14.9.12

Automatic Flowerpot Smoker

Can't afford a Big Green Egg? You can build a ceramic smoker from a flowerpot in a matter of minutes — Alton Brown showed how on "Good Eats". Here I show how to add temperature control to your flowerpot smoker so that you can "set it and forget it". With automatic heating you can take the fiddling and guesswork out of using your smoker... and still have an excuse to hang out in the garden drinking beer.


Flowerpot smoker with PID controller


Flowerpot Smoker


To build the basic smoker you will need a large ceramic flower pot, the largest you can find. The idea of using a flower pot is that the ceramic walls retain moisture as well as heat — which is ideal for slow cooking. You will need a lid for the smoker too: a matching base will do fine, but a ceramic bowl of the right width or duplicate flowerpot turned upside down will allow taller objects on the grate. Prop the flower pot on ceramic feet or otherwise arrange it so that air can come up through the drain hole. Then take a single ring electric burner. Remove the element from its casing and reconnect the spade connectors directly to the electric cord, bypassing the temperature dial. Put the burner in the bottom of the flower pot and feed the cord out of the drain hole. You may need to lay the element on a brick to get it level. Next put a metal tray of wood chips on the burner. A pie pan will do fine, but avoid anything with a nonstick surface. Finally prop a circular BBQ grate inside the flower pot. Watch this video to see the master at work:



Temperature Controller


The heating element will be governed by a PID controller that is connected to a solid state relay (SSR). A PT100 temperature probe measures the temperature inside the flowerpot. The controls will fit in a 6" x 6" x 4" PVC junction box if the heatsink for the SSR is mounted on the outside, otherwise a larger box will be needed. The controller box will also need a fuse to protect the controller, on/off switches, and sockets to plug in the burner and the temperature probe. I used separate on and off switches connected via a power relay, but a simple rocker switch will do fine as long as it is rated for 110 V and 15 A. 3 pin XLR connectors are handy to attach the probe using a microphone cable. I recommend protecting the outlet receptacle from the weather with an in-use cover.

Internals of PID controller box


To assemble the controller box, use the circuit schematic below (click the picture to make it bigger). If you don't already have them, you will need a soldering iron and a crimper to make the electrical connections and a multimeter to test them. An electric drill will be useful for making holes in the box and attaching screws.

PID controller box schematic


Get Cooking


Put damp wood chips in the pan, slap your favorite cut of meat on the grate, and set the required temperature on the controller. Then sit back until the food is ready. A probe thermometer can be used to monitor the internal temperature of the meat.

Perhaps try customizing the smoker to your personal requirements. A simple way to ventilate the smoker is to drill small holes in the lid using a masonry bit and cover them when necessary with with stones. While you're at it, make another hole for the temperature probe. A handle for the lid is a very useful feature. To make a mobile BBQ station, cut a circular hole in a butcher block using a jigsaw or router and mount the flowerpot inside.


Did you know?

You can also use the PID controller to cook
sous vide using a crockpot or electric kettle.



Safety


Please remember to use mains electricity safely. The controller is designed to provide some protection against the weather, but it is not completely waterproof. Always plug the controller into a GFCI protected receptacle when cooking.  Undercooked food can cause illness: calibrate your probe if what you are cooking requires accurate temperature measurement.


Construction tips


This project is one for the Expert. Do not attempt to build the controller unless you can competently wire up mains electricity. The flowerpot smoker itself is easy to assemble but the 110 V supply is potentially Dangerous.



Materials


Flowerpot smoker


PID controller


You will also need




19 comments:

Anonymous said...

From Alton's video:
> The best thing: I spent exactly $47.32.

Where the heck does he shop?? I couldn't find a terra cotta flower pot that size for less than $50, and that doesn't include the lid. Add in a lid, a new electric burner and a replacement thermonometer, and the bill would have come out to $114.someodd in my area. That didn't even include the pie plate for the wood chips.

Tom said...

I think that video is a few years old now. Home Depot is the cheapest source near me but they don't always have the larger sizes.

Levi Ottwell said...

I have been looking for a month or so for a PID design that only controls heat. Your design is clean, recent, and well thought out. Anyway you could include a better schematic for people to look at? Even when enlarged its a bit fuzzy.

Thanks

Levi Ottwell said...

If you have any other pictures of the construction they would be welcomed I'm sure

Tom said...

Thanks Levi! I've updated the schematic, I hope the bigger size is easier to read. I don't have any other pictures of the controller build but I'll see if I can take some shots of inside the flowerpot smoker itself.

Levi Ottwell said...

A few more shots of the inside of your controller would be more helpful, the smoker construction process is widely found on the internet.

Anonymous said...

Hi, nice post. I've been thinking about upgrading my smoker to a PI or PID (right now it is on/off with temp sense), as well as build a curing chamber with this sort of temp control. I'm happy to see that these PID controllers can be had for so cheap. Last time I looked into them, I was only searching on one brand that was going for over a hundred dollars.

Question about 2 of your relay connections: Why do you have the output of the over-temp relay connected to two non-coil terminals on that DPDT. This doesn't seem to do anything, but I may be missing something.

Also, what type of switch is that power-reset? Is it a rocker with the other side unused (e.g. essentially SPST)?

Thanks
-Mike

Anonymous said...

Ok nevermind my two questions. I should have spent another minute or two looking at it. I saw you had "latching" on the DPDT but didn't think it through. So I understand your power-set and reset, and I'm guessing the unused terminals were just what was available on the mushroom switch.

-Mike

Tom said...

Yes, that's right Mike. Some mushroom switches are NC only, but the one I used had terminals for both NO and NC operation.

William Miller said...

Tom, I'm not very familiar with EE design and would like to know the values for the resistor and capacitor on the latching relay circuit. If I understand the circuit, when there is an alarm (Overtemp) this circuit will kill the power to the latching relay which in turn kills the power to the heater. This is a great safety feature for very little added circuitry. With the DPDT relay, the line voltage for the heater is separate from the line voltage for the controller and it could be 240VAC if needed for the heater. Should there be a second fuse for this heater line? There is also a resistor in the SSR circuit. What is its value?

Tom said...

William (1) The resistor and capacitor form a snubber circuit intended to help prevent arcing across the relay terminals when switching the latch. I used values of 100 R / 0.5 W and 0.1 uF / 250 VAC. (2) The circuit is designed for 120 VAC operation. To switch 240 VAC a different layout would be needed and I would probably choose a 240 V thermal breaker rather than 2 fuses. (3) The resistor in the SSR circuit is 330 R. It was included as a precaution because no datasheet was available for the SSR that I had.

Anonymous said...

the good eats episode was from 2003. yeah it cost less then. :P

patrick benavidez said...

i bought a 30in pot @ my local home depot last week for summer flowers . was thinking of doing this project this summer with my girlfriend. we're big on pit style slow cooking

Tom said...

That's a good size! I wish mine was bigger.

Anonymous said...

Just built this with good results. Would like to hear what settings you've used for P, I and D.

Scott

Tom said...

That's great to hear! I just set the controller to auto tune, but I'll have a look at what it comes up with next time I grill something. :)

Kili.... said...

Tom, is there a clean diagram for your PID? the bigger picture is not clean on my nexus :-) . if there's a link for the diagram can you post.

Thanks.
Yves

Tom said...

Hi Yves, I don't have a smart phone so I am not sure how to help. On my laptop, if you click on the picture you can see it bigger, right click to download.

Kili.... said...

Tom,thanks for the reply and I did the download of the diagram
months ago and its not clear. I want buy everything and give that for xmas present. So a clear,readable diagram would help.

Thanks,

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