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I have been told me that a shunt resistor can be made with a welding electrode, and you just have to calibrate it, any one have experience doing this or anything similar?

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  • \$\begingroup\$ I've made a resistor once out of pencil lead. It didn't worth it. What are you trying to do? \$\endgroup\$
    – Eugene Sh.
    Commented Jul 8, 2015 at 1:53

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The shunt resistor material shuld have a very low limit influence of the temperature and very low winding inductance. So the best properties of the material is the one with small temperture coefficient and high resistance (resulting a short coil) and off cource the required diameter.

Bellow is a table with sample materials and its main specs that is required to select and design a shunt resistor.

enter image description here

A welding electrode usually is made with a similar composition to the metal being welded (i.e iron or tungsten), making this materials one of the worst for choice.

The last column of the table is useful to calculate the thermoelectric voltage caused when the shunt resistor connected to the rest of the circuit (both ends of a copper wire or copper in PCB), which contribute to the total voltage drop.

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If you can precisely measure (or know) the resistance and temperature coefficient of the electrode, you can use it as a shunt resistor.

But you'll probably be better off buying one for the purpose, since they're fairly cheap and require precision.

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  • \$\begingroup\$ Yeah that's just the problem, where a live there is no much to choose, I only could buy an 0.001 ohm resistor an it it's a pretty small value, and getting quite big problems with the CMRR, and can't find either precision resistor to solve the problem. \$\endgroup\$ Commented Jul 8, 2015 at 2:02
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You could use almost any metal, though "galvanic corrosion" could be an issue when connecting some types of metals, also you may have a problem soldering some metals. https://en.wikipedia.org/wiki/Galvanic_corrosion

For prototyping and/or engineering purposes, you could parallel multiple resistors. For example, ten 1ohm resistors in parallel would provide 0.1 ohm resistance, which is an easier solution.

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  • \$\begingroup\$ I will try that, it worries me the change of resistance with the temperature in a standard resistor, but looks simpler than make the resistor from scratch. \$\endgroup\$ Commented Jul 10, 2015 at 0:49

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