I thought that ulracaps could be better than electrolytic ones for filtering after a bridge rectifier in a compact switching power supply due to their higher energy density. But, for some reason, I can't find any high-voltage supercapacitors on ebay or amazon. I could, of course, put a bunch of low-voltage ultracapacitors in series but that would defeat the whole purpose of a power supply being compact. Is there any reason why there are no high-voltage supercapacitors? There already are 5.5V ultracapacitors, which are basically two 2.75V caps in series, so why they can't go higher? Did I miss something? Are they hard to manufacture?
Electronic – Why aren’t there any 400V ultracapacitors
filteringhigh voltagesupercapacitor
Best Answer
A high-voltage super-capacitor/ultra-capacitor would be a contradiction in existing technologies. They achieve their high capacitive values by having a super thin dielectric of special materials, hence the low voltage limit.
To build a 400 volt capacitor means having a thicker 'solid' dielectric with more common materials, which 'fattens' up the size a lot.
There are large 450 volt electrolytic capacitors to 20,000 uF or more. To have a super-capacitor with the same voltage rating would be duplicating the large can-type electrolytics.
Super-capacitor/ultra-capacitors have been around a couple of decades now, mostly changing in materials to cut down on self-leakage. Graphene is the latest trend. The laws of physics and chemistry limit the size of such capacitors, or we would already have them to buy.
Engineers would love to have giant super-capacitors for cars, etc, so there is an on-going effort to reach that goal.
This is a snippet from Wikipedia: