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From: boB gudg
Subject: Re: Open air current sensing PCB mount shunts...
Date: 14 Dec 2002 15:13:10 -0600
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On Sat, 14 Dec 2002 09:51:59 -0800, John Larkin
>On Sat, 14 Dec 2002 17:33:52 -0500, "Klaus Vestergaard Kragelund"
>>"John Larkin" wrote in
>>> 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?
>>> Isotek makes pcb-mount shunts, too.
>>> We punch our own from sheet manganin, but that's a hassle unless you
>>> need a whole lot. Manganin does have pretty good tempcos...
>>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 coefficient
>>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
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