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Interesting observation today; I set up a series stack of 4 cheap electrolytic capacitors (10V 220u) and after about 5 mins of applying 30V the lower most cap had settled at -300mV. The other three were at different positive voltages with the sum total being 30V.

Can anyone please explain why this cap went negative? I understand that different capacitances will lead to different equilibrium voltages but not why one would go negative.

Thanks in advance.

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    \$\begingroup\$ Please provide a schematic of how they were wired, also provide the method of how you measured the voltage. \$\endgroup\$ – Voltage Spike Oct 23 '18 at 20:14
  • \$\begingroup\$ what is the voltage on the other side of the lower most cap? \$\endgroup\$ – jsotola Oct 23 '18 at 20:19
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    \$\begingroup\$ Were all the capacitors discharged when you applied the 30V? If this is not the case (different initial voltages), redo the assembly. \$\endgroup\$ – Dirceu Rodrigues Jr Oct 23 '18 at 23:27
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If they were ideal caps, then their individual voltage could not be defined and they could have endless combinations of voltages, even negative ones, as long as the sum is 30V. That’s why you need a balancer circuit for e.g. two supercaps in series. I think this is also true for real caps.

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