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Unread 08-16-2011, 11:06 AM   #8461
CBW1999
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Default Temperature variations solution

Just a couple of thoughts on why long probe vs short probe thermometers read differently in the UDS.

Looking at the pictures as I read through the thread, I noticed that pretty much every thermometer shown, that had been used- has a build up of contaminants (seasoned). This will cause the thermometer to give false readings to some extent.

The heavier the contamination, the more fluctuation. As the contamination is uneven and acting as an insulator initially and then possibly a heat sink, I can see why it takes time for adjustments to be noticeable.

Even though it is minor differences for the most part it still is likely avoidable. I think that cleaning the probes after each use will help with this. It is probably he only part of the UDS that can survive without being seasoned.....

I know this doesn't address the issue of thermal mass and convection as a cause of varying temperatures, but is one possible causation that maybe we can eliminate.

IMHO
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Unread 08-16-2011, 11:15 AM   #8462
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ok thanks.. all my other hardware is stainless... it wasn't that much more at depot
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Unread 08-16-2011, 11:28 AM   #8463
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Quote:
Originally Posted by CBW1999 View Post
Looking at the pictures as I read through the thread, I noticed that pretty much every thermometer shown, that had been used- has a build up of contaminants (seasoned). This will cause the thermometer to give false readings to some extent.

The heavier the contamination, the more fluctuation. As the contamination is uneven and acting as an insulator initially and then possibly a heat sink, I can see why it takes time for adjustments to be noticeable.
I think this normal build up you speak of is pretty negligible. IMO it would take several millimeters this gunk to cause concern as to whether it will cause any effect.
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Unread 08-16-2011, 11:48 AM   #8464
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I agree, the buildup is likely not the problem. I'll get a rough heat map this afternoon when its seasoning - I've got 6 ports lined up for sensors (2 12" analog, 4 stoker) plus the vent in the lid.

My suspicion is that the convection inside is going to give you warmer air in the center over the fire, cooling on the food/lid and dropping down the outside. (That would also explain the condensation some people are getting on the lids - a pretty big temp drop when it hits the top..)

You could defeat that a little with something like a pizza stone, and still get the 'burnt juices'. I'm going to give it a try - it should heat up enough to sizzle, plus pushing the hot air to the walls so it mixes better.
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Unread 08-16-2011, 07:41 PM   #8465
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I didn't get all the probes in that I wanted but here's what I've got:
2 digital (one 2" from outside of barrel, one centered)
1 12" probe
1 vent probe (weber lid)

The digital probes are showing about 30 degrees difference between the center (over the fire) and the outside. (220 and 190 right now)

The 12" probe everyone likes from wallyworld is showing 300-320 degrees. Basically useless.. (Swapped it out for the other one and same problem, so the probes might be ok but not in this use.)

The lid is showing about 20 degrees warmer than the digitals (or was about 20 minutes ago, its outside..)

This is a "standard" BDS with 1" intakes (3 closed, 1 raised/valved open) and 22" between the bottom of the fire and the grate. Weber lid.

Wanna see?

Update: Opened the lid to take a peek, then opened a vent (so 1.5 1" openings) and it spiked to 270. Re-closed that vent and set the valve at half. Its pretty much stuck right at 270 still. The 30 degree inside/outside offset is still holding steady. I've got stokerlog running to pull temps, I'll post the chart and pics of the probes tomorrow when it finally burns out. As this burns, I'm really thinking the baffle (water pan, pizza stone, bowl of sand, whatever) is necessary to even out the temperatures across the grate..

Oh, and you can watch it semi-live on twitter - @dissmoker. :)
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Last edited by Disconnect; 08-16-2011 at 09:04 PM..
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Unread 08-16-2011, 10:31 PM   #8466
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Quote:
Originally Posted by soapy_junk View Post
quick quesiton.. i am purchasing parts to build my smoker.. have read this thread 3 times over and am very excited..

regarding the 3/4 black pipe nipple and the ball valve.. i will be doing a NON welded unit.. everyone says use the 3/4 electrical conduit lock nuts.. i purchased them.. but they look like they are coated.. are they?.. are they ok to use that close to the firebox?

thanks,
Ditto smokindave74 from what I understand (and that's not much) but most grates you buy are Zinc coated!
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Unread 08-16-2011, 10:51 PM   #8467
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Btw gotta update my earlier post. Turns out one of the probes was falling out of the smoker. Sigh. The temps are a lot closer than I thought.

Update: No, no they aren't. Now that the center probe is back where it belongs (and labelled correctly), we're 40 degrees higher there still (288 edge, 321 center.) Lid reads about 270. No more posts until tomorrow, when I'll have pretty charts and stuff.

Last edited by Disconnect; 08-16-2011 at 11:41 PM..
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Unread 08-16-2011, 11:10 PM   #8468
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Working on mine right now. I got a drum for free, I forget the height but it was supposed to be used for oil waste. It is Dept of Trans certified, which means it is thicker metal, has an extra rib for strength, and a hell of a lid. It was not used much at all, mostly sat in my step-dad's warehouse.
I burned it out twice, (man that thing is heavy as heck) and sanded it to bare metal. If I were to do another build, I'd pay to have it blasted clean. The money spent on sandpaper the time I put into it, and the filth caked all over me says blast it.
I have the holes drilled out for the intakes. I made them 7/8" and placed them every 18 inches. My drum measured out at 6' total diameter, so that's 4 intakes. I'm using the 3/4" pipe nipples with caps.
I am going to have my top grate 4" from the top, the second grate will be at 10". I drilled those holes and will use stainless screws and nuts and washers as the pins to hold the cooking grates.
I have two coats of paint on the drum so far. This drum will be two colors- green and gold. the ribs of the drum will be gold as will the lid. Flat parts are green. I want the smoker to work correctly so it'll be Green Bay Packer colors.
I think I'm going to use a sheet of rolled aluminum as the smoke stack.
I still have to build the charcoal basket, a heat shield (probably wait for that until after a few cooks) and tweak what ever needs doing.
I think I'll use a valve on one of the intakes for closing valve half way or less)

------------

Lessons learned the hard way:

GET YOUR DRUM BLASTED. IT'S WORTH IT.

Do NOT rely on the "guy at Home Depot" to tell you all the right bits for yer pipe nipples. Rely instead on THIS HERE THREAD.

Do NOT sand the snot outta your drum and then wait two days to apply paint. Even though it's in the garage, the humidity will put some rust on there.

Perhaps most importantly-
This thread is a guide. Not spoken gospel. (ok maybe it actually is gospel) Do what YOU think is best for YOUR drum. All of us are doing the same general thing, but there are neat differences. My drum is not like yours. Yours is not like that dude's. His is not like mine.

If you don't want to spend a lot of time carefully taping out lines for your smoker, paint it all one color.
Taping took me a long time and I still loused it up I bet.

More to follow as I progress.

Oh- maybe the hardest lesson for me in this and in all things. BE PATIENT. Ya can't get ahead of yourself and expect not to make mistakes. I get all bent outta shape and want to see progress. I make dumb errors that way. GO S-L-O-W-L-Y.
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Unread 08-17-2011, 09:58 AM   #8469
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Quote:
Originally Posted by soapy_junk View Post
regarding the 3/4 black pipe nipple and the ball valve.. i will be doing a NON welded unit.. everyone says use the 3/4 electrical conduit lock nuts.. i purchased them.. but they look like they are coated.. are they?.. are they ok to use that close to the firebox?
I would not worry about the zink, but keep that black nipple well oiled. They rust fast and then getting the cap off is all but impossible. A couple bucks on brass nipples is money well spent.
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Unread 08-17-2011, 01:27 PM   #8470
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Default Distributing the heat in UDS

Hey guys... since you're talking about putting in something to distribute the heat, thought I'd bring up this older post I put up with a picture of my previous versions of my smoker, but also my version of something to distribute the heat. The picture is the last one and unfortunately a little dark. I'm not talking about the first picture which is of 2 baffles I made. That does work, but.. it's a bit tedious to work with.

http://www.bbq-brethren.com/forum/sh...postcount=7619

I made it by using a regular cooking grate, and some angle iron and bolts with big fender washers. The angle iron was cut and drilled and laid out on the grate. Then bolted to the grate. So this allows the meaty goodness to drip down and fall into the fire which is key; that creates for extra smoke and yumminess. :) But the thickness of the iron and its shape makes a huge difference in evening out the heat.
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Unread 08-17-2011, 01:59 PM   #8471
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Arrow Heat Differential

Here's my update on heat. TLDR: There is a 30 degree difference between the center and the edge of the cooking grate. (Even with both probes actually inside the cooker where they belong..) The 12" thermometers I got are worthless, they read as high as 425 when the grate digital said 230.

The first spike is fixing the probes and opening the lid for a few minutes. (That is why the temps inverted - the red/center probe was actually resting inside the port, not in the center of the cooker where it belonged.)

The 2nd and 3rd are from opening the lid and/or more vents.

The probes are reading ok - they landed together at about 75 degrees when the fire finally went out. (Next time I'll switch their positions mid test to be sure, but they have been reliable so far.) Oh, and I had no stoker on it, just the probes.

Thumbs link to larger versions:
Full chart (starts about 20 mins after dropping in a half-lit half-chimney of RO on a full basket)




The overnight section (the '5 vents' label is actually 1"x1.5 vents, its cut off)



Pic of sensors - the UDS isn't oval, the grate isn't falling off, its just a cellphone pic this morning :) Oh, and the center probe isn't in a clip but it is not touching the metal anywhere, its hanging ~1/4" below the grate.




I'm going to try another seasoning burn today with both probes in clips (no more falling out) and a pizza stone resting on top of the charcoal bin. If I remember (and the mosquitoes aren't too vicious) I'll switch the sensor positions to expose any calibration issues. (And I'll move it closer to the house so I can check the vent temp periodically along with the digital probes.)

After that, I'm done burning it empty and its time to make a fatty and some ribs :)
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Unread 08-17-2011, 02:11 PM   #8472
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Quote:
Originally Posted by coewar View Post
I made it by using a regular cooking grate, and some angle iron and bolts with big fender washers. The angle iron was cut and drilled and laid out on the grate. Then bolted to the grate. So this allows the meaty goodness to drip down and fall into the fire which is key; that creates for extra smoke and yumminess. :) But the thickness of the iron and its shape makes a huge difference in evening out the heat.
Hmm. I wonder... would standard "flavorizer" bars work just as well?

Those in particular are 21" long.. (and expensive, but they're just the first set I found.) I love the pizza stone idea but I the more I think about it the more I suspect its going to have way too much thermal inertia to work.. (Wif came up with it, she wants a new stone and figures if she lets me burn this one up I'll get her one )
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Unread 08-17-2011, 02:23 PM   #8473
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I experimented with an 18" pizza screen last week which kept edge to center temps reasonably close, while allowing drippings to hit the coals. I like this set up so far.

(I wanted to add a little smoke to the corn before finishing them off on another grill)
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Unread 08-17-2011, 03:59 PM   #8474
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Quote:
Originally Posted by Disconnect View Post
Awesome. I think I'm gonna keep the 2 barbs I have (pretty brass ones ) for the 12" under-grate analog probes, and I'll pick the halex parts up tomorrow for the stoker sensors. (2 per grate, plus I need to add at least 1 more to my WSM.)

So far its going well - lid temp is showing about 300, lid leaks like a sieve, and its humming along slowly. Gotta find a better way to seal the lid, or (ideally) to re-round the barrel. (When I dumped the water out it got out of true and the old weber lid isn't up to the job..)

Also, fyi, if anyone gets this far before building one :) The lowes here couldn't find nuts to fit the threading on the barbs, but the plumbing guy was interested in the challenge. There is a piece that basically looks like a bolt/cap (male) but is open through and fits the female barbs. So drill, push the piece from the outside, add a couple of washers and tighten the barb on. (I don't have it in front of me, I'll edit tomorrow w/ better info)

I also used a brass 1/8" hose barb with a MIP male thread that I drilled a hole to fit the male threads and fit through the barrel side from the inside and a MIP matching thread cap that I drilled a hole in for my thermometer probe to go through. With the cap on the outside and tightened it makes for a stable point for the thermometer to be introduced to the interior of the smoker. It also makes it easy to remove my thermometer after I smoke my meat, and that makes it easier to get my grills out and my charcoal basket out. I placed mine 1" below the bottom grill which is 8" below the top rim of my barrel.
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Unread 08-17-2011, 04:52 PM   #8475
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Quote:
Originally Posted by coewar View Post
Hey guys... since you're talking about putting in something to distribute the heat, thought I'd bring up this older post I put up with a picture of my previous versions of my smoker, but also my version of something to distribute the heat. The picture is the last one and unfortunately a little dark. I'm not talking about the first picture which is of 2 baffles I made. That does work, but.. it's a bit tedious to work with.

http://www.bbq-brethren.com/forum/sh...postcount=7619

I made it by using a regular cooking grate, and some angle iron and bolts with big fender washers. The angle iron was cut and drilled and laid out on the grate. Then bolted to the grate. So this allows the meaty goodness to drip down and fall into the fire which is key; that creates for extra smoke and yumminess. :) But the thickness of the iron and its shape makes a huge difference in evening out the heat.

I think I'm going to try the angle iron trick on mine. I lost temp to 150* after I started up mine for the first time last weekend. When I finally got it back to temp of 225* it acted like it wasn't able to climb on up past that. That was even with 2 of the caps off. And it wasn't producing much smoke. I took the Loin Back rib meat off and put it in my oven to finish up in foil until it was done. At the time I shut it down, closing all the vents, it was finally starting to smoke again. The next morning I observed the juices were on the charcoal and might have contributed to the lower temp that occurred. I was trying to think of a way that wouldn't cut the flow of heat and smoke down in an unnatural way. I think the angle iron diffuser idea is a good one and I have an 18" grill from my old Charbroil bullet smoker that will be a good donor source for the grill to place them onto and permanently mount them. It would help burn the juices in a way that wouldn't possibly slow the charoal heat, and still allow for the juices to evaporate into the smoke for flavor enhancement in the cooking meat

In the first photo, you can see the lack of burn and the juices on top of the charcoal, and the second one you can see my coffee can that had the charcoal dumped into it from the chimney starter. It only used about 2" of charcoal by volume in a 5 hour burn. I believe if I could keep the charcoal packed in a pile towards the center, after the coffee can was removed to begin the minion method of burning, it might actually be more effective. On YouTube, I saw a video that just distributed the lit charcoal from their chimney around on top of the charcoal and that was the minion method they used to start the burn. I don't know which is the better method, center out or top down. I also noted that they used lump charcoal to light it off with. maybe that was part of my trouble - mixing the two in the basket. Maybe using lump to start the minion method which burns hotter (or it seems to be hotter) in starting the other Kingsford.
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Last edited by hankll; 08-17-2011 at 05:14 PM..
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