The relays are latching types and are likely are not designed for the coils to be continuously energized (although this doesn't seem to be mentioned in the data sheet). That's why they are getting hot. You need to modify the control circuit so it only applies a short pulse (100ms minimum) to switch the relays.
You can build a test circuit that has an LED (with suitable current limit resistor) in series with each contact and a power supply. The LED will light when the contacts are closed.
Hi crutschow
Thanks for replying.
They can be constantly energized coils as long as they are driven by the correct voltage in my case (24V). However, the reliability of the relays becomes really bad after prolonged use, not as much burning out but it just disrupts the measurements from the rest of the test system.
The way the PCB is currently etched already has LED's to show that the relay is switching between NC and NO, however this is controlled by I2C (serial connector) interface which is not user friendly at all. See schematic below:
**broken link removed**
The final solution that will test all four relays has to have a simple connection procedure and simple result so that anyone will be able to test the relays on the board.
What I had in mind was:
- Create a timer circuit in an external box that will connect to each of the four relays in parallel and then open and close each of the relays one at a time.
- Each time one of the relays has been able to toggle between an open and close, a green LED would light up for that one relay indicating a pass, red indicating a failed open/close.
- Repeat the process for the 3 remaining relays.
- Stop after all four relays have been tested.
This would mean I would need to use a 555 timer, four flip flops to latch a pass/fail, 4 green and 4 red LED's and a gate to store the results?