A 340μF epoxy?

  1. PhysicoRaj

    PhysicoRaj 430
    Gold Member

    Hi there..
    I was experimenting with capacitor discharge arcs. I charged a 340μF cap to 9v and shorted the terminals of the cap. Zap! Sparks!.. Then the terminals got stuck to each other as if they had been glued together! It took me 3-4 seconds pulling at them to separate them. It happens every time I do it and with all other caps. Can anyone tell me what's happening here?
    Last edited: Feb 9, 2014
  2. jcsd
  3. davenn

    davenn 4,346
    Science Advisor
    Gold Member
    2014 Award

    you are arc welding the ends of the wires together

    1 person likes this.
  4. PhysicoRaj

    PhysicoRaj 430
    Gold Member

    Why.. yes.. Thanks a lot Dave, I'm gonna save 500 g of lead and 2.25 kWh of electricity every year now onwards. :cool: :biggrin:
  5. Be careful if you decide to scale up the experiment. The current is only limited by the resistance of the wire and any resistance in the capacitor. Very large currents are possible with the right capacitors and they have the potential to explode (although connecting them with reverse polarity is a better bet if you actually want them to explode).
  6. AlephZero

    AlephZero 7,244
    Science Advisor
    Homework Helper

    Very true. I remember once working on a mains-powered amplifier where the smoothing caps were something like 40,000 uF at 50V.

    Before attacking it with a soldering iron, I decided to check the caps were properly discharged by shorting the terminals with a screwdriver.

    There was a loud bang, and the screwdriver was a few millimeters shorter, and bladeless.
  7. PhysicoRaj

    PhysicoRaj 430
    Gold Member

    I've only caps of a few hundred microfarads, a combination would fetch around a max of 5 mF. I have worked with these and they only pop, and harmless unless you hold your face right into them. The worst experience I had was when I was a small boy, I tried making a step up transformer by connecting a 240v-6v step down transformer in the reverse way! I plugged the 6v secondary ends to the 240v mains and waited for the 9600v arc at the primary. But before I could even wait the fireworks had been unleashed... Even today I triple check everything when i hear 'transformer'
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