For the Rundbuntplasma I wanted that the main power supply (a big 20A/5V supply) could be hard disconnected (aka operating the main power switch in our hacker space) from mains and the Raspberry will still shutdown nicely automatically. The idea is to buffer the 5V for the Raspberry using two big Supercapacitors (EDLCs) with 50F each from Nesscap. The circuit was designed to be as simple as possible, the drawback is that the capacity is not used efficiently and has only enough time for a proper short shutdown (about 30 seconds). Another drawback is that the power supply comes up slowly at startup (takes about 10 seconds before Raspberry starts booting) and also powers the Raspberry for quite a long time after the shutdown so the system must be unplugged for about 10min before it will boot up again. But there main advantage over batteries is the lifetime of supercaapacitors: They can be charged and discharged completely a few 100.000 times and are quick to charge – after ~2min they carry enough charge for proper shutdown.
So no worry of proper shutdown anymore – just unplug it or operate the main power switch and the Raspberry will detect it and shutdowns nicely while the supercapacitors provide the power for this time.
PLEASE NOTE: This article is mostly in English, but the site it is on is a German site. Therefore, the schematic diagram on the page is in a European format that may not be familiar to North American readers. However, it is simple enough that anyone that knows how to read a schematic diagram should have no problem with it. The only thing that confused us a little was the use of designations such as 1.5R and 100R on the resistors. As best we can determine, R is used in place of Ω (ohms) in Europe, but you may want to verify that with another source (and please leave a comment if we’re wrong on that point!). We are only providing a link to this article and it should be noted that we have neither built nor tested this device, therefore should you decide to build one of these, you do so at your own risk, and we will NOT be responsible for any damage or injury that may result.
Full article here:
Raspi EDLC UPS (Über Hackerspace Ffm)
