ELVESolar

Solar Powered DIY Levelup Modules for Traditional Swiss Army Flashlights

Mission: Fit a solar-charged, battery powered lo-energy function into an ubiquitous milspec case for nomad use. Keep it simple, sturdy, sleek. Minimize waste energy, maximize efficiency. Learn some stuff about transistors on the way...

Since such lamps can be opened like a book, creating a shallower and a deeper box of equal width and length, it seems to make sense to fit some solar cells inside. While the shallow side (left, when open, usually containing some optics) poses an interesting challenge to go really flat, the other side's depth is about double (the right side used to house the battery, lamp and switch). Because the halves can be more or less easily separated, this being a wartime product made from bent sheet metal, straight wire and other crude parts, they can be planned as such. Imagine you always have a nightlight plus some fancier function, f.ex

powerbank
microcomputer, mediaserver, dac, etc.
bentobox with peltier cooling
calling card case
whatever you want and can make to fit

Show it to the sun during the day, have some light at night. Prototype charges in 2 days, runs for 2 weeks.

Parts

0. Flashlight case

Find one in your grandparents attic and give it a new life.

Swiss model probably based on early 20th century german design, many many different versions produced. Of course many different international versions exist. Some are quite fancy andor ingenious, some are plain crap. Both kinds deserve a new life, the nice ones because of reasons and the crappy ones would have been plain waste otherwise. Those flashlights are a study in industrial production techniques and resource management by themselves.

Read more here: https://www.armeemuseum.ch/wp-content/uploads/2015/05/Lampenkatalog_03-08-1.pdf Katalog der Lampen und Laternen in der Sammlung des Schweizer Armeemuseums (Bearbeitungsstand März 2008)

1. Solar Panel

5.5v, high-efficiency

charging from sunup until sundown, no matter the weather

2. Charge Controller

Lithium is very energy dense, don't mess with that. See http://www.batso.org/

3. Secondary Cell

3.7V Lithium 1000mAh

Please be aware that every battery will expand when malfunctioning / shortcircuited / punctured / too hot etc. Lithium battery safety is an interesting topic by itself. So no, this will never be on sale here. Build your own if you know what you're doing. Ask your friends and listen to them, if not. As for battery life, since this is liquid chemistry, you don't want to stress it. Meaning low or overcharge, mainly. If you allow for 10% at each end, meaning you neither fully charge nor discharge it, livespan can surpass 10 years.

Again, any safety systems contained on the cell are there for the cell, not the user and thus should be regarded as nonexistent.

This project considers at least three separate safety aspects: using a commercial charge controller tailored for the cell used, using a commercial battery matching the charge controller, physical safety to ensure the pack can expand somehow. You have been warned. It's not even about electricity, it's just that Li is number 3 in the periodic system, number 1 is hydrogen. If you don't understand that, don't even start.

Creating a dedicated pcb is done exactly for safety reasons only. The effort is worth it because it improves efficiency as well.

4. Lights