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-   -   UDS question: How stable is stable? (http://www.bbq-brethren.com/forum/showthread.php?t=145758)

junyo 10-10-2012 04:20 PM

UDS question: How stable is stable?
 
...for temps?

This is my first, a classic UDS build; straight, no chaser. Seems fairly air tight. 14"x24" fire basket, caps and ball valve vents. Two 1" ID chimneys.
http://imageshack.us/a/img6/9735/imag0272vd.jpg
http://imageshack.us/a/img35/5120/imag0271o.jpg

I can take the fire up or down at will, so air control doesn't seem to be the issue (I think). Doing the test burn, and my temp creeps up (maybe 1 deg every 5 mins) or down, can't seem to get it to lock in. 2 out of 3 vents closed, just working the ball valve, 70-60 deg ambient temp/60% humidity on the test day. I'm giving 20-30 minutes between adjustments.

So my question is what should I realistically expect as far as temp stability:
  • Dead nuts on the temp for hours, +/- a couple of degrees
  • The gradual delta I'm seeing?
  • An over/under fluctuation of 30/40 degrees? (I guess this is not mutually exclusive from the former condition)

Any guidance would be greatly appreciated.

Cliff H. 10-10-2012 04:31 PM

Mine will react to adjustments within a couple of minutes.

Once the temps come up to ( 270-280 ) and after the meat is on and the fat starts dripping In the fire and I shut my two intakes down to 1/4 and the weber lid daisy wheel is full open the UDS will find the temperature that it wants to run at for an extend amount of time.

Mine likes 265-275. It will ride between those temps for hours.

I have issues when I try to force lower temps, say in the 220 range.

colonel00 10-10-2012 04:56 PM

Yeah, fluctuations every 5 minutes is to be expected. Just plan on cooking within a range. As Cliff H. mentioned, they tend to find ranges and sit within them.

Bludawg 10-10-2012 05:27 PM

Mine will not go lower than where I set it it my ride up as much as 10* then settle back. If it starts to fall usually around 20 hrs I know it is running out of fuel.

chicagokp 10-10-2012 05:42 PM

Mine will run between 250-275 without much tending. After 5-6 hours, temps will start to drop due to ash and a swift kick will get it going again. That being said, I use my IQ 110 now and set the temp and quit watching now.

Pappy 10-10-2012 09:49 PM

My UDS was hard to "set it & forget it", until I add a clay pot base for a diffuser. I also have the IQ-110.........so now I do "set it & forget it".

Daggs 10-10-2012 09:59 PM

What size are your intakes. I have 2, 3/4" intakes and a 2" exhaust. The highest spike I have seen was 312* after openi g the lid for much longer than I should have but is settles down to a +\- 10*. I cheat though I have ball valves on both intakes and the exhaust.

landarc 10-10-2012 10:02 PM

My UDS is very solid at 275F and up to 325F, all depending on where I set it. But, it does not have a large enough fire basket, so it burns out fast at 325F. Still, I am getting very good, controllable cooks at 300F and getting good cooks out of it.

Durzil 10-10-2012 10:50 PM

You'll see more fluctuations with no meat in it imo (lack of heat sink). I set mine at 275*ish by letting it get to 250*-260* and then closing my ball valve down some. Once it stabilizes (hopefully 270*-280*) I put my meat on (I always shut it all the way down (2-5 mins) prior to minimise spiking) I then put it back to my previous setting. Watch the temps for a bit. Make an adjustment as needed. 30-40 mins later, then let it ride from there normally. After 2 hours I'll use a stick to bang against the basket to clear ash and adjust as needed from there. I don't see constant swings but will see it change in longer periods of time as the fire moves around or ash starts to build up. Once you get to know your pit well it'll get predictable and repetitive. I'd smoke a nekid Fattie and then a pork butt to season and get to know your pit starting out as there forgiving to learn on.

Hook_Line_and_Sinker 10-11-2012 12:44 AM

I'm just thinking aloud here, but is two one inch exhausts = the area of eight 1/2 inch holes? I'm thinking you may need more exhaust area !

But in the 5 UDS I have built the temp stays +-8 of the seting once the meat is on. Until ash buildup or outside temp or wind changes a lot

Not that I think your exhaust is causing temp issues, I'm more concerned that it may not be as clean or blue as it should be.

martyleach 10-11-2012 01:04 AM

I find that at lower temps (230-250) it holds within +/- 15 degrees very solid. If you want higher temps that is a whole different deal as the drum will turn into a heat machine with its own mind and the temps become way more difficult to control.

GreenDrake 10-11-2012 08:10 AM

I agree with Marty, mine finds it's sweet spot right about 230 at the top grate. I use a simple heat deflector made from the lid of the original drum, just resting on top of my charcoal basket. So very happy with my cooker build, it's more fun than my other three pits to cook on.

willbird 10-11-2012 08:57 AM

For some reason mine on "manual" (I have an Auber too) is more consistent pulling intake air through a "plain" opening (I have street ells) than through the ball valve.

Bill

jmoney7269 10-11-2012 09:09 AM

If it set mine on 225, 275,350 it stays there dead nut.
The BBQ guru is worth the $300 and paid for itself manytimes over in comps or me
http://i897.photobucket.com/albums/a...t/0660586d.jpg

junyo 10-11-2012 09:46 AM

Thanks for all the helpful replies. So I guess I shouldn't freak out, just need to give it some time to level set and to tune this drum in (already got the second one in the works, trying to run before i can walk :-D ).

Quote:

Originally Posted by Hook_Line_and_Sinker (Post 2240443)
I'm just thinking aloud here, but is two one inch exhausts = the area of eight 1/2 inch holes? I'm thinking you may need more exhaust area !

Might be, I didn't have a bung in the lid, so I guessed at the correct amount of exhaust. The pics are right after start though, and i assume that some of that was the grease and what not burning off; the smoke got cleaner quickly. Maybe I'll put in another chimney or two.


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