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From: boB gudg
Subject: Re: Open air current sensing PCB mount shunts...
Date: 14 Dec 2002 16:02:20 -0600
References: <firstname.lastname@example.org> <email@example.com>
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Where are you getting the manganin ?? (or cupron?)
And sheets? Rolls ?
On 14 Dec 2002 15:13:10 -0600, boB gudg wrote:
>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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