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Please help with discharging capacitors

  1. Mar 25, 2016 #1
    Hello,
    I have a bit of a problem with my project and it is as follows: I am trying to discharge a capacitor bank (2x 470uf 400V capacitors in parallel). I tried making a MOSFET switch to use that as a switch, but it kept burning out the mosfets (they were rated for 600V and around 100A), then I went and grabbed a laundry style clip (the plastic thing you use to hang clothes) and made a switch from that, HOWEVER, here is the problem. When I close the switch, there is always an explosion on the contacts of the switch (they become black aswell). I guess it's because the current is so high it just explodes on contact or something, i don't know. After these explosions, the capacitors are completely empty (they go from 400V to 0V), so the problem I have is that all the energy stored in the capacitors is discharged on that switch explosion, and I am wondering what kind of switching device or circuit or whatever I can make for there to be NO loss in energy on the actual switch, so I can actually use the energy stored in the capacitors for my project.

    Thanks!
     
  2. jcsd
  3. Mar 25, 2016 #2

    berkeman

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    Staff: Mentor

    Why are the capacitors charged in the first place? It sounds like you are dealing with voltages and energies higher than you should be. Why not just use a large value resistance bleed resistor?
     
  4. Mar 25, 2016 #3
    I'm not sure you understand, I am charging them with a DC power supply and trying to quickly discharge them on something. I know how to deal with high voltages, I have been doing this for a long time. My question was how to large capacitors with no energy loss on the switch. :)
     
  5. Mar 25, 2016 #4

    berkeman

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    Staff: Mentor

    Are you using capacitors specifically made for quick discharge of high energy? If you are using standard caps, there is a good chance they will be damaged by a rapid discharge.

    What reading have you done on this so far? I did a quick Google search of high energy capacitor discharge, and got lots of good hits.
     
  6. Mar 25, 2016 #5
    Put a inductive load in the discharge circuit. A suitable inductive resistance will prevent the switch contact arcing, as it opposes the discharge current surge.
    To prevent oscillation, remember to also include a dampening diode parallel to the inductor.
    And, just my personal preference, in such circuits, I include a one ohm, high wattage, inductively neutral resistor in the discharge path.
    Among other things, it makes a handy test point for troubleshooting.
     
  7. Mar 25, 2016 #6

    Averagesupernova

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    Gold Member

    My question would be what other components are in the discharge circuit? So far we know about capacitors and a makeshift switch. Exactly where do you want this energy to go?
     
  8. Mar 26, 2016 #7

    Drakkith

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    Staff: Mentor

    Thread locked for moderation.
     
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