Hi Matt and Sean,

I have seen issues in the past where output capacitors in a boost
DC-DC converter gaining voltage, till it breaks down. Read somewhere,
to put a small dummy load resistor, which keeps it stable at the
required voltage. Can't recollect which one though. In the
explanation, IIRC the capacitor is getting charged due to harmonics
and or spikes (I dont know, if my memory serves correctly).

That said, this is not a switching power supply, nor are there any
unwanted spikes and or harmonics. With all that, the only thought was
that, till what voltage would it climb ?
The point to be noted is that, it reached 80V within a day or two
probably. If I leave a meter connected across, I can see the voltage
climbing very slowly.

Cheers,

Manu

On Mon, Oct 22, 2018 at 4:57 PM Sean Breheny <shb7@cornell.edu> wrote:
>
> Matt,
>
> As far as I know, the effect you mention cannot produce a higher voltage
> than the capacitor was charged to recently.
>
> Sean
>
> On Mon, Oct 22, 2018, 7:20 AM Matthew Miller <matthew.miller.va@gmail.com=
>
> wrote:
>
> > You're seeing an effect called "bounce back". This commonly occurs
> > with high 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-gainin=
g-voltage-over-time
> >
> > Take care.
> > On Sun, Oct 21, 2018 at 6:04 AM Manu Abraham <abraham.manu@gmail.com>
> > 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
> > > 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
> > > Bridge rectifier, the output of which is smoothed out by a 680uF/200V
> > > capacitor, providing about 16VDC (12 x 1.4142). The power supply
> > > worked well and good enough.
> > >
> > > The transformer was left connected to the mains for a while, in absen=
t
> > > minded mode of operation. A few days later, just before wanting to
> > > test a small board measured the voltage on the power supply, saw it
> > > was about 80V.
> > >
> > > Sat in thoughts for about an hour what was wrong, thought maybe the
> > > transformer windings had sprung a leak. Thought about it for a moment=
,
> > > then thought probably the capacitor was getting charged due to no
> > > load.
> > >
> > > Discharged the capacitor with a huge spark. Things pretty much settle=
d
> > down.
> > >
> > > At least thoughts burned up a few hours, where that 80Vdc was coming
> > from.
> > > After that, sat back and laughed at myself.
> > >
> > > Cheers,
> > > Manu
> > > --
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