PID CONTROLLER HELP!

[essexsmoker]

Hi all,

I finally built my pit controller the other day and have been trying it out but without much success.

http://s44.photobucket.com/user/essexsm ... t=3&page=1

The first time I used it I put it direct onto the ball valve on my UDS, but the temp kept falling. So, I opened up the other valve and port and hey presto the temp came back up. So, to me that indicated an air supply problem.
Looking inside I could see that the air supply was no where near the coals, so I made a copper frame to deliver the air directly under the fire basket.

I tried that today but with much disappointment the same thing happened. I have removed the frame and put the fan directly onto it to check for air and I can feel an airflow pretty much all the way around. However, obviously there is still an airflow problem.

So, before I go drilling bigger holes and potentially ruin it I wanted to ask what people thought.

The fan is 18cfm or so it says in the spec. From what I've read 10cfm is quite common, so I thought this would be overkill and I could throttle it back with the valve if necessary. The pipe is 15mm, my thinking being that the fan would fill a smaller bore pipe and blow all the way around it. The holes are 2mm, again so that the fan would blow all the way around.

I should say that the coals are in a snake.

So, my question is, has anyone else done this and what size fan and holes did you have?

I have a slightly larger fan but that means a fair amount of rebuild and it wont be half as neat and convenient.

Thanks for your your help!

[JamsCowbell]

I've got a 10CFM fan blowing through 2 15mm input pipes, I have about 16 or 17 holes on the copper 'air burner' and the holes are 6mm. I started with less holes that were smaller and had to increase the number and the size of the holes so that I could reach 120C quickly and hold it comfortably without needing the fan on full blast all the time.

Some pictures here https://www.dropbox.com/sc/752f2fyg3n96 ... -agIVwGs0a

I can't see the pictures you put up though.

[essexsmoker]

Thanks Jams, that's great. only just upped the holes to 3mm but was thinking they probably need to be bigger. I have about 5 holes on 3 sides so about 15 total. Will up it to 5mm to start with knowing that I should be fairly safe.

Photo bucket is playing silly buggers again!

[JamsCowbell]

With hole size I was worried about the fire being able to draw air through if I made them too big but it doesn't seem to do that. I wanted to be able to drive the temps up above 120C fairly easily if I wanted to, I seem to be able to reach 130C but I'd like to hit 150C so I'm looking at some modifications or maybe a bigger fan.

[essexsmoker]

I've read that you want the fan to run at 40% of the time. Obviously I've still not been able to get mine going properly yet. I've got another bigger fan already to go anyway but didn't want to over Stoke. Though I can throttle back with the valve. How stable are your temps?

[JamsCowbell]

temps are solid enough for me to go to bed without worrying, it only really varies when I open up the hatch or take the lid off.

I'm going to try going with foil over sand in the water bowl next, I also want to try and get the fuel burning more evenly which is tricky with lumpwood.

[essexsmoker]

Wow, sounds good! That's what I'm hoping for. Yeah you might struggle with that one. Let me know how it goes.

[essexsmoker]

Try this link instead. https://drive.google.com/folder/d/0B0oX ... x4Tk0/edit

[JamsCowbell]

I love your little fan holder, is that 15mm all the way around? My 2x 15mm inlets feed into a 22mm 'square' inside the smoker and as mentioned my holes are a lot bigger. I suppose if I pre-planned enough I could work out total airflow through X holes of Y size given Z throughput but I'm more of a seat-of-the-pants kind of chap

[essexsmoker]

Thanks. You can see why I didn't want to change it. It's really light and neat. I put the wire through the front so that I can turn it upside down if it rains.

Ahh, so the pipe inside is 22mm? Think I need a rebuild.

I did another burn last night and I still had hell with it. I now have the same surface area in holes as you do. It was a very strange burn. With my fan 100% I still needed both ports open to get to temp. I also had to crack the lid a bit to get it to rise. At the end I had a look inside and all the coals had lit but the bit at the start had gone out and was only half burnt.

I have another design in mind so might just go with that.

How long does your unit take to get to temp from the start?

On the bright side I did a brisket and 2 racks of ribs for 3 or 4 hours then finish in the oven. First time I've done brisket and it was amazing. Didnt need a sauce or anything. Mmm.