Ebay fake 10 leds dynamo torch: make it a real one!

If you want to buy a dynamo torch from ebay, beware: they are most likely to be fake! Just like the one I bought: there is a crank dynamo, but there is no built-in rechargeable battery, just regular batteries. The crank works, but it only powers the leds "live", it doesn't charge anything.
I had to do something with it, so I "pimped" my torch :)

Material List:
1 led
1 supercapacitor (1F, 5,5V)

Step 1 Open the torch

First remove the "head" by pulling it. Be gentle, because the wires are thin and you don't want to break them by pulling the head off. Just pull it enough to separate it from the body about 1cm.
Then remove the 2 screws. Be careful when separating the 2 halves because the spring of the crank is very hard.

Comments

[shawon]

Can i use a rechargeable battery instead of the capacitor? Coz i could not find that specification...

[furcino]

Yeah... batteries will probably just act like huge resistors... I made one of these myself and the battery approach didn't work. I mean the battery charged, but didn't light anything :D I'm a noob though so if you succeed let us know. I used two 500nf capacitors and those did work.

[knektek]

The only difference is that caps release their energy more quickly.

[furcino]

yeah... but you're limited by the amps you get. with a battery you'll most probably need to deliver more than is possible from such a tiny thing. maybe if I kept on pumping it, it would eventually work (and for longer than the capacitors) but it seemed it just didn't really go into the battery and rather just magnetically charged the coil or something and dissipitated.

[Filipe]

I don't think so because a battery is not a capacitor. You have to use some electronics to charge a battery.

[alex-sharetskiy]

not necessarily

[90mp11]

when the battery is charged, try reversing the polarity...i think batteries have to be charged in reverse to the normal operating polarities

[alex-sharetskiy]

not true...


if you have a rechargeable battery, you charge it with the same polarity

[billbillt]

I have one these. It seems to me the design idea here is you can still get light with dead batterys. This it does.

[furcino]

you could actually just seal the whole circuit or put the switch between the led and capacitor only. That way you could charge it live... That is how I did mine. Mine is really weak though... The dynamo delivers just 2.5 V and not that many Amps either. Did you measure your output? Sweet safe though ;)

[BrianH]

Glad to see you got it working.

Here's an alternate circuit you might consider... It's called a 'Full wave Bridge Rectifier'. The idea here is to improve the efficiency of the circuit. I'm assuming that the dynamo is creating an alternating current (as you've indicated by the schematic symbol - a circle with a squigly line in it). Referring to your diagram, when the upper wire goes positive, the diode conducts and the capacitor is charged a little bit. When the AC signal swings the other way, the diode does not conduct, and no charging occurs. With the Full Wave circuit, charging will occur on both the positive and negative swings of the AC signal - so you get twice the charging effect! You're not really getting something for nothing here, the additional load should increase the force you must use on the crank - but it may not be that noticable.

[Filipe]

I must confess that I don't know if the dynamo delivers AC or DC current. But I would go for AC. I will try to implement this. I think I will replace the led with diodes since the led (1,6V) does consume some part of the power delivered by the dynamo.

[furcino]

The dynamo delivers DC ... don't worry about it. Dynamos always deliver DC. Alternators deliver AC.