Home-Made Fan Assisted Stoker for my Side Fire Box

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ski-freak

Meat Mopper
Original poster

I saw some expensive thermostatically controlled blowers being sold for forcing more air into the air intake of various smokers, and was pretty floored that they get $300 for some of these things. I thought about it and the times I would really want to stoke my firebox would be to help it heat up faster during initial starting, and to help re-heat again after opening a door. For those uses it probably isn't necessary to get fancy with a sensor and a control circuit. A simple switch, and maybe even a few variable speeds would do me fine.

I took a look at my Oklahoma Joe Longhorn Offset Side Firebox Smoker/Grill and realized that the air intake butterfly has a post/lever that could support a plenum, and all I would really need to build a plenum would be a 9" diameter and couple of inch deep stainless steel pie pan. I found one for $5. The post is 2.800" away from the center pivot, and the post is 0.4375" diameter (7/16").

I had a few extra muffin fans left over from an electronics project, so one of them would do. The fan I picked is a NIDEC TA450DC 12 VDC (nominal) Muffin Fan that was purchased at a deep discount ($10). It has a cast metal frame and a ball bearing motor and is rated to operate over a voltage range of 7 - 14 VDC while drawing 0.47 Amps. Life is specified as 57,100 hours. The fan is rated at a maximum of 112 CFM (cubic feet per minute) operating at its nominal rating of 12 VDC but will pump less air at lower voltages.

I marked up the pan finding its center and making my post hole 2.800" from the center and then positioned the fan below the post hole and traced it on the pan. I drilled the holes and used a hand nibbler tool to make the big hole for the airflow. Then I used a brass hammer with a small anvil to flatten the nibbled edge.


I assembled the fan and added a length of high temperature wire I had on hand (red/black twisted pair #18), with a double banana plug hi-fi connector at the end.


I already had a small 12 VDC switching power supply that had cost $20 from a discount electronics supplier that would provide the juice. It is capable of 12 VDC at 2 Amps, and also has settings for 9 VDC, 7.5 VDC and 6 VDC that will run my fan at maximum airflow (12 VDC setting), and allow several lower levels of airflow as well. This would be the easiest way to get going but there are many options for power including using a 12 VDC battery with switched voltage dropping resistors or a power rheostat for variable voltage/speed, but that all could come later.


I expected to have to run a die over the steel post on my butterfly to thread it to accept a wingnut to hold the pan in place, but decided to try things out by just slipping it on and letting it hang - and amazingly it stayed in place just fine, so no need to even figure out which die to use and then find a wingnut.


So this little project represented $35 of parts, most of which I already had on hand, and it will stoke the fire for sure since the maximum airflow of the fan I used is rated as 112 CFM. Now I need to try it a few times and see if it helps!
 
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One more member that lays awake at night thinking of stuff to do with their smokers....   
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....  Dave
 
Initial feedback is that it does seem to help start a new fire, stoke a new load of wood, and help recover from opening the door(s), but does not actually make an earth shattering difference. I need to experiment with the lower voltages/speeds/CFM and my chimney valve settings a bit more - but so far it's definitely NOT the blast furnace I was expecting.
 
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Sitting here thinking about it... I'm not sure what it is your trying to achieve.. Is your smoker not getting hot enough ?? From my understanding, the stokers are controlled by a thermostat so if it needs heat, the fan comes on... If too hot the fan turns off and doesn't let ANY air in the firebox... In your case when you turn the fan off the air is still gonna flow into the firebox as the vent is wide open and the air flows threw the fan blades... I don't know.. just confused
 
Sitting here thinking about it... I'm not sure what it is your trying to achieve.. Is your smoker not getting hot enough ?? From my understanding, the stokers are controlled by a thermostat so if it needs heat, the fan comes on... If too hot the fan turns off and doesn't let ANY air in the firebox... In your case when you turn the fan off the air is still gonna flow into the firebox as the vent is wide open and the air flows threw the fan blades... I don't know.. just confused
I am using manual control of my fan, on/off and four different rates of airflow (four voltages that will spin my fan at four different speeds producing four different airflow rates), while I am visually reading the thermometer that's mounted on my food chamber. It's no different than a fancier $300 version, except that theirs is in theory automatic based on feedback from a thermostat/thermister switch/control, while mine is manual based on feedback from reading my thermometer while I stand there operating my manual controls. Plus, at my highest voltage I get more airflow than any of the ones I've read about - but, I do have a pretty large volume smoker/grill: 20 inch diameter by 40 inch long food chamber, plus 20 inch diameter by 20 inch long firebox.

Please advise if I'm mistaken, but I don't see how any fancy version doesn't let any air into the firebox when as you say: "If too hot"? None have any valves or vanes that close off the air intake, and they all do exactly what mine does when I turn it off (stop the fan, and yes air can flow through any fan's blades when it's idle).

What I'm trying to accomplish is get back up to temperature more quickly after opening the firebox to add wood, or opening the food chamber to mop, turn, rearrange food. That this step is manually controlled by me is fine for now, since I had to be there to open the door(s) anyway. More importantly, if I can't make this manual process work on my smoker/grill, then there's no way a fancier automatic one will work either. BTW, building an automatic control circuit isn't particularly hard, it's just not necessary at this point.

I need to experiment more, and in particular with lower rates of airflow, before I can determine if forced air will allow dynamic control of my smoker/grill.
 
I did a little more experimenting using several thermometers and some smoky wood so I could watch the smoke flow out the stack, and it seems like I have too much airflow with the fan, even at the very lowest voltage that will run the fan. I'm pretty sure I need to swap out the fan for a lower airflow fan with the same dimensions to continue testing this concept.
 
I did a little more experimenting using several thermometers and some smoky wood so I could watch the smoke flow out the stack, and it seems like I have too much airflow with the fan, even at the very lowest voltage that will run the fan. I'm pretty sure I need to swap out the fan for a lower airflow fan with the same dimensions to continue testing this concept.
Yes, too much air flow is not good either

Can you regulate the voltage on your fan?
 
Yes, I can regulate the current fan to 4 voltages/speeds/airflow-rates that it will start reliably and run at (12, 9, 7.5, and 6 VDC from the small lightweight regulated power supply with multiple voltage settings pictured above), but from the latest testing I believe even the lowest voltage is still too much airflow. I think I my initial assumption that more intake airflow would just be hotter was wrong, and apparently there is a point I crossed where the opposite occurs. My fan was one I happened to have on hand, and is a very high quality fan (metal alloy frame and ball bearing motor) with a lot of airflow for its size (reasons why they were purchased in a small quantity for another project). At 12 VDC it's rated at a maximum airflow of 112 CFM. It will start and run reliably at 6 VDC but I don't know how much airflow that represents. The manufacturer had no voltage to airflow graph, and I have no manometer to measure the flow. I also am pretty confident the relationship of voltage to airflow isn't linear.

At this point I am going to try swapping in a lower CFM rated fan with the same hole pattern as my current fan, and/or try a PWM (pulse width modulation) circuit to downwardly expand the lower speed/airflow adjustment range of the fan.
 
Great job so far.

But, there is a big difference and that is I can leave my Rock's Stoker manage pit for hours on end and the temp with remain close to constant.  

Just a suggestion here, you could add a PID for about $50 and a thermocouple or RTD for $15 to $20 and you would have a fully automatic airflow management system.  You would have to use a 110 AC fan or used a Rock's Stoker which uses 12 Volts DC.

I run my pellet smoker using a PID system augmented with a Rock's Stoker.
 
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Thanks Savannahsmoker for mentioning their name. I found their web site and saw that they offer 3 blower sizes for their range of stokers: 5, 10, and 25 CFM. They do make some pretty sweet looking stokers!

Yup, those CFM ratings confirm that my 112 CFM fan, even if it only runs at 40-60 CFM at half voltage, is just way too much airflow. I will keep proceeding with reducing my airflow until I experience the right effect, and then will consider automation as you mentioned. When I get there I may ask you for more info if you don't mind.
 
I would not set up a fan to blow into the firebox, but rather to draw out from the chimney. Yes it will get a bit greasy and need replacement. But it will also ensure that heat is not being wasted... and will keep ash from being blown onto your food. Additionally, it will mostly prevent 'backwash' where air blows into the chimney on windy days.

If you think in terms of a kitchen, it makes complete sense. Kitchens do not eliminate smoke and fumes by blowing air in, they do it by drawing air out. Of course, if you go this way you will need to ensure that the door of your smoker seals pretty well.
 
I would not set up a fan to blow into the firebox, but rather to draw out from the chimney. Yes it will get a bit greasy and need replacement. But it will also ensure that heat is not being wasted... and will keep ash from being blown onto your food. Additionally, it will mostly prevent 'backwash' where air blows into the chimney on windy days.

If you think in terms of a kitchen, it makes complete sense. Kitchens do not eliminate smoke and fumes by blowing air in, they do it by drawing air out. Of course, if you go this way you will need to ensure that the door of your smoker seals pretty well.
Interesting concept and I think would actually relieve rather than be complicated by any remaining firebox air gap issues, however I suspect it would quickly prove impractical for several reasons. First, as you pointed out there is a lot of smokey grease that could build up on the blade. Second, most of the type of fans we can easily speed control have small inexpensive fan blades that are plastic and would likely deform at the exhaust stack temperature (225F plus). Third, even the best of these with the highest quality sealed ball bearing motor would have a greatly shortened operating life when subjected to the stack heat - since the motor is right in the very middle of the fan and the heated airflow. These are probably the reasons why the fancy temperature controlled smoker/bbq units all work on the fresh air intake side. The kitchen analogy is a bit different too, since it's not a reasonably well sealed cooking chamber.

Having pointed these challenges out, it's indeed an interesting concept and I think could be made to work with a lot of mechanical engineering. A metal fan blade with a high temperature bearing and a sprocket, mounted within a stack extension plenum, turned by a chain driven by a motor outside of and alongside the stack could feasibly overcome these issues. A commercial range top squirrel cage blower might accomplish some of these goals, but these units are big and expensive and really, really hard to clean out - plus they run on serious power since they have huge airflow.

In the end, we would still get back to how much airflow does it take to get the right effect, and where do you cross the line with too much airflow.
 
My replacement muffin fan arrived from Hong Kong (only $4 shipped). This new fan has much lower airflow, only 26 CFM at 12 VDC versus my previous fan which had 112 CFM at 12 VDC. The new one is much thinner and has a lighter plastic frame and a sleeve bearing motor versus the higher quality alloy frame and ball bearing motor of the much higher output fan I had on hand but proved to have too much airflow.

I swapped the new fan onto my stainless pan plenum easily enough since it had the same exact mounting hole pattern. Interestingly because it has a lighter weight blade, and more delicate motor, it turns on reliably at 4.5 and 3 VDC, the remaining two voltage settings on my power supply that would NOT run my previous fan. This new fan will output 26 CFM at 12 VDC, and lower airflow rates at 9, 7.5, 6, 4.5, and 3 VDC - so I will now have 6 different airflow rates with my lightweight power supply starting with a maximum of 26 CFM. I am looking forward to seeing how it works on the smoker/grill !!!
 
Messed with this some more and am only getting a slight increase in temp, and only at the very lowest fan voltages. The higher voltages actually cause the temp to start to drop. Looking at some of the fancy expensive rigs (and holy cow some are waaay more expensive than I thought) I see they are all using a blower style of fan rather than the muffin style of fan I'm experimenting with, which would create more of a
directed stream of airflow rather than simply an increase in air pressure in the firebox.

I took out my fireplace bellows and tried that and wow if you aim it at the coals through the butterfly damper hole it has a much more profound effect.

I think my pie tin plenum with muffin fan is NOT providing the right type of airflow, so I am going to redesign it to develop a more directional airflow, a narrower column of directed air, rather than just the ineffective cavitation and air currents it seems to be causing. I do like this current fan though in that it runs at all of the power supply voltages, and it's CFM rating is more in line with the fancy expensive rigs. I think I'm going to try remoting the fan to a box/plenum and using a pipe to feed the airflow directionally to the firebox so the air flows more like my bellows through the butterfly opening.
 
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Version 2:


I started with some scrap box tubing steel pipe in my steel bin, and also some 16 Gauge sheet metal, and built a plate that would slip over the butterfly damper post on my OK Joe and set securely in place by hanging weight alone. I had to drill a clearance hole for the central butterfly nut/washer pivot so it set flat in place. I marked the holes of the butterfly damper from the inside onto the new steel plate with a Sharpie Marker and decided to make the hole for the box tube stoker through the lower butterfly hole, but angled up at the bottom corner of my charcoal basket. Then I welded the box tubing in place while using a magnetic welding clamp to hold it at the right angle.

I also prepared a large surplus die cast metal box to become the new air plenum that would attach to the steel plate and hold the new 0-26 CFM Fan. The purpose of the box is to provide an internal space pressurized by the 6 speed adjustable fan, with the aimed box tube stoker pipe being the only exit for airflow. 

The internal dimension of the box tube stoker pipe was 1" X 1" so I settled on making it 5" long thinking that I would get a good steady column of air exiting the stoker pipe.


Note that the air pressure inside the plenum box has to find its way out of the box tube stoker pipe, which is 5X as long as its cross-section and should form a steady column of directed airflow:


Note that the 12 VDC fan is powered by an adjustable power supply (max air output of this fan is rated at 26 CFM at 12 VDC, but fan voltages/speeds are to be selected via a rotary dial switch of 12, 9, 7.5, 6, 4.5 and 3 VDC. I located the fan on the bottom of the plenum box as far away from the firebox as possible thinking it will be better shield the fan motor from rain and heat: 


The Plate and Plenum Box hang on the outside of the side firebox door, and the end of the box tube stoker pipe is aimed up through the lower butterfly hole so its column of airflow will be directed at the bottom corner of my charcoal basket:


Mechanically and Electrically everything seems good, as does the airflow, however the real test will be in actual operation! More to follow...
 
I am just not getting the effect I was hoping for with this experiment.

I have the airflow condensed into a column and aimed directly at the bottom corner of my charcoal basket, and I can vary the speed of the airflow from very low, to very high (26 CFM) over 6 speeds.

I have experimented quite a bit and must be missing something, or more likely my side burner is just not right for a fan/blower assisted configuration. I never even got to the point of incorporating a thermistor based heat controller since I never achieved consistent heat increase with any speed or configuration I have tried. Sure glad I didn't spend hundreds of dollars on a fancy version and I just experimented!

Instead, I am heading in a different direction and dealing with air intake flow into my Oklahoma Joe Longhorn like this:

http://www.smokingmeatforums.com/t/129311/side-burner-air-intake-butterfly-modification#post_879750
 
Overcoming the challenges that you outlined is simple. Instead of mounting the fan directly in the stack, you would want to cut a hole in the side of it, then weld a pipe at a downward angle from it with the fan mounted on the end of that pipe. The fan is mounted so that it blows up the smoke stack, creating a draw. This way you could completely remove the fan from the direct heat and grease. 
 
there is a much easier and less expensive ATC for this. I use it for my WSM clone, it works great.

I just got an OK Joe and will adapt it at some point and see how it works, I have been told by others that have it that it works well with it. It includes a PID controller with programmable alarms, a blower with a door that shuts off the intake when its not blowing, and a nice temp probe.

http://www.auberins.com/index.php?main_page=index&cPath=14_27
 
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