Dielectric soakage.=20 https://www.electronicdesign.com/analog/whats-all-soakage-stuff-anyhow -----Original Message----- From: piclist-bounces@mit.edu On Behalf Of Matthe= w Miller Sent: Monday, October 22, 2018 5:17 AM To: Microcontroller discussion list - Public. Subject: Re: [EE] Voltage accumulation You're seeing an effect called "bounce back". This commonly occurs with hig= h voltage caps. Putting a 1M resistor across the cap will help with the safety here. Lots of info in the answers to the stackexchange question: https://electronics.stackexchange.com/questions/282972/capacitor-gaining-vo= ltage-over-time Take care. On Sun, Oct 21, 2018 at 6:04 AM Manu Abraham wrote= : > > Hi, > > I did not forget to put the sq brackets this time, Bob . :-) > > Not a query, but tripped on this one, wondered for a while, later on=20 > alone realization dawned. > Thought about sharing this one on the list. > > Have a 230V/12-0-12 CT transformer, of which 0 &12 connected to a=20 > Bridge rectifier, the output of which is smoothed out by a 680uF/200V=20 > capacitor, providing about 16VDC (12 x 1.4142). The power supply=20 > worked well and good enough. > > The transformer was left connected to the mains for a while, in absent=20 > minded mode of operation. A few days later, just before wanting to=20 > test a small board measured the voltage on the power supply, saw it=20 > was about 80V. > > Sat in thoughts for about an hour what was wrong, thought maybe the=20 > transformer windings had sprung a leak. Thought about it for a moment,=20 > then thought probably the capacitor was getting charged due to no=20 > load. > > Discharged the capacitor with a huge spark. Things pretty much settled do= wn. > > At least thoughts burned up a few hours, where that 80Vdc was coming from= .. > After that, sat back and laughed at myself. > > Cheers, > Manu > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .