More Ultracap measurements

Early this morning I took a lot more measurements with my Maxwell boostcap BCAP0650 ultracapacitor. After anayzing all of the following data, it is becoming more clear that lower charging current equates to less capacitance, which could indicate excess energy. Although further measurements are required.

Measurements taken today show strong indication that the ultracap capacitance increases with an increase in temperature. The room temperature was a considerably lower this morning as compared to last night. For this reason, it is best to conduct short term measurements due to the increase in the ultracaps internal temperature. This means the capacitance shown in the higher current measurements would be even lower yet if the internal temperature was the same as the lower current measurements. I cannot measure the internal temperature, only the external temperature, but it's safe to say that the rise in internal temperature is related to the amount of charge added to the ultracap, and the time duration.

Yesterdays two measurements on the ultracap showed a considerable difference in capacitance. Today's measurements starts out with a relatively small difference, which was puzzling. Although, as more experiments took place, the capacitance difference became more noticeable. Could this suggest that the effect increases with temperature?

All of the following measurements consist of placing a current source on the ultracap. The current was measured. Then the time required to charge the ultracapacitor to a predetermined voltage was recorded. The measurements, continuing from yesterdays two measurements,

Recorded in chronology order; i.e., measurement #3 was taken before measurement #4.

Measurement #3:
Capacitor initial voltage: 413 mV
Capacitor final voltage: 423 mV
Capacitor voltage increase: 10 mV
Current source: 206.2 mA
Time duration: 26.9 sec
=======
Calculated capacitance = 555 F

Measurement #4:
Capacitor initial voltage: 425 mV
Capacitor final voltage: 435 mV
Capacitor voltage increase: 10 mV
Current source: 22.9 mA
Time duration: 245.7 sec
=======
Calculated capacitance = 563 F

Measurement #5:
Capacitor initial voltage: 436 mV
Capacitor final voltage: 446 mV
Capacitor voltage increase: 10 mV
Current source: 22.8 mA
Time duration: 250.6 sec
=======
Calculated capacitance = 571 F

Measurement #6:
Capacitor initial voltage: 450 mV
Capacitor final voltage: 480 mV
Capacitor voltage increase: 30 mV
Current source: 202.0 mA
Time duration: 82.0 sec
=======
Calculated capacitance = 552 F

Measurement #7:
Capacitor initial voltage: 485 mV
Capacitor final voltage: 515 mV
Capacitor voltage increase: 30 mV
Current source: 201.6 mA
Time duration: 84.8 sec
=======
Calculated capacitance = 570 F

Measurement #8:
Capacitor initial voltage: 516 mV
Capacitor final voltage: 526 mV
Capacitor voltage increase: 10 mV
Current source: 22.7 mA
Time duration: 263.0 sec
=======
Calculated capacitance = 597 F

Measurement #9:
Capacitor initial voltage: 527 mV
Capacitor final voltage: 537 mV
Capacitor voltage increase: 10 mV
Current source: 22.7 mA
Time duration: 262.5 sec
=======
Calculated capacitance = 596 F

Measurement #10:
Capacitor initial voltage: 540 mV
Capacitor final voltage:570  mV
Capacitor voltage increase: 30 mV
Current source: 204.0 mA
Time duration: 83.0 sec
=======
Calculated capacitance = 564 F

Measurement #11:
Capacitor initial voltage: 580 mV
Capacitor final voltage: 610 mV
Capacitor voltage increase: 30 mV
Current source: 203.7 mA
Time duration: 85.85 sec
=======
Calculated capacitance = 583 F

Measurement #12:
Capacitor initial voltage: 615 mV
Capacitor final voltage: 645 mV
Capacitor voltage increase: 30 mV
Current source: 203.1 mA
Time duration: 87.9 sec
=======
Calculated capacitance = 595 F

Measurement #13:
Capacitor initial voltage: 650 mV
Capacitor final voltage: 680 mV
Capacitor voltage increase: 30 mV
Current source: 202.9 mA
Time duration: 87.6 sec
=======
Calculated capacitance = 592 F

Measurement #14:
Capacitor initial voltage: 685 mV
Capacitor final voltage: 775 mV
Capacitor voltage increase: 90 mV
Current source: 202.6 mA
Time duration: 272.2 sec
=======
Calculated capacitance = 613 F
comment: Higher ultracap internal temperature due to higher "Capacitor voltage increase."

Measurement #15:
Capacitor initial voltage: 775 mV
Capacitor final voltage: 785 mV
Capacitor voltage increase: 10 mV
Current source: 22.4 mA
Time duration: 334.8 sec
=======
Calculated capacitance = 750 F
comment: Higher ultracap internal temperature due to previous measurement.

Measurement #16:
Capacitor initial voltage: 785 mV
Capacitor final voltage: 795 mV
Capacitor voltage increase: 10 mV
Current source: 44.9 mA
Time duration: 148.7 sec
=======
Calculated capacitance = 668 F

Measurement #17:
Capacitor initial voltage: 795 mV
Capacitor final voltage: 798 mV
Capacitor voltage increase: 3 mV
Current source: 201.2 mA
Time duration: 8.7 sec
=======
Calculated capacitance = 583 F

It was becoming obvious to me that the ultracaps internal temperature was increasing the capacitance, which is why I decided to make measurement #14 a long term high current experiment, 90mV increase, which as expected increased the capacitance significantly. This was followed by measurement #15, a low current experiment, and even though this was only a 10mV  increase (low energy addition, and long duration = more time to cool down due to thermal conductivity), the results show high capacitance, 750F. That might not seem possible because the rated capacitance is 650F, but lets remember that the datasheet specs are for a certain temperature.

Since it seems apparent that higher internal capacitance temperature increases the capacitance, it would be better to conduct shorting charging periods. Also, the "Capacitance voltage increase" for the higher current charging measurements should be the same as the lower current charging measurements. This will probably result in even further capacitance differences between high & low charging current.

What I would like to do for the next line of measurements is to conduct short charge times, and the high current charging measurements should have the voltage increase as the low temperature. That should make the caps internal temperature closer between both measurements. Also, the capacitor should rest for at least 1 hour to cool down the capacitor. Not that they getting that warm, mind you, but it appears that even a small increase in temperature makes a significant difference in capacitance. It is expected that the difference in capacitance will be even more pronounced.

I have to admit, these capacitors are puzzling!

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