I am using the GHI-RELAY-192 eblock and the Panda II to switch between a battery charger and a load for testing Li-Ion batteries. The test pulls the relay in to apply the load, and this can take up to 3 hours to drain a battery. I have 3 test systems, and two seem to have an intermittent relay. I wrote a separate app to test the relay, there is only 1 line of code to pull in the relay (in an interrupt routine) and no code to release the relay. What I see is that the relay will release randomly (usually after an hour) and then pull back in after 10 minutes. (I log the data to an SD card). I am using a digital pin to control the relay, and I have moved to different digital pins with no improvement in reliability. When the relay releases, I can see the status LED flash on the relay module.
Since I am pretty sure I have eliminated the software as the cause, I wonder if anyone else has experience a problem similar to this.