Is it normal for car relays to get hot?

Update:28-08-2020
Summary:

Car relays get hot. From the perspective of physics, it […]

Car relays get hot. From the perspective of physics, it is a process in which heat is generated by mechanical motion, and mechanical energy is converted into heat. This is a normal phenomenon. This is why a radiator is installed in many machines. A lot of heat is generated during the movement of the machine, and we will install a heat sink to lower the temperature. If the temperature is too high, this is an abnormal phenomenon.

It is normal for the relay coil to be slightly hot during normal operation, but if the contacts are hot, it means that the service life of the relay has expired and should be replaced. Otherwise, the contact resistance of the contacts will be too large and lead to line failure (excessive voltage drop). If the contacts are not replaced, the contact resistance will heat up and cause further oxidation. The hot phenomenon will be more serious. In extreme cases, it may cause a fire.

The phenomenon and reasons of hot relay are as follows:

1. Abnormal heating occurs in the center of the contact, and the contact is fused, melted, dissolved and solidified, etc., and the operation is not good. That's because the repeated switching of the contacts causes the continuous occurrence of opening and closing arcs.
2. The internal circuit of the relay is fused and the contacts are melted and solidified, and the action is not good. This is probably due to an abnormal overcurrent that exceeds the rated current of the contact.
3. The coil is partially short-circuited and fused, the coil is disconnected, and the coil remains abnormally heated. It may be an overvoltage applied to the coil.

The solutions to the above phenomena are:
1. For AC specification relays, the voltage should not be lower than 90% of the rated voltage; for DC specification relays, the voltage should not be lower than 79% of the rated voltage; avoid high-frequency switching.
2. Carry out safety design on the circuit to prevent the rated current exceeding the contact from flowing through the contact circuit.
3. Do not apply a voltage above the rated voltage to the coil.

The car relay is not normal when it is hot. We first judge the temperature. If the temperature is too high, it is an abnormal phenomenon. If there is an abnormality, we must eliminate it. Don't delay it, the problem will be more serious when it is delayed. If we cannot solve it by ourselves, then we must seek help from professionals and try to minimize the loss.