# Automatic Split-Damper temperature control



## geek with fire (Dec 18, 2007)

Warning: Science Content.....

I'm going to experiment with adding some forced air to my temperature control system. Several weeks ago, I wrestled with a large wind storm and even with the plywood shelter, I still had problems. I placed a box fan in front of the firebox, and the issue calmed a bit.

This got me thinking about adding a dc fan to control system. However, I still like the idea of the rotating damper, and wanted to add the fan only for rapid increases. For example, if I don't monitor my fuel well, and have to add fresh lump to the box, it takes some time to heat up again. The fan should resolve this.

To aid in the control (and this is where the "science content" warning applies....turn away if your brain gets sore easily
	

	
	
		
		



		
			






 ) I added the ability to "overlap" the percentage of use between a primary and secondary damper. In my case, I'm going to have the primary control operate the rotating damper, and the secondary control operate the fan. From the illustration below you can see that I am going to start with about 75% overlap. This means that the secondary damper overlaps the primary damper on the last 75%. So the primary damper can operate up to about 40-50% will little or no help from the fan. As the control gets higher, the fan RPMs start to increase to the point of.......well, possibly melting the fire box (let's hope not).

I'm going to start extensive tests during the Christmas break, but issues I'm sure I will be dealing with are:
1.) fan will I'm sure blow ash into the smoking chamber. That will need to be dealt with.
2.) ????.....ideas from you guys....what do you think?


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## fatback joe (Dec 18, 2007)

What size fan were you planning on using?


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## geek with fire (Dec 18, 2007)

Well, I'm starting out with a fan made for cooling computers.  I'm sure it's way overkill, but it works well with the motor controller that I can operate from my computer.  It's about a 150 CFM fan, but I hopefully won't ever need it to operate at it's full power.


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## fatback joe (Dec 18, 2007)

Hmmm......150......yeah, that might blow some ash running wide open, but like you said it should not have to.   I was thinking that I have never heard complaints of the guys running the gurus and similiar gadgets, but most of them aren't going over 25 cfm that I have seen/heard. So it might be tough to draw much comparision between the two.

I guess there is one sure way to find out. 
	

	
	
		
		



		
		
	


	





   LOL

I would think that the angle of the fan in relation to the opening from the box to the cook chamber could play a factor as well...........hmmmm.   Can't wait to see your results.

Good luck.


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## ron50 (Dec 18, 2007)

Josh:

I'd like to help ya, but my brain is already hurting. Good luck with your testing.


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## richtee (Dec 18, 2007)

A> Suppose you add the fan to the exhaust stack. You'd need a metal blade, maybe even a 'squirrel cage" design, but it would greatly increase airflow, and not be blowing directly on the ash.

OR

B> contemplate a reverse flow design, perhaps with interior baffles thereby dumping any blown ash into the recirc cavity.


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## geek with fire (Dec 18, 2007)

yea, I was thinkin' I wanted to try the reverse flow concept at some point anyhow, so I may do that.  I'll have to move the stack, so it won't happen for a while.  For now, I've got some thick stainless mesh that I'll stand up in the smoke chamber during my testing, just to see how much stuff I collect.  Really though, testing should prove that I don't need to move that much air, and I can calibrate the fan not to run that high.


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## smokebuzz (Dec 18, 2007)

Why don't you just "drive" your fan motor down to a manageable/controllable speed?


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## bbq bubba (Dec 18, 2007)

May be a lil overkill Josh, i think the Guru run's a 10 cfm blower, unless you can get it slowed down?


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## geek with fire (Dec 19, 2007)

Yea, at full power, it is definately overkill.  However, as I understand how the Guru and Stoker work, at regular intervals full power "puffs" engage; basically just turning it on and off as needed to increase oxygen, fueling the fire.  I'm, however, using an electronic motor controller to set a specific RPM based on what is needed to fuel the fire to the desired temperature.

So, to your point (BBQ Bubba), normal operation wouldn't require the fan to operate at full power.  But, I will have to plan around things like opening either the smoking chamber lid, or firebox lid.  Both will cause a temperature drop the the control system will try to offset, maxing out the damper and fan until the desired temperature is met.  Now there are a dozen ways I can deal with that, but there's no sense doing anything until I see what damage the full power fan does in a controlled test.  Then scale it back until I get the results I want.

This week, I'm finishing up an enclosure that will house the fan and servo-damper, that will be connected to the firebox by a 4.5" diameter metal tube.  Once I get that done, I will post some pictures; possibly a video.


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## richtee (Dec 19, 2007)

Well thought out, Sir!


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## wavector (Dec 19, 2007)

I like the fan idea, and I use one sometimes on my vertical from a distance. Originally, I had the fan in the proximity for use on me.

I still believe in the concept of having a stack on the firebox too. This would allow the billowing smoke to escape and give time for a fresh log to be brought up to temp. By closing the damper during this process, the ash would then have time to escape with the billowing smoke and give time for the TBS to be achieved before opening the damper to the smoking chamber. Monitoring temperatures inside the firebox and visually observing the TBS and corresponding temperatures would give a base with which to work. I also believe in a heat transfer through the metals used for both the smoking chamber and the firebox. I believe in a thicker steel used for the fire box which would seem, in theory, to conduct to the smoking chamber steel thus allowing for less fuel to maintian stable temperatures.


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## peculiarmike (Dec 19, 2007)

Ya know Geek, it's getting closer and closer to the day I make a run to Sedalia to check out your rig. When the weather warms a bit keep an eye out for an old gray haired fat guy on a lava red Harley.


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## geek with fire (Dec 19, 2007)

I like that idea.....a lot!  The only issue with that is the temperatures in the firebox typically exceed the usable range of the common thermistor probe.  It would work for me, because I use thermocouples and have one that will go up to 1200 degrees.  But they are very expensive and I'm trying to keep the "common man" in mind when I design this incase I go public at some point (I'm not more well off than the common man, but I'm willing to spend the extra dollar for the geek factor!).

No problem, but make sure you've got yer leathers....I'm out in the boonies!


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## billybones (Dec 19, 2007)

Yes but clearly you've ignored, like most people, the increased fluctuations in heat output due to the self contained vector modulations in the coal sub-molecular data stream. 
So then, assuming X is constant:

.47f(x)/yx will be roughly = f(y)/x^3+(y^2*.47)= smoke some food, drink some beer, rinse, repeat!

...and I think we all know what that means!


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## fatback joe (Dec 19, 2007)

Billy,

I think you got your 2 and your 3 reversed in the equation.  LOL


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## geek with fire (Dec 19, 2007)

dude, you had me at "vector modulations"....you had me at "vector modulations"


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## billybones (Dec 19, 2007)

My god....you are so right. I completely ignored Saddlebaum's phony forum math principle which states clearly: "When creating a phony math formula on an online forum, always use sequential numbers to further enhance the illusion that you know what the hell you are talking about!"


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## billybones (Dec 19, 2007)

You complete my vector modulations....


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## promise'cajunbiker (Dec 19, 2007)

I definately would encourage the reverse flow design. I built mine a couple months ago and thoroughly enjoy it. I think there are pictures in roll call. It's a little crude but it works.


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## packplantpath (Dec 20, 2007)

Doc:  I'm almost positive a flux capacitor would greatly aid in this endeavor.  

Marty:  But Doc, this is the 21st century, they don't have flux capacitors yet.  Even if we could find a flux capacitor, where we gonna get 1.21 Jigawats of electricity.

Doc:  My boy, we smoke in thunderstorms.

Looks good man.

What are the odds that the fan melts?  I'm not sure where you are mounting it so that may be a non-issue.


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## geek with fire (Dec 20, 2007)

That's the $58.38 question at this point.  But the odds are high that something gets crispy.  I just hope it's not my $25 servo controllers or my servos.  I'm going to put one of the temperature probes in the fan box when I'm testing, to monitor for this.

Made progress on the box last night.  I got the servo and the damper mounted in the box.  I just need to cut the holes in the box for the damper to breath and make a mount on the tube to connect to the firebox, and I will be ready for a test.  Getting closer.


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## virgo53 (Dec 20, 2007)

regarding the pix above, what model number and make of controlller, and where do you get those kinds of toys?

That level of control is highly interesting to me
Virgo53


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## geek with fire (Dec 20, 2007)

It's all custom built stuff using hardware intended for robotics projects.  I'm doing the programming using VisualBasic.NET


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## ajthepoolman (Dec 20, 2007)

"Did you ever know that your my heeeeerrrooooooo!!!!"

Now slap a SQL2005 database on the backend that will insert the various temperatures and the outside weather conditions so that in a couple years time, the program can compare the current weather and temps to what was recorded in the database and make it's own corrections!

Who would of thunk that Artificial Intellegence would emerge from the SMF!


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## richtee (Dec 20, 2007)

Heh.. I consider mine artificial sometimes   ;{)


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## fatback joe (Dec 21, 2007)

The way this thread has turned reminded me of an email I got a few years ago and saved because it always made me laugh.

Here it is.


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Email his details to me at: [email protected]

Please do not reply directly back to this email as it will only be bounced back to you.


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## packplantpath (Dec 21, 2007)

Geez, I just relinquished my patent on one of those because I thought no one was interested.


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## geek with fire (Dec 22, 2007)

OK, it's late so this might be choppy.  I have the protype rig with the fan mostly built and gave a test run on the computer, so I thought I'd take some pictures.

Here's the basic unit: a sealed enclosure will hold the fan, the damper, and the servo that controls the damper.  The electronics will be mounted outside the box incase it gets hot in there (won't know until I test on the smoker).....yes, the tube is a paint can....it's a protoype, not the floor model.







Here are 2 shots inside the box.  I chose a plastic box only because it's easier to work with and cheaper than a metal enclosure.  I have a bad feeling that it's going to melt, but we'll have to see.











The open end of the paint can will mount over the stock opening of the firebox.  Most likely will add some fireplace gasket to keep contact heat from getting the can hot.  It will also help seal the unit to the firebox.

We'll see this weekend how it runs!


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## wavector (Dec 22, 2007)

http://cgi.ebay.com/P-N-TYP8105G-80X...QQcmdZViewItem

http://cgi.ebay.com/Electronic-Speed...QQcmdZViewItem

Or, something along these lines. I'm concerned about the NEMA 3R box melting. I would consider, with this prototype, not mounting it directly to the firebox. Maybe go with flexible aluminum dryer venting material that is found at Lowes or Home Depot. I wish I was there to help you.


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## smokebuzz (Dec 22, 2007)

I think it will be fine, kinda self cooling.

How are sensing position,? i think i only seen 3 wires.
Does that acuator have internal limits?

I like it


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## bubba t (Dec 22, 2007)

...I would have to agree with Buzz on the self-cooling-- the fan intake air will keep things under control...if you did find the 'guts' were getting too hot from the nearby firebox you could install a simple metal shield on the back of the fan housing facing the firebox leaving a small air gap ...say 1" +/-... to help insulate.
  What safety do you have in mind to protect/shut off fan when actuator closes dampner completely?..
  I think your project is sweet!!...


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## geek with fire (Dec 22, 2007)

Not sure I understand your question, Buzz, but the temperature measurement is done with a Type-K thermocouple mounted in the pit.  The current temperature is bounced off of a PID loop which calculates what percentage of the damper and fan need to be open at any given time to maintain the desired the temperature.


I'm going to mount an oven probe in the box while running just to keep an eye on things.  I think I will be able to catch a problem before it causes any damage.

As far as safety for the fan, check the program interface from the first of this thread.  The program will maintain the positions of both the fan and the damper.  If the program sends a signal for 0% airflow, the damper will close and the fan will shut off.


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## smokebuzz (Dec 22, 2007)

How does the controler know where the damper/vent is positioned?


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## geek with fire (Dec 22, 2007)

Servos are closed loop systems, meaning, you send them a signal of where they are supposed to be, and they move until they hit that point; and they maintain it.  In the setup of my program, I simply state the position of fully open and fully closed.  From there, I send the servo a percentage that I want it set to, and it goes there.

Same concept on the fan.  I tell it what percentage of usage to run at and it tries to maintain that.  The difference is that the fan is not a servo, so the program has no idea if the fan is doing what is told.  Now, I can fix that by mounting an encoder on the fan that tells the program what RPMs it is running at, and make corrections if needed.  However, and this is hard for me to admid, I think that would be overkill at this point.


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## smokebuzz (Dec 22, 2007)

Would'nt a TACH be more appropiate for the fan?
My experiance with servo motors is, i always needed a encoder/resolveror some type of position feed back, otherwise i was always have to recalibrate and take into consideration of drag on my moveing components.
With no position feed back, would you be positioning on time of movement fwd/rev?


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## geek with fire (Jan 1, 2008)

Well, I'm trying to recover from pneumonia, so I haven't been allowed to go outside to smoke anything. I tried to explain to my wife that the smoke would be good for my lungs.....yea, she didn't buy it either.

Anyhow, I've been spending time down in the "bat cave" and got the prototype completely wired up. Today, I got it mounted to the smoker. Anyhow, I snapped some shots just in case I melt the crap out of it tomorrow.

The black box below the fan box houses all of the electronics: I/O Card, 2 servo controllers, and speed controller. It looks a little bulky, mounts pretty solid.









Here's the inside of the firebox. The rig mounts to the hole in the stock pivot.


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## bubba t (Jan 1, 2008)

..I was wondering how progress was coming on this sweet project!!... Hate to hear you been ill...Get better man....


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## geek with fire (Jan 2, 2008)

Well, I'm still coughin' up large chunks of lung (yea, that was a bit too much information on a cooking forum!).  And, the wind chill today would cause snot-cicles, so I gave up on testing the new temperature control setup this weekend.  As soon as I feel better and/or the temperature gets a bit more reasonable, I'll give it a shot, take some pictures, and post some data.

Peace out (that would cause my wife to roll her eyes.....I never could pull off the whole "peace out" thing)


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