Common Problems for Electrical Contacts of Relays

We know that contact components failure is the core of relay failure. When selecting the relay, you should choose the appropriate relay according to the actual load condition in order to avoid frequent faults. Regarding common problems for electrical contacts of relays and common faults of contacts stamped parts in the relay, we will summarize in this article.

1. The problem of current and voltage

It is important to know the current and voltage that will pass through the electrical contact parts since they will influence the size and material composition. When the actual switching load voltage of contact part is less than the arcing voltage and the current is less than 1A, especially at medium current, low level or dry circuit which refers to the relay contact is closed first, and then connected to the millivolt microampere load, the failure mechanism and failure mode of the contact in actual operation are completely different from the actual switching of the rated power load.

We know that different products have different requirements in design, manufacturing process, and testing in order to meet the different requirements of different loads. Therefore, you must not mistakenly believe that the contact switch of relay is suitable for all loads from zero to the specified rated value when you select relay products. It should not be considered that the actual load through the contact is more than the rated load specified by the product standard.

In order to better understand, here we will give an example. A contact stamping part that can switch a 220V, 10A load may not switch a 10mA actual load. Of course, it also cannot switch to a low-level or dry circuit load. Therefore, for medium-current, low-level, dry circuit loads, it is recommended to use metal cover fully sealed products with excellent contact parts, especially the relays used on anti-theft devices on automobiles and motorcycles which are powered by batteries, and the voltage and current are unstable, so there will be higher requirements in terms of manufacturing and materials.

2. Arc problems

When the contact current reaches 100 mA, the arc effect of the contact is significantly weakened, and the carbonaceous substances precipitated under the high temperature condition of the contact cannot be burned by the arc and deposited on the surface of the contact, which will increase the contact resistance of contact and affect contact reliability. When the contact parts load is used below 10 milliamps or below 50 millivolts, the contact reliability is significantly reduced, because at this time the voltage cannot break down the film resistance on the contact surface, and low-level failure will occur. Especially under high temperature conditions, the oxidation of the contacts is accelerated, and the low-level failure is more serious. Therefore, the load above 10 mA and below 50 mV is called low-level load.

Although the load stress of the relay cannot be too small, the load stress given in the technical conditions is the maximum rated value of the contact. But it is only a parameter that should not be exceeded.