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Building a current shunt?

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TERRA Operative:
I want to whip up a basic current shunt (well as basic as they are already...), and I'm looking for a few pointers to make sure I get things right without making any basic mistakes as I tend to do...  :-BROKE

The HP service manual for my 6644A is asking for a Guildline 9230/15 or equivalent for performance testing, which is a 0.1 Ohm, 15A shunt with 0.04% accuracy.
Problem is that these things are just a tiny bit too expensive for my taste, so I want to build one and I'm not too fussed with it being such a tight tolerance, just somewhat reasonably accurate.

Has anyone built something like this? I was thinking of just using a bunch of power resistors in parallel, or maybe stringing up some nichrome or kynar wire?

What's the general go-to for building a semi professional looking and performing current shunt?

Kleinstein:
Actually building a shunt is difficult, as the hard part is getting the right material. For low resistance shunt the usual choice is Manganin alloys. AFIAK this alloy is suitable for soft soldering.

Soldering a bunch of resistors in parallel is possible, but the connecting wire part can be an important part and this part tends to be pure copper and thus high TC.

So I would more like look for a cheaper shunt. Quite often there are relatively cheap ones on Ebay - meant to be used with Panel meters. The DIY part could measuring the actual value if one has a good meter available.

TERRA Operative:
I have a 34461A benchtop meter, so I can get 4-wire measurements with an average level of accuracy.

It seems most ebay shunts are rated at 75mV at their rated current, whereas what I need seems to be 1.5V at 15A, ir 75mV at 7.5A, something which doesn't seem to exist in the ebay ones.
I guess I can get one that's close and trim it to spec with a hand file?

Kleinstein:
The burden-voltage is a compromise between noise and thermal EMF problem at low voltage and self heating at higher voltage. So higher current shunts tend to us a smaller burden voltage.  For panel-meters 75 mV burden voltage is kind of a standard, at least for higher currents.

1.5 V at the shunt is rather high and causes quite some heating. So the resistor would need to be rated for really high power. 1.5 V and 15 A are some 22.5 W. For use as a precision shunt the rule of thumb is using more like 1/10 the normal power rating to limit the self heating.
So the 0.1 Ohms shunt for 15 A would indeed be quite large power rating and unusual. If really needed this way I would consider resistors possible several  that can be mounted to a heat sink and a fan. The actual needs may be lower and the quoted part just a relatively common high end shunt found in cal labs.

One may get away with directly using the DMM to measure the current (use the internal shunt) or using a lower burden voltage shunt, as the 34461 is reasonable good in measuring small voltages.

ArthurDent:
I have a Leeds&Northrup model 4360 .1 ohm 15A precision shunt that I use and it is big enough and has so much surface area that heat dissipation isn't a problem. It's probably over 60 years old but still works like new. I believe I paid less than $25 for it many years ago. It seems kind of odd to use something so old to check modern equipment but it works!

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