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'[EE] Max current in a conductor, pulsed not averag'
2011\09\13@090415 by Electron

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Hi!
can a 1 mm2 conductor carry thousands of amperes for very short times? (uS or less)

I mean, is there an intrinsic limit, other than temperature (which for pulsed operation
if the average is low, should not pose problems) and of course Joule effect (I^2*R)?

Greets,
Mario

2011\09\13@092309 by Isaac Marino Bavaresco

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Em 13/9/2011 09:53, Electron escreveu:
> Hi!
> can a 1 mm2 conductor carry thousands of amperes for very short times? (uS or less)
>
> I mean, is there an intrinsic limit, other than temperature (which for pulsed operation
> if the average is low, should not pose problems) and of course Joule effect (I^2*R)?
>
> Greets,
> Mario
>


The conductor's inductance will limit the initial current

2011\09\13@092551 by Michael Watterson

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On 13/09/2011 13:53, Electron wrote:
> Hi!
> can a 1 mm2 conductor carry thousands of amperes for very short times? (uS or less)
>
> I mean, is there an intrinsic limit, other than temperature (which for pulsed operation
> if the average is low, should not pose problems) and of course Joule effect (I^2*R)?
>
> Greets,
> Mario
>
Skin effect, capacitance and inductance.

So length of cable, placement, return wire and voltage are all significant too.

Even a not very long wire will limit current of 1uS pulses due to inductance and Skin effect.

It's the I^2^R that melts or evaporates  the wire. Easier the shorter it is, assuming supply wires are much larger

2011\09\13@122440 by Harold Hallikainen

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Besides the electrical characteristics others have mentioned (inductance,
etc.), it all comes down to temperature rise. For steady state current,
you can use I^2*R to get the power dissipation for a certain length of the
wire. Then calculate the temperature rise based on conduction, convection,
and radiation. The current limit will be based on the temperature limit of
the insulation (if any) or the conductor itself.

For non-steady state, you can use the RMS current in the above formula.

For short pulses, you have to consider the heat capacity (joules per
Kelvin) of the conductor. If, for the moment, you don't consider power
dissipated by conduction, convection, and radiation, the number of joules
(watts * seconds) times the heat capacity of the conductor will raise the
temperature that number of Kelvins.

I think heat capacity of the determining factor for short pulses.

Harold




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2011\09\13@122934 by Adam Field

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On Tue, Sep 13, 2011 at 8:53 AM, Electron <spam_OUTelectron2k4TakeThisOuTspaminfinito.it> wrote:
>
> Hi!
> can a 1 mm2 conductor carry thousands of amperes for very short times? (uS or less)
>
> I mean, is there an intrinsic limit, other than temperature (which for pulsed operation
> if the average is low, should not pose problems) and of course Joule effect (I^2*R)?
>
> Greets,
> Mario

I have done repeated (about 5Hz rep. rate) capacitor discharge tests
at >2KA with the capacitor leads being 1.2mm diameter tinned copper.
The discharge was a decaying sinusoid (ringing at resonant LC
frequency) that typically lasted 200us. I could never noticeably heat
the leads unless the connection was bad

2011\09\13@125351 by Electron

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At 15.23 2011.09.13, you wrote:
{Quote hidden}

But the tables I see that report wire size with max current are calculated
mostly due to the Joule effect, right? Can I safely assume higher currents
for very short periods? Ok, not thousands times higher.. but maybe ten times
perhaps?

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