Adding a Temperature Controller to an Original Bradley Smoker

(Updated with schematic 10/31/2007)

I've been trying my hand at some Charcuterie, and have been working my way
through recipes in the book Charcuterie (Ruhlman, Polcyn, and Keller).

When my original smoker, a Cabelas combination BBQ/Smoker, ceased to work due to  defective gas regulator, I did some research to find a replacement.  I like
to use LP gas, mostly because I have a built in gas outlet near our
deck where I do most of the smoking.

However, the Bradley was appealing because of the ability to load up the
unit with meat and wood pucks, and be able to do other things (go to work,
etc.). It's also easy to coach less-dedicated BBQ chefs (my wife) on what to
do...

After using it successfully to make a number of slabs of Bacon, a couple of
hams, and hot and cold-smoked salmon, some things became apparent:

1) the internal box temperature is highly influenced by the external air
temperature
2) the internal box temperature is influenced by the charring of the wood puck.
Different pucks seem to char at different temperatures; I'm not sure if the
humidity of the puck influences this, but I think it's a factor
3) the 'dimmer' temperature control on the bottom of the smoking box is not useful
for setting a particular temperature

What I needed was a way to measure the temperature in the smoke box, and control the emperature with a thermostat or controller.

Looking at what others have used, I found a PID-type controller (with thermocouple)
 on eBay for $35.  It's a TET-612 model, which is apparently identical to a VTC-620 which can also be found readily.

 I happened to have a Solid State Relay (SSR) hanging around from something else
(doesn't everyone?) so didn't need that -- mine originally came from All Electronics
(http://www.allelectronics.com ). I also had a terminal strip to allow easy connection/disconnection of the thermocouple.  I found a DPDT toggle
switch rated for 125v/10A to use to bypass the controller.

Here's a schematic of how I tied it together...

In this picture, the smoke generator is shown, along with the PID controller, thermocouple, and terminal strip.


(continued)

Others have housed the controller in it's own box, and have dangled
the thermocouple into the smoke box through the top vent; I chose to mount
the controller in the smoke generator, and mount the thermocouple through the back
wall of the smoke box, right next to what I believe to be an over-temperature
cutoff switch.

I began the project by spreading out newspaper on the kitchen table, and disassembling the smoke generator.

** DISCONNECT ALL POWER CORDS FROM THE SMOKE GENERATOR BEFORE DISASSEMBLING **

** DON'T WORK ON ANYTHING WITH THE POWER CORD PLUGGED IN **

The screws circled are the ones to remove to get the unit apart.

(continued)

The two sides of the unit can be separated by gently disconnecting the white
double-wire cable (with the white connector in this picture) as well as
unplugging the red and black wires at the terminal strip.

Looking inside the unit, it appeared that the upper-left-hand portion of the front panel
could hold the temperature controller without it hitting anything inside.
I cut a sticky-note paper to the size of the whole I needed (about 4 cm) and
positioned it where I wanted it, and marked the edges.  I also wanted to bypass
the temperature controller for 'factory' operation; a good spot for that is
just below the temperature controller.




(continued)

The terminal strip and Solid State Relay were next -- I chose a spot on the back panel just above the socket for the smoke box connector

** NOTE that this is the WRONG PLACE to mount the SSR, it interferes with the internal shelf -- DON'T mount the SSR in this location **

THE SSR can be located over the louvered opening on the left side of the unit.






I next mounted all of the parts, and wired the controller to the front panel toggle switch and the SSR.

I lifted the hot conductor originally going to the smoke box, and ran that to the toggle switch and ne side of the SSR.  The other side of the SSR goes to the smoke box connector, and an additional wire goes from the smoke box hot to the other side of the toggle switch. 

In one position, the temperature controller is powered, and 'HOT' for the smoke box comes through the SSR. n the other position of the toggle switch, the temperature controller gets NO power, instead the power goes directly to the smoke box connector.

After wiring everything up, checking three times, I applied power without the
thermocouple, and saw 'EEEE' when the toggle switch was in 'controller' mode -- That's GOOD!

EEEE indicates the thermocouple is not attached.

(continued)

Referring to the manual (Here's the TET-612 manual ), I went into the controller setup mode (enter 0089, SET), and set the type of thermocouple to K (the type I had), told the controller that I'm HEATING instead of cooling, display the temperature in Fahrenheit, and that I'm using a SSR instead of a relay to control my heating element.

INTY=K (thermocouple), OUTY=2 (SSR output).

If you want to get really fancy, you could calibrate the thermocouple to the degree by messing with the psb setting as well. I left that at zero.



Attaching the thermocouple, I received '68' with power on, indicating 68 degrees. Holding the thermocouple to warm it up yielded DECREASING temperature display -- NOT RIGHT. After removing power, I reversed the thermocouple connections at the terminal strip, turned everything back on, and noted that  holding onto the thermocouple yielded INCREASING temperature -- all was well.

(continued)

On to the smoke box. Removing all of the screws from the back of the smoke box,
one can see the power coming into the unit from the bottom, the wires to the
heating element, and wires running to the over-limit switch just to right of center
in the picture



I drilled a 1/4" hole just to the right of the thermal switch to mount the thermocouple.
The material lining the box is very thin, so a light hand, sharp drill bit,
and something to back up the hole is useful to not tear it.



I tilted the panel back onto the unit, and marked THROUGH the hole to drill for
the thermocouple leads -- then drilled another 1/4" hole through the rear
cover.

(continued)

I mounted the thermocouple with a 1/4" stainless nut, taking care to hold the
thermocouple in place as I tightened the nut to NOT bend or tear the smoke box material.


I buttoned everything back up, taking care to get the leads through the drilled
hole. If my thermocouple leads were not shielded, I would use a grommet or other
type of protection on the edges of the rear cover to not nick or wear on the wires.




(continued)
Moment of truth -- After checking all of my wiring again, then re-assembling, I plugged the smoke box into the generator, plugged the unit into the wall, and slid the smoke box temperature slider to FULL ON (right most).

I toggled to 'temperature controller', and adjusted the set value (SV) to 214
degrees. I also pressed and held the > arrow key on the controller, which
tells the controller to 'learn' how the thermocouple and heating element
work together (it's this step that many people DON'T do). 

I then watched as the controller turned on the heating element (the power
indicator light at the bottom of the smoke box turned on) and watched the temperature climb. After about 1/2 hour, the controller indicated that the box was at 214 degrees (verified by the thermometer on the front of the unit) -- success!

FURTHER exploration...

Cold Smoking is ideal for all of the salmon and trout that we have here in the
Pacific Northwest -- but when the air temperature is above 50 degrees, it's hard
for the smoke box not to rise above 80 degrees just because of the charring
of the puck.  The TET-612 unit has a feature that can be used to set the TET-612's relay output for temperatures inside or outside of a temperature range.

I'm considering using one of the relay outputs to TURN OFF the bisquette heater
if the temperature of the box goes above 78 degrees, to be able to cold smoke
on cool days.  One more relay (115v coil) and one more toggle switch should
be all that I need to hook it into the bisquette heater/advance circuit.