UM2 Power Supply at 110V

[mbef 0]

Hi,

 

I noticed that when I touch the metal surfaces of our UM2, I could feel a slight electrical buzz in my fingers, which was stronger when not wearing shoes. This includes the Z-axis guide rods, and the thin exposed metal on the edges of the laser-cut front panel. The buzz feeling was still there when the UM2 was switched off.

 

So I checked the power supply DC connector with a multimeter, and I can see 100-110V AC between the connector's outer and real ground (checked against a PC back-panel, and a gas pipe). It's got almost no power behind it - which is why we're not in hospital! - but it's clearly floating to somewhere around mains/2 (mains is UK nominal ~230V). I measured the current to ground through a 2k2 resistor and saw 0.8mA => 1.7V under load => 1.3mW.

 

Seems unusual - but a weak floating ground isn't automatically evil. But I don't remember the tingling being there before... does anyone else have this? What is the local ground on a UM2 PSU normally?

 

Cheers,

mbef

 

 

Edited May 20, 2018 by mbef