Originally Posted by Pasmadj
Well, I have completed the outward appearance of my UDS. I still have some stenciling to do on the lid, and I have to fabricate the basket.
Other than that, the drum is functional.
Since the yellow and blue "engine paint" cans said to cure the paint at 200 deg for 1 hour, I did that for my first "burn".
I used my charcoal starter chimney since I have not yet made a basket.
I filled the starter 1/2 with Kinsgsford blue, and dropped a lit starter cube on top of them. When I was sure that the coals were beginning to catch, I put on the lid.
I have 2 3/4" inlet pipes, and 1 1" ball valve inlet. I have 4 1" exhaust ports.
Initially I had all of the inlets open 100%.
I monitored the temps with my iGrill - probes on a cooking grate.
When the temp started climbing fast, and reached 110 deg, I capped one of the 3/4" inlets.
When the temp reached 160 deg, I capped the other 3/4" inlet.
When the temp reached 180, I turned the valve to about 50%. I did not want to over shoot and risk overheating the paint.
I was real happy with how I was able to control the temp rise.
The temp peaked at 192, and then started dropping.
I began to tweak the valve in an effort to stabilize it around 200 degF.
This is when the head-scratching began.
When I opened the valve just a little further, the temp would rise past 200 to 210 or 215.
When I adusted the valve back a little (very little, it seemed), the temp would drop back and keep going past 200 - down into the 180s.
I monitored and tweaked for about 2 or 3 hours - chasing the temp up and down. My top priority was to keep the temp around 200 for about 2 hours - for the paint. After that, I tried hard to get it to flatten out and stabilize. I never did accomplish that. My small amount of charcoal ran out after about 4 hours.
I really took my time building this UDS. I don't think there are any air leaks - that I know of.
Is the amount of charcoal and what I put it in (chimney) significant?
I know that it is not good to restrict the exhaust - better to control temps with the inlets. The area of 4 1" holes is equal to 1 2" hole - which is what many have used. Does the size of the exhaust significantly affect the temperature stability?
Read N8Man's thread on lighting the basket. You must follow it at least three times before you deviate.
Here is my quick and dirty method.:
FILL the basket.
Open all intake and exhaust ports.
Fire up the basket (using the 10-15 coals you set aside when you read N8Man's thread).
Let's say your target temp is 225.
Leave the exhaust alone (The only time you should mess with this is as a last resort, or when you are done cooking.
Leave the Ball Valve alone (this is your "Trimmer")
When the temp reaches 190, cap ONE inlet and watch your gauge
When the temp reaches 215, cap the SECOND inlet and watch your gauge
If the temp is still climbing, use the ball valve and close it 50%.
If the temp is not climbing, then remove the cap on the SECOND inlet, and close the BALL VALVE 75%. Use the Ball Valve to raise or lower the temp.
Assuming you have no leaks, this should solve your problem.
On my UDS ("Redneck thread" version on the post with a ball valve with a 2' extension and a weber lid for exhaust), I usually wind up with one valve capped, the second open, and the ball valve in the 50-75% range closed to get 225-275 (depending on wind conditions).