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

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.

Comments

[curious youth]

how would i go about doing that for one of these ?
http://media.uxcell.com/uxcell/images/item/catalog/ux_a06070700ux0009_ux_c.jpg
aswell as the fact that im modding one to make a hand crank phone charger from this instructable
http://www.instructables.com/id/Hand-crank-LED-flashlight-hacked-now-also-USB-ch/

[-max-]

you should consider replacing the leds with brighter ones.

[djzadjza]

sweet

[808create]

Also, what kinds of household electronics can capacitors be pulled from?

[Jodex]

Kinda from anything..=D

[Biotele]

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.

[808create]

Will a capacitor last forever, theoretically?

[Biotele]

as long as the plastic insulator lasts. They should last decades if operated within specified parameters.

[bahi]

Very useful, thanks!

[Biotele]

welcome

[Pasketti]

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]

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.

[mikedoth]

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!

[Pazzerz]

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]

I added a joule thief circuit which made it brighter. See step 5.

[Biotele]

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.

[Scott_Tx]

I'd say so, I think most are rated for at least a million cycles

[Biotele]

that is if they are properly charged and discharged. In this application batteries die out very fast.

[PKM]

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]

D5 is a zener diode. It limits the charging voltage.

[Biotele]

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.