How to Use Shunt 75MV/20A: Examples, Pinouts, and Specs

A shunt is a precision resistor designed to measure current by generating a small, proportional voltage drop across its terminals. The Shunt 75MV/20A is specifically calibrated to produce a voltage drop of 75 millivolts (mV) when a current of 20 amperes (A) flows through it. This makes it an ideal component for current measurement in high-power circuits, where direct current measurement is impractical.

• Current measurement in power supply systems
• Battery monitoring and management systems
• Industrial equipment and motor control
• Energy meters and power monitoring devices
• Integration with microcontrollers and data acquisition systems

• Maximum Current Rating: 20A
• Voltage Drop at Maximum Current: 75mV
• Resistance: 3.75 milliohms (calculated as 75mV / 20A)
• Accuracy: Typically ±0.5% or better
• Material: Manganin or similar low-temperature-coefficient alloy
• Operating Temperature Range: -40°C to +85°C
• Mounting Style: Screw terminals or solderable connections

The Shunt 75MV/20A typically has two main terminals for current flow and two smaller terminals for voltage measurement. These are described in the table below:

1. Placement in the Circuit:

   • Place the shunt in series with the load whose current you want to measure.
   • Ensure the current flows from the Current Input (+) terminal to the Current Output (-) terminal.

2. Voltage Measurement:

   • Use a high-impedance voltmeter or an analog-to-digital converter (ADC) to measure the voltage across the Voltage Sense (+) and Voltage Sense (-) terminals.
   • The measured voltage will be proportional to the current flowing through the shunt, based on the formula: [ I = \frac{V}{R} ] where ( I ) is the current, ( V ) is the measured voltage, and ( R ) is the shunt resistance (3.75 milliohms).

3. Connection to Microcontrollers:

   • If using a microcontroller like an Arduino UNO, connect the Voltage Sense (+) terminal to an analog input pin and the Voltage Sense (-) terminal to the ground (GND).
   • Use the ADC to read the voltage and calculate the current.

• Power Dissipation: Ensure the shunt's power dissipation does not exceed its rating. For the Shunt 75MV/20A, the maximum power dissipation is: [ P = I^2 \times R = 20^2 \times 0.00375 = 1.5 , \text{W} ]
• Wiring: Use thick, low-resistance wires for the current-carrying terminals to minimize additional resistance.
• Temperature Effects: Avoid placing the shunt near heat sources, as temperature changes can affect its resistance and accuracy.
• Calibration: Periodically verify the shunt's accuracy using a known current source and a precision voltmeter.

The following code demonstrates how to measure current using the Shunt 75MV/20A and an Arduino UNO:

// Define the analog pin connected to the Voltage Sense (+) terminal
const int shuntPin = A0;

// Shunt resistance in ohms (3.75 milliohms)
const float shuntResistance = 0.00375;

// ADC reference voltage (5V for Arduino UNO)
const float adcReferenceVoltage = 5.0;

// ADC resolution (10-bit ADC for Arduino UNO)
const int adcResolution = 1024;

void setup() {
  Serial.begin(9600); // Initialize serial communication
}

void loop() {
  // Read the raw ADC value
  int adcValue = analogRead(shuntPin);

  // Convert ADC value to voltage
  float shuntVoltage = (adcValue * adcReferenceVoltage) / adcResolution;

  // Calculate current using Ohm's Law (I = V / R)
  float current = shuntVoltage / shuntResistance;

  // Print the measured current to the Serial Monitor
  Serial.print("Current: ");
  Serial.print(current, 2); // Print current with 2 decimal places
  Serial.println(" A");

  delay(1000); // Wait for 1 second before the next reading
}

1. No Voltage Reading Across the Shunt:

   • Cause: Improper wiring or no current flowing through the shunt.
   • Solution: Verify the connections and ensure the shunt is in series with the load.

2. Inaccurate Current Measurement:

   • Cause: High resistance in the wiring or incorrect ADC reference voltage.
   • Solution: Use thick wires for current connections and ensure the ADC reference voltage is correctly set in the code.

3. Overheating of the Shunt:

   • Cause: Current exceeds the shunt's maximum rating.
   • Solution: Ensure the current does not exceed 20A. Use a higher-rated shunt if necessary.

4. Fluctuating Readings:

   • Cause: Electrical noise or poor connections.
   • Solution: Use shielded cables for voltage sense lines and ensure all connections are secure.

Q1: Can I use the Shunt 75MV/20A for AC current measurement?
A1: No, this shunt is designed for DC current measurement. For AC, you would need additional circuitry, such as a rectifier and filter.

Q2: What happens if I exceed the 20A current rating?
A2: Exceeding the current rating can cause excessive heat, damage the shunt, and reduce measurement accuracy. Always stay within the specified limits.

Q3: Can I use this shunt with a 3.3V microcontroller?
A3: Yes, but ensure the voltage drop across the shunt does not exceed the ADC input range of the microcontroller. Adjust the code accordingly for the 3.3V reference voltage.

Q4: How do I improve measurement accuracy?
A4: Use a high-resolution ADC, minimize noise in the circuit, and ensure proper calibration of the shunt and measurement system.