From: Alan Pearce <kiwiantipodean@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Fri, 7 Feb 2020 03:15:54 -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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For that use I would look at getting several resistors designed for
current monitoring in motor drivers and putting them in series.
I'm thinking something along this style (although this one is too low in va=
lue)
https://uk.farnell.com/tt-electronics-welwyn/oars-xp-0r01/current-sense-res=
-0r01-5-3-5-w/dp/1292588

You could possibly make something suitable yourself if needed. Do you
really need a full ohm?

Here is one three times the value of the one above (picture is representati=
ve)
https://uk.farnell.com/tt-electronics-welwyn/oars1-r050fi/current-sense-res=
-0r05-1-2-w-smd/dp/1200356

On Thu, 6 Feb 2020 at 17:16, Jason White
<whitewaterssoftwareinfo@gmail.com> wrote:
>
> 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 ig=
nition source".
> >
> > -----Original Message-----
> > From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> On Behalf Of Bo=
b 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 (625=
W) for 1ms?
> >
> > Hi Jason,
> > Look for fusing currents of PCB traces, there are a couple of good pape=
rs 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 =
batches aside, the thermal coefficient of copper is pretty huge. Plus you a=
re going to have a huge temperature jump unless you make the board very lar=
ge 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 spok=
es as current shunts. It sorta worked on the bench.
> >
> > Friendly regards, Bob
> >
> > ________________________________________
> > From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Ja=
son 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) f=
or 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 =
than 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 vibrat=
ion 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=
 have what it takes power wise. With few other options I am considering usi=
ng PCB trace resistance as my 1 ohm resistor. The trouble it is difficult t=
o 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/c=
hange your membership options at http://mailman.mit.edu/mailman/listinfo/pi=
clist
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>
>
>
> --
> Jason White
>
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

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