what do I measure here?? - ac voltage between PE and floating output of smps

[andia]

I have made a small bipolar powersupply with 2 meanwell ac-dc modules (meanwell irm-20-24). the modules outputs are followed by dc-reguualtors to be able to bring down the the voltage to +-16V.
today I put the supply into its chassis with the rest of the pcbs and started measuring the outputs and the ac-input side before connecting the powersupply to the pcbs. all measures fine on the ac input side and also the dc output side. I then measured ac-voltage between PE chassis ground and 0V output of the powersupply, it showed 100V AC, the same goes for the other terminals, all showed the 100V AC. also when measuring between L and the DC output terminals I saw such high AC voltages.
the output of the smps powersupply is floating and the 0V is not connected with chassis or PE.
Why do I see these Voltages? what are they? cant the DC Output be floating? should I connect the signal ground to chassis/PE (I did for testing and the AC voltages are not there anymore.)?
thanks.

 

[rock soderstrom]

Where are you located? Germany?

 

[andia]

Austria.

 

[rock soderstrom]

Austria.

In terms of electricity, the situation is identical in Austria. Provided your switching power supplies and your electrical house installation are not defective, I believe that without a ground reference, a voltage will can build up (at the output of your PSU) that is current less and AFAIK poses no danger.

Why not ground the 0V output of your power supply? It seems to solve the "problem" and ensure clear conditions.

#Have you tried to "feel" the potential difference between the 0V output and the PE? I bet you won't feel anything because the supposed voltage collapses. This test is at your own risk...

 

[Newmarket]

Floating supplies as typically found in Class 2 devices will generally end up at somewhere around half supply voltage due to eg capacitive voltage division. The AC is high impedance and little risk. Eg I've had a slight but noticeable tingle from touching the phono outputs on a Sky box.
Similarly (though not the same) see "phantom voltages" that can be measured on electrical wiring eg on the switched live feedc when switched off. Putting a dummy load on them rectifies the measurement.

 

[KA-Electonics.com]

Why do I see these Voltages? what are they? cant the DC Output be floating? should I connect the signal ground to chassis/PE (I did for testing and the AC voltages are not there anymore.)?
thanks.

The voltages you're seeing are quite normal for the situation and are due to leakage currents usually from the switching supplies' AC line input filter X-Y caps. Depending on the meter input impedance measuring it, the voltage will be one-half or less than one-half the line input voltage which I'm assuming, based on your locale, is 230/240V.

The more relevant measurement between the AC input safety PE ground and DC 0V is the leakage current which should be µA.

I would connect the DC 0V supply output to chassis PE with either a wire or low-value resistor. Caps are also commonly used.