Shakelight cap loses power in 10 min., why?

[tawa]

I bought a shakelight brand light. It is the little one. It has a magnet moving through a wire coil which charges a capacitor. The light is a white LED light. Anyway, when I shake it to charge it, the charge is lost completely if I wait 10 minutes with the light off. Why is this? Is this the nature of capacitors?

Can this be fixed? While I know soldering, I'm no electronics expert. I do make my own battery powered LED lights though.

Thanks.

[dnix71]

Maybe a bad diode. You have one of the real shakelights, apparently. The ones that failed specs had button batteries put in them so they look real but aren't. Those work until the batteries fail.

I buy mine from the 7-11 when hurricanes are near. They buy in bulk and resell for $5.

Even if I get one with batteries, it's still worth $5.

I don't remember them to be difficult to open. Test the cap and diode and replace them if need be.

[Jeff]

I have yet to see ANY of the "real ones". They have all had batteries, and yes, a little pc-board with micro diodes and caps. BUT, the "magnet" turned out to not be magnetic at all, and the wires from the coil (if you use a magnifying glass) don't even hook up to anything!

Take the guts out. The case, switch, and LED are useable. Put in two AA alkaline or rechargeable batteries. For the cost & bother, you might just as well buy a small LED flashlight that uses regular batteries, or rechargeable.

[ghurd]

The majority of mine don't have batteries, and actually work!

Sad, because most of mine retail for $5 or less.

Check the diodes, cap, and LED.  

I saw a few 'newer versions' with SMD parts.  Not very repairable for the avaerage guy.

G-

[JamesJackson]

I would say that a capacitor losing its' charge in 10 minutes is about normal. You have to remember. A capacitor is NOT a battery. A capacitor has characteristics that will cause it to not hold a charge and drain down to zero volts over a period of time.

The main difference - and the reason for using super-capacitors in these handheld flashlights is that they (the capacitors) can be recharged for an almost infinite amount of times. Rechargeable batteries can not.

So... it would be better - next time - if you spent the effort to sling that magnet back and forth to charge the super-capacitor - turn on the flash light. You may get 10 minutes of light out of it (or less).

Regards,

James Jackson

[vtpeaknik]

Alternatives to the "shakelight":

(1) Battery-operated LED flashlight + alkaline batteries.  For emergency use, this is fine, it'll work when you need it, the batteries' shelf life is 5 years or more.

(2) Battery-operated LED flashlight + rechargable batteries.  This is good if you use it often.  The batteries will still die after 5 years or 10 at the most.  And you'll need to open the thing and remove the batteries to recharge.  Some models have a built-in charger but it's usually not a "smart" charger so it'll overcharge and shorten the life of the batteries.

(2) an LED flashlight with a "crank" (or "wind-up" or "dynamo") - a hand-operated generator to recharge the capacitor/battery.  The shakelight is an example, but there are many other models, usually with a rotating motion.  Having a battery in it instead of a capacitor has the advantage that it will usually give you some light right away when you need it (from last time you cranked it).  But the batteries will die after 5 years or 10 at the most.  Can replace them then if you're handy with a soldering iron.

I got this crank model and it seems fine, the light is brighter than I expected:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95266

This one runs on 4AA, not a problem if you have rechargables sitting around, and it is VERY bright - the best focussed-beam LED light I've seen:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=96947