How to choose a power relay
1. Measure contact resistance
Use the resistance file of a universal meter to measure the resistance of the normally closed contact and the moving point. The resistance value should be 0, (the resistance of the contact can be measured within 100 milliohms in a more accurate way); The resistance of the point is infinite. From this, it can be distinguished which is a normally closed contact and which is a normally open contact.
2. Measuring coil resistance
The resistance value of the power relay coil can be measured with the R×10Ω file of the universal meter, so as to judge whether there is an open circuit phenomenon in the coil.
3. Measure the pull-in voltage and pull-in current
An adjustable regulated power supply and an ammeter are found, a set of voltage is input to the power relay, and an ammeter is connected in series in the power supply loop for monitoring. Slowly increase the power supply voltage, and note the pull-in voltage and pull-in current when the power relay pulls in and out. For accuracy, you can try several times to get the average.
4. Measure the release voltage and release current
It is also a connection test as described above. When the power relay is engaged, the power supply voltage is gradually reduced. When the power relay hears the release sound again, write down the voltage and current at this time. You can also try more 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 of the system poses a threat, and the selected work is unreliable.