#relay test

[hardmoonier]

Electrical Relay: What is a Relay? and How does a Relay works? search basic idea from the video and get more info from Electrical Relay Functions and Applications

video source: https://www.youtube.com/watch?v=1_YfuH_AcxQ&t=47s

[hardmoonier]

How to Test a Bad Relay in Your Car?

Automobile is absolutely necessary for human daily life. So have a general idea of it is very useful when your car has some problems outside. There are a lot of parts on the car, let's take a little part of it, that is automotive relay.

1 Automotive Relay Relays are widely used in automotive circuits, such as starting system circuits, wiper circuits, and rear window heating circuits. When the vehicle starts, a larger starting current is required. If the ignition switch is used for direct control, the starting contacts will ignite and burn, which will affect the service life of the ignition switch and even cause serious consequences such as line ablation and fire. Using a relay to control a large current with a small current will not cause the above problems. When a certain voltage or current is applied to both ends of the electromagnetic relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the core, yoke, armature, and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature attracts the pole face of the iron core, making the normally closed contact to open and the normally open contact to close. When the voltage or current at both ends of the coil is less than a certain value, the mechanical reaction force is greater than the electromagnetic attraction force, and the armature returns to the initial state: the normally closed contact is on and the normally open contact is off. One of the automobile relays functions is a switch; the other is  load overload protection; the third is a fault protection.

2 Common Faults of Automotive Relay Including coil burnt, short circuit, insulation part aging, contact ablation, etc. (1) Relay Malfunction When the controlled circuit is required to be closed, the relay will not act, on the contrary, when the controlled circuit is not required to be closed, the relay will act. This kind of problems occurs mainly because the interference voltage in the circuit exceeds the allowable range of the drive circuit of the relay. When designing the circuit, pay attention to the factors that can cause interference (such as chip command errors, short circuits, grid fluctuations, etc.).

(2) Relay Burned There are many reasons for burnout. For example, the actual switching current exceeds the rated switching current of the relay, and the actual inrush current exceeds the rated switching current of the relay. According to design experience, in order to avoid these problems, the rated current should be selected to be 2-3 times the actual switching current, and the impact current of the relay is 2-3 times the actual current.

(3) Contact Welding Generally speaking, the temperature rise of the AC conversion relay coil is higher than that of the DC conversion relay. This is because of the eddy current loss and hysteresis loss in the magnetic circuit. In addition, when the AC conversion relay is operating at a voltage lower than the rated voltage, a bounce phenomenon may occur. This will cause burnout, welding of contacts and damage to the relay or disconnection of the self-protection circuit. Therefore, measures must be taken to prevent fluctuations in the power supply voltage. In addition, regardless of the length of the fluctuation time, it will cause the failure of the relay. So ensure that there is a power supply with sufficient capacity.

(4) Coil Temperature Rise is Too High The loss of magnetic materials such as copper wires and iron cores or the heat transfer of the contacts will cause the temperature rise. Therefore, the heat resistance of the insulating material and the distance between the relay and the heat-generating device should be paid special attention in the circuit design.

3 Detection Method Static detection: check the resistance of the coil and the resistance of the normally closed contact. Dynamic detection: energize the coil and detect the resistance of the normally open contact.

4 Specific Operation 1) Turn on the ignition switch and hear whether there is a pull-in sound in the control relay or feel the relay with your hands for vibration. If so, it means that the relay is basically in routine use. The failure of the circuit may be caused by other reasons. On the contrary, it means that the relay is faulty. 2) Replace the relay to be tested with an identical working relay. Turn on the switch, and if the electrical equipment is working normally, it can be determined there is a problem with the relay to be tested. 3) Use the multimeter Rx100Ω gear and combine the resistance of each pin of the circuit to analyse. If the conduction and disconnection are normal, it means that there is no problem with the relay, otherwise it means the relay is faulty. 4) Open the relay shell to check whether the contacts are ablated or oxidized. If there are bumps and rust on the contact, it means that the contact is ablated or oxidized and does not work properly. 5) Check whether the coil is ablated or discolored. If the coil is ablated with jelly, the coil is black or has a gluey smell, which means the coil is short-circuited by ablation.

This is the part of relay test, if you want to get more info about it, check the source Electrical Relay Testing Methods