DC induction heater control circuit capacitor blew up, don't know why

Discussion in 'The Projects Forum' started by steltzer, Nov 14, 2015.

  1. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    Hi Guys,
    Total noob here, let me know where I have stuffed this up.

    I am up to the next part in my induction annealer control circuit project.

    I have run into trouble.

    I wired up the circuit (Drawing attached. Sorry about the drawing. Free online circuit drawings don't allow some components, so I have drawn them as text boxes, hope that's ok).

    When I plugged it in, Capacitor C1 blew up within 1 second.

    The whole electrical process is meant to go as follows:

    1 - 36V DC from the meanwell supply is feed to the relay contacts, to run the induction circuit when called by the relay
    2 - The LM2575T Adj drops the voltage from 36V to 12V, so I can run the 12V relay coil
    3 - The LM317T Adj drops the 12V power to 5V so I can run the arduino and other control components (Momentary switch, Time setting pot, LED, and MosFet which switches the 12v relay)
    4 - The LED lights up and shows when the is power being supplied to the MosFet

    The application for this circuit is basically a timer, controlled by arduino (and code).
    When the momentary switch is pushed, 5V power is feed to the MosFet gate.
    The circuit closes the 12v relay for a period of time.
    This period of time is set by the timer set pot (up to 10 seconds, as an input into the arduino).
    This allows the induction circuit to be on for that period of time.
    Once the timer runs out, the 5V feed is dropped from the MosFet and the relay turns off, turning off the induction circuit.

    I am very new at this.
    This circuit is kind of a bit of a frankencircuit, as I grabbed all the necessary circuits I needed and put them all together hoping it would work.
    It probably has some heaps of parasitic capacitance, or stray inductance or the like.

    I just want to know why C1 popped (as it is a requirement for the LM2575 circuit), and how to fix it.

    Thanks in advance guys. [​IMG]


    Untitled Circuit_Circuit.png
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Couple of reasons,

    1) capacitor is wrong voltage rating.
    2) its been put in reverse.
    3) inrush current too much.
    4) back emf oscillations from the induction circuit are too much.

    Whats the circuit in the induction circuit box?
     
  3. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    hhmm....polarity....I didn't check that.
    It is a 63V 100uF cap, running on a 36V circuit, I would think it should be fine. I might be wrong there.
    The induction circuit will draw like 9 amps-ish when running.
    I hadn't pressed the go button yet when i plugged it in, so there should have no inrush to the induction heater.
    Seeing as it is only driving the relay coil and the arduino (through the LM317) I wouldn't assume too much inrush.
    Back EMF...No idea even how to check for that LOL

    The induction circuit is one of these:
    http://www.ebay.com.au/itm/12-48V-D...284724?hash=item1c409f95f4:g:ulAAAOxyIPNTddX8
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,773
    1,103
    What is the output current rating of the 36V supply? If it is being overloaded by surge current it may turn off-on-off-on..... That would cause a lot of ripple current through C1.
     
  5. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    The current rating of the supply is 13.8 amps. But when i plugged it in, I did not have the induction circuit or the arduino connected. I just expected it to sit there, producing the needed power supplies. So tere should have been no current flow, just the correct voltages.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Sounds like the capacitor was in the wrong way round.
     
  7. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    Unfortunately, I removed the popped cap before posting here, so i didn;t get the chance to check. I put a new in the right way round......lasted maybe 4 seconds before a fizzle and smoke...looks like something else is the issue
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Ok, have you got a voltmeter across the capacitor when its switched on, what is the dc rating of the capacitor?
     
  9. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    yeh i will need to do that. First i need another cap, as I only had 2 LOL. I will have to check it tomorrow. I will get back to you.
     
  10. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    63V 100uF cap BTW
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    You do know that Electrolyic capacitors are polarised, the Negative side has a silver stripe down the side!!!
     
  12. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    ok.....I decided to wire up just the LM2575 circuit on the breadboard, and see what was going on.
    I have found a problem with the drawing I did.
    The C2 cap should be on the other side of the inductor. I actually had it wired up correctly, but drew it wrong.
    So having cleared that up, and having it wired up the right way, let's continue.

    I wired it up, and I popped the 330uF cap.
    I replaced it and made sure my wiring was correct, then popped the 330uH inductor.
    I thought it might be dodgey parts....replaced them again, popped the 2nd 330uH inductor and the 2nd 330uF cap.
    I am lost, I have no idea what I have done wrong.

    I still used the pot in place of R2 (on attached diagram), so I could adjust the pot to get a different voltage if I needed it.

    No idea.


    Screen Shot 2015-11-15 at 2.18.09 pm.png
     
  13. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    Oh and no polarity was not the issue, I double and triple checked the capacitors polarities. They were all correct on the breadboard.
     
  14. steltzer

    Thread Starter New Member

    Nov 14, 2015
    13
    0
    I got it working!! I went back to the drawing board, got all the bits together, followed it exactly...no smoke. I just must have had it wired wrong without realizing it? I dunno.
    Guys you have been the most help!
    Thanks so much.

    image1 (1).JPG
     
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