I am concerned about an ultracapacitor (2.7v, 3000F) that I received today. I set my power supply to 2.5v with a current limit of 1A, then connected a diode to the positive lead such that current would only flow to charge the capacitor. I then connected the end of the diode to the positive terminal of the capacitor and ground from my PSU to the negative terminal of the capacitor.

However, only about 2mA was drawn. The diode I am using has a low diode drop (~0.3v), so I figured it should still charge the capacitor to around 2.2v. I then adjusted the voltage such that there would be 2.7v across the capacitor (~3.0v from the PSU), and it slightly increased the current drawn, but the change is negligible.

I can't see anything wrong with this charging setup, so is it likely that the capacitor is bad? Perhaps the polarity indicated on the capacitor is incorrect? Is reverse voltage harmful to ultracapacitors, meaning that I shouldn't check? Thanks.

  • \$\begingroup\$ Can you share the datasheet of the ultracapacitor? Are you sure the capacitor was discharged before you connected? Also, what is the output voltage of the PSU when you first connect to the capacitor? \$\endgroup\$ – The Photon Oct 15 '18 at 22:29
  • \$\begingroup\$ @ThePhoton unfortunately I can not find a datasheet for this capacitor. I suppose this is the price I pay for saving a few dollars by buying the cheap Chinese brand from ebay. Here is the listing for it on aliexpress if it helps at all. I am sure that the capacitor was discharged before connecting it to the power supply. I checked with my multimeter to find that it was charged to 11mV, so I shorted the terminals just in case. The output voltage of the PSU was either 2.7v or 2.5v (I forget). \$\endgroup\$ – John Leuenhagen Oct 15 '18 at 22:36
  • \$\begingroup\$ At 1 A, it should take ~2.25 hrs to charge the capacitor to 2.7 V. Are your sure your PSU didn't just shut down because it thought it was shorted? \$\endgroup\$ – The Photon Oct 15 '18 at 22:43
  • \$\begingroup\$ A datasheet (or at least model number) for the PSU might help guess whether this could explain it. \$\endgroup\$ – The Photon Oct 15 '18 at 22:46
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    \$\begingroup\$ @ThePhoton If I short my power supply, it will supply the max current set. \$\endgroup\$ – John Leuenhagen Oct 15 '18 at 22:48

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