Modifying the ASDA wind-up torch to use a capacitor rather than a Lithium Ion battery.
As sold from ASDA, the wind up torch uses a Lithium Ion Battery to store the electrical energy between winds. Unfortunately this battery has a shelf life of only a few years (less if the torch is used often due to an absence of protection circuitry to avoid over charge or over discharge, either of which will quickly damage a Lithium Ion Battery).
For a major collapse event (TEOTWAWKI) I wanted a torch that would work for decades, long after all batteries (including rechargeables) had died. So my plan was to open the torch up and swap out the Lithium Ion battery for a capacitor.
Remove the four screws on the bottom (actually you don't *need* to remove the two that hold the winding handle on but I found it easier to work with once the handle was removed too.
Once these are removed split the top from the bottom with a screwdriver. The two sides and clipped into both the top and bottom and tend to resist this action, you have to get quite aggressive to open it (without being *so* aggressive that you break it).
The torch apart.
De-solder the two tabs holding the Lithium Ion battery in place.
Now I could do some tests on the unit.
The first thing I discovered is that with the LEDs off I could get he Voltage up to about 12V by winding aggressively. If I wanted to use a 5V or 5.5V capacitor I'd need some form of over Voltage protection to ensure I didn't damage the capacitor.
I had three capacitors to hand
(Image of the three capacitors and the Li Ion battery (The battery is the yellow one, middle right))
The capacitor I'd hoped to use was a memory back-up capacitor, the little black and gold one (far right) rated at 0.22F 5.5V. Unfortunately a few quick tests showed that it had a very high internal impedance, it could not be charged in a reasonable amount of time and could not supply current to the LEDs fast enough when it came time to discharge. It was a total failure.
The big green capacitor (middle left) was one I was given by a friend (yes I'm the sort of person who gets given capacitors by my friends) I don't have a source for more of these which makes it a poor recommendation. It's also too big to fit in the case in place of the battery. It's rated at 0.22F 5V.
Time for some back-to-back tests.
Since measuring the brightness of the LEDs is somewhat subjective I used a Voltmeter to measure the Voltage they were supplied with, at 3V they were still bright and 2.8V they were getting a little dim to comfortably read with. I used the time to these two values as a baseline.
Using the Lithium Ion Battery and 10 winds it took on average 45 seconds to dim to 3V and 1 minute 26 seconds to dim to 2.8V
Using the green 0.22F 5V capacitor took 13 seconds to dim to 3V and 40 seconds to dim to 2.8V, noticeably less than the battery but still acceptable if only:
1] It was small enough to fit in the case
2] I knew where to source more of them
The big Black capacitor (far left) is a simple electrolytic capacitor 0.056F 16V, the Voltage rating is excessive (although it would permit me to avoid any over Voltage protection) but I just happened to have it on hand.
It took a mere 1 second to dim to 3V and 4 seconds to dim to 2.8V.
In theory it should have lasted about 1/4 as long as the 0.22F capacitor but in fact the especially low internal impedance of the electrolytic meant that the LEDs light brighter but for not as long. Of course this capacitor is far too big to fit inside the case of the torch.
So right now this project is on hold until I find a capacitor that has
1] A large enough capacitance (ideally 0.22F to 1F).
2] A small enough internal impedance.
3] A small enough physical size to fit inside the case.
I fear this is an impossible combination of requirements.
I've found an electrolytic capacitor that would meet my needs (electrically) 0.47F 25V for 'only' Ã‚Â£75. It's also 221*77 mm (far too big).
I also fear that all 'wind-up' items (Radios etc) are using Batteries to store the charge since capacitors are more expensive for less storage and require more physical space. Any 'wind-up' items you have stored away thinking they're going to last forever probably only have a shelf life of a few years.
Of-course they'll still work provided you wind them continuously, perhaps not too much of a burden with a radio but a pain if trying to use a torch (Since it ties up both your hands).
Edit: To add clarity to the picture of the caps and battery as to which is which.