Random relay reset?

I am using an NCD5500 Ethernet controller with a 32 channel relay controller board (ZADSR325PROXR) and 32 channel expansion relay boards (XR315).

It seems that the relays randomly turn off or reset to their default positions. Did not notice any issues with Pings timing out and access to the web interface still works. While in this state, if I try to command a relay from the web interface, the command seems to go through but the corresponding relay does not activate. The only way for me to regain control of the relay board seems to be by power cycling.

Any tips on what may be causing this behavior would be appreciated.


Are you switching inductive loads with the relays?

Can you turn on all of the relays at the same time and see if this triggers the issue? If yes this could indicate you need a larger power supply. Each of the 5 amp relays requires 30mA to activate the coil.

Thanks for the response.

The relay boards are part of an automated test setup and are powered by a programmable power supply set at 12V/6A. Based on the logs for this power supply, I am staying at around 0.5A when this behavior is observed. The NCD relay boards are used to control a bank of higher power relays (CIT’s A2K series).

When I see this behavior, it seems as if the relay board gets into a strange state where the Ethernet Controller is able to accept commands but the relays get reset and are not able to change to the newly command states.

Side note:
I also continuously pinged the relay controller and timeout was not observed. Wireshark captures also indicate that packets were normal. So there doesn’t seem to be an issue with connectivity or commands. I am also using the LabVIEW library from NCD for controlling the relays

Did a bit more troubleshooting and probed some signals on the relay board while in the “bad” state. Here is what I noticed:

  • Busy LED blinks when commands are sent
  • Tx and Rx lines on the NCD5500 toggle when commands are sent (did not verify content but wireshark captures show correct commands are sent and ack is sent back)
  • SRCK signal on the TI chip (TPIC6B595) is continuously toggling with a period of about 12us (toggles for about 4ms, then pauses for about 40us, and then toggles for about 2ms. This pattern continuously repeats and looks to be presents on all the TI chips’ SRCK)

So it seems all components for controlling the relays are active but the control logic got into a strange state where it continuously toggles the clock, making it look like the relays reset? Any thoughts on what could cause the control logic to get into this state?

Hi Jacob, do you have any updates on this behavior? would sending commands/queries too fast cause this sort of behavior?

Hi David,

Are you sharing the power supply providing 12VDC to the relay board with any other load? If so the issue could be caused by induction.

How are you sending commands to the board when this happens? Simply by using the web interface or are you using other software(if so what software)?

Thank you David,
Travis Elliott