Hand cranked generators from wind up torches

[vk3yedotcom]

A few days ago I saw reference to a video or website discussing cheap wind-up torches. 

I never saw it properly but the gist was that so-called rechargeable torches actually had non-rechargeable batteries.  So the cranking and winding would not have charged the battery.

Anyway I had a similar unit that's never held its charge.  So it was worth taking apart.  Even though the battery in mine actually says it's a lithium ion rechargeable (similar size to CR2032 button cell).

Still the LEDs and generator are perfectly OK.  The latter could run external items. The video below shows my measurements of voltage across certain loads.  Output was greater than I thought and it could be useful for hand-cranked projects. 

Below is the video which is pitched more at a beginner level.



 

[Bored@Work]

I have taken a few of those apart in the past. Mine all had broken LR2032s or LIR2032s. Not surprising, because mine all had absolutely no charging regulator, only a bridge rectifier. So the harder you crank the faster you kill the cell. They are speced for something like 4.5V constant voltage, 15 mA constant current charging (I am to lazy to look up the exact figures).

[G7PSK]

I have tried a number of cranked and solar rechargeable torches and in all of them bar one the cells have given out within the year on the one that did not the gears stripped so that it could not recharge, I also found that there was no charge control in any of them. I cannot understand why they don't fit proper charge controllers after all it would not cost a lot and it would be possible to charge more for such an item as it would actually work well compared to the rest.

[IanB]

See this thread:

http://www.candlepowerforums.com/vb/showthread.php?350618-Freeplay-Sherpa-hand-cranked-light-in-2012

The torch has a proper NiMH battery and a fairly solid mechanical arrangement.

Since the battery pack is like the replacement packs for cordless phones it could be replaced if it fails.

However, NiMH batteries do benefit from some routine maintenance like cycling them through a full charge and discharge now and then, so if you own this torch do keep it active. Don't lose it in a drawer for a year or two and then call on it in an emergency and expect it to deliver full performance.

[NiHaoMike]

Wire a few white LEDs (two in inverse parallel to each phase) to a stepper motor out of an old 5" floppy drive. No battery, no gears, and very simple.

[SeanB]

Old steppers out of a printer work as well. Add a knob on a crank to turn it and you get a good emergency light.

[amyk]

Those torches really torture their cells... essentially treating them like caps. Replacing it with a suitably sized supercap (along with a zener to prevent overvoltage) will work.

6V @ 500mA is 3W, if you can estimate the average force and RPM you're cranking at you can calculate the efficiency.

[IanB]

That Freeplay torch above has a very large battery compared to the generator output, so overcharging the cells would be difficult. The user guide says you would have to crank for 40 mins to fully charge the battery. I think a bigger danger would be over discharging the battery and reversing one or more cells in the pack. You would have to make sure to recharge at the first sign of the light fading.