DCC1120 / SAF2020 remaining current after power cut

[*++argv]

After switching off the power to SAF2020 connected to DCC1120, some strong current remains on the boards for a few seconds.

This is not surprising but, in my opinion, a LED showing there is some current remaining would not have been superfluous.

Anyway, could anyone tell where would be the best places on the boards to connect a voltmeter (or LED) to check for residual current reliably?

Thank you.

[jdecoux]

Can you please elaborate what you mean by a strong current persisting when unplugged?

By your usage, it seems you may be referencing the supply voltage keeping the processor of the DCC1120 awake for a few seconds when power is unplugged?

Your easiest solution is probably to just monitor the VoltageInput channel from your DCC1120, which would provide a measure of supply voltage until the remaining power runs out and the channel disconnects. Similarly, you can monitor the voltage across the supply terminals of the DCC1120 yourself if you would prefer.

[*++argv]

Thanks for the quick reply. To elaborate, the system remains capable of powering the motor for several seconds after the main 24V power supply has been disconnected.

My hypothesis is that the capacitors on the SAF module and/or the DCC1120 controller retain a significant charge. The controller's logic remains powered via USB, allowing it to accept new commands and discharge this stored energy into the motor.

Reproduction Steps

• The system is fully powered (24V supply connected to the SAF, USB connected to the PC).
• I run a C application to operate the motor, then command it to stop.
• I physically unplug the 24V power supply from the SAF module. The USB connection remains active.
• I restart the C application and send a command to activate the motor.
• Result: The motor runs for a couple of seconds, even under load, with no power supply connected.

Next Steps & Goal

Your suggestion to monitor the VoltageInput channel on the DCC1120 is excellent, as it should confirm my hypothesis. I will try that next week.

My ultimate goal is to address the safety implications of this behavior. A system that can still move after the main power is cut presents a potential hazard. I need to find a reliable method to detect this "latently energized" state to ensure the equipment is truly safe to service.