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I recently bought a Oubel Laboratory Power Supply 60V/5A, that I'd like to use for hardware diagnosis. When measuring the - and + outlets, the oscilloscope picks up ac voltage, that propagates through the pcb with Buckconverters. Is this ac current normal and/or dangerous to lets say a GPU?

The ac in the following image can be measured on both outlets, the bottom graph is the fft of the signal enter image description here

WhatAMesh
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  • An oscilloscope measure voltage normally and so you have to tell us what amplitude that is. Forget about the FFT stuff, what's the amplitude of the 50 Hz signal you see in volts peak-to-peak? – Andy aka Mar 02 '21 at 13:19
  • @Andyaka Of course, its 25.3 v, the gpus have 12v~ on the main power rail – WhatAMesh Mar 02 '21 at 13:21
  • https://electronics.stackexchange.com/questions/524885/laptop-charger-leaks-ac-while-giving-dc-voltage-at-the-same-time-how/524888#524888 and https://electronics.stackexchange.com/questions/326763/how-can-i-get-shocks-while-charging-my-phone-in-the-train/326818#326818 and https://electronics.stackexchange.com/questions/408769/electric-shock-from-outdoor-security-cameras/408773#408773 and https://electronics.stackexchange.com/questions/268597/coupling-between-hot-ground-and-cold-ground/268602#268602 - plenty of answers on the same subject as to why this happens. – Andy aka Mar 02 '21 at 13:23
  • @Andyaka Thank you! – WhatAMesh Mar 02 '21 at 13:23
  • Please show a diagram of your measurement setup – user253751 Mar 02 '21 at 14:01

2 Answers2

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The proper way to measure Ripple is AC Coupled into 50 Ohms or any low value. But this shows 10Vpp of 50 Hz ripple which seems excessive for a floating DCDC converter. Probe ground must be connected to V-. If not then you would get this waveform.

Tony Stewart EE75
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Do not connect the scope directly to the grid, use a 1:1 isolation transformer between scope and the grid.

Das D.
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