A current shunt resistor
is a low Ohm, high precision resistor which is used to measure the current
flowing through a circuit. Current is calculated by dividing the voltage drop
of the resistor by the resistance of the resistor (I=V/R). These resistors
are sometime referred to as “ammeter shunts” because of their ability to
measure amperes. They are used when the current to be measured is out of the
range of the measuring device. Depending on their rating, shunt resistors
are usually designed to drop voltage by 50mV, 75mV or 100mV.
Let’s say you have a 100 Amp current shunt resistor used to measure the current flowing in or out the the battery bank of a renewable energy system, such as solar or wind turbine. You can connect a standard multimeter (0-100mV) to the shunt resistor’s leads to monitor how much current the batteries output or how much current is being used to charge the batteries.
In our example, the 100 Amp shunt resistor is configured to drop the voltage by 100mv when the current flowing through it is 100 Amps. The resistance of the shunt resistor is calculated by dividing the voltage by the current 0.1/100=0.001 Ohms. The resistance value changes in linear proportion to the current flowing through the circuit. You can determine the amount of voltage dropped in a circuit using a standard multimeter. If the voltage drops by 18mv then the current flowing though the circuit can be determined by dividing the voltage drop by the resistance (0.018/0.001= 18 Amps)
There is, of course, a “cost of doing business” with a shunt resistor. The power lost when the shunt resistor is doing it’s work is calculated by multiplying the voltage by the current. In the previous example that would be 0.018V * 18 Amps = 0.32 Watts.
Current shunt resistors are not designed to be used at their full capacity continuously. “Continuously” is defined as being more than 2 minutes of use. Doing so could overheat and damage the resistors which would give inaccurate measurements. If a shunt resistor becomes too hot for too long will be permanently damaged. Most shunt resistors have a “derating factor” of 66%. This means that you would not operate the 100Amp shunt resistor in our example at more than 66 Amps.
Current shunt resistors can be used in a wide variety of applications including automotive, marine and renewable energy systems.
Let’s say you have a 100 Amp current shunt resistor used to measure the current flowing in or out the the battery bank of a renewable energy system, such as solar or wind turbine. You can connect a standard multimeter (0-100mV) to the shunt resistor’s leads to monitor how much current the batteries output or how much current is being used to charge the batteries.
In our example, the 100 Amp shunt resistor is configured to drop the voltage by 100mv when the current flowing through it is 100 Amps. The resistance of the shunt resistor is calculated by dividing the voltage by the current 0.1/100=0.001 Ohms. The resistance value changes in linear proportion to the current flowing through the circuit. You can determine the amount of voltage dropped in a circuit using a standard multimeter. If the voltage drops by 18mv then the current flowing though the circuit can be determined by dividing the voltage drop by the resistance (0.018/0.001= 18 Amps)
There is, of course, a “cost of doing business” with a shunt resistor. The power lost when the shunt resistor is doing it’s work is calculated by multiplying the voltage by the current. In the previous example that would be 0.018V * 18 Amps = 0.32 Watts.
Current shunt resistors are not designed to be used at their full capacity continuously. “Continuously” is defined as being more than 2 minutes of use. Doing so could overheat and damage the resistors which would give inaccurate measurements. If a shunt resistor becomes too hot for too long will be permanently damaged. Most shunt resistors have a “derating factor” of 66%. This means that you would not operate the 100Amp shunt resistor in our example at more than 66 Amps.
Current shunt resistors can be used in a wide variety of applications including automotive, marine and renewable energy systems.
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