Control system for the drum

[geek with fire]

I'm going to mount the temperature control system to the drum this weekend, and I have a couple comments and some questions as well.

On the horizontal, I use both a fan and a servo controlled damper. Since the drum really doesn't need much help, I'm thinking of going with just a fan. The thermocouple will be constantly feeding data to the PID loop which will in turn tell the fan how much air to blow in order to maintain the proper temperature. No problems there.

Questions:
1.) Do you think (1) 1" intake will be sufficient? The fan has quite a bit of power to it, but the diameter of the whole will most likely be the bottleneck.

2.) The Stoker system (and probably the Guru for that matter) uses a flapper to choke the intake when the fan isn't running. I don't really want to deal with that but I'm thinking if I make the intake tube long enough, it should choke it by itself, when the fan isn't running; Correct? I'm basing this on the reports that Bubba noted when he tried to extend his intake and mount the ball valve in a higher location.

Any other suggestions/comments?

 

[bbq bubba]

I think 1" will be fine but not sure about choking the intake.
You'll need a constant source of air to keep the drum running, probably running the stoker into a 2nd intake to just add air as needed....

Problem with that is once the intakes are set, theres usually not a need for more air, more like just a kick to clear the ashes once in a while.

Are you thinking of all this in just one intake and then shutting off the air when the fan quits?

Have you seen the redneck guru yet??

 

[geek with fire]

Well, the fan will operate at whatever speed needed to maintain the correct airflow. I think I need to start with only one intake. Otherwise, the fan will try to blow out the other intake, possibly causing an airflow issue.

I may even do a "trumbone style slide" intake to lengthen tube, just to find the sweet spot.

As for the redneck guru, hopefully mine will be prettier than a hair dryer...it will for darn sure be more complicated!

 

[geek with fire]

I thought of another question. What about extending the inside of the single intake to the center of the drum (plug the end, cut a hole all the way through the pipe for air to go straight up and down. That way the air will not stoke one side of the basket and burn uneven. Is that overkill, or do you think it will help? I might have an ash blockage issue, though (boy that's sounds painful if you say it outloud!).

 

[richtee]

What about a hi-current driver to "kick" the ash pan every time the system calls for heat...just in case? A rod thru to the outside mounted to a solonoid you hit with a couple pulses?

 

[bbq bubba]

Interesting thought!
I start my basket by leaving a space in the middle and dumping the coals in that, always seems to burn from the center out.....

Ash blockage.....sounds like that could hurt!

 

[geek with fire]

Then what would my son do? "Isaac....go kick the drum" ....twannnngggg, there he goes!

 

[yankeerob]

Why not just purchase the fan from guru/stoker? It has the choke already attached as well a heat sink so the fan don't melt. Stoker is TTL (5v) and guru 12v. I used to be in electronics but migrated to software. What's a PID? Got a schematic?

-rob

 

[dbarnett66]

Looks like I have some learning to do. I thought you could pretty much start the lump and walk away once the ball valve was correctly set. Now I am watching this thread develop into high tech thermo control and charcoal basket refreshing.....I have a feeling that my expensive UDS build budget is going to be revised.....

 

[richtee]

Sorry Isaac... don't mean to step on yer toes, Bud. Wear soccer shoes, speaking of toes.

 

[geek with fire]

Nothing against the commercial stuff, but I'm a build it from scratch kind of guy. As far as their fans go, they're kind of expensive, so I just steal them from old computers.

PID is a control algorithm. It stands for Proportional Integral Derivative. The algorithm allows a set point to be maintained with a set amount of tolerance. The output is contantly adjusted to maintain the setpoint based on feedback from the input. In my case, the PID controller is softwareb based, but there are other PID systems out there that you plug a probe on the input side and a fan on the output side.

 

[yankeerob]

What are you using to interface your computer to the outside world?

I've thought about doing this with hardware - temp probe, potentiometer, op amp, output transister, fan. It would be pretty cheap.

But, like you, I like gadgets so a bought a stoker and a guru. I'm going to eventually write some software for the stoker but I'm booked until mid August with contests and catering.

-rob

 

[yankeerob]

check this out. Pretty simple:
http://www.cpemma.co.uk/thermal.html

-rob

 

[geek with fire]

I use several different brands of DAQ cards. Some are serial based and some are USB based. I'm sure if I added up all of my costs, I'm way over what Guru and Stoker charge. But, I get exactly what I want, and I get to play with the big boy toys.

I've been working on a web page that is pretty sloppy at this point. Do a Google search for something very similar to my SMF name, if you are interested.

Great link, I'll have to look at that a little deeper.

 

[geek with fire]

Well, I was all stoked (boom boom chick) to do a dry run of the control system on the drum today. I built a protype mount for the fan and found that the 4" computer blower fan couldn't push air through 1" black pipe; major bummer dude! I'm going to run to Lowes today to get some stuff for plan B. If it works, I'll post pictures of the prototype. (If it doesn't I'll deny that I spend the money on junk when I should have just bought a stoker or guru fan).

This same project worked great on the chargriller, but for some reason is giving me trouble on the drum.

To be continued...

 

[geek with fire]

So last night I assembled my "plan b" blower fan for my drum. This one puts out, what looks to be, enough air to power the drum constantly. I'm also hoping there is enough restriction to choke the intake when the fan isn't running. Otherwise, I'll have to build in a flapper. Anyhower here's a shot of the prototype. Basically the fan will simply be an impeller between 2 tubes. The impeller will draw in air from the upper tube, and force it down the lower tube; compressing it through the 1" whole in the bottom:

Here's a shot with the lid off; showing the fan:

Here's the bottom side where the 3/4" inlet of the drum will screw in:

I was hoping to test this out on a bag full of charcoal tonight, but when I was at wally world yesterday, I found a whole brisket that had to be mismarked (I fealt really bad.....for about 30 seconds and then looked for another one):

Anyhow, I will have to pospone the test to cook up the brisket tonight.

Again, to be continued...

 

[gorillagrilla]

 

[geek with fire]

Well, testing is on......kinda'. I am using the new program and I never tested the PID loop, and it evidently doesn't work. So, tonight I ran the drum up over 300 and mounted the blower assembly on it; the fan's not running. I'm seeing how long it takes to run the temperature down and it's not looking good. It's been over a half an hour and has only dropped to about 275....looks like I'm going to have to build a flapper to choke it. When it gets lower than 200, or stalls out, I'll turn the fan on full bore and see how high it can go. Anyways, here's some pictures:

All inlets other than the blower assembly are closed. (note to self: paint would be a good idea!)

Here's how it mounts to the drum. It's a nice slip fit; it just sets down on the 3/4" nipple:

Rot roh! Looks like somebody is lying....wonder which one is wrong?

 

[geek with fire]

For those interested, I compliled the data from last night's test into an excel file. The tests are inconclusive at this point as there were too many variables that I didn't control, but I do believe that it answered the primary question: The drum needs a flapper or check valve as any opening on the bottom will keep the fire burning.

http://www.geekwithfire.com/img/uds072308chart.xls

Not quite back to the drawing board yet, but I sure need to ge my pencil sharpener out.

 

[tn_bbq]

These flapper valves used for dryer vents might help.