Help Making Circuit

[Used_Cars]

I want to "go" on a project that has been rolling around in my head for years. I did 4 years in the Marines and have basic electronics knowledge and radio fundamentals. Have not touched my electronics training since I left almost 20 years ago.

The idea is a temperature regulated and controlled wood smoke barbeque. The basic design is what's called a "Texas Two-Stage" where you have one metal container for the burning wood and a second metal container affixed next to it for the meat. The smoke "flows" from the side where the firebox is through and across the meat and then vents out on the other side.

It's all about the brisquet.

In Texas, we do an apron steak, aka a "brisquet" which is a huge, 20 lb. slab of fatty and collagen-laced meat. The collagen makes the meat very, very tough to the point that it's inedible. To cook it you need to keep the meat at 225 deg. F. for about 10 hours. Some say 12. Personal preference comes into play here, but the primary reason for the extended cooking time is that it takes that long and that low of a temperature to break-down that collagen into fat, and so at the end of the cooking process you have a very tender slab of meat that is very moist due in part to the collagen breaking down into fat. (It's also very fatty to start with.)

The best way to do brisket is with wood, either oak, or mesquite or a combination of both. You can use any sweetwood like hickory, but in texas it's either oak or mesquite or both.

So the problem is maintaining a constant 225 deg. temperature in the cooking area using highly volatile wood. It's a constant, all day long affair of fiddling with air intake, and exhaust and not opening the lid of the meat, etc... You have to "fiddle" with it, constantly. And the temp falls to below 200, extending cooking time, or the temp soars to above 300 deg, which scorches the meat and degrades flavor, and it dries it out and sometimes there are fires due to the excess fat dripping off and catching on fire.

The solution, my solution, is to build a barbeque that has an electric fan, like one of those small squirrel cage fans you have in your bathroom's ceiling mounted "fart fan". The fan forces air into the firebox based on the temperature of the cooking chamber. In general, when the temp is low, more air gets forced into the firebox, and when the temp is high less air is forced. There might be some kind of a one-way "flapper" vent thing like what you have outside the house for your dryer, so that if the fan stops the flapper drops down and closes off the firebox so that no air gets into the firebox at all, which will cool a too-hot fire quickly and get things back to normal temps.

So I anticipate a lot of experimentation in terms of cubic feet per minute. Too much and you are blowing ash from the firebox all over the meat, so there will be a "hard" limit on CFM, therefore motor rpm, which will be a specific voltage (AC). So somewhere between "off" and "x" VAC are my parameters.

One thing I wonder if the fan should be either full-on or off, maybe high, medium, low, off, or totally analog.

Another benefit I imagine it will have, in addition to more consistent temperature and so therefore shorter cooking times, is that the wood will burn more efficiently, since the "highs" of the highs and lows consume more of the wood than is needed.

So that's the general idea. What I'm looking for, for my first prototype, is a basic electronic circuit, a temperature sensor and a fan.

[stj]

Re: Help Making Circuit

maybe a motor on the air flap and a process-controller running it.
similar to the controllers used on reflow units.

[Longbow]

Re: Help Making Circuit

This subject can be quite interesting and complex, as it is used commonly in manufacturing and industry. My first question would be: does a fan actually regulate the cooking temperature as you suggest? The second question is: if you control a fan to regulate the cooking temperature, then you have to keep the heat source relatively constant. Otherwise you are asking your system to control both the fan and the heat source, whilst controlling only one of these things is sufficient. Controlling the heat source is the most common method.

Other ideas to think about are how wide a temperature range are you willing to permit? As you narrow the allowable temperature window, you must increase the power levels that are used to control it - either the fan speed or the heat source.

This project is a closed-loop control system. Each system is usually tuned to a specific set of variables and specific equipment in use. The simplest approach would be to use mechanical temperature limit switches to set the upper and lower temperature limits. Signals from the thermostatic switches would speed up or slow down the fan, which in this case would be a simple 2 speed arrangement. Whether you could do it that simply is the question. For fun and amusing bed-time reading, do a search on PID controllers, which would be the most exacting approach, but also the most difficult.

Good Luck!

[Andrew F. Ali]

Re: Help Making Circuit

Probably a thermal switch, I think the black tip one is 225 deg F, to turn on a relay connected to a fan to force draft the smokeover the meat???

[stj]

Re: Help Making Circuit

a pid controller with a thermocouple would be best.
something like this

[Andrew F. Ali]

Re: Help Making Circuit

a pid controller with a thermocouple would be best.
something like this

This is something we would use in one of our Oil Refinery Plants....

[stj]

Re: Help Making Circuit

is that a code-word for a rum-still?

[Andrew F. Ali]

Re: Help Making Circuit

No.......Petroleum products only......Jet A-1, Gasoline and Diesel......Alcohol (rum) would be from the Angostura Refinery....next to the Dildo Plant...

[A1toadstool]

Re: Help Making Circuit

The easiest way I have seen to do a cold smoker or what your talking about is on an eposide by Alton Brown - on the food network. I'm sure it's on youtube.Maybe that will help.

[Used_Cars]

Re: Help Making Circuit

The easiest way I have seen to do a cold smoker or what your talking about is on an eposide by Alton Brown - on the food network. I'm sure it's on youtube.Maybe that will help.

I'm watching YouTube videos tonight about this and will look for one by Alton Brown.

This is something we would use in one of our Oil Refinery Plants....

Yeah that's a bit over the top. I read the specs, most were meaningless to me.

Probably a thermal switch, I think the black tip one is 225 deg F, to turn on a relay connected to a fan to force draft the smokeover the meat???

Yes. The closest analogy I can think of is a HVAC thermostat system, with the temps elevated to say 210 to 240 def. F.

This subject can be quite interesting and complex, as it is used commonly in manufacturing and industry. My first question would be: does a fan actually regulate the cooking temperature as you suggest?

Well I haven't tried it but airflow controls temperature yes. As you restrict or open "air in" or "smoke out", the fire burns hotter or cooler, which affects temperature in the cooking chamber.

The second question is: if you control a fan to regulate the cooking temperature, then you have to keep the heat source relatively constant. Otherwise you are asking your system to control both the fan and the heat source, whilst controlling only one of these things is sufficient. Controlling the heat source is the most common method.

I think you are confused. By regulating the air flow to the burning wood, the temperature will be controlled. More air, hotter fire, hotter cooking chamber. Less air, cooler fire, cooler cooking chamber. No air, no fire, no heat in the cooking chamber at all.

Other ideas to think about are how wide a temperature range are you willing to permit?[/QUOTE]

I've been thinking about this. I'd say "acceptable" "green" cooking range is between 210 and 240 degrees Fahrenheit. That's 225 (optimal) plus or minus 15 degrees. I think anything more than 275 should be "panic mode", where all air is closed off to the fire in order to prevent scorching the meat, and at the other (lower) end of the spectrum, an extended period of time below 210 degrees with air flow at "max" should cause an audible alarm as that would indicate that the fire has gone out, or is so weak that no amount of air will get it hot enough, or perhaps the wood (fuel) has been expended.

As you narrow the allowable temperature window, you must increase the power levels that are used to control it - either the fan speed or the heat source.[/QUOTE]

Heat source is a wood burning fire. I think that's the part you missed.

This project is a closed-loop control system. Each system is usually tuned to a specific set of variables and specific equipment in use. The simplest approach would be to use mechanical temperature limit switches to set the upper and lower temperature limits. Signals from the thermostatic switches would speed up or slow down the fan, which in this case would be a simple 2 speed arrangement. Whether you could do it that simply is the question. For fun and amusing bed-time reading, do a search on PID controllers, which would be the most exacting approach, but also the most difficult.

Right well I'm looking for specific hardware, circuits, premade controllers, etc... Also I'm wondering about this squirrel cage fan and what kind of resistance range I'm going to need. It seem much too beefy to allow it to run at 100% ever, as I think that would blow ash into the cooking chamber and ruin the meat. So I'm going to have to experiment with CFM testing, and resistance. Btw, I had the idea of testing the correleation between resistance and CFM (cubic feet per minute) of air movement by using the fant to fill a large garbage bag and timing the fan on how long it takes to fill a (for example) 50 gallon bag. Have to do some conversions between gallons and cubic feet, but I'm pretty proud of my "thinking outside the box" skills on this one.

Example: At xxx ohms resistance the fan motor turns at yyy rpm which causes zz cubic feet per minute of air flow.

What I don't know is how to measure motor RPM, and if I even need to.

maybe a motor on the air flap and a process-controller running it.
similar to the controllers used on reflow units.

I've never seen those. I wonder if that couldn't be used as an exhaust control, where the chimney closes off completely if the temperature exceeds (for example) 300 degrees, which would choke off the whole system completely, no matter what the fan side of the system is doing. Extreme temps in the cooking chamber might indicate a grease fire, and having a (what's that word called, where you have two metals that expand and contract at different rates) "bimetal" something-or-other?, so that as soon as a "too hot" temp is reached, the metal bends, closes off the flue/chimney/whatever the word is, and chokes off the system at the exhaust end.

[stj]

Re: Help Making Circuit

the pid controller is really simple, you can program it to raise a temperature over a specific time to a specific level - then hold that temperature for a specific time, then lower it at a specific rate afterwards.

it does this by monitoring a temperature sensor and controlling something - normally a heater.

[redwire]

Re: Help Making Circuit

There are already several projects out there for controlling a wood stove that could be used on a smoker. Generally use an Arduino and a motorized damper to throttle it.

http://hackaday.io/project/786-ardui...ove-controller
http://hackaday.com/2016/03/06/wood-...arduino-power/
http://hackaday.com/2016/02/08/a-wir...stove-monitor/

[Longbow]

Re: Help Making Circuit

I think you are confused. By regulating the air flow to the burning wood, the temperature will be controlled. More air, hotter fire, hotter cooking chamber. Less air, cooler fire, cooler cooking chamber. No air, no fire, no heat in the cooking chamber at all.

No, not confused. I don't think you realize how difficult it is to quantify the individual parts of the system into a working unit. If you are using a wood fire, someone will have to stand by and keep feeding wood at a regular rate into the smoker - and that defeats the purpose of the project. If you are trying to increase the heat by blowing air below the coals (similar to a blacksmith forge) then you will need something other than a fan blowing air across the top of the burning wood. The air speed/volume problem is complicated because you must construct tables of your actual empirical test results. The data will tell you how fast the fan has to be running to raise or lower the temperature, and how fast the correction takes place.

The more exacting the temperature needs to be, the more complex are the requirements of the temperature control AND the heat source parts of the equation. It is not a trivial problem, unless you can live with a simple thermal limit switch controlling power to the fan. Taking into account the time and cost associated with the project, you would come out ahead by paying someone to stand next to the smoker and make manual adjustments as necessary.

Right well I'm looking for specific hardware, circuits, premade controllers, etc...

Yes, all these things exist and are easily available but the cost is prohibitive for the home experimenter. The part that is missing from your system is that there is no reliable regulated heat source. The controller needs to control something. And whatever that something is, must actually affect the temperature in a reliable and predictable way. Turning off a heating element will cause its temperature to drop. Restricting air to a closed firebox will also cause the temperature to drop, but it will take a long time. How long? What will the controller control?

[Longbow]

Re: Help Making Circuit

the pid controller is really simple

NOT

you can program it to raise a temperature over a specific time to a specific level - then hold that temperature for a specific time, then lower it at a specific rate afterwards.

That description is not a PID controller. it is simply a software programmable heater control. You might take a PID system and use only the proportional function, but then why go to the trouble?

True PID controllers are found on things like robotic arms and optically sensed automatic machine tasks that must perform in a highly specific way. Each PID controller, if all 3 feedback methods are actually implemented, must be carefully tuned in software for the task and the specific equipment used (such as motors, solenoids, heaters, fans, etc.) There is lots of interesting math that accompanies each setup. Once again the final configuration is found through empirical testing.

I doubt if a meat smoker merits even a software programmable controller, but if the OP is up for it this would be a neat project. I would scout around for a variable speed motor and find a constant fan speed that runs the cooker near to the right temp. Over temp, you would shut the fan off. Under temp would run the fan at the preset speed. What could be fairer than that?

BTW, I volunteer to evaluate the finished smoked meat to see if the controller is working as expected.

[Used_Cars]

Re: Help Making Circuit

No, not confused. I don't think you realize how difficult it is to quantify the individual parts of the system into a working unit. If you are using a wood fire, someone will have to stand by and keep feeding wood at a regular rate into the smoker - and that defeats the purpose of the project.

Not true. In the two-stage smoker, I load the wood into the fire chamber, get it hot and as long as it does a long, low burn, that will last long enough to finish the entire brisket. When temperature fluctuates wildly and the wood burns too hot, it consumes more of the wood than is necessary to maintain the magic 225 deg. temperature. I've been reading-up on this idea of using forced air to control smoker temperature and others are doing it, and one of the secondary benefits being reported is that it requires less wood as it is being used more efficiently.

If you are trying to increase the heat by blowing air below the coals (similar to a blacksmith forge) then you will need something other than a fan blowing air across the top of the burning wood. The air speed/volume problem is complicated because you must construct tables of your actual empirical test results. The data will tell you how fast the fan has to be running to raise or lower the temperature, and how fast the correction takes place.

The more exacting the temperature needs to be, the more complex are the requirements of the temperature control AND the heat source parts of the equation. It is not a trivial problem, unless you can live with a simple thermal limit switch controlling power to the fan. Taking into account the time and cost associated with the project, you would come out ahead by paying someone to stand next to the smoker and make manual adjustments as necessary.

Yes, all these things exist and are easily available but the cost is prohibitive for the home experimenter. The part that is missing from your system is that there is no reliable regulated heat source. The controller needs to control something. And whatever that something is, must actually affect the temperature in a reliable and predictable way. Turning off a heating element will cause its temperature to drop. Restricting air to a closed firebox will also cause the temperature to drop, but it will take a long time. How long? What will the controller control?

I think you are making WAY more out of this than is realistic. Have you ever ran a wood smoke barbeque? It's like this. You walk outside and look at the temperature gauge. If it's lower than 215, you open either the air intake at the firebox or the exhaust/chimney on the cooking side. Go inside and watch some more TV. Come back outside and see what the temp is doing. If it's good, leave it alone. If it's too cold still, open either intake, exhaust or both. If it's too hot, restrict either the intake or the exhaust. Go back inside to watch TV. Come back out 15 minutes later and check temperature. Eventually you find a "groove" and it will work for an hour or two or three, and then "something changes" and you have to find new settings.

In a forced air setup, you either don't need an exhaust and can just force the air in and let it seep out the cracks & gaps of the cooking area (under the lid), or you could get fancy and to some kind of one-way gate thing that's spring loaded, so that when air is getting forced in, exhaust (smoke) is getting forced out. Either way, going from a passive system where you need to massage both the intake and the exhaust at the same time, to an active, forced-air system reduces your variables of "things I have to fiddle with" from TWO to ONE. Either the air is being forced in, or it's not. That's it. Binary, on/off.

It's possible that there is a magic fan speed where the fan's output (in terms of CFM) is "perfect". High enough to get the wood going, but low enough so it's not blowing ash all over the food. This is what I was trying to allude to earlier. The first thing to do is establish boundaries. How much voltage to produce how much fan speed to generate how many cubic feet of air flow.

Sure, there will be testing. But having real time monitoring so that the instant the cooking chamber temp drops below 215 the fan kicks on, while I sit inside and watch TV. And, when the temp reaches 240, the fan shuts off, and when the fan is off there is ZERO air flow. In terms of your question, how long does it take to "cool down" the cooking chamber if airflow is restricted completely, it's less than 15 minutes. Maybe 5 minutes. So now there's a sort of "duty cycle", where it's on for a period of time, then off for 5 minutes, then on, then off, etc...

It's possible that there could be a more analog relationship between the fan and the cooking chamber, so that at 215 degrees the fan moving "5" Cubic feet of air per minute and at 240, that drops down to "1" Cubic feet of air per minute, with a straight 1:1 relationship between all those points somehow programed in, using an expensive controller that, as you say, makes the whole project cost ineffective, but then what do you gain from that? The meat doesn't care if it's maintained at exactly 225 for 9 hours, or if the temp varied between 215 and 240 during that time. We're not making refined uranium or some space-age plastic. Or crystals grown in zero-G (or whatever science-y thing a person might think of). It's MEAT. Yum YUM! You could probably get away with 300 degrees for 7 hours. The tolerances aren't that exacting. You can't do 200 degrees though. The meat would never cook. I think 215 is the very lowest temp you can allow in the cooking chamber. 225 seems to be the consensus but then you have to consider that when running one of these wood burning smokers, you are fluctuating wildly between 175 and 400 sometimes. It's crazy. Especially if you get a grease fire. And that's ANOTHER reason why this is better. I had a grease fire in my propane barbeque just last week. A particularly fatty brisket decided that it didn't WANT to slow cook at 225 so it decided to set itself on fire and I only caught it because I could smell it from the other side of the yard in the garage.

"Somethings burning..."

Almost ruined 20 dollars worth of meat. A grease fire in a forced-air smoker would cause the whole thing to shut-down and choke-off the fire before it got started. I think I'm going to call this a "forced air smoker", btw. It has a catchy ring to it.

I just don't see it being all that complicated. This is a HVAC thermostat operating between 215 and 240 degrees, instead of 55 to 100 degrees.

[Andyy]

Re: Help Making Circuit

It's possible that there is a magic fan speed where the fan's output (in terms of CFM) is "perfect". High enough to get the wood going, but low enough so it's not blowing ash all over the food. This is what I was trying to allude to earlier. The first thing to do is establish boundaries. How much voltage to produce how much fan speed to generate how many cubic feet of air flow.

I just don't see it being all that complicated. This is a HVAC thermostat operating between 215 and 240 degrees, instead of 55 to 100 degrees.

When you mention voltage/fan speed vs. airflow proportionality, you're alluding to some sort of PID control. PID can be complex.

HVAC thermostats on the other hand are simply full on or full off, no setting in between. Thermostats are simple.

For this application, I think the thermostat full on and full off should be sufficient. If the temperature goes above 240 degrees, turn the fan on. If the temperature falls below 215 degrees, turn the fan off. There's no need to work out an "intermediate" setting.

A PID for this application seems to be overkill, but if you want to learn about them it would be a great little project.