As the sales of electric vehicles continue to rise, EV Chargers have experienced explosive growth. The components needed for EV Chargers have become increasingly well-known, including AC and DC contactors, surge protectors, emergency stop buttons, fans, molded case circuit breakers, and more. Today, we will focus on sharing information about shunts.

What is a Shunt?
A shunt is a device made based on the principle that a voltage is generated across a resistor when a direct current passes through it.

How are Shunts Classified?
Shunts used for DC current measurement can be classified into slotted and non-slotted types. The shunts commonly used in EV Chargers are generally 300A 75mV.

What are the Functions of a Shunt?
Shunts are used to measure DC current. A shunt is essentially a resistor with a very low resistance value. When DC current flows through it, a voltage drop is generated, which is used by a DC ammeter for display. The DC ammeter is actually a voltmeter with a full-scale value of 75mV. The DC ammeter and the shunt are used together.

Principle Analysis of the Shunt
Shunts are mainly used to measure large DC currents. The common charging pile shunts are 75mV and are often used in DC screens, excitation cabinets, and other DC current monitoring applications. A shunt is a low-resistance device capable of carrying large currents. When current flows through the shunt, a millivolt-level DC voltage signal is generated across its two terminals. This signal causes the needle of the DC ammeter connected across the shunt to move, and the reading on the meter indicates the current value in the DC circuit.

Note: The measurement principle of the shunt is based on voltage drop. For example, using a multimeter in DC voltage mode to measure the DC voltage across the two small terminals of the shunt, if the measured value is 30mV, then based on the formula Ue/e = U/I, i.e., 75mV/100A = 30mV, the actual current is 40A. This method can be used with a clamp ammeter to test the accuracy and condition of the shunt.

How to Select a Shunt？
Determine the DC load, choose a suitable range shunt, and select the corresponding meter. When a shunt is used with a magnetoelectric pointer ammeter, the signal connection wire should be a pair of fixed resistance wires that match the ammeter. If the shunt's sampling voltage is used as the input signal for a digital meter, ordinary wires can be used. If the range of the digital meter is adjustable, it should match the parameters of the shunt.

What Issues Should Be Considered When Selecting a Shunt?

1. The cable (or copper busbar) of the shunt's primary circuit should not have any artificial contact resistance at the connection point with the shunt, and the sampling points for the secondary voltage should not be taken from non-sampling points.

2. The two small screws connecting to the instrument's signal input terminal should ensure correct signal polarity. The end where the current flows into the shunt is the positive terminal, connected to the positive input of the instrument's signal input terminal; the end where the current flows out of the shunt is the negative terminal, connected to the negative input of the instrument's signal input terminal.

3. It is recommended that the actual operating current (for long periods) should not exceed 80% of the rated current.