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Wind-up torch modification: battery to Capacitor
5 September 2011, 13:16 (This post was last modified: 5 September 2011 13:47 by Skvez.)
Post: #1
Wind-up torch modification: battery to Capacitor
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' £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. Sad
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.

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5 September 2011, 13:24
Post: #2
RE: Wind-up torch modification: battery to Capacitor
Thanks for this. It explains why they use the batteries anyway. They appear to have few options.

I'm going to have to revisit all my wind up items and check them.

Skean Dhude
-------------------------------
It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change. - Charles Darwin
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9 October 2011, 20:24
Post: #3
RE: Wind-up torch modification: battery to Capacitor
Any progress on this? I find that wind-up stuff is generally of very poor quality and wouldn't last any decent length of time.
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10 October 2011, 13:33
Post: #4
RE: Wind-up torch modification: battery to Capacitor
@SC1
I've not yet found a suitable capacitor.
I have been using the torch every night to read in bed with and I'm getting the 'feeling' that my usual 10 winds don't last as long as they used to. I must do a Voltage measurement on this to see if it's the case. If so the battery is degrading faster than I anticipated.

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10 October 2011, 13:35
Post: #5
RE: Wind-up torch modification: battery to Capacitor
That sounds about right. Built to a price rather than for longevity.
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16 November 2011, 06:25
Post: #6
RE: Wind-up torch modification: battery to Capacitor
Skvez, Has this now given up the ghost? Kenneth Eames.
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16 November 2011, 13:36
Post: #7
RE: Wind-up torch modification: battery to Capacitor
I've not given up the hunt for a suitable capacitor but I'm not hopeful at the minute.
I'll be ordering a couple of options when I place my next order to RS or Farnell.

Torch 1 was the one I did the initial testing on. I had to de-solder the battery to test the capacitors so that one still sits in bits on my desk.
Torch 2: Is being subjected to frequent use. I plan to take this one apart and report back on the performance of the battery at some point.

Torch 2 doesn't appear to be lasting as long as torch 1 was when I did the testing on it but the battery in torch 2 might not have been as good when I got it. (I should really test Torch 2 and then test it again in a month to see degradation)

I do plan to report further at some point.
I'd still recommend you pick one of these up but don't expect it to last many years (either on the shelf or in use).
However you can afford to pick one of these up every couple of years as a prep. It's certainly paid for itself in comparison to just the cost of batteries for a normal torch.

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16 November 2011, 19:08
Post: #8
RE: Wind-up torch modification: battery to Capacitor
Thank you for your reply. We do not have an ASDA here only Tesco and co-op, When I go to Glasgow after Christmas I will try to find an ASDA there and buy one. I do have one made by Draper (the tool Makers)and it has lasted me for three years and is still going well. Kenneth Eames.
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19 November 2011, 19:01
Post: #9
RE: Wind-up torch modification: battery to Capacitor
Do any one know the shelf life on glow sticks? ,And i bet you the goberment have bought all the glow in the dark T-shirts ;-)

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19 November 2011, 20:20
Post: #10
RE: Wind-up torch modification: battery to Capacitor
I hope so. They make excellent targets.

I don't know about shelf life but I have used some that areover 10 years old. However, as they are chemicals I would guess storage, cool, lightfree and dry, is important.

Skean Dhude
-------------------------------
It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change. - Charles Darwin
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