Any experience with Draft Fans?

[geek with fire]

So as it gets colder around here (and windy) I'm sure I don't hold the monopoly on extra effort keeping temps in the smoker up. So I was at the hobby shop the other day and grabbed an Electronic Speed Control. These are normally used to Accel/Decel/Brake the motor in a toy car, but I'm going to use it, in conjunction with my temperature control system, to drive a 12volt DC brushless motor (computer fan). Being an IT guy, I have all kinds of these fans lying around, so they are the obvious choice. However, in looking at the spec's, it looks like the one in the best shape is a 130CFM dude. The other guys that market these control systems use 10 and 20 CFM devices. Now, mine will adjust the speed of the fan from 0-100% (they just cycle there's on and off), and since it is a fan and not a blower, I'm hoping it won't be an issue. Anyone have any first hand experience they would like to share?

 

[bbq bubba]

Are ya trying to mimic a Guru or a Stoker?

 

[geek with fire]

Not really. I still like the idea of regulating the temperature via my servo actuated damper adjustment (not forced air), but there are times I want to add forced air to the equation; bursts of high wind for example. What I'm expecting to do is have the system engage the fan when the computer detects that full damper isn't increasing the temperature. Start ramping up the fan from about 20% to 100% until the temperature starts to approach the desired setting. Then, turn the fan off until needed again.

 

[navionjim]

"There are times I want to add forced air to the equation; bursts of high wind for example."

Geek, no offense intended, but wouldn't it be easier to just put up a wind brake? I'm into verbose engineering myself but to me that would seem to be the most adequate answer to the temp control problem.
Jimbo

 

[geek with fire]

No offense taken, and yea that's worked in the past. In fact I've moved mo smoker into my mower shed, so it isn't as much of an issue when it's running in there. I'm probably just tinkering more than anything, but I want to see how accurate I can get this thing. If the lid stays closed and the conditions don't change abruptly, I can maintain a few degrees either way of accuracy. I'm just trying to add another control (but really, mostly just tinkering!) to handle a change in the conditions.

 

[geek with fire]

Well, I hooked up the big fan tonight to the computer control. At 100%, the thing will blow my hair at 2 feet away. So, I'll need to be carefull, lest I melt the firebox. I'm also curious how it moves ash around; don't want anything competing with my rubs! Anyone with a Guru or Stoker want to comment on the airflow? Are the air "puffs" substantial, or light?

 

[goat]

Geek, I think that Allied Keno sells one mounted in the chimney. I had a small computer fan mounted in a cooler that I had Southern Engineered. Cooler quit but the fan is still running.
Here is a link: http://www.alliedkenco.com/catalog/p...oducts_id/2754

 

[geek with fire]

Thanks for the info Goat! I spent some time last night on the programming side. I'm trying to figure out the equations to make a seamless transition from 0% air flow (damper closed, no fan) to 100% (Full damper, full fan). The hope would be that 100% is never needed so that an under temp situation never occurs (making sure to keep the feller fueled!). Hopefully will get to test a prototype this weekend.

 

[wilson]

I'm a big fan of the draft at Talladega!!!!

Seriously, It sounds like what your doing is simmilar to the fan in an Southern Pride Pit.
Because you worried about the volume of air moving inside the pit,I would control the fan by varying your incoming voltage to the fan, using a volatge regulator circuit looped it into your thermostat. So it will only power on in when your thermostat tells it to, but only to a set speed.
The speed being the variable in the equation.........I'll leave it up to you to do the math because I am sure the volatge curve to it will be logrithmic.

Example: as the temp drops the fan turns on, but also the speed at which the fan spins is "x" percenatge per degrees in drop of temperature, and as the temp stablizes ( rising to set thermostat temp) the speed of the fan slows to "x" percentage or in other words: "go into a maintenance mode" thus decreasing the chances of blowing ashs of your food.
I....think???

Ron

 

[geek with fire]

Thanks Ron. Actually that is covered already in the existing program. The program uses a PID loop, which without going into the boring specifics, isn't like a typical bang-bang thermostat. Based on the difference in set temperature and actual temperature the PID algorithm calculates what percentage of output (from 0-100%) is required every second to maintain the set temperature. What I am working now is to take my existing situation (a servo actuated damper that just opens and closes; 0-100% airflow) and overlap the fan system as needed. I want user to have the ability to adjust how my overlap the fan range meshes with the damper range.

For example, if the user selects 50% overlap: from 0% airflow the damer is fully shut, with no fan. The damper begins to open. When the damper is halfway open, the fan engages, but at low RPMs. When the damper is fully open, the Fan is operating at half its capable RPM. Finally the fan can continue to rise until it reaches its full RPMs.

In another exmple, with 100% overlap: as the damper begins to open, the fan engages at the same time. When the damper reaches 100%, the fan is at Full RPM.

The idea being that the program will be allow the user to adjust the airflow ramp to a point that it can be tuned for any style and size of smoker.

Yer' head hurt yet? Perhaps this stuff doesn't interest you guys, so I'm sorry if I bore you. I know the geek side of the situation. I'm relying on your all's experience with different smoking equipment and situations to make sure I cover all of the bases. At some point, I hope to try to make it work your all's while....if you so choose.

 

[fatback joe]

Josh,

You ever check out the Stumps Forums? They got a whole section for threads on stokers/gurus........may have some of the info on there or might get some of your questions answered with a post there.

http://www.stumpssmokers.com/phpBB2/

Many of the members there use gurus.......heck the new models comes with it built in.

Might be worth a shot on getting some more info on the fans............then again, might be total flat out bust. LOL

 

[wilson]

Hi Josh,
Cool, Actulally my head doesn't hurt I like this stuff. Where is the damper situated on your pit?? Intake, inbetween fire box and cooking chamber or are you talking about the exhuast damper???? Keep up the tinkering!!

Who said food and electronics don't go together...........I heard that Tesla made killer Pork Butt with nothing but a lightning rod, a coil, and voltage bridge

.
Ron

Proud Supporter of MSBSA ( Mad Scientists Barbecue and Smokers Association)

 

[fatback joe]

I heard it was a brisket, but you know how the details get changed over time. LOL Good one.

 

[geek with fire]

Thanks, I'll give them a shot. I hit the Virtual bullet last night. They have a section on this as well. I'll be honest, of all of the forums I hit, SMF has the most BS-free knowledge of them all (not trying to suck up, but you guys know your stuff).

Currently, the servo is connected to the firebox damper on the Chargriller pro. What I will eventually do is build a tube that has its own damper and fan assembly built into one unit. This will mount onto the fire box, covering up the full open stock damper; I hate to use the term "turnkey", but that's the idea.

 

[wilson]

Josh,
I have a Chargriller too, this is very interesting, So the servo just moves an arm that's attached to the fire box damper? Where does the fan sit? do you have any pics of your setup??

What are you using for fuel? charcoal or wood or combo??

With my chargriller I start with a basket of charcoal and some wood for flavor. Then when I get a good bed of coals going I just add a stick of wood every hour or so as needed.

Also are you using any type of insulation on your pit??? I have an old blanket that I throw over the cooking chamber to help mainatin temps in the wind and cold not as high tech as your ideas.......
Thanks

 

[geek with fire]

The servo sits under the firebox, with a connecting rod driving the damper. My web host is down (ASPIX is pathetic! Don't ever use them!) so I can't get to the pic's right now. The fan is a new process that I've just tested only in the bat cave; haven't mounted to the smoker yet. I'm sure my first test on the smoker will include plenty of bailing wire and 200MPH tape!

Also, yes I'm using lump as the main fuel. I don't have a basket, so I have to refuel about every hour. I put one of the small cast iron grill grates in on the right side of the firebox. I put my wood up sticks there. They smoke well there without burning too quick. When they cook down to embers, I roll them off into the lump and replace with a new one. That keeps the smoke light and even thoughout the process.

 

[wilson]

ROFLMAO