Electronics > Projects, Designs, and Technical Stuff

Building a current shunt?

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joeqsmith:
I attempted to make a shunt for a cheap meter.   Played around a bit before ending up with the one shown installed.    Turned down the ends in the lathe and silver soldered them to the wire.   I wasn't looking for your 0.04% and  0.01 ohms meant it could be fairly small. 

Some of the shunts I have are indeed filed, so I see no reason you couldn't do this assuming the tolerance of the one you bought was low.   

tszaboo:
Your specification doesnt make it easy. At 15A, your shunt will dissipate 22.5W. No matter what you use, the shunt will heat up. Say, it heats up by 100 degrees, then your tempco has to be less than 4ppm. There are only a handful of metals that would even come close to this, and you need a lot of this material, because you need to dissipate 22W.

This is easyer to buy than to build. Here is a resistor:
https://www.digikey.com/product-detail/en/riedon/FHR4V-0R1F1/696-1809-5-ND/7867339
Bolt it on a heatsink, and calibrate it.

maginnovision:
https://www.digikey.com/product-detail/en/riedon/RSN-100-100B/696-1764-ND/6819384 This is what I use for my "precision" shunt. Nice thing is it has a large range meaning you can use it more than once, bad thing is the precision isn't quite as precise as I'd like.

Kleinstein:
I don't think one would really need exactly that value of shunt. The main point would be to get an accurate current reading for a large current (e.g. some 5 A or 10 A depending on the exact supply type).  If you happen to have a suitable meter to directly measure that current with sufficient accuracy it is also OK. Not many meter are very accurate with more than some 2 A and thus the external shunt. However modern meters could well work with a smaller shunt resistance. Another option might be a precision DC current transformer - these are also a good modern alternative for high currents, though usually not cheap.

jbb:
Possibly threadjacking, but people have been mentioning cooling a shunt...

I've got a task at work which needs a pretty good shunt, and I was wondering if anyone here has any experience or comments about adding extra cooling to reduce the temperature rise.  The shunts I have on hand are round cylindrical (encapsulated) types with 4 wire legs.  Would blowing a fan across them be suitable, or would I risk inducing big temperature gradients and increasing the tempo and/or thermocouple effects?

The resistors I've got are Ohmite 17FPR100E (4 wire though hole, 0.1R, 7W, 50ppm, 2uV/C) and my expected currents are 3.4A, 2A and 0A.

In fact, the FHR4V-0R1F1 mentioned by NANDBlog probably would have been a better choice.

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