Adding Super Capacitor to Solar USB Charger (Grateful Novice!) - Page 1
Forum section: electronics / beginners

author: macmillan
author_rank: Newbie
timestamp: August 02, 2014, 12:05:20 am
content: First and foremost, thank you very much to anyone who takes the time to comment, I really do appreciate it. I usually take the time to learn on my own, but I have a bit of a time crunch and I need to see if my idea is viable or not. I have genuinely looked for prior threads on this topic, but I couldn't find anything related to my concept (or I was unable to do the mental gymnastics to comprehend what I was reading).A while ago I built a simple solar USB charger to charge my smartphone or battery pack while on ultra-long distance hikes. Generally speaking it worked well - in unobstructed sunlight - butif there was a cloud or I briefly passed under a tree, the current from the solar panel would take a dive and the smartphone would stop recharging. As you would expect.Here is a (super) simplistic breakdown of what my charger looks like now:5.5V 1000mA (peak) solar panel --> Schottky Diode 1N5817 --> DC-DC converter tuned to output 5V to the module's USB port --> Smartphone/battery pack.I was hoping to rectify my problem by adding a Super Capacitor between the solar panel and the DC-DC converter (or should it be between the DC-DC converter and the USB output?).I'm not looking for a miracle, maybe just 2-5 seconds of "buffer".Is this do-able? If so, what capacitance and voltage rating should I be looking at? Locally I've found some Kemet 5.5V 1.5F SuperCaps, but I'm thinking that I probably need a higher voltage part and maybe higher capacitance too.Once again, any guidance is appreciated and I will be diving deeper into some EE books as soon as I can

author: bgsteiner
author_rank: Contributor
timestamp: August 02, 2014, 12:45:47 am
content: for a 3 second discharge at 2 amps you would need a 12F cap but I wouldn't recommend using a cap instead think about making it a solar battery back by adding some NiCd batteries or a lithium battery to handle the problem. I have a plan for a solar charger that uses a lithium battery as the backup and the solar panel is tied into a single cell lipo charger and dc to dc converter that ups the voltage to 5V. Here is what I planned to usehttps://www.sparkfun.com/products/8484https://www.sparkfun.com/products/11231this will allow you to change even without sunlight and charge with clouds in your way.

author: macmillan
author_rank: Newbie
timestamp: August 02, 2014, 01:34:11 am
content: Thanks for the reply.Out of curiosity, where did you get the 2 amp figure from? My smartphone generally just draws about 600mA max.The reason I was looking at super capacitors is because it would be a potential quick fix (can just add it to my current setup) and because they are really light. Wecrazylong distance hikers go so far as cutting our toothbrushes in half to save weight, so I was hoping to avoid more battery weightI do like your idea though, and will probably build something like that from scratch in the future from normal day-to-day use

author: bgsteiner
author_rank: Contributor
timestamp: August 02, 2014, 01:45:19 am
content: I chose 2 amps as the arbitrary max for any device that has fast charge although it can go up to 2.3A for something like an iPad for a 600ma draw you need atleast a .36F so a 1F would be fine just make sure you limit the current that cap can give out so you don't fry anything.