Four steps to correctly select power relay

Update:31-07-2020
Summary:

How to choose the power relay correctly, which is divid […]

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 precise 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 power relay coil can be measured with the 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. When the power relay is pulled in, gradually reduce the power supply voltage. When you hear the power relay release 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.

When selecting power relays, 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.