Blair:
You are very right. If the voltage is AC the impedance is
reactive due to the magnetic flux and if the voltage is DC then the
impedance is resistive. due to the turns, more length of wire. The
resistance of wire is measurable. If it did not have any resistance than it
would be a superconductor. In other words all wires due to their resistance
dissipate heat.
Regards,
Ramon
> -----Original Message-----
> From: Blair K. Hogg [SMTP:[log in to unmask]]
> Sent: Wednesday, October 08, 2003 10:53 AM
> To: [log in to unmask]
> Subject: Re: [TN] Max Current Brain Teaser
>
> Ramon,
>
> That's true, however, impedance only comes into play when the current
> changes, e.g. AC current or step / ramp changes. If the current is
> constant, like DC, the reactive impedance is essentially meaningless, and
> the pure resistance is what matters. It was not stated in the original
> post whether the current was steady DC or pulsed or AC.
>
> Blair
>
> >>> [log in to unmask] 10/08/03 09:36AM >>>
> Blair:
> It has more impedance to current. The word impedance is used
> instead
> of resistance due to the fact that it is an inductor and not a resistor.
> So
> the more impedance the part has the slower the current and more of the
> electrical energy turns into heat. A comparison would be a straight pipe
> versus a pipe that is coiled where water runs through each one. The
> voltage
> behind the coil would relate to the pressure the water is pumped through
> the
> pipes
> Regards,
> Ramon
>
> > -----Original Message-----
> > From: Blair K. Hogg [SMTP:[log in to unmask]]
> > Sent: Wednesday, October 08, 2003 8:27 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Max Current Brain Teaser
> >
> > Brian,
> >
> > Does the coiled wire get hotter due to the proximity of adjacent coils,
> > the concentration of heat in a small space, or a combination of both?
> > Or do they sound like the same effect expressed differently?
> >
> > The straight wire and the coiled wire, if they have the same properties,
> > should dissipate the same amount of power in watts, correct? It is the
> > proximity and space constraints that cause the temperature to increase.
> >
> > Thanks,
> >
> > Blair
> >
> >
> > >>> [log in to unmask] 10/08/03 02:42AM >>>
> > A coiled wire will get much hotter than a straight wire for a given
> > current, always. However, I disagree that you should care how hot it
> > gets. It can go through phase changes which will reduce the springiness
> > if it gets too hot. I don't have phase diagrams for BeCu, so cannot give
> > you a max. However, BeCu is precipitation-hardened at about 300°C for
> > most usual alloys, so I feel it would be unwise to exceed ~200°C,
> > depending on the % of Be.
> >
> > Brian
> >
> > Jack C. Olson wrote:
> > > Does anyone out there enjoy brain teasers?
> > > I was asked an interesting question today.
> > >
> > > We need to have current traveling across a spring.
> > > The spring connects a connector pin to a SMT pad.
> > > We don't care how hot the spring gets as long as
> > > it doesn't melt the board.
> > > When the spring is compressed it is only 20 mils
> > > away from the board, but the current may have to
> > > travel around the circumference, so the distance
> > > may be more like 200 mils.
> > > The spring material is berrillium copper and the
> > > thickness is equivalent to AWG26. So even though
> > > a wire of this thickness may be rated 1.7 amps:
> > >
> > > What is the maximum current we can push
> > > through this short distance continously?
> > >
> > > We have been discussing the fact that even though
> > > the wire in your house may be rated for 10 amps
> > > and it won't get hot even on a 200 foot run, how
> > > much current can you drive through a half-inch
> > > piece? Especially if you don't care if it gets hot?
> > > Nothing I found on Doug Brook's site (temp calc
> > > and fusing current study) seemed to help.
> > > ( http://www.ultracad.com )
> > >
> > > thanks,
> > > Jack
> > >
> >
> >
>
>
>
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