How to measure current using a voltmeter? how to calculate shunt resistance value?
Answer:
To measure current using a voltmeter, install a suitable shunt resistor and measure its voltage drop. Divide the voltage drop by the resistance of the shunt to obtain the current. To calculate the value of the shunt, estimate a maximum current for the circuit, then select a resistor for a shunt which will have sufficient voltage drop at that current to give a minimum sufficient indication on your voltmeter. Also check that the power rating of the shunt will not be exceeded via P=I^2R.
For example, you have a circuit you wish to install a shunt in, and you estimate the max current at 10 amps. Your voltmeter's max resolution is 0.1mV. You decide you'd like about a 0.1% number, therefore you want your voltage drop to be 1000 times that, 0.1V. 0.1V/10A=0.01ohms, and 10A^2*0.01ohms = 1W.
i am not a electricial technician, but my friend told me this, which i am telling you as my ans,
if you have a voltmeter, for example you are masuring somethings's volts and then you need to know a wire is copper or Aluminium , so you can know resistance accroding to copper or aluminium cross sectional area,
now you have " V" = volts and "R" Resistance
now you can calculate this : I = V/R ( This you can use only for DC Current) and if you want to calculate AC current you need to calculate I = V/R * Frecuncy
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