Introduction

How is relay’s contact test performed? How is the mechanical characteristics of the relay contact (NO/NC) after multiple usages evaluated? Relay can change the electromagnet to generate mechanical switching action by the received electrical signal. It is often used to receive electronic signals to control other electronic devices. By applying a voltage to the coil of relay, the current passes coil and magnetizes the core, and the armature is attracted to the core by electromagnetic force, therefore, the related mechanical actions are produced.

Figure 1. Internal structure of relay

Relay connection architecture of electric vehicle

The diagram of relay applied to the electric vehicle is shown below. When the starter is started, the load current will be also synchronously turned on.

Figure 2. Relay connection diagram for EV

Load current sequence

The load current sequence of the electric vehicle relay component can be simplified into the following sequential diagram:

Figure 3. Load current sequence

Simulation test equipment

As shown below. A power supply is connected in series with relay and electronic load, and the electronic load is set to Sequence load current. The NO/NC COM current withstand is tested each time when the NO/NC COM terminal of relay is turned on. At the same time, the power supply’s sequential power output is used to generate a control signal to control the ON-OFF state of the relay's NO/NC COM terminal.

Via GW Instek’s test solution, users can plan the power supply control signal according to the actual test requirements. Users can control the voltage, current, time and period of the signal, as well as determine the number of loops during execution. Users can definitely generate various control signals to test relay. The electronic load verifies the relay's specifications, including withstand current value and withstand current time to ensure the shipment quality of relay.

Figure 4. Using test equipment to substitute the actual situation diagram

Tests for multiple sets of relays

If the rest time in the middle of the relay cycle test is used to test other relays, several folds of test time can be saved. The action sequence can be expressed by the following figure.

Figure 5. The test sequence for multiple sets of relays

Connecting method for testing multiple sets of relays

The connection method for the equipment of testing multiple sets of relays is shown in the figure below, wherein the power supply for controlling different relays can be multi-channel power supplies.

Figure 6. Connecting method for multiple sets of relays diagram

Measurement instrument settings

When all the devices are connected and collocated with the software control of the computer to control the channel of relay and load current, etc., the test requirements of multiple sets of relays can be achieved. The actual waveforms are represented by the following diagrams:

Figure 7. Sequence setting for the test instruments

In the above diagrams, the top waveforms are the load current set by the electronic load, the middle waveforms are the reed switch of the relay channel, and the bottom waveforms are the actual load current. It can be seen from the diagrams that the current load of the relay starts and stops synchronously with the reed switch of the relay.

Test execution

The test program is written by the custom-made software requirements. It can set the number of steps and the number of cycles of relay current load. It can set the load voltage of relay and relay channel switch, and adjust the time of the test sequence. The interface is as follows:

Figure 8. Interface for test software

Test results

When there is an abnormality in the test, the program will immediately stop the test and indicate the status of the abnormality, show the abnormality of the relay, and reveal whether the abnormal state is permanent open circuit or permanent short circuit.

Figure 9. The second relay is abnormal: permanent short circuit

Figure 10. The third relay is abnormal: permanent open circuit

Continuous testing

The test software also provides a special function. When the abnormal relay is replaced with a normal relay, the program can continue to perform the test. The replaced relay test data will be re-counted, and the test data of the relay not being replaced will continue to accumulate. This function can be implemented through Chan and Resume in the program. 

Test equipment table

The test equipment for the entire system is shown on the table below. Different required test specifications can be fulfilled by changing equipment models.

Conclusion

Relay components are common components of many modern mechanical or electronic devices. The life cycle, characteristics, and stability of components are evaluation indices of product quality, therefore, it is necessary to test relay components.