Views: 12 Author: Site Editor Publish Time: 2023-01-06 Origin: zhihu
A relay is a switch that disconnects or conducts a circuit under certain conditions. If you do not pay attention to protection during use, its life will be shortened. Therefore, in addition to comprehensive parameter testing and effective screening when selecting a relay, the Proper use of relays also requires an effective approach to reliability.
The pull-in voltage of the relay is generally only one-half to two-thirds of its rated working voltage, but when using the time delay relay , it must work under its rated working voltage, instead of taking its pull-in voltage as the working voltage. It is because under the pull-in voltage condition, although the relay has been activated, the pressure between the moving contacts has not reached the specified value, which will easily lead to a large contact resistance between the contacts. If the contacts work under high current conditions, It will increase the contact power, which will easily cause contact ablation and shorten its working life.
Although the allowable contact power is given in the technical index of the relay, and the corresponding electrical life is given at the same time, the contact of the 24v relay is allowed to be switched when it is live, but it should be avoided if possible. No current switching will greatly increase the service life of the relay.
Since the ac relay has a failure mode of low-level failure, try to avoid the timer relay contacts working under low-level and micro-current conditions, and choose solid-state relays and analog electronic switches instead of relays when possible.
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The winding of the electronic relay is an inductance, and there is an armature in the winding, so the magnetic energy will be stored after the winding is energized, and the release of the magnetic energy will generate a high back EMF (sometimes as high as hundreds of volts) when the winding is de-energized. On the one hand, it is easy to break down the devices (such as transistors and integrated circuits) that drive the relay. On the other hand, it will cause spike interference and interfere with the normal operation of the whole machine and other lines in the system. A peak elimination diode is connected in parallel on the winding.
When a relay is required to switch a large current, try to use a relay with a large contact current instead of using the method of connecting contacts in parallel (whether it is multiple sets of contacts of a relay or the contacts of multiple relays in parallel), which is Because it is difficult to ensure the same contact resistance for each group of contacts of the relay, uneven current distribution is likely to occur in parallel use, and it is also difficult to ensure consistency in the contact action time, so it is easy to appear in a certain group at the moment of switching. The phenomenon that the instantaneous current of the contact is too large.
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