I have various Phoenix Contact Mini DC Power supply units (Pheonix Contact MINI-PS-100-240AC-5DC). It gives the correct DC Voltage across output terminals, as its supposed to. But I also noticed that its also showing an AC Voltage of around 70 - 80 V between the O/P terminals and Ground as well as Neutral.

Is this normal?

I am using this power supply to use in combination with a relay, to serve as a Digital signal (5 VDC) source for monitoring status of certain devices in a system. I am using a National Instruments DAQ+modules and am worried that this AC voltage might damage the DAQ and modules(which are grounded through the DAQ chassis) which are extremely expensive.

Kindly explain if this a fault with my DC Power supply or if its normal.

Thanks in advance.

  • $\begingroup$ Looks like Phoenix Contact has many power supplies in their portfolio. Can you please share the model and the O/P voltage from the power supply. Example are you using 6VDC, 12VDC etc. $\endgroup$ Jun 11, 2020 at 11:01
  • $\begingroup$ It is a 5VDC DIN rail Mountable MINI Power supply ---- Model Number Pheonix Contact MINI-PS-100-240AC-5DC. $\endgroup$
    – ZenMaster
    Jun 11, 2020 at 11:35
  • $\begingroup$ Sounds like a grounding issue. $\endgroup$ Jun 11, 2020 at 14:29
  • $\begingroup$ The Power supply has only a Line & Neutral port (no GRND) on the I/P side. Is this the cause? Or is it a fault with the wiring of our building? Is there a way to avoid this , so that AC current may not flow through the DAQ? $\endgroup$
    – ZenMaster
    Jun 12, 2020 at 6:14
  • $\begingroup$ When you respond to a person use @personsname? Otherwise this becomes just a comment. $\endgroup$ Jun 12, 2020 at 11:31

1 Answer 1


Based on the technical data there should not be a 70-80V AC signal in the output terminal. Either you are measuring incorrectly, a wiring issue, grounding issue or defective device.

Per the technical data there could be a 40mVpp residual ripple. If this is an issue I suggest applying a filter to pass only the DC components. Below is the high level block diagram for the power supply.

enter image description here

Here is the Output specification for the power supply.

Power supply Output data

Additional technical data can be found at Power supply unit - MINI-PS-100-240AC/ 5DC/3 - 2938714

  • $\begingroup$ Thank you for the info. $\endgroup$
    – ZenMaster
    Jun 12, 2020 at 6:11

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