Wow, this technology has sure advanced since I last looked. It seems there are two different and disparate uses.
Some supercapacitors are used because of their low internal resistance. They supply high power for short periods, as for example during the annoying “boom, boom” bass notes one hears from certain cars whilst driving in the 'hood. And, within a short time, they are recharged from the car’s battery.
But, as described in this thread, others (new to me) are used as long-term backup for things like station memory in car radios. This is very low current, over long times–just the opposite of the audio application. That wouldn’t require low internal resistance, and in fact seems similar to backup from a rechargeable battery. This second application seems to be associated with the very small supercaps.
So are there two different technologies? Would appreciate your comments, Ray.
I don’t know that there are multiple technologies. SuperCaps are just suited to many different uses. They do store energy, just like batteries. But they also have higher energy density, and MUCH lower internal resistance and leakage. Cost has come down really dramatically in the last few years, making them practical for a wide range of applications. For example:
I did a project for a friend about two years ago that involved a bunch of RaspberryPi Linux boards scattered all over the place, talking to each other over WiFi. They were AC powered, through wall-warts, but with Linux, and RPi’s in particular, if you simply pull the power, you risk corrupting the filesystem, and rendering the board unbootable. We got around that by designing a power supply board with a SuperCap on it. When the AC iis unplugged, the RPi continues to get powered by the SuperCap. The board sends the RPi a signal telling it the cord has been unplugged, and we can then do an orderly shut-down of Linux, avoiding a potential “bricking”. Those SuperCaps were only a few $ each - about the same as a battery, but without the tricky charging requirement.
Regards,
Ray L.
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Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
64
This explains it pretty well – although it is long and technical:
It’s now much better than it used to be - the lights can be 12V AC but they are now run through an isolating transformer. An isolating transformer has no relationship to earth - so a person cannot get caught between a live situation and earth - there is no means for a current to flow. Paul
