Current measuring shunt

Graham_Wright said:
Best material? I'm minded to use stainless - poor conductor and corrosion resistant.
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Conductivity (thats 1/resistance):
copper: 58.5*10^6 S/m
316 stainless: 1.37*10^6 S/m

so,for a given length and cross sesctional area a SS shunt will give only 42 times the voltage.

To be honest thats not a big enough difference to warrant adding 2 more connections (each end of the shunt) into a circuit where simply stripping a bit of insulation and attaching sense wires will do.
 
If you are prepared to make and calibrate a piece of stainless steel for a shunt (which is quite a reasonable approach.) you might like to try using a moving coil sensitive meter ie 50 mv connected between the ends of your feed cable. Thus the feed cable either pos or negative which has an inherent resistance can serve as a shunt. If you get enough indication then you can calibrate by fitting a potentiometer or simply tapping along the wire or even by adding more wires in parallel to reduce volt drop so reading.
If you are trying to feed a digital meter these usually need 200mv for max count so much less sensitive than moving coil meter so you will need a shunt which obviously can lose some of your power as volt drop unless you fit an amplifier or hall effect sensor.
olewill
 
The meter is digital with an internal shunt. The connections to it are, in my opinion, inadequately sized. I have blown a couple as it seems the current took a strange route. Passing up to twenty amps, which is the maximum declared current, seems dodgy. I intend to remove the internal shunt which is inherently dangerous as the full current would then blow the sensor. I have used the resistance of the feed cable to produce the necessary voltage but the danger is that even a temporary break (loose connection) will blow the meter. If I take two leads both to the shunt (i.e. not the battery terminal itself), that should be safe. It should be easy to calibrate the shunt with another meter in series.
 
After a few measurements, I have found it adequate to measure the volts drop across the power lead. Even though it is substantial, the meter is sufficiently sensitive to give a meaningful reading. I have followed the same route for measuring the current into the glow plugs on my engine. Fsd = 24 amps = four glow plugs drawing current.
 
halcyon said:
Shunts use a special alloy that has a constant resistance over a temperature range, most metals the resistance varies with temp, thus volt drop varies.

Brian
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For this application precision isn't a requirement. More likely is it there and which was is it going?!

I think for copper the temperature coefficient of conductivity is around 0.4% per degree C.
 
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