From: Jason White <whitewaterssoftwareinfo@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 6 Feb 2020 09:11:38 -0800
Subject: Re: [EE] PCB trace as a 1 Ohm resistor,	Peak pulse 25amps (625W)
 for 1ms?
Thread-Topic: [EE] PCB trace as a 1 Ohm resistor,	Peak pulse 25amps (625W)
 for 1ms?
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Thanks David,

I have decided against doing it - fireproofness definitely trumps most
of my other concerns. Embarrassingly, I missed that fact that pulse
rated SMT resistor families like D/CRCW-IF e3 exist. If I use a pulse
rated resistor and make a few design compromises my problems are
solved.

Thanks everyone!
-Jason White

On Thu, Feb 6, 2020 at 12:03 PM David Van Horn
<david.vanhorn@backcountryaccess.com> wrote:
>
> The conductive debris can also lead to ignition of the PCB.
> I wouldn't ever do this, after reading "Low voltage, the incompetent igni=
tion source".
>
> -----Original Message-----
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of Bob =
Blick
> Sent: Thursday, February 6, 2020 9:40 AM
> To: Microcontroller discussion list - Public. <piclist@mit.edu>
> Subject: Re: [EE] PCB trace as a 1 Ohm resistor, Peak pulse 25amps (625W)=
 for 1ms?
>
> Hi Jason,
> Look for fusing currents of PCB traces, there are a couple of good papers=
 about it on the web. Also there are calculators for the resistances.
>
> But using copper for a resistor, especially PCB traces, is only useful if=
 tolerance is ignored. PCB copper thickness variation between vendor and ba=
tches aside, the thermal coefficient of copper is pretty huge. Plus you are=
 going to have a huge temperature jump unless you make the board very large=
 to accommodate the width and length you'd need for something approaching a=
 safe, non-fusing value.
>
> That said, give it a try. After all, I once used stainless bicycle spokes=
 as current shunts. It sorta worked on the bench.
>
> Friendly regards, Bob
>
> ________________________________________
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Jaso=
n White
> Sent: Thursday, February 6, 2020 8:15 AM
> To: Microcontroller discussion list - Public.
> Subject: [EE] PCB trace as a 1 Ohm resistor, Peak pulse 25amps (625W) for=
 1ms?
>
> Hello everyone,
>
> The Vishay D/CRCW e3 SMT resistor family spec. says that one of their
> 1 ohm 2512 resistors is rated to withstand a 1ms pulse of 40W (6.32
> amps) 8000 times. I have an application when I need to push a bit more th=
an 25 amps through a 1 ohm resistor for 1ms which is a roughly 625W pulse. =
Low duty cycle, only needs to survive 1000 times total.
>
> I am looking for a small, lightweight solution that won't affect vibratio=
n testing. Big through hole resistors are frowned upon due to their mass an=
d height. A TO-220 on its back might be acceptable but they don't seem to h=
ave what it takes power wise. With few other options I am considering using=
 PCB trace resistance as my 1 ohm resistor. The trouble it is difficult to =
calculate the transient thermal response of a PCB trace on FR-4 material to=
 determine the required width and length.
>
> Does anyone have any advice about handling this pulse?
>
> --
> Jason White
>
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/cha=
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Jason White

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