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To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 6 Feb 2020 08:59:36 -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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The conductive debris can also lead to ignition of the PCB.=20
I wouldn't ever do this, after reading "Low voltage, the incompetent igniti=
on source".

-----Original Message-----
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of Bob Bl=
ick
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) f=
or 1ms?

Hi Jason,
Look for fusing currents of PCB traces, there are a couple of good papers a=
bout it on the web. Also there are calculators for the resistances.

But using copper for a resistor, especially PCB traces, is only useful if t=
olerance is ignored. PCB copper thickness variation between vendor and batc=
hes aside, the thermal coefficient of copper is pretty huge. Plus you are g=
oing to have a huge temperature jump unless you make the board very large t=
o accommodate the width and length you'd need for something approaching a s=
afe, non-fusing value.

That said, give it a try. After all, I once used stainless bicycle spokes a=
s current shunts. It sorta worked on the bench.

Friendly regards, Bob

________________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Jason =
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 1=
ms?

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 than=
 25 amps through a 1 ohm resistor for 1ms which is a roughly 625W pulse. Lo=
w duty cycle, only needs to survive 1000 times total.

I am looking for a small, lightweight solution that won't affect vibration =
testing. Big through hole resistors are frowned upon due to their mass and =
height. A TO-220 on its back might be acceptable but they don't seem to hav=
e what it takes power wise. With few other options I am considering using P=
CB trace resistance as my 1 ohm resistor. The trouble it is difficult to ca=
lculate the transient thermal response of a PCB trace on FR-4 material to d=
etermine the required width and length.

Does anyone have any advice about handling this pulse?

--
Jason White


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