Extech 382260....... ----- Original Message ----- From: Sean Breheny To: Microcontroller discussion list - Public. Cc:=20 Sent: Monday, December 5, 2011 4:47 AM Subject: Re: [EE] Question of bench PSU safety. Hi John, What model of bench PS are you using? Sean On Sun, Dec 4, 2011 at 11:41 AM, John Chung wrote: > Hi guys, > > Had an eventful night...... Tried to power a circuit "which" I thought wa= s a DC circuit ONLY to be greeted > by a power trip and my bench power supply was smoking...... > > Needless to say I opened up the bench power supply to find that the trans= former leads to the > banana jack had it's enamel coating melted... I found out later that the = DC ground was > actually tied to the AC ground....... 145volts on the tested circuit and = the bench PSU banana jack was hooked to AC ground too....... > There was some reactance between the bench banana jack to AC ground which= KIND of save the PSU life...... The > bench PSU still powers up and works*despite the transformer's enamel bein= g melted.* > > To NOT repeat history here are some questions: > > 1) Do I need to check ALL DC circuit to determine if it is tied to AC gro= und? > 2) When the DC circuit*tied to AC ground* is tied to ground hooking up to= the PSU which is also tied to ground would ruin it.... But IF the > =A0=A0 PSU is NOT tied to ground, would it be safe to use. Since it canno= t be grounded since the PSU has not connection to AC ground. > 3) Case scenario. The notebook DC ground has resistance of 1MOhm to AC gr= ound which is okay to hook up a scope probe BUT it was a reactance of 1Kohm > =A0=A0=A0 it would be hazardous? > > > > Thanks, > John > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .