Coal ash from Harman Mag Stoker

titleist1 wrote: ↑

Tue. Nov. 27, 2018 7:46 am

Very interesting idea, using the internal temp probe for feeder control.

Do you still have the distribution blower plugged into the Harman controller to make use of the shut down delay timer?

Where do you power the combustion fan.... from the Harman controller, your controller, or is it running all the time?

It sounds like you had to adjust the feed rate frequently and experienced a lot of outfires when using the Harman controller. You mention babysitting it hourly and I am curious what your timer setting were at that made that necessary?

Well last question first:
My timer settings and feed rate settings were every possibility I could make them, and I was at it diligently for weeks if not months. The thing that probably was the biggest problem in getting what I wanted, was that I needed it to put out a very low (but advertised) btu rate, like 5000btus. At those low outputs the beast was not happy at all, and would make me suffer by forcing me to always be on alert for too high coal feeds or too low. Invariably the fact that the coal feed was always coupled to the internal air stoker blower, meant that the coal was always in danger of dumping into the ashpan, instead of being burned in place before needing more.
I really could not get it to work the way Harman wanted it to, UNLESS I increased the btu output to something like 15K or higher, THEN it would work the way it was designed, but not as advertised to be able to go down to 5K or less. Believe me, if I could have tweaked it using the built in controller I would have. I came to conclude that the machine is simply not designed to have a quiescent internal temperature lower than an output of about 10K btus. My redesign of the controller came out of extreme frustration of the embedded controller.

As to the internal thermometer, mine did not have one as part of its design. I had to add a thermocouple type thermometer, mounting it in the little threaded hole right beneath the door (am posting pictures now): I ran the wire up through the internal casing to the chimney stack and out to the controller: I do still have the distribution blower plugged into the Harman controller, to both use its periodically timed "on" state (about 1 minute every 10 minutes) as well as the shut down delay functionality (about 1 minute beyond the internal blower being turned off): I have the wall thermostat plugged into my controller, and my controller's output controlling the internal combustion blower via the Harman thermostat input port (combustion blower is plugged into the Harman controller) and separately controlling the coal feed: My controller keeps the internal temperature between set temperatures (currently between 195 and 215F), activating the internal stoker blower (combustion fan) on and off to keep the internal temp in that range, but NOT feeding any coal into the stove.
Then, at some point, when that internal temp cannot be maintained and goes below 195F, the controller assumes there isn't enough coal on the burn pan, and will only then feed coal into the unit.
So what happens is, the coal that has been fed onto the burn pan stays there and burns up, and until then no more coal is fed. The efficiency goes up, the internal set temp is tighter, and the stove needs no more babysitting. The only thing I think I might eventually add, is the remaining functionality of the pre-existing Harman Vertiflow controller, so I can do away with it entirely.

Thanks for the additional info and pictures!

If I understand correctly..... you only ever feed coal if the internal stoker temp drops below 195. Does that translate into the stove only needing to run at a high internal temp of 215 to keep the space heated adequately... so your room 'stat never needs to make a heat call? Or is there a way for a room 'stat call to also run the feeder motor in your set up?

The scenario in my workshop, the room 'stat never makes a heat call. It is a well insulated 24 x 20 space where i have a mag stoker. The stoker in idle mode (3 min run time 15 min off) keeps the shop at mid 70's temps well above 'stat set point. I don't have trouble with outfires at those settings but could probably get more efficiency by tweaking things. I was thinking of just running the combustion blower at a lower speed continuously and tweaking the timer setting to feed coal periodically. I'll have to experiment to see if that would give the same result as a separate controller like yours?

Some might say I should just get a smaller stoker but i like having a backup to the house mag stoker for parts if necessary. And I open up the shop to the garage section occasionally in the winter to work on things and the mag stoker is big enough to warm it to a comfortable level.

I REALLY like the 'utilitarian' version of your controls. Things like a brick to support it and keep it protected from the heat

After years in R&D and prototyping, it brings back memories

Keep up the good work!

titleist1 wrote: ↑

Wed. Nov. 28, 2018 10:44 am

Thanks for the additional info and pictures!

If I understand correctly..... you only ever feed coal if the internal stoker temp drops below 195. Does that translate into the stove only needing to run at a high internal temp of 215 to keep the space heated adequately... so your room 'stat never needs to make a heat call? Or is there a way for a room 'stat call to also run the feeder motor in your set up?

The scenario in my workshop, the room 'stat never makes a heat call. It is a well insulated 24 x 20 space where i have a mag stoker. The stoker in idle mode (3 min run time 15 min off) keeps the shop at mid 70's temps well above 'stat set point. I don't have trouble with outfires at those settings but could probably get more efficiency by tweaking things. I was thinking of just running the combustion blower at a lower speed continuously and tweaking the timer setting to feed coal periodically. I'll have to experiment to see if that would give the same result as a separate controller like yours?

Some might say I should just get a smaller stoker but i like having a backup to the house mag stoker for parts if necessary. And I open up the shop to the garage section occasionally in the winter to work on things and the mag stoker is big enough to warm it to a comfortable level.

Yes, the coal is never fed unless the internal temperature drops below 195F. The combustion blower goes on between 195F and 215F, with the that 20F band as hysteresis. All those set temps are adjustable, and I could go lower, but at these temps the room temp hovers around 80F when the outside is about 40F.
As to the wall thermostat, it definitely has a say in activating the coal stove. I have it running through my controller, and currently have it set for 77F. If the room temperature drops below 77F, as it will if the outside temp gets around <35F, the thermostat tells my controller to turn on the combustion blower AND the coal feed, and not to stop until room temp reaches =>77 -- However my controller puts a limit on the internal stove temperature of about 650F, at which point it will shut off just the coal feeding, and continue the combustion blower; the internal temperature can go much higher nonetheless, I've seen it go to ~900F where it levels off on its own.

On your setup -- you have managed to make it output a low enough heat like that so that the room temp is mid 70s? without babysitting it? I could never get it to do that. Either it would go out, or it would spit unburnt coal into the ashpan. I got really tired of constantly tweaking things, so I made the smarter controller, which had to have some kind of internal temperature feedback to know exactly what it was doing. At this point all the tweaking is done in-line and automatically, and the coal feed rod setting in the back is at maximum.
People also told me that I should have gotten a smaller stove, but I really wanted the flexibility for more capacity; the biggest problem I have there is not having an active warm air distribution system from the kitchen to the rest of the house, which is 2700 sq.ft. and three storeys high. Right now it mostly works in a passive distribution sense, as the house is old, and I believe way back when it actually was also heated by a stove in the kitchen -- I see passive floor/ceiling vents all over the place.

I appreciate all the feedback from here, one can get excited over a technical working project, and everyone around you is not an engineer or techy type, and their eyes glaze over when I explain the "amazing" details and solution.
I wonder if coal stove mfrs have instituted something like this in their more modern models.

garyonthenet wrote: ↑

Thu. Nov. 29, 2018 11:46 am

On your setup -- you have managed to make it output a low enough heat like that so that the room temp is mid 70s? without babysitting it? I could never get it to do that. Either it would go out, or it would spit unburnt coal into the ashpan.
.
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I wonder if coal stove mfrs have instituted something like this in their more modern models.

I think the Colatrol probably comes the closest to the controller you created.

I have no issues with outfires using the timer settings of 3 on and 15 off. However, there is room to improve the completeness the coal is burned. Others have seen improvement in running the combustion blower at a reduced speed all the time and that is what I will try this year. I only run it in real cold weather (30's & below) and the shop stays at mid 70's although the doorway to the garage is not sealed well so there is "thermal dumping" happening there.

titleist1 wrote: ↑

Thu. Nov. 29, 2018 3:14 pm

I think the Colatrol probably comes the closest to the controller you created.

I have no issues with outfires using the timer settings of 3 on and 15 off. However, there is room to improve the completeness the coal is burned. Others have seen improvement in running the combustion blower at a reduced speed all the time and that is what I will try this year. I only run it in real cold weather (30's & below) and the shop stays at mid 70's although the doorway to the garage is not sealed well so there is "thermal dumping" happening there.

Yeah, I've seen that thing here and there on 'net, and I have't seen much else.
The thing with the Coal-Trol http://www.automationcorrect.com/ when I last looked at it in any detail, was that it wasn't much more than a PID (proportional-integrative-differential) type wall thermostat, to replace a simple on-off type wall thermostat. I don't think there is any provision for monitoring and reacting to the internal temperature of the stove.
Here is their user manual: http://www.automationcorrect.com/documents/Coal-t ... Manual.pdf
I also got the impression that they may not be in business anymore, cause their website only references things from years ago.

A PID thermocontroller tries to make predictive responses to existing temperatures and the current instantaneous rate of change, and a pre-programmed propagation delay that it knows exists between its servo and the temperature it feels.
Although that is definitely better than a simple thermostat, it is still missing the crucial informational element of knowing what the state of the internal coal stove temperature is.
This is might be encouraging for me on my device in maybe marketing it, as there may seemingly be nothing out there (in an aftermarket device) that does this. I think maybe perhaps some of the mfrs are doing it by sensing the stack temperatures.
fyi, I did also consider at some point as a solution to run the combustion blower continuously, but without some feedback control on that, I think it will also be a continual balancing act of too much or not enough air. I also noted that when i have the combustion blower on a speed controller, there is an accumulation of dust/fibers on intake grate of that blower that can get so bad as to block it.

The Harman Mag stoker is tough to adjust so temps will be steady etc? on my Super Mag I set the feed to 2 1/2 and temp to 70 deg.. and I leave it there and it will stay that way 24/7 for 7 yrs now.. from Oct 1st to April 15ish..

I've read many posts sort of about the adjustments of the Mag stoker and I'm glad I don't have one.. correct me if I'm wrong.

I think Gary's is a case of running in idle mode at >35* and trying to get as efficient as possible with coal usage. The on/off timer controls don't give him the high efficiency his custom controller does. I think in other cases i remember it was a matter of getting the initial feed / air settings set.

My house stoker is pretty much set it and forget it for normal operation in normal temps. Stove is downstairs, 'Stat is upstairs and stays within 1* and I'm happy with how thoroughly the coal is burned, never an outfire. A friend of mines is the same trouble free operation and once the air is set to match his draft it's hands off.

I do tweak mine during the occasional polar vortex, I have increased air and feed to squeeze a few more BTUs out of the stoker since it is marginal for the sq ft and less than optimal heat distribution for temps in the teens or lower. My friends is connected to his duct system for much better heat distribution in a smaller house and his has no issue keeping up at low temps.

The stoker I have in the shop runs mostly in idle mode unless i have the garage open to it and in idle mode the coal could be burned up more completely. Using the timer settings at 3 / 15 i have no issues with outfires but the shop is warmer than it needs to be.

captcaper wrote: ↑

Sat. Dec. 01, 2018 6:13 am

The Harman Mag stoker is tough to adjust so temps will be steady etc? on my Super Mag I set the feed to 2 1/2 and temp to 70 deg.. and I leave it there and it will stay that way 24/7 for 7 yrs now.. from Oct 1st to April 15ish..

I've read many posts sort of about the adjustments of the Mag stoker and I'm glad I don't have one.. correct me if I'm wrong.

Well I have not had much contact with other keystoker type coal stoves. I did have a regular coal stove many years ago, and that is a whole different animal. The thing I hated most about that was the art form you had to learn to stoke its ashes manually.

So, I can only report on the one Harman Mag that I bought and have. And that one I could not set in such a way that remained stable with the existing controller.
I would keep futzing with the doohicky in the back (pushrod coal speed adjuster), and it was either too fast or not fast enough.
I would play and adjust the on time vs off time on the combustion blower control. I simply could not get to that goldilocks setting. I could get it to work acceptably if had the unit outputting a higher heat level, but it was much more than I needed; at the lower levels I needed, I just kept playing with it, and kept hoping that I wouldn't see an ashpan full of unburned coal, either because it went faster than the burn (and there would be lit coals in the ashpan) or because it went out and the system just kept feeding it.
Now I don't worry about it with the controller I made, and it fully burns the coal just right, not too fast not too slow, only feeding coal when what is in the combustion plate has been burned.