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From: "Klaus Vestergaard Kragelund"
References: <email@example.com> <firstname.lastname@example.org>
Subject: Re: Open air current sensing PCB mount shunts...
Date: Tue, 17 Dec 2002 23:30:51 -0500
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Organization: TDC Internet
"boB gudg" wrote in message
> On Sat, 14 Dec 2002 09:51:59 -0800, John Larkin
> >On Sat, 14 Dec 2002 17:33:52 -0500, "Klaus Vestergaard Kragelund"
> > wrote:
> >>"John Larkin" wrote in
> >>message news:email@example.com...
> >>> On 13 Dec 2002 15:59:17 -0600, boB gudg wrote:
> >>> >
> >>> >I'm looking for sources for current sensing shunts in the 1 to 2
> >>> >milliOhm and 2 to 5 Watt range. I have seen OAR series from IRC
> What kinds of problems do you have just soldering the stuff to the
> circuit board ? I had heard somewhere thay you had to use silver
> solder for best results but maybe that's why you have big solder
> How about Cupron as opposed to manganin ? And are you used the
> round wire instead of strips?
I seem to remember that we opted not to use silver soldering. I think partly
due to issues of the silver and copper adding up to form a thermoelement in
> >>> Isotek makes pcb-mount shunts, too.
> >>> http://www.isotekcorp.com/
> >>> We punch our own from sheet manganin, but that's a hassle unless you
> >>> need a whole lot. Manganin does have pretty good tempcos...
> >>> John
> >>I've used Manganin in a previous job. Great tempco as you say - but some
> >>people in our department was worried about the thermal expansion
> >>when the shunt is mounted on FR4. They worried about the thermal cycles
> >>destroying the PCB. Have you experienced anything like this?
> >we normally punch a shape into the manganin that includes both the
> >current and sense contacts. The contacts are bent at 90 degrees to fit
> >into PCB pads, so there's some flex designed in. IRC's 'oar' shunts
> >are omega shaped, which also gives some compliance. Some of the Isotek
> >parts are really planar, like a huge surface-mount resistor, but I
> >wouldn't suspect this to be a problem; the solder joints will be huge,
> >and although the pcb material has a high tce compared to almost
> >anything else, it's soft so the forces won't get very high. But if the
> >shunt self-heats a lot, that might be nasty... in that case I wouldn't
> >solder a flat shunt to a pcb without strain relief somehow; that could
> >well rip the pads off the board.
> >We often heat-sink the shunt, which helps.
> >This is similar to the problem of attaching a big ceramic package to a
> >pcb. I've read of cases like that that failed after a few dozen wide
> >temperature cycles.
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