PID to open a Triac?

Discussion in 'The Projects Forum' started by jcran17, Sep 22, 2013.

  1. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    Hello, this is my first post and I can most certainly be classified as a complete novice when it comes to circuits. In reading about this project, I have learned some new schematic symbols and new parts I have not heard of before, so please bare with me.
    My project: I have an old analog immersion circulator (uses and op isolator to open a triac that turns on the heating element, attached schematic) that I want to update with a PID to allow precise temperature control for sous vide cooking and beer making. The cleanest way for me to do this is to use the SSR output of an 1/32 DIN Auber PID (8VDC, 40 mA) to open the triac (datasheet attached, model #Q4015L5 under “15A” on pages 4 and 5); this way I can keep everything inside the original case.

    Question: Can I wire the SSR output of the PID to control the heater, or do I need to get an SSR and wire it up that way?

    Other potentially helpful info: I tried using a DMM to test the triac gate and found the following:
    1.) Black to general ground (screw in case) red to triac gate- oscillates between -0.2 to +0.2 VDC regardless of heater status
    2.) Black to the “meter reference point” red to triac gate- 8.76VDC with heater off & 8.59VDC with heater on

    Much appreciated
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You said you are "a complete novice when it comes to curcuits".

    Since this is a difficult thing to make and works at deadly voltages etc, my suggestion would be to browse Ebay for "PID temperature controller module".

    I have seen a few lately, they are cheap, have digital temperature dsiplays, settable alarms, and many come complete with a temperature sensor.

    You just install the temperature sensor, press a few buttons and it will directly drive your AC mains heater.
     
  3. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    RB,
    Appreciate your reply and collective cautionary note. I suppose it would be more accurate to say I am a novice at designing circuits, but have experience in soldering, misc. electrical, replacing broken things on boards, etc.

    To your point, I think I wasn't descriptive enough in my original post as to the the project. The circulator I am working on is 120V and similar to this: http://thermoworks.com/products/baths_circulators/polyscience_immersion_circulators.html
    and I am looking to add a PID temperature controller similar to those you note on ebay: http://www.auberins.com/index.php?main_page=product_info&products_id=14

    As you note, I can simply use the PID controller to run an SSR which can directly run the ~10-15A heater, however, this will require me to mount the SSR & heat sink outside of the factory casing (it isn't big enough to put inside) in some sort of water/touch proof casing.

    It is for this reason that I would prefer to use the PID controller which has an 8VDC, 40 mA output (designed to trigger an SSR) to open the factory triac's gate which is already mounted internally with appropriate heat sink (position Q1 on the board). I will not be using any of the factory heat monitoring or controlling and will be cutting power to that entire part of the board. Thanks again.
     
  4. THE_RB

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    The specs on theat PID temperature controller seem to say that it will drive 40mA output (for SSR use) so assuming it's output is isolated you can drive the TRIAC gate directly as 40mA should be enough for that.

    Otherwise, just use it's 3A relay contacts to drive the TRIAC gate. :)
     
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  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    That unit you have now looks more than proper for doing what you want. It could have an analog PID inside. I know a lot regarding Sous vide cocking. And is not magic, some temperature fluctuation say a few degree celsius plus minus does matter much. Given that the temperature regulation in your unit still work as it should. I would have settled for just adding a thermometer to your system. And use that to fine tune the temperature setpoint. I can also recommended volume two in "Modernist Cuisine - The Art and Science of Cooking" It has a good sous vide section.
    http://modernistcuisine.com/books/modernist-cuisine/
     
  6. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    There is an issue with the internal thermostat, so I needed to go digital and figured why not use PID vs. standard temp controller. I have used them on my espresso machines with great results.

    I am sure you are right about that one, but $40 for the PID didn't seem too bad for complete control.

    I have the whole set; agree they are awesome books.
     
  7. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    Thank you very much RB. I am just realizing that the files I attached aren't in the original post..not sure why. Maybe it's a new member thing. I spoke with Auber and they said the SSR output is isolated, so I am excited that it seems this will work. Two final (I hope) questions:

    1.) Is there any concern that the triac says max gate trigger voltage is 2.5V given the PID output is 8V? http://www.jameco.com/1/1/1768-q4015l5-400-volt-15-amp-triac-ic-220-package.html

    2.) The SSR output of the PID has + and - terminals; for the above noted suggestion, I connect the + to the gate of the triac and the negative to ?? http://auberins.com/images/Manual/SYL-1512A2instruction 1.0.pdf

    I will definitely report back one I get it up and running. thanks again
     
  8. killivolt

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    Jan 10, 2010
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    Last edited: Sep 24, 2013
  9. THE_RB

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    Sorry to the O.P. (and thanks to Killivolt) as i had not opened the TRIAC datasheet and checked its Ilatch (Igate?) spec.

    Normally 30-40mA is plenty to latch a TRIAC up to about a 25amp one, most will latch ok with only 20mA or so.

    Re using the "SSR output" all you need is a resistor to set the current into the TRIAC gate, I would do a test with about a 120 or 150 ohm 1/2w resistor;
    R =E/I = approx6v/0.040A

    You may find that will drive the TRIAC fine, but if not then you will need to try another solution. :)
     
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  10. t06afre

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    Sorry if I am ignorant but I can not find any link for the 15A SSR datasheet, can you repost it:confused:
     
  11. killivolt

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    t0, I didn't see a first post of the Data Sheet, I think a schematic might be useful, too!

    The OP referred to it, they may not know it didn't upload?
     
  12. jcran17

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    Mar 8, 2013
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    Hopefully they will attach this time.
     
  13. t06afre

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    Now I see it clearer. What you can do is to rip out the current electronic in the box. Besides some of the parts. As I see it. The speed switch for the pump, the pump, the safety thermostat, and the on/off switch. Maybe also the current triac heatsink Then you install your own electronic. What you must do for own sake, and as a imperative safety measure. Is to isolate the triac from the PID. By using a Zero Voltage Crossing Optically Isolated Triac Drivers. They are common and quite cheap. Here is an very good app note http://www.fairchildsemi.com/an/AN/AN-3004.pdf. Your load is almost purely resestive. And since you use zero crossing switching settle for a RC snubber network http://application-notes.digchip.com/005/5-10156.pdf capisce!:p
     
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  14. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    I am reading the datasheet for the triac as saying 50ma is the max, not the min, but as noted, I am new to this. I look to other with more experience to decipher the datasheet.

    Thanks RB, haven't thought about ohm's law since college. Happy to see it hasn't changed and I get to use it in real life;)

    Seems simple enough to add the resistor in line on the positive output of the PID, but I am still at odds with what to do with the negative output?
     
  15. jcran17

    Thread Starter New Member

    Mar 8, 2013
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    Just seeing this post now...Thanks t06afre

    This is precisely what I planned to do!!

    My fear is that this project is going to get out of my league....I will read through the app note and see if I can understand it and come up with something.
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I make the excuse up front, I skimmed through the posts but not in detail.
    But if you are controlling an heater or element, the current way to do it with a SCR or triac is by burst switching, same as your home stove does.
    By burst switching you always switch at zero cross over of the AC rather than phase angle switching, and just regulate the amount of pulses depending on the temperature required, also with large slow heating elements, you need a PID controller of some kind, otherwise you get overshoot and undershoot in temp.
    (I see that t06afre mentions this in his app note!)
    A snubber is not often need when zero cross switching a resistive circuit.
    Max.
     
    Last edited: Sep 25, 2013
  17. killivolt

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    Jan 10, 2010
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    Max, he's hacking one, it's used for cooking and beer making. So, you are correct, but just missed out on it.

    kv
     
  18. t06afre

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  19. killivolt

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    Jan 10, 2010
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    We used a AN3004 to dim to control a light bulb on shooting ranges. I can't remember if we used an SSR or not.

    "Phase Angle" is how they dim house lights with sliders in a light box, right?
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, These are usually triac phase angle control, this is why they can kick out a lot of RFI.
    Max.
     
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