The main steps of selecting power relay

How to choose the power relay correctly, which is divided into 4 steps, I hope it will be helpful to everyone's study.

1. Measuring contact resistance

Use the resistance file of the universal meter to measure the resistance of the normally closed contact and the moving point. The resistance value should be 0, (the contact resistance can be measured in a more accurate way within 100 milliohms); while the normally open contact and the moving point The resistance of a point is infinite. It can be distinguished which is a normally closed contact and which is a normally open contact.

2. Measure coil resistance

The resistance value of the coil of the power relay can be measured with a universal meter R×10Ω, so as to judge whether the coil has an open circuit.

3. Measure the pull-in voltage and pull-in current

Find an adjustable regulated power supply and an ammeter, input a set of voltages to the power relay, and string an ammeter into the power supply loop for monitoring. Slowly increase the power supply voltage. When you hear the sound of the power relay, write down the pull-in voltage and pull-in current. For accuracy, you can try several times and find the average.

4. Measure the release voltage and release current

The connection test is also like the above. After the power relay is pulled in, the power supply voltage is gradually reduced. When you hear the power relay releasing sound again, write down the voltage and current at this time. You can also try several times to get the average The release voltage and release current. Choose five steps under normal circumstances, the release voltage of the power relay is about 10-50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it cannot be used normally, which will affect the circuit The stability is threatened, and the selection work is unreliable.

The working principle of power relay:

1. The principle of action when the contact is closed. When the moving contact and the static contact of the relay touch each other, the contact bounce occurs, that is, the uncontrolled intermittent opening and closing, the arc and energization that occur at this time The Joule heat generated by the current greatly affects the opening and closing ability of the relay.

2. The principle of action when the contact is disconnected. When the contact is disconnected to cut off the load, dazzling sparks and arcs will be generated. The arc will continue until the arc voltage drops below the minimum arc voltage value. Cause greater damage. The different contact materials and the size of the contact gap directly affect the emission state of arc electrons and the difficulty of occurrence, so they are the important influencing conditions for determining the arc.

When selecting a power relay, the power supply voltage of the general control circuit can be used as the basis for selection. The control circuit should be able to provide enough working current to the power relay, otherwise the power relay will be unstable when it is closed.