Making a capacitor is pretty easy. Just get two conductors close together. The bigger area you can get and the closer you can get them, the bigger the capacitor you can make. [BigClive] found some fake capacitors that were supposed to be very high value, but weren’t. Taking them apart revealed the capacitors didn’t have the electrolyte inside that gives these units both their name and their high values. What did he do? Mixed up some electrolyte and filled them back up to see what would happen. You can see the video below.
Electrolytic capacitors have a secret weapon to get the two electrodes as close as possible to each other. The electrolyte forms a very thin insulating layer on one electrode and the capacitance is between the conductive fluid and that electrode — not between the two electrodes. This allows for a very narrow gap between the conductors and explains why a small electrolytic can have a much greater capacitance than most other technologies in similar form factors.
There are other tricks at play, too. For example, the anode side of the capacitor is usually etched or otherwise roughened to provide more surface area than a similar flat material. During manufacturing, a forming voltage causes the oxide layer to form and also sets a polarization on the capacitor. Reversing current through the device is likely to cause a short and quickly destroy the device.
Did [Clive’s] homemade electrolyte of boric acid and antifreeze work? Sort of yes and sort of no — watch the video and find out. Understanding how all this works can help you repair old electrolytics. Every once in a while, we toy with making our own capacitors for educational purposes or very high voltages.