Bias magnetic effect of micro relay
1. Overview
While we’re at it, this article will give you an in-depth look at a unique miniature relay. Although this relay is small, it can operate with double pole and double throw at 5V voltage. When I was conducting experiments recently, I discovered that by driving the relay through the emitter of the triode, it can work normally without an additional freewheeling diode. This led to speculation: Does the relay have a freewheeling diode inside it to avoid flyback voltage? In particular, this relay has clear requirements for the voltage direction, and the relay does not respond when the voltage is reversed. In order to unlock the secrets, I am going to disassemble two identical relays and explore their internal structure in depth.
2. Disassembly, observation and discovery
First, use diagonal pliers to easily open the casing of the relay, and what you will see is its precise and compact coil structure. In order to observe more carefully, I used a magnifying glass to examine its internal structure, paying special attention to whether there is a freewheeling diode. On one side of the relay, the structure of the electromagnet can be vaguely seen. Then, I used a sharp awl to gently push the inner armature reed and found that even though the coil was not energized, the armature still seemed to be attracted by the electromagnet. Further disassembly revealed more internal structures, but no trace of the diode was found. Surprisingly, even when the armature is removed, it is still attracted to the electromagnet, revealing an added bias magnet on the electromagnet. This design significantly reduces reliance on current flow and explains why the direction in which the voltage is added is critical to the relay's operation.
Through disassembly, it was observed that the electromagnet of the relay is attached with a permanent magnet as a bias source. This bias significantly reduces the relay's dependence on the coil current. When the direction of the magnetic field generated by the input current is consistent with the bias direction of the permanent magnet, the two reinforce each other, allowing the relay to operate. On the contrary, if the two directions are opposite, the magnetic field of the armature will be weakened and the relay will not operate. This unique polarity requirement is the subtlety of miniature relay design.
Summarize
Through actual disassembly experiments, this article deeply discusses the magnetic bias phenomenon inside the micro-relay and its working principle. We found that despite its small appearance, the internal design of the relay is extremely delicate, especially the added bias magnet, which not only optimizes the efficiency of current use, but also determines the specific response of the relay to the direction of voltage. Through this in-depth analysis and experiment, we not only have a more comprehensive understanding of micro-relays, but also provide valuable reference for further applications and optimization.