WSM Automatic Temperature Controller

I decided I wanted a temp controller for my wsm. Not because there is a great need for it. I would have and have left my wsm cook all night while I sleep without a remote thermometer or alarms. I really just thought it would be a fun project and be handy for things like stoking up a hotter fire in a hurry if needed and for days like yesterday when I wanted to put some brats on and come back an hour and a half later without having to wait for it to come to temp or stabilize first. I did want to try to keep this to something of a budget though so I've been using parts I already had in my junk bin where possible. I'll post part numbers or other info when I have it. No fancy tools are being used, a drill/dremel, soldering iron, tin snips, and a screwdriver are all I've used so far.

I decided that I should start by finding out how to mount the fan to the smoker. For me the wiring and electronics would be the easy part, the mechanical interface is where I'm less confident. I found that when the 22" wsm was released several people modified dog food bowls to use as mounts so I picked one up at walmart. I dug an old nidec gamma 28 A34342-16 blower out of my parts bin. It is a 12v dc fan that draws a tiny .28 amps and can put out 9cfm. I also found an old sheet of aluminum roofing flashing from the hardware store and a scrap of slightly thicker aluminum that I used to make some dampers with previously.

I found the flashing sheet was just about a perfect fit to roll around the blower outlet once fully plus one side again. I figured the inner seam would help seal it and let me bolt the newly made tube together.

I used the thicker scrap piece to make a mount for the fan. It extends past the fan outlet a little bit. At that point I put a bolt through it to hold that end of the outlet tube together, and to hold the outlet tube to the fan mount.

Next I decided that I liked the idea of a baffle/flap in the fan tube. I hoped it would help eliminate the natural draft effect giving my controller more control and let the fire extinguish naturally when I'm done. I also hoped that with it closing the tube off, it might help protect the fan from some heat. I cut a small piece of aluminum in roughly the correct shape to fit, rolled the top of it to make a hinge, then drilled the sides of the tube. I straightened a paperclip out, ran it through, and twisted it on the top to make the hinge. It isn't pretty, but it is functional. At least I hope, I suppose I can't say that for sure until I run it and the fan doesn't melt. I also cut/bent the ends of the fan tube to turn them into mounting ears

I drilled mounting holes in the dog food dish and cut a hole for the fan with my dremel. Here you can see the flap closed.

And then open. You'll notice I added another bolt immediately behind where the flapper so when the fan stops and gravity pulls it down, it will stay fully closed and not fall open backwards.

To try to illustrate that idea better

There's the fan assembly together

On the cooker I used a long bolt with a fender washer inside

Then on the outside another fender washer and a wingnut to make the mount. At the end is another small wing nut and washer that are used to clamp the fan assembly to the charcoal bowl.

Here's the assembled unit in test operation. With the fan running a noticeable breeze comes out of the exhaust vent but I don't think its strong enough to disturb the ashes or anything

My control box wired up temporarily to test out the mechanics. Obviously it still needs the pid added. The power supply is an adapter for an old acer eee netbook. The connector on the laptop end got flaky long ago so I bought a new adapter. Now I just clipped that end off and wired it in direct. It can supply 3 amps which is far in excess of what this rig will consume. The ground is shared between the led and the ring of the fan connector. The 12v+ lead goes into the master power switch, then out and is shared to the power on led and top of the fan connector. The 12v+ to the fan will of course be controlled by the pid when it arrives. I think I should probably put a small fast action fuse on the fan. Maybe if weather causes a short it will save the pid. And yes I'm using cat5 for the wiring because I have a bunch of it laying around.

To complete the electronics part of this package I settled on the SYL-1612B pid from auber instruments. I decided to go with an entirely 12v system in case I ever decide I want to compete. I estimate the max draw of the system to be 3.6 watts or .3 amps and only 1.5 watts when the fan isn't running. A cheap 12v jumper pack would probably be all the juice I'd need for any cook. At this time I did not wire in a connector for straight 12v, but in the future if I decide to it will be easy to add. I also ordered a panel mount connector for a k thermocouple. Probably not really totally necessary but at only $5 worth the convenience to have. Here is the PID installed.

Inside the wiring is finished unless I decide to add a fuse on the output of the ssr. I'm not sure its worth it. If the fan shorts out and takes out the ssr I'm not out much. The ssr (pictured in the top right) is the 5amp DC ssr from auber. I'll be glad to answer any wiring questions. Green wire is the negative lead. It comes from the source and is shared to led-, the ring of the fan connector, and to the - of the pid. 12v+ runs into the switch and comes out the other side as the blue wire. From there it is shared to led+ (resistor in line under heat shrink), pid 12v+, and ssr load +. The two brown wires run from the ssr - and ssr + terminals on the pid to their respective terminals on the ssr. The orange wire is the switched 12v+ to the fan tip coming from the 12v- load connector on the ssr. The ssr and some of the wire bundles are held in place with hot glue.

The thermocouple I purchased (the connector is part of the kit from Auber).

I run the thermocouple wire in through the top of the access door and hang the end from the probe hanger that came with the ET-73.

Unit in operation.

2qt stainless dogfood bowl $3.16
assorted stainless nuts/bolts $8.61
electrical junction box $11.92
fan connections and heat shrink $12.72
Panel mount thermocouple connector $4.95
5A DC SSR $7.29
SYL-1612B PID $36.95
Shipping of PID components $8.50
16' K-Type thermocouple $12.09
 
Total $106.19

Final review is that the unit works pretty well. I could probably keep adjusting the PID controller values to dial it in further but this seems to work pretty well as is, temperature swings seem to be at worst 10-15 degrees high or low, usually less. Lump charcoal seems to respond much more quickly to the fan and stays closer to its set temperature. A commerical unit like the Stoker would offer more fun features, but this still keeps me out of the cold. The values I wound up using are P=0.6 I=10 D=170 souf=.2 ot=12 filt=0

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