Picture of Hand Cranked Flashlight Mod plus Joule Thief
I have a couple of hand cranked flashlights laying around and I was never satisfied with their performance.

When I got them fresh out the box they worked great. But when their batteries ran out it was too exhausting to recharge the batteries manually. And after a couple of years, it was almost impossible recharge the batteries because they were too old. Now, a hefty 5 minutes of cranking produces only 20 seconds of light.

I decided to mod one of the flashlights by switching the lithium ion rechargeable battery with a super capacitor.

Surprisingly, the mod was easy and the results were very satisfying. Now, with just a mere 5 seconds of cranking I get 5 minutes of light. A major improvement.

In a further mod I added a joule thief which increased brightness (see step 5)

Step 1: The Back Up Super Capacitor

Picture of The Back Up Super Capacitor
A super capacitor acts like a battery in computers and electronic devices, and therefore it can serve as a back up power supply.

The neat thing about super capacitors is that they last much longer than rechargeable batteries. They are easier to recharge because they have almost 100% efficient while the batteries lose between 50% to 30% of the energy when recharging.

I am using a 1 Farad super capacitor. But you can use bigger values. The bigger the super capacitor the longer the flashlight works.
how would i go about doing that for one of these ?
aswell as the fact that im modding one to make a hand crank phone charger from this instructable
-max-4 years ago
you should consider replacing the leds with brighter ones.
djzadjza4 years ago
808create5 years ago
Also, what kinds of household electronics can capacitors be pulled from?
Jodex 808create5 years ago
Kinda from anything..=D
Biotele (author)  808create5 years ago
anything that regulates or converts power. Old computers have tons of capacitors in them. Electronic balasts for lights also have a lot of caps in them.
808create5 years ago
Will a capacitor last forever, theoretically?
Biotele (author)  808create5 years ago
as long as the plastic insulator lasts. They should last decades if operated within specified parameters.
bahi6 years ago
Very useful, thanks!
Biotele (author)  bahi6 years ago
Pasketti6 years ago
Where did you get that capacitor? I have several of those lights. The only supercapicitors I've been able to find won't fit in the space available.
Biotele (author)  Pasketti6 years ago
I got it from one the electronic retailers. You can Google them. I have a supercapacitor that is big and I opened a hole in the case to accommodate it.
mikedoth6 years ago
I'm going to order a bunch of these suckers. I have a couple of these lights and they suck (and luckily I haven't taken them apart yet for other projects). This might make them useful after all!
If you have a Harbor Freight in your area you can pick them up there. I have one of these and this sounds like a good mod. If a super capacitor can outlast the little lithium ion battery, then its worth it.
Biotele (author)  Pazzerz6 years ago
I added a joule thief circuit which made it brighter. See step 5.
I'd say so, I think most are rated for at least a million cycles
Biotele (author)  Scott_Tx6 years ago
that is if they are properly charged and discharged. In this application batteries die out very fast.
Biotele (author)  Pazzerz6 years ago
It can outlast old batteries but not fresh batteries. Batteries can store more charge than super capacitors. But I rather have a light for 5 minutes that I can get by cranking for 5 second, then to hand crack a fresh battery for 2 hours to get 1/2 hour of light. I use a 1 farad supercap, however the bigger the capacitance, the longer the light will last. Capacitors also don't die out like rechargeable batteries. After a couple of years the battery based hand cranked flashlights become useless. This mod just makes the flashlight more convenient.
PKM6 years ago
Is that part under "battery charging circuit" a one-way rectifier without the diode voltage drop? That's pretty cunning. Are capacitors 100% efficient? I thought they were only ever 50% efficient, sure I remember deriving that in A level physics. Still, from an engineering point of view they sound much better than the old batteries. If I can find a place to get them around here there might be a bike light 'Ible in it.
Biotele (author)  PKM6 years ago
D5 is a zener diode. It limits the charging voltage.
Biotele (author)  PKM6 years ago
they are never 100% efficient, but get very close. Their efficiency is dependent on their internal resistance which is orders of magnitude lower than that of batteries. Put your hand on a charging battery, it is usually hot. A charging capacitor is usually cold.