Do not forget to select the input capacitor for low leakage current (with maximum used input voltage active).
I fear that bipolar capacitors will have more leakage current than unipolar standard 85 deg C types.
(But you will shurely measure it and report here).
With best regards
Andreas
I have done some tests on various Electrolytic capacitors. 11 were tested comprising of 8 individual types. The data is presented in a table as well as three bar charts.
Note that the time tested for various caps was not equal. I tended to end the test when the current was well below 5nA and/or I established a trend in the data upward/downward. Most tests were started with the caps pre-charged tp 10.0 volts for some hours beforehand. One test was started at 9.7V which is what my 9V battery had pre-charged the capacitor too before the test. Another test was started at 0.0V and run overnight.
I built a steel enclosure and special cables to do these tests. The enclosure was made by Hoffman and is heavy gauge steel. All seams were sealed with conductive glue copper tape as well. Contact surfaces between the lid and box were also copper taped. The cables were made from RG58 coax with the shields terminated just short of the banana connection points to the power supply or bench meter. Only one connection between box/shield ground was made at the power supply to avoid any ground loops. All cables were fitted with ferrite cores as well. This resulted in an exceptionally quiet setup.
Leakage current was measured across a metal film 1 Meg ohm resistor. The meter used was an HP34401A with 1Gohm input impedance selected. This allowed me to get 1mV per nA on the meter. Noise floor was estimated to be typically below 100's of pA based on the observed fluctuations of the readings.
One bar chart shows starting and ending currents by capacitor number (1-11). Another chart shows the leakage current per uF of capacitance for an easier comparison of types. the third chart shows the rate of change in the data to get an idea of the average trend when the test was stopped. Note 2 capacitors had an upward trend in leakage current. I would reject these two capacitors.
Overall the Nichicon Gold Audio caps are favored by me at present. One of the three had upward current trend, but the other two performed very well. Second choice would be the Nichicon KL series. The Bi-polar types had very low leakage currents if you soaked them long enough in the direction you intended to use them in. I think they would also work.
One photo shows the test setup on my messy workbench. The capacitor being measured at 540nA was fully discharged before the test began. This test is to get and idea of how long conditioning takes from a cold start. Note the various caps being pre-charged on the protoboard on top of the steel box used for testing.
I will be leaving on a vacation soon, so If I may be slow to respond to comments depending on when they are made.