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Watts vs [email protected] Rating

Discussion in 'General Electronics Discussion' started by Raven Luni, Sep 2, 2012.

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  1. Raven Luni

    Raven Luni

    Oct 15, 2011

    One of those noob questions that doesnt come up till you need to ask it, but I was looking for some decent wire to use with some ultracapacitors I got recently (3kF, 2.7V). I went for some standard 3 core stuff rated for 16A @ 240V. Does this mean that it can handle 3840 watts of power regardless of current and voltage and therefore 1422 Amps @ 2.7V ?
    Last edited: Sep 2, 2012
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    No, it means that 16A and 240V are the maximums. So also 16A at 2.7V.

    The maximum current depends not only on heating of the wire, but also how much voltage you are prepared to drop across it, and that means the maximum current will depend on cable length too.
  3. CocaCola


    Apr 7, 2012
    In addition to what Steve state the rating is just a dumbed down 'rule of thumb' rating... In the real world the rating is dependent upon LOTs of other variables, and should be calculated on a case by case basis... Also these ratings are not necessary a 'wire' rating but more so a combined wire/insulation rating with heavy emphasis on the insulation... One big variable is distance, over a short distance the resistance of the wire is nil compared to a long run, thus it can theoretically handle a lot more current at short distances before it heats up vs a long run...
  4. Raven Luni

    Raven Luni

    Oct 15, 2011
    Thanks. I doubt I'll be doing anything requiring more than a few amps but just wanted to be sure. As for keeping them shorted while not in use, I guess I should use a resistor to limit it to no more than 16A?
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Another thing. The wire has resistance, proportional to the length. Thicker wire has lower resistance. This resistance limits the current you will be able to draw from the ultracapacitor. Even just 10 milliohms of resistance in the wire will limit the maximum current to 270A. And if you short the wires together with a fully charged ultracapacitor, the wire will dissipate 729 watts, which means the insulation will melt immediately and the wire will glow red hot!

    So although you're not in danger of getting an electric shock from 2.7V, the extremely low internal resistance and enormous current available from an ultracapacitor means they're still dangerous. Don't wear any conductive jewellery while you're working with them!
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