Building a control box for Electric beer kettle with temp regulation

Hello all,

I am designing a control box for a 15 gallon beer brewing kettle (brew-in-bag method) that will control a 5500 watt 240v heating element. I already am familiar with what the schematic would look like and parts needed to wire up a PID and probe into a thermowell (pt100) that will then use a 40a SSR relay mounted to a heat sink.

My question is this: what can I do to the design if I wish to ALSO control the element with a pot-style knob and bypass the PID entirely, for when I want to go from maintaining a precise temperature to using the knob to attain and maintain a rolling boil? (reason for the knob is to keep from endlessly tapping buttons on the PID to get it to the boil I want- a knob such as a stove uses would be much simpler) I thought about using a double pole, on-off-on switch in between the PID and SSR (connecting the SSR to the center terminals) as one possibility, but am getting confused with the knob type control-this is where I need guidance- I'm not sure what parts are necessary to accomplish the knob control circuit or if this can even be achieved. The PID puts out dc voltage on the output terminals to the relay...so what about the voltage needed for the knob pot, and for that matter, what type of knob?

If it was me I would switch the input of the SSR between the PID controller and a PWM controller running at a very low frequency. (I think I would try about 0.1 HZ I.E a time period of 10 seconds.)

Les.

depends on power requirements for control side of relay , probe resistance, knob resistance and power supplied , specs on those would help,

OR

if you have source code and able to program pid , and have read analog capabilities on pid, adding a common pot(or even 2) plus resistor(s), on a/d pins, would be easy to add to code, and you could do more such as:
set max with pot1, set min with pot2
or
set pot1 for temperature,
set pot2 for tolerance range,
or even
set pots as on/off time , timer controls

also it would be expandable....

If you are too lazy to push a few buttons on a a PID controller to make changes temperatures are you sure you have the focus and determination to brew homemade beer or turn a knob for that matter?

I mean you could end up with a stiff knob and where will that leave you? Tired fingers that's where thus ruining the whole beer batch.

Oh yea and how many buttons did you have to push to type this question to us any way? Cripes those alone had to be the equivalent of over a hundred beer temp adjustments on a four button PID controller.

Did you already but the PID controller ? If not then simply buy one that has a power control mode in addition to PID mode. For example eurotherm 3208. There are cheaper options than eurotherm that have this feature but I can't remember any names

Thanks so far for the replies. I guess I should have expected SOMEONE to give some input of "Oh Cripes, man, pushing buttons is too much work???? lol.

To clarify the whole story, I am a tool nut, a person who loves to build one-offs, and have background in electric, plumbing, carpentry,woodworking, data communications, alarm systems, light welding and metal working, I now work in automotive etc,etc,etc.
The project before me is a Christmas gift to my son who has been brewing beer for a few years now, making do with an induction hot plate, a 5 gallon brew pot, and spending lots of $ doing extract brewing. He, however, does not possess the mechanical knowledge to get himself to the level of all grain. I decided to give him the gift of help in designing, building, and paying for the material necessary to give him the ability to perform a brew-in-bag setup, with temp control and much quicker way of getting to a boil. He gave me a case of home brewed beer for Christmas (not knowing I had this planned for him, and I didn't know he was brewing for 3 people...damn near pulled his hair out trying to brew 3 batches with the setup he has)
You are right, tcmtech, that I probably do not possess the patience to brew beer....I'd rather be dreaming up my next original build, No offense taken

What I AM trying to bring to the table, is enough research and knowledge I have put into it so far, about beer brewing equipment, to be able to give him options....my thinking is that due to his lack of mechanical savvy, we might wind up building something that could be good, but unless I am aware of further possibilities, could turn into something great with my input of, "hey, you know, with a little more work or materials, we could do THIS" that he would not otherwise have known. I had no idea about what it would be like to control a PID in manual mode, having never used one, but I did see a YouTube video showing a controller using a pot...and that seems like a great way to quickly raise and lower a boil rate, so figured I would see what it would take to incorporate that into the design. My way of building things tends to complicate the design, but with the hope of building something that is a joy to use, clean, maintain, etc. and saves him much time and furthers his efforts in brewing.

Long winded, I know. Thanks for listening so far.

Oh, one more thing...we are still in the design stage. no parts have yet been purchased until I hammer out the features and costs of said features.

I was into home brewing for about a year. Spent a lot of money on a lot of gear, made a lot of beer, and then got bored and sold it all on Craig's list for pennies on the dollar.

I'm not the only one doing foolish craps like that . You can find a lot of good stuff on CL for cheap.

...and ya know, you can brew just as well with a bayou classic propane cooker. But don't use the aluminum pot that comes with it, use stainless.

Strantor.... the 62 quart Bayou classic with steamer basket is the pot I had planned on using. I also found that stainless can be silver soldered together and have found fittings that would allow me to equip the unit with tri-clover fittings, allowing quick breakdown of the assembly for cleaning. the completed unit would have a removable heat element mounted in a 2" tri-clover flange, and removable thermowell mounted in a 1" tri-clover flange, and a bottom drain with leg standoffs to raise the pot to accomodate a tri-clover quick-disassembly ball valve. The rest would be a Chugger pump that would connect to the bottom drain and recirc the wort to a homemade sparge arm over the basket. The control I was looking to create would be simple to operate and have a small learning curve, but allow growth later on in case we wanted to add features such as timer, alarm, etc. My son is good with learning by doing, I have always had the strength of learning by research, his weak side. By joining forces, I felt I could give him something plus the satisfaction of helping build it and owning a piece of home-grown ingenuity....something I have enjoyed for many years now. I waited to see where his endeavors would take him before committing the funds for such a project. I have looked on CL, but nothing too great (in my area) yet.

Les...
I looked up PWM and found articles regarding the 555 chip and a timer PWM. Would this be sufficient enough to accomplish what I am trying to do?

check it:
https://www.amazon.com/RioRand-Rect...1455851515&sr=8-4&keywords=scr+controller+220

Hi EzRider62,
A 555 is probably the simplest way to control the SSR. You would have to check the drive current requirements of the SSR and you may need a transistor between the 555 and SSR to provide enough drive. Most PWM controllers run at a much higher frequency than I suggested so you would need a larger timing capacitor. The SSR will also probably zero crossover switching which reduces interference caused by switching at random points on the waveform. The link provided by strantor would probably work even though it is only rated at 220 volts and you are using 240 volts. This is a phase control design which switches on at a variable point in the waveform and switches off at the zero crossing. Some power companies do not like the use of this method with large loads such as yours.

Les.