In article ,
EngineeringGuy wrote:

When connecting "super capacitors" in series to increase the working
voltage above the level of the individual capacitors, does anyone have an
active voltage clamp that would not discharge the capacitors when the power
supply is disconnected? Most "super" capacitors have a working voltage of
2.5 or 2.7 VDC... I would like to connect 10 capacitors in series for a 25
VDC capacitor stack. Most suggestions call for connecting equalizing
resistors in parallel with each capacitor, but I would rather have a
circuit that would not discharge the capacitors when the power is off...
anyone have any ideas?

Thanks,

Bill

You can probably find just the right color of power LED that can shunt
700mA. Just make sure they don't get thermal runaway faster than they
can drain the cap. If you don't like all the glow, shunt voltage
references and trickle charger shunts have current consumption that's
low compared to ultracapacitor leakage.

But there's a catch...

The capacitors will eventually loose equalization through
self-discharge. When you apply power again, shunts on less-leaky caps
could be exposed to the full power supply current. It's not a big deal
from a solar trickle charger but imagine trying to make practical shunts
if your supply is over 10 Amps. That's why resistors are simpler when
you need balancing.