Current detection method of multimeter in automobile
There are various ways to detect current in cars, and we will introduce three common detection methods here.
Method 1: Use a regular multimeter current mode, connect it in series into the circuit, and measure it.
Method 2: Connect a small test lamp in series between the battery cable and the battery pole for testing.
Method 3: Use a clamp type DC multimeter for testing. This method does not require disconnecting the original vehicle line, but instead clamps the induction clip of the DC multimeter onto the measured wire for inductive detection.
The specific operation of Method 1 is as follows. When using a regular digital multimeter to detect battery leakage current, the positive pole or pole clamp of the battery should be removed, and then the red probe of the multimeter should be inserted into the 20A socket, and the black probe should be connected to the common terminal (COM). Then, the multimeter gear switch should be pulled to the 20A current gear, and connected in series between the disassembled battery pole and the battery clamp. The schematic diagram of using a regular multimeter to detect current is shown in the figure.
The specific operation of method 2 is shown in the figure, which is a schematic diagram of using a test lamp to detect leakage current.
The simplest method to detect whether there is leakage in the electrical equipment of the entire vehicle is to connect a small test lamp in series with the battery line for testing. This method was not used as frequently as digital multimeters in the early days. Using a small test lamp to connect the battery pole and the wire in series, and judging whether there is leakage based on the brightness of the bulb, this method is recommended but cannot clearly display the specific leakage current. It is no longer used. Because the price of a multimeter is already very cheap, it has now switched to method 1 or method 3 for testing.
This method is more convenient to detect, but the main issue is that disconnecting the circuit for detection may result in the following problems.
1. If the battery cable is disconnected, many parameters of the original car need to be reset, which increases the workload of detection. Furthermore, modern cars adopt a networked design. Every time the network is disconnected, it takes several minutes or even half an hour to put the entire car into sleep mode, which is a very time-consuming method.
2. Due to the fact that some plugs have multiple wires sharing a single plug, unplugging the plug can cause related circuit breaks, making it inconvenient to detect current. For example, for the plug of a cooling fan, the positive and negative poles of the fan motor and the speed control resistor are usually concentrated on one plug. When we want to measure the working current of the fan, we disconnect the fan plug and both the positive and negative poles are disconnected, which cannot form a circuit and no current flows through the fan, making it impossible to measure.
Taking into account the aforementioned unfavorable factors, it is generally not recommended to use the traditional method of disconnecting the circuit in series with an ammeter to measure current in modern automotive electrical maintenance. Instead, it is advisable to use a clamp type multimeter induction measurement method.
