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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, Equipment and just outdoor cookin' in general, hints, tips, tricks & techniques, success, failures... but stay on topic. And watch for that hijacking.


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Unread 02-22-2013, 04:07 PM   #1
frankH
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Default My Updated Gravity Feed design

There are some expensive commercial smokers out there that can control fire temp separately from smoker temp, and that sounds like a great idea. I think lots of off flavors and the dreaded white smoke come from fires temps that are too low.

I have no idea how those smokers control temps, but hereís my plan for my gravity feed smoker. Iíve been planning this on and off for a year, and would appreciate any holes you can poke into my idea.

Iíll use my Stoker to operate a fan based on a high temp probe in the fire box to maintain my fire temp. A second probe will be in the smoking chamber which will maintain 225 degrees by opening or closing a bypass damper off the firebox.

Fire probe is low: Fan kicks on
Fire probe is high: Fan shuts off
Smoker probe is low: controller energizes actuator which closes bypass, directing heat/smoke to cook chamber
Smoker probe is high: controller de-energizes actuator, which allows a spring to open the damper on the bypass, directing the heat away from the cook chamber

Iíll have to find an actuator, and build a damper for the bypass.
Iíll need to buy a non-stoker probe that is rated for fire temps.
Unless they will sell me one separately, Iíll need to sacrifice a stoker fan, to connect the actuator to the Stoker with the appropriate connector/wire.
And Iíll need to tune the size of the fire box and by bypass in order to ensure the fan is on as much as possible.
Controller interaction may be an issue since two separate PID controllers will be interacting.

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Unread 02-22-2013, 04:21 PM   #2
jonboy
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Quote:
I’ll use my Stoker to operate a fan based on a high temp probe in the fire box to maintain my fire temp
Are temperature probes rated for the temp in the firebox?
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Unread 02-22-2013, 04:25 PM   #3
frankH
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You can buy probes rated up to 1400 degrees pretty easy. Not from stoker or guru though.
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Unread 02-22-2013, 07:48 PM   #4
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I'm no engineer but I see a few issues.

The bypass will defeat the main operating principal of the gravity feed design. All the fuel needs to be contained within an oxygen deprived envorment, letting air in will not provide the controlled burn you expect. It is best to introduce air in the combustion chamber.

You have the blower blowing air into the ash pan, I suspect that will blow ash along with it
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Unread 02-22-2013, 07:52 PM   #5
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You dont wanna controll the temp in the firebox area. You wanna controll in the temp in the cooking chamber to allow for different amounts of meat to be cooked.
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Unread 02-22-2013, 08:01 PM   #6
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" I think lots of off flavors and the dreaded white smoke come from fires temps that are too low. "
You basic concept is wrong, in turn mod. will be meanless.
"dreaded white smoke" is key factor to smoking.
If you dislike dreaded white smoke, why do not you use electric/gas pit directly.
Indeed there is so called cold smoke generator to creat "dreaded white smoke" in purpose
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Unread 02-22-2013, 08:05 PM   #7
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Even you want to maintain high temperature of fire and low temperature of pit, your design is wrong too.
1.You can use thin single wall to build your pit instead of insulated double walls.
2.You can have two outlets on the fire box, a SMALL one leading to pit, the other to open air. You simply open or close outlet to open air.
3.You need fire box as small as possible
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Unread 02-22-2013, 08:33 PM   #8
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the idea kinda reminds me of an Oyler, how if controls the airflow by opening and closing a damper.
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Unread 02-22-2013, 08:53 PM   #9
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Quote:
Originally Posted by WineMaster View Post
You dont wanna controll the temp in the firebox area. You wanna controll in the temp in the cooking chamber to allow for different amounts of meat to be cooked.
If it works right, smoker temp could be set for any reasonable temp I want.
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Unread 02-22-2013, 09:10 PM   #10
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Quote:
Originally Posted by woodpelletsmoker View Post
" I think lots of off flavors and the dreaded white smoke come from fires temps that are too low. "
You basic concept is wrong, in turn mod. will be meanless.
"dreaded white smoke" is key factor to smoking.
If you dislike dreaded white smoke, why do not you use electric/gas pit directly.
Indeed there is so called cold smoke generator to creat "dreaded white smoke" in purpose
I've always heard lots of white smoke is the sign of a low fire temp and off flavors.

I'd like to keep my fire at a constant 750 degrees. The smoking chamber will e kept at hot and fast or low and slow temps.
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Unread 02-22-2013, 09:20 PM   #11
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It looks like you're trying to re-invent the gravity fed wheel. The only smoke that comes from my gravity fed cooker is during initial startup. I couldn't be happier with how it works. I also don't see the need for an extra chute for wood, I throw about 5 chunks in while loading the chute. If you get this off the ground, I'd love to hear how it works!
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Unread 02-22-2013, 09:25 PM   #12
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you dont need a wood chute u put your wood chunks in your ash pan and the ambers drop on the chunks and create your smoke
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Unread 02-22-2013, 09:53 PM   #13
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Quote:
Originally Posted by frankH View Post
If it works right, smoker temp could be set for any reasonable temp I want.
I think your overthinking a simplex design.
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Unread 02-22-2013, 10:15 PM   #14
BRBBQ
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by your design, how does the wood would even smoke? Looks like the wood is before the heat..
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Unread 02-22-2013, 11:17 PM   #15
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Quote:
Originally Posted by BRBBQ View Post
by your design, how does the wood would even smoke? Looks like the wood is before the heat..
Air inlet is at the top of the ash pan on the left. Ideally the wood and temp probe is at the hottest point of the charcoal.

I'll likely get rid of the wood hopper, but I do want a simple way of adding wood throughout a burn. Maybe a door on the side or something.
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