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Unread 09-03-2013, 09:34 AM   #11334
Got Wood.
Join Date: 06-13-12
Location: Charlotte, NC
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Default First "Burn" temperature control struggles

Hello All.

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.

Any thoughts?

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?
Attached Images
File Type: jpg 130902-19 first run - paint cure - Small.jpg (26.4 KB, 408 views)
22.5" Weber OTG, 22.5" Weber OTS, Dacor Dual-Burner Nat Gas, UDS (under construction)
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