Question about AC voltage in a floating ground SMPS

[AVRrajan]

Hello,

We have got one Dual output SMPS from a vendor. It has three input terminals (L-line,N-neutral,E-Earth ).The earth terminal is connected to the chasis (metalic enclosure) of the SMPS alone. He has not used this anywhre in the circuit part.

We have tested the power supply and found that the dc voltages are well with in limits(+5v Dc and +24V dc) and current ,out put ripple are also found satisfactory.

But when i ve kept my multimeter common probe on Chasis(Earth)with respect to any of the outpot terminal(+,-) the meter shows 80V AC !

Is it a common mode volatge?
Will it cause any electric shock if somebody touches the terminal with respect to Earth?
How can we resolve this issue?

Thanks in adavnce...!
Happy to hear your valuable suggestions..

 

[embedsys]

Re: Floating Ground SMPS

analog ground and digital ground are different from each other? if my guess is right, you have tested dc output with Earth..
to get a proper result, you ground it manually with some wires or keep the chasis in the floor and test it..
but dont get scared.. it wont give any electric shock if somebody touches..

 

[AVRrajan]

Re: Floating Ground SMPS

Thank you embedsys,

The DC voltages are tested with respect to DC ground (between +,- terminals)using multimeter in DC mode and volatges are perfect.

The volatge i was talking about is " AC voltage",with respect to chasis ground(Earth) and output terminals(+.-)

 

[mtwieg]

Re: Floating Ground SMPS

It's not surprising that there's some AC common mode voltage between the outputs and earth, but it should be a high enough impedance to not transmit much current (if it was properly designed). 80VAC seems like a lot though. I would try probing it with a scope, so you can see the waveform in detail. A multimeter probably won't give an accurate reading if the voltage is high frequency.