What is a current shunt & its use?
Answer:
It is a heavy piece of metal that is used with a current meter. The meter's internal parts are made to take a small current (like .001 Amp and deflect full scale when they detect that. If you want to measure a current that is large like 20 amps you need to make a path for all the current beyond that .001 Amp to bypass the meter. By making the shunt a very low resistance the current is divided up so most goes through the shunt and the tiny remainder feeds the meter.
to make your current meter measures more than it's rating, you can also make your own shunt by the formula:
Rs= Rm/(n-1)
where: Rs= resistance in ohms for shunt
Rm= resistance of meter
n= ratio for stepping up range of meter
Ls=Rs/(Xv)/1000 ft.
where:Ls= lenght of copper wire shunt
Xv/1000= resistivity of copper wire at a certain gage
Ex; #18 awg magnet wire has a resistance of 6.386 ohm/1000 ft.
say you have a 0-1 ma and would like to measure up to 1 amp., meter resistance= 70 ohms.
Compute:
Rs=Rm/(n-1)
0-1ma meter, 1 amp range, 1ma=0.001 amp
n=1 amp/0.001= 1000
Rs=70/(1000-1)=0.070 ohms
for a shunt of #18 awg magnet wire;
Ls= 0.070/6.386/1000=10.96 ft.
you can coil 10.96 ft. of #18 awg and connect it in parallel with your current meter and measure up to 1 amp.
Note:
the thinner the wire, the lesser the lenght.
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