Converting my MES40 to PID control...

[Grant H.]

So, this forum says it's for the DIY stuff that might be of interest to everyone... So here we go...

Glossary:
MES = Masterbuilt Electric Smoker
PID = Proportional Integral Derivative Controller
SSR = Solid State Relay

As anyone who pays attention to the "Latest Purchase" thread will know, the control unit of my MES failed during my last smoke, and appears to be completely dead. As such, I decided to buy a PID Controller, Thermocouple, and a SSR to control the smoker's heat element and temperature of the chamber.

The advantage of the PID controller is that temperatures will be more accurate and dramatically more stable over time.

I have a MES40, 40" tall unit, with a 1200watt heating element that I bought from Lowes a couple years ago. This plays into the process here because I haven't found a relevant set of instructions that fits my version. That is one downfall of the MES line, they have about 47 million variations that are all different in the process for modding them.

This one, as it turns out, is the simplest to modify for PID control...

A little background:

To control the MES with a PID, you must change the wiring of the MES to be a dumb heater. This means heating when power is present, and off when power is removed. Depending on the model you have, this can be very simple or more involved with cutting the heating element wires and connecting them straight to the incoming AC wires.

Once this is accomplished the power to the heating element is controlled by the SSR, which is driven by the SSR output on the PID controller.

Note: If you want to follow this, you must be aware and purchase a PID that supports SSR's. Otherwise you will have to use a standard relay. The downside to this is that they have a finite cycle life, and if it fails closed, you risk burning the smokehouse to the ground (more on this later, as you'll see).

So, finally, onto the process of converting my smoker to PID Control...

I started by opening all of the covers on the back and bottom of my smoker. This way I could start digging through the wiring with my meter and figure out what needed connected where. Based on previous reading on the 'net, I expected to have to cut some wires, add connectors, and then put it all back together.

My plans of following other modification processes went out the window as soon as I had the covers open and it looked nothing I expected...

20190328_105721 by ARNEWB, on Flickr
20190328_105728 by ARNEWB, on Flickr

I opened the back first, and that was where I found the MES over temp safety (in the oval opening on the left of the picture), and the connections for the heating element in the square opening on the right of the picture.

Since this didn't look like what I was expecting from other write ups, I laid it over and started opening the other covers. On the bottom, I found the middle compartment was nothing but the power cord coming in, and the other compartment is the confuser (sorry, YT reference).

Note 2: One of the things that I wanted to do if possible, was retain the factory over temp protection. Basically, even if the PID fails or the SSR fails closed, the heater will get shut off once it gets too hot.

So, as I was starting to track wires (ohms on the meter) I realized that the oval opening on the back was the temp shut off, not the temp sensor for the controller. This was good news, because I was wondering where the extra set of braided red wires was (set on the heating element, set on the temp shut off). Turns out, they are in series... Problem solved.

Now I started looking at how best to bypass the confuser and tie the element straight to the incoming AC cord.

Single easiest conversion??? Yep!
The incoming AC connection and the connection from the confuser to the element/shutoff circuit actually use the same plug set.
Also awesome, is that the connectors just so happen to be correctly setup, so that they plug together!!!

20190328_111907 by ARNEWB, on Flickr


So, here we have the now defunct control box that I don't want or need...
20190328_111854 by ARNEWB, on Flickr

From the bottom:
The two plugs with the colored wires are the control lines from the control panel at the top of the unit.
The plug with the two white braided lines are the temp sensor for the control unit.
The plug with black and white is the AC into the controller
The plug with the two braided red wires is out to the heating element circuit.

Next up, I mounted the new thermocouple, so that it was stubbed into the chamber, and then modified the back plate to fit. A little silicon and it is water proof again!
20190328_114023 by ARNEWB, on Flickr
20190328_120603 by ARNEWB, on Flickr

On the inside, the temp probe sticks farther in, which will give a more accurate reading. I kept the thermocouple low, to keep the feedback loop pretty tight (the closer the element is to the probe, the less overshoot there is (to a point... lol, always some sorta gotcha)).

It is right next to the temp shutoff sensor, and you can see the old temp sensor that sticks out about .75" in the middle...
20190328_114032 by ARNEWB, on Flickr

With the rack back in, the rack above is where I usually smoke things, so it will keep temp as close as possible where the meat is sitting.
20190328_114059 by ARNEWB, on Flickr

So, with the PID temp wired together, I did a test run and it works flawlessly.

In my next post, probably tomorrow, I will detail out the wiring of the PID, SSR, Thermocouple, and show the box that I am putting it all into for weather proof purposes.

Hope this helps someone!

[wyome]

Seen ppl retrofit pellet grills to use the Savannah Stoker temp controller, but this is a first for me. Great job

So what's the first test cook? And did it make a difference?

[ChickNorris]

Super interesting. Thanks.

[Grant H.]

Seen ppl retrofit pellet grills to use the Savannah Stoker temp controller, but this is a first for me. Great job

So what's the first test cook? And did it make a difference?

First food test will be over the weekend, once I get the control box finished.

Test run with it hacked together on the top of the smoker says that it will keep it within +/- 1 F.

The planned recipe is the "Poor Man's Burnt Ends" using Chuck Roast.

Super interesting. Thanks.

Sure. I figure someone might want to try it too, so I might as well document!



Temp assembled controller...
20190328_203516 by ARNEWB, on Flickr

[FoxtArt]

Never thought about a relay failing on. Good writeup, will help (in completely unrelated projects). I'd previously resort to an ardunio controlling a relay in any kind of related project, now I have the bug re-inserted in my ear. At least nothing would burn down, it would just freeze my $ss to the bed sheets.

[Grant H.]

Never thought about a relay failing on. Good writeup, will help (in completely unrelated projects). I'd previously resort to an ardunio controlling a relay in any kind of related project, now I have the bug re-inserted in my ear. At least nothing would burn down, it would just freeze my $ss to the bed sheets.

It certainly happens.

I developed an automated firmware test for radios that are used in industrial data networks and used a relay bank for controlling aspects of the test. One of the relays failed closed (current flowing), and it caused a high power resistor to get a little warmer than it was supposed to.

The whole building stunk of melted plastic and scorched OSB for a few weeks...


I've done a lot of building, goofing around, etc with Arduino's, Raspberry Pi's, and Beaglebones and I contemplated using one for this. The problem is PID's are too cheap and they handle heat control better, and more simply than trying to do it myself. PID's are purpose built to run heating elements like this, or my Lee Lead Casting Pot, and maintain stable temps. Their "fuzzy" logic works wonders on hitting and maintaining temps.

[Not_A_Llama]

PID's are purpose built to run heating elements like this, or my Lee Lead Casting Pot, and maintain stable temps. Their "fuzzy" logic works wonders on hitting and maintaining temps.

Are you running PID or fuzzy? I love that I can buy a PID + SSR combo + thermocouple for like $20 prebuilt. I haven't seen many fuzzy controllers out there yet.

Next go-around, you might also want to look at some of the fuzzy implementations on the various microcontrollers.. I've found they all work super well on a smoker. Adding in inputs like ambient temp sensor, lid open sensor (more of an arrestor), and then a PWM output for less than bang-bang warming element or induction fan is really nice. Other things I haven't had a chance to play with are NO2 sensors or a dedicated NO2 generation mode to improve smoke ring, or a smoke color characterizer to aim for that thin blue.

Let's see that first cook, though!

[Grant H.]

Are you running PID or fuzzy? I love that I can buy a PID + SSR combo + thermocouple for like $20 prebuilt. I haven't seen many fuzzy controllers out there yet.

Next go-around, you might also want to look at some of the fuzzy implementations on the various microcontrollers.. I've found they all work super well on a smoker. Adding in inputs like ambient temp sensor, lid open sensor (more of an arrestor), and then a PWM output for less than bang-bang warming element or induction fan is really nice. Other things I haven't had a chance to play with are NO2 sensors or a dedicated NO2 generation mode to improve smoke ring, or a smoke color characterizer to aim for that thin blue.

Let's see that first cook, though!

So, getting into the brass tacks of it all...

Most low cost PID units available (MyPin TA4 - Currently on lee lead pot and this Auber on the smoker) are actually a combination of true PID and Fuzzy logic. They run PID control of the heater, but then use fuzzy logic to dynamically adjust the gain. Just to make the water extra muddy, right?

True PID (for instance the electronic test temp chambers I used to be responsible for at a previous job) require details of the heating element, and the rest of the system (basically statically setting the gain for the system). This is true in the heat treating industry (friends of mine own a business that does nothing but heat/cryo treating metals) where I have helped with replacing PID's and setting it up.

As my wife can, and will happily (jokingly, she knew who she was marrying... ) tell you, I have a LONG history of over complicating projects that I get into. Since she and I love eating smoked barbecue, I opted for the simple path that nets me the solution I wanted. This was 2-3 hours of effort to get the smoker back into working condition. I am contemplating building my own smoker at some point (different layout, better distribution of heat, etc) and if I do that, I will run a much more involved controller as I will want multiple temp probes, E-stop systems, and a few other nice to haves. But, for now, this setup was cheap (cheaper than buying the replacement controller from Masterbuilt, little more than my MYPIN for the lead pot) and gets the smoker going again.

An added side bonus of changing to this setup, you can go higher than the 275 limit of the MES control board. I ran it up to 300 as part of my test, and it did it just handily. I don't know that I will take it any higher than 300 as there are concerns of the box itself not handling it well, but it's nice to know that I can go to 300 if I want to expedite something once it's wrapped.

I haven't gotten the control box built, as the box I was planning on using (work scrap stainless enclosure) is not deep enough for the PID controller. So, this ran with the above pictured controller that was cobbled together, but it turned out well!

3lb Chuck Roast with Salt, Pepper, and Garlic Powder:
20190331_155046 by ARNEWB, on Flickr


The smoker setup - One note about converting to a PID, to get good, continuous smoke, you will want either the MES Cold Smoke box (what I have attached) or the proverbial "Mail Box Mod" rather than just the chip tray in the MES. The chip tray still works, but it's less consistent...
20190331_155107 by ARNEWB, on Flickr


After about 2.5-3 hours at 250, getting wrapped in peach butcher paper:
20190331_180546 by ARNEWB, on Flickr


Internal temp of 185, ready to get cubed up, sauced, and finished.
20190331_203133 by ARNEWB, on Flickr

Cubed:
20190331_203905 by ARNEWB, on Flickr

Sauced and headed back to the cooker for a bit:
20190331_204130 by ARNEWB, on Flickr

And done, with a some missing (my wife was snacking while finishing dinner):
20190331_210515 by ARNEWB, on Flickr


I started these too late, so they weren't the best I've ever done, but they are certainly tasty!