Modular Controller Build with PWM, PID and Direct Fire

Greetings to the List and happy holidays.... This forum is fantastic and I appreciate the knowledge and wisdom of everyone here.

First let me say that I fully understand the consequences of screwing with electricity and that now matter what experience I may think I have, one wrong move could end in disastrous consequences. I have also read and understand the disclaimer in the terms of service. Anyone that uses these diagrams should know that too.

I am planning to build a modular controller - for me it would include three of the following schematics but depending upon the size of the boiler and available power it could have any number. I am also hoping it would work on any single phase power source. I am building for 220v 50hz but sometimes i will take the unit to 110/60hz. I understand that voltage reduction from 220 to 110 will reduce my heating power because of V=I*R. That's all good because i have a smaller boiler on the 110v side of the atlantic and I have checked the volume heat equations and am happy with the time to boil. What I am not sure about is the consequences for the SSR and using PWM to adjust my elements with 50 vs 60hZ. This is my first question, what can I expect with the same SSRs in different frequencies?

The design takes Cotherman's PWM ideas from another and adds a couple relays to choose between the element control source.


Not shown here is the main breaker in the box sized for the total load and individual GFCI's sized for each element. Neither is my PID which is in another box currently. The main part of the panel is the 4 way switch, shown here as each individual single pole single throw. Each of these selections then will allow me to close a contactor which either

  1. directly connects the boiler to mains for fast heat up,
  2. connects the PWM module to the SSR to control the output with a dial,
  3. connects my PID to the SSR to keep the boiler or mash tun at temp, or 4) off.

Well everything was fine with this design and I had a cheap 110-240v 12v power supply but then I found a lot of 30A schneider contactors on ebay for 10$ each... They required a 24v control source, so now I need to adjust the voltage to the PWM module as well replace C1 with a 2.2uF capacitor. I just dont want to have too many voltages in the box if I dont need to.

Here is a detail of the PWM with voltage regulation...


So here are my questions...

  1. is this usage of the 7812 VR correct?
  2. I am using these LED's. The data sheet doesn't say they have resistors in them but it looks like they do. Do I have to worry about any bleed through the LED's affecting other parts of my control circuit?
  3. If I wanted to put in an emergency stop, would it be best to wire the control voltage through a normally closed ES so that then all the contactors opened? What is considered best practice here?
  4. Do people normally wire other safety interlocks the same way for instance a float switch in the boiler to prevent a dry run? This box will always be in a locked work space but I am sometimes forgetful.

I'm sorry if these questions are irrelevant or foolish,
Thanks in advance for your input.

control box circuit.jpg
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  • Why are you overcomplicating it with that PWM control? I don't think you gain much of anything by doing that over a traditional resistance based SSR.

  • I have a SD controller and its great. Right now my other two elements are direct fired and the system has given me no problems. I would rather however have options for future expansion and this way I can drive the same SSR with either the PWM or PID. Having the SD controller (resistance) and a PID would require a contactor to turn either one on and off so this seemed like a good solution. I am open to other options though if experience shows this to be overly complicated or not dependable.

  • edited December 2017


    I built my controller before the SD controller was around. a PSR was the closest thing available then, but not the cheapest.

    My setup uses a PSU from a server modified to think its in a server. it puts out up to 45A @ 12v. It powers the control circuitry.

    My 4 way switch is 1 - off, 1 - full power to element, 2 - PWM, 3 - PID. Positions 1-3 all drive a single SSR by using various methods to supply / control the 12v supply to the SSR. I modified the PWM module off envy to set the duty cycle to 1 sec by changing 1 capacitor. It works well.

    The NO EPO switch drives a NC 3 phase contactor paralleled up on the input to the box. When the button is hit the coil energises opening the contactor.


    My controller has 2 control circuit's, the first for a 4.8kw element. The 2nd is for a 6kw element in my boiler or steam generator. The PID on the 6kw element is a ramp / soak model for doing step mashing using a rims or herms.



    The PWM modules can be seen on the top left on the inside pic

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  • edited December 2017

    Why not use that little Auberins distilling controller.

    They have a version that has two additional relay outputs, DSPR400. You can run startup elements off the relay and a control element off the controller.

    They also have some slick little boil/mash controllers.

    Why reinvent the wheel?

    Another option is to use 4-20ma SSR modules and use PID controllers (with auto/manual control) to control the proportional output directly. In this case, if you ever want to upgrade to a PLC or computer control, 4-20ma is easy and standard.

  • OK Cool - I like the NO EPO and NC Contactor!

  • Oops too late for the edit... It looks like one of the locations I will be using however has three 30A feeds instead of one 100. Is there a best practice in this situation for the EPO?

  • This all begs the question. What do you do for ATEX approval on your panels because clearly they are not or are panels exluded ??

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