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I am very new to hardware development. I am learning all the basics to design a battery management system for electric vehicles in the future.

I would like to know how to select a shunt resistor for my circuit. I have searched in google and got many results. Mainly using Ohm's law but still I am bit confused of choosing a value for shunt resistor for my circuit.

The battery pack I am using is 10s 36v 2.5 ampere hour = 2.5 amperes for one hour.

As per the battery datasheet the maximum current the load can withdraw (discharge) is 2C, so 5 amperesmps for half an hour.

I learned the concept of shunt resistor the value should be small so that it will not affect the load.

I would like to measure the current flowing from the battery to the load so that if it reaches the threshold (5A) I can cut-off the discharge flow. For that I am using a shunt resistor.

I learned the concept of shunt resistor the value should be small so that it will not affect the load, but I am confused how to select the resistor value for above specifications of my circuit.

I know it is basic, but I am really confused please help me in learning it.

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A shunt resistor value is a trade-off between how many millivolts you can afford to lose, and how easy it is to measure the voltage. Common values for the voltage drop at the rated current are 50 mV or 100 mV. If you want 50 mV for 5 A, then the resistor would be 0.05V/5A = 0.01 ohms.

If you can afford to lose a higher voltage, then it will be easier to measure. If you want to lose a smaller voltage, it will be harder to measure.

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  • \$\begingroup\$ Than you so much Sir for clearing my confusion. and can we take any voltage value that we can able to afford (for example 30mv) apart from 50 mv and 100 mv and is this 50 mv and 100 mv are common values for easy calculation or is there any other reason \$\endgroup\$
    – Muthu
    Commented Mar 25, 2020 at 18:41
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    \$\begingroup\$ When analog meters were more common, it was more important to have a standard. A 50 mV meter would have alternate face plates for different standard current ranges. \$\endgroup\$
    – Mattman944
    Commented Mar 25, 2020 at 21:57

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