PID Build - Updated

Brent Dowell

Administrator
Staff member
Messages
16,540
Location
Reno NV
<< Removed content >>

Need to update directions.

I put together the first controller using this wiring diagram. However I'm learning there are big differences in pid controllers....

The second one I'm building requires a different configuration. Will update later.

Suffice to say the parts list is fine, but I'll need to put together a different wiring diagram.

<--->

Check the last message. I'm quite happy with the way this turned out and after spending some time experimenting with the pid, happy with the way the pid controls the temps.
 
Last edited:
Thanks for all the details Brent. I was going to go for some of the bundle options on ebay, but I like the thermocouple you have chosen. At least it will get inside the smoker with the longer probe and the cable is a nice length too.

Will also look to add a resettable circuit breaker to the unit inline with the mains just in case something goes wrong.

You might be interested to know that on my return from BW when I was telling family of my plan to build this and get the smoker, I asked youngest son if he had learnt about PID control at University given he is taking engineering and had done the calculus and was quiet into the subject. Answer was nope. So we had a chat about the practical side of the implementation of calculus and how its applied in a controller like this. Then it clicked to him because they had being doing similar problem solving but only in the math class not in practice. Downside is I don't know what its going to take to get his generation excited about techie stuff like this, they were born into it all so its just kinda blah to them. Here I am still marveling at the path we have lived from vinyl to tape to cd to mp3 and he simply cannot relate to it.

Sharon :rofl: I had to look up the farmers only part to get the last bit, site should have been farmers lonely lol

Having been shocked myself a few times I don't think its the electrics that you need to worry about. :D


On the side anyone here ever had a shock from DC ?
 
You can definitely get things cheaper on Ebay.

The one thing I don't understand about all the bundles on ebay is that they bundle a DA (DC-AC) SSR instead of an AA SSR (AC-AC).

Can you run AC into the DC side of an DA SSR to trigger the SSR? I couldn't find much info about that, but in my mind, if they make AA, then that's what I'm going to buy and use.

The longer cable and longer probe I think are important to try and get a good reading in the Smoker.

Yeah, I got a bit of a zip the other day, wasn't too bad, and when I was putting the original together, I did manage to get things wired completely wrong. That made a bit of a POP when I plugged it in.

What kills me is how cheap this tech is nowadays. IT's hard to believe how reasonably priced it is to get this much accuracy.
 
What kills me is how cheap this tech is nowadays. IT's hard to believe how reasonably priced it is to get this much accuracy.

That's what amazed me when you first mentioned it and I looked it up. Few years back we would have paid a fortune just for the digital display part never mind the control. It makes for exciting times. I don't even want to go looking for some of the stuff I am thinking of just trying to stay focused at the moment. :D
 
Ok, As I was putting together Carols, I discovered that there is a big difference in the way some PIDS work.

I was able to get everything working, but do not use the wiring diagram I put together for this particular pid.

All of the parts will work, but I need to change the wiring diagram.
 
Yeah, and it hurts! I got a 6000vdc jolt from an aircraft radar set (AN/APN-59) I was working on once. Knocked me clear across the maintenance van!

Jim I got one heck of a DC hit when tying together a whole battery box for a battery powered locomotive for the mines when I was 15, not the same level of voltage but boy it threw me back too :) . After the adjustable wrench melted and I got up off the ground, I then got punched again by the journeyman who owned the now shorted adjustable wrench. :) The punch was for wrecking the tool.

Oh Jim and for $55 you can have a bit of nostalgia if you like and buy the cooling fan for the APN 59. :rofl:http://www.ebay.com/itm/COOLING-FAN-ASSY-HD-150-APN-59-RADAR-SYSTEM-C-130-KC-135-/180964156982
 
Here is my revision of the original post. The revision has to do only with the parts list and the way the pid works. The original PID I used basically had a relay in it that would switch AC current.

The second PID I bought did not work the same way. Instead of a relay, it actually output a 24 volts of DC current that can trigger an DA SSR (dc input/ac output). I have revised the parts list and wiring diagram to reflect this.

=============================================================================

First and foremost, Let me state I am not an electrician. I am not an engineer. Heck, I probably have no idea what I'm doing.


This project involves main voltage electricity and is dangerous.

I am not suggesting anybody do this, and I sure don't suggest you do this if you are not comfortable with projects that involve voltages and currents that could be very dangerous!


I am only posting this because some people were asking me to show how I put together my PID.


Got it? Don't do this. Don't try this at home!


That being said, Here we go.


I had decided that I wanted an electric smoker. I've had lots of grills, and lots of smokers, from charcoal to gas to wood fired. But I had recently gotten into sausage and jerky making, and I wanted a unit that would be very easy to use and control, and not have to worry about stoking with fuel. Don't get me wrong, I love my fire powered smokers, but I wanted something that would allow me to do things on weeknights and that could run all night and not need a whole lot of attention. To me, that spelled Electric.


So I got a Masterbuilt Smoker from amazon for 149$ with free 2 day shipping, thanks to amazon prime. When I got it, I liked it, but found the analog thermostat to be a bit finicky to control. Sure, I could get it set, but it really took a bit of futzing with to get it to the temperature I wanted. Also, there would be fairly wide swings in temperature due to the nature of an analog thermostat.


An electric thermostat operates by having one point where the heating element comes on, and another where it goes off. This can vary by quite a few degrees.


So I decided I wanted to use a PID. A PID controller use an algortithm that allows it to 'predict' temperature fluctuations due to inputs, and can maintain a very fine control over the temperature.


So Here is the parts list.


Pid Controller 19$
SSR DA 20amp Relay 8$
Aluminum Heat Sink 5$
Type K thermocouple 7$
Enclosure (1/2" baltic Birch Scrap) 2$
Switch/Outlet Combo 3$
Misc Wire (10ga), Fasteners, DooDads 1$
------
45$


Now I could have gotten the electronic version of the smoker, but I've heard different things about those control units, and I'm not 100% sure if they use a pid or not, anyhow, I had already purchased all of these items for another project I had in mind (diy sous vide), and I just kind of re-purposed them.


Plus with this unit, It's kind of all purpose. I CAN use it for a sous vide controller if I want. It's completely stand alone. And if it breaks, I know how to fix it.


So Here is the basic wiring diagram. Your pid may/will not look exactly like this, but it should be similar. Be forewarned, some pids may use a relay to trigger the SSR, and some may output DC current to do so. It will also have a connection for the thermocouple. This connection may be configurable for different types of thermocouples that require different numbers of connectors.It may have additional switches that can be used for alarms/etc.

pidwiringdiagram2.gif

I'm using a standard household switch/outlet combo. I don't have them attached in this diagram for ease of understanding. These combo switches have a tab that connects the outlet to the switch. For this purpose, that tab will need to be removed.


The PID has a solid state relay built into it, but it's only capable of handling a small number of amps. In this case, the SSR on this pid can only handle 3 amps.


If I were to hook it up directly to the smoker, it would get fried. The smoker is rated to pull 12.5 amps. I tested it out last weekend and was able to get the empty smoker up to between 350 and 400. This amount of current requires using a seperate SSR. I chose to use a 20 amp SSR.


When running at low temps, i.e. 225, the power does not come on very often, or for very long. But when running at higher temperatures, it runs more often and longer. Due to the way SSR's work, they can generate some heat of their own when they are switched on. To alleviate that, I chose to get an aluminum heat sink to attach to the SSR to help dissapate the heat. From my research, it could get to as high as 125 degrees. I have not tested this yet, so I do not know if that number is accurate or not. Once I run some more tests, I'll see if I can get some empriical data on what temp it can get to when it is running flat out.


Ok, So here is a picture of what I'm shooting for. PID on the front, Switch and outlet on the side. I used a Cat5 plug and jack for the thermocouple, but I'm not liking that design. On the actual build, I'll be swapping that out for something else. But this is functional, and it's mine, so it's what I'm using now.
FWW-4529.jpg


Here are the basic parts, in their unassembled configuration, wires and screws not included.
FWW-4525.jpg


Here is a detail of the thermocouple documentation. It has a switch for an alarm, the SSR, the power in, the attachments for the thermocouple, and that's about it.

FWW-4527.jpg


Have you priced enclosures? Try and find something out there this size reasonably priced. Plastic, Metal, Eh, they all cost a bunch.
Nothing wrong with wood. So I grabbed a little baltic birch and got to work. On the back half of the box I put ventilation slots on the sides and top so that the SSR can cool down, if it needs to. This is what makes this marginally woodworkign related.
FWW-4526.jpg
 
Ok, So I had some concerns about this PID. When putting it into 'Auto Tune' mode, it would do a great job of getting the temperature right were I wanted it, then it would 'fast cycle' the heating element.

What that means is it would turn the element on for a second, off for a second, and so on, and so on. Now I did a lot of research, and from what I could find that was it's way of doing 'proportional', or throttling back the heating element to be able to keep the temperature accurate.

I could not much on the internet to let me know if that would be a bad thing for the heating element, or the old fashioned thermostat connector on it. My best guess is that as long as the thermostat on the smoker is at wide open full on, there really shouldn't be any kind of an issue.

The SSR can handle much faster switching than that, so that would not be a problem.

But I did find a solution. Some PIDS apparently have a cycle time parameter, but no such luck with this one. What this one does have is a 'CTL' parameter, that allows you to set it for either 'SSR' or 'RELAY'. Mechanical relays can't handle as fast a switching as SSR's can so I put the PID into Relay mode and all feels right with the world. It will still cycle a bit, but it's more in the range of several seconds.

I ran tests on it all yesterday and found some settings that seem to work pretty with.

Mypin TA4-SNR settings
P - 3
I - 132
d - 36
Hys - 1
CTL = 020 (relay) mode.


The one other change I did make was to use some real thermocouple wire and connectors to connect things up. My cobbled together method seemed to introduce too much resisitance to the sensor and caused the temps to be off by several degrees.

http://www.auberins.com/index.php?main_page=product_info&cPath=7_34&products_id=119

These are 'polarized' so that you can only attach the thermocouple in the right way. It also makes for a much cleaner and standard way of attaching the thermocouple.

So with that, I can say that I feel pretty happy with this project, and confident in it's ability to do the job.

So this one is winging it's way to some where in Arizona!
 
Last edited:
That's good info.

Just curious, can you put a second thermocouple on for a meat probe and have it drop and hold at a lower temp once the second probe hits its target?
 
It only has the ability to monitor one probe, but it can trigger external 'alarms' that could do things like turn lights/fans on/off.
 
Thanks for taking the time and effort to debug this setup for us Brent. I aint got around to mine yet. So good to know whats ahead.
for what its worth technically I don't see the prior setup having any negative effect on the element. The element gets cycled anyhow by the thermostat when its in normal use minus your setup. Sure that's at a lower duty cycle but that's because of the way the thermostat works and its own built in delay. I am guessing but the basic unit is probably just a bi metal strip thermostat, hence the hysteresis that we trying to get rid of by using the PID controller. I think the best answer here is to open up the thermostat and mod it so the connection to the element is direct and remove the bi mental strip part. That's what I will do when I get around to it.

I like Darrens idea too wonder if that unit can be programmed to do this. I see an arduino somewhere in my future. :rofl: Darren you got the code done yet? I don't think my aging brain is going to take well to learning to code again. :(
 
I see an arduino somewhere in my future. :rofl: Darren you got the code done yet? I don't think my aging brain is going to take well to learning to code again. :(

I've got one of the TC4 shields (https://code.google.com/p/tc4-shield/) assembled. It is this winter's project to work on. I've got an LCD display going with it now, but still trying to get the wifi board working with all of it.

I did find some thermocouple meat probes that were reasonably priced here: http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=56

That board supports 4 thermocouples at the same time, so have one allocated to the chamber temp, the other three will have meat probes connected.

:threadjacked:
 
Top