it was scrolling by so fast! Windows is such a pig! And STILL shakey, after all these years!!! And, of course, all the Windows perils noted in the previous post.

Given what I know from my Alaska Channing, the fans are all AC motors. Controlling the speed of an AC motor can’t be done with a simple rheostat. Basically, they’re either on or off. It takes some level of electronics to be able to chop the circuit, or whatever “they” do to make it happen. And if they’re synchronous motors, eg, using the 60 hertz of the electricity to set their speed, they can’t be adjusted, period! Sometimes I wish I had pursued my electrical engineering degree instead of going into computers 42 years ago.

I suspect one could simply purchase a new or used state-of the art digital devices that would both control the motors AND be driven by computer command. Whether it uses a simple LAN connection, or a firewire, or whatever connection, the matching connections would be need to be purchased and installed on your computer.

Also, it would be necessary for the computer to ‘speak the language’ of the connection and the devices at the other end. I can program proficiently in 5 different computer languages and numerous version and vendor-specific ‘dialects’ of COBOL, FORTRAN and PL/I. I lost count of how many assembler languages and databases I’ve learned and forgotten… (4 different 14xx IBM models I used way back in the mid-late 60’s each used a variation of Autocoder, and then came the 70xx boxes….). Bottom line, there’s a learning curve just to get everything ‘talking’.

Meanwhile, another heating season slips by and you’ve been making your local oil dealer happy just to stay warm…

Bratkinson wrote: COBOL, FORTRAN and PL/I. I lost count of how many assembler languages and databases I’ve learned and forgotten… (4 different 14xx IBM models I used way back in the mid-late 60’s each used a variation of Autocoder, and then came the 70xx boxes….). Bottom line, there’s a learning curve just to get everything ‘talking’.

Well your talking my language now I still remember coding the cc tapes for the 1403's when I was in the AirForce. Installed a BASIC compiler on the 360 system. Mostly wrote in Fortran IV, later in SAS, lator wrote the IODFs for the mainframes. HCD was a nice improvement over the old card-image setup. That was a LONGGGG way from today's Z/OS systems (which I love!)
Yep, I'm still happy with the controller in my DVC-500. Thats why I bought it. I have no interest in Over-designing something that probably wouldn't do a better job anyway.

I'm no electrical or computer whiz,however I have a 27 year old black and decker corded, plugs into the wall electric variable speed drill,how far you squeeze the trigger varies the speed,it was inexpensive when new which says to me rheostat,ie vary the voltage,my powervent also varies the motor speed with a rheostat adjusted by turning a knob.If you love to tinker have fun with it,or buy a coaltrol and watch football all warm and toasty. RichB

A PIC micro evaluation board and all the development tools to go with it can be had for well less than $100. Implement PID (Proportional, Integral, Derivative) controls in the PIC micro and you're good to go. To start... keep it simple, I think perhaps 2 PID loops running concurrently with might work best:

1. put a temperature sensor on the top of the stove and run at a constant temperature (say 3~400*F or so)
2. modulate the convection blower speed to control the ambient (room) temperature

With PID controls implemented, You should not need a rheostat or variable speed controls... Just modulate the motors. However, I am not sure if all stoker feed mechanism is designed to be modulated continuously. Additionally, unless the blowers are moved out of the room the on/off may drive you crazy.

I've been thinking/planning for a general stove controller, not just a smart thermostat. The Arduino controller is my target system; they are cheap, scalable, and well supported.

Official system home page
http://www.arduino.cc/

example PID routines
http://www.arduino.cc/playground/Code/PIDLibrary

Parts suppliers
https://www.sparkfun.com/commerce/categories.php?c=2
http://www.adafruit.com/index.php?main_page=index ... f2e1f43684
http://www.nkcelectronics.com/arduino.html
http://evilmadscience.com/directory
http://www.makershed.com/SearchResults.asp?Cat=43

The Arduino controller is a solution looking for problems. Give it some consideration.

John

There is a fellow on a Chunk wood burner forum -- that made a pc based system. He is taking orders for it now, but the hi-light I wished to point out was he produced a variable speed circulation -- by switching thru various fixed speed reducing devices = So if boiler was at x temp, he turns on the pump via Y switch and it runs at Z speed -- etc.

Cool, I'm glad I'm not the only person that's had these kinds of ambitions. My wife says it "must be a guy thing" to want to "control" stuff I realize I could have a coaltrol and have more free time, but I enjoy the challenge of a project like this, which is well suited for winter time since I can't work on any outdoor projects...

I actually have this system working, so I'm past the theory stage. I am currently using an older HP PC (<1ghz) as a dedicated controller running a fresh, clean install of XP. XP is actually pretty stable as long as you don't have tons of stuff installed on it (though if I had the knowledge, I'd rather do it with a Linux...but alas) As for some of your other concerns...it will not have internet connectivity so auto updates/reboots are no problem. Currently my program is set to load at startup so if there is a power failure, the PC will reboot automatically and with only the OS loading, it boots to desktop in under 30 seconds. All important variables are written to disk every time the program cycles through the control loop, so upon reboot the program can "pick up where it left off". Though all that asided, a UPS is in my long-term plans.

The interface I use is a Phidget (http://www.phidgets.com) which has digital and analog inputs and digital outputs and connects to the PC via USB. That is really the key piece to my setup and w/o that I wouldn't be able to do this. The second key piece is that I was able to use the Phidget C+ API with Clarion (Clarion is a somewhat obscure, but very powerful language I program in and is the only language I have any skill in these days). I do think that Arduino piece looks nice and if I wasn't already commited with this particular setup, I probably would consider it. Another setup I did consider was using MS Robotics Studio, but after my initial tests with Clarion were successful, I abandoned that idea quickly since it would've meant learning a whole new language.

Regarding the blower control, I am using the Phidget interface to turn the fans and pusher motor on and off using solid-state relays I pulled from old copiers (which are a treasure trove of components ) I don't plan on trying to modulate the speed of the fans, only turn them on/off for variable periods of time. I think the Phidget interface can turn on/off it's outputs pretty quickly so theoretically I could control the speed by turning them off/on rapidly but I'm not sure that would be good for the motor. Old copiers also have a multitude of 24v DC fans which could be modulated by voltage but unfortunately, Phidgets does not make an interface with analog outputs so I currently have no way of controlling devices other than with on/off.

eelhc, I do plan on using a thermal probe to regulate the stove temperature, however my goal is to regulate it in relation to the outside temperature (as well as the inside) and run the distribution blower constantly. I feel like if the stove is producing heat and I'm not utilizing it, then it is being wasted, so I'd rather lower the stove temperature when less heat is needed and keep the blower constant than vice versa. Although I may change that idea once I install the DHW coil.

Cheers,
Wissaman

A buddy I work with made his own stoker unit and control system....works pretty good. Runs off a laptop.

Homemade Automatic Feed for Hand fired Coal/Wood Stove

It's been 3 decades since I was young electronic tech and changed professions,however I do vaguely remember something about a large load when STARTING motors,high current draw,turning it on and off constantly may result in a large electric bill,you'll have to measure it I guess and see what happens.Just a thought. RichB

WNY, whew that is pretty elaborate! Does it remove the ashes automatically? THat'd be sweet!

bustedwing, that is a good point about the extra load required to start a motor. I have one of those "Kill-A-Watt" power meters, I'll have to put it on my system and see what the total power consumption is under various circumstances.

Actually, YES, it does a sweep on the bottom into the ash pan as you can see. Not sure if it's still works that way or not, been a while since I have seen it....