Introduction: Broken Torch to Emergency Phone Charger

About: Hey, in 1968 I wanted to be an Electronic Engineer. I graduated from Middlesex University (Enfield Campus - North London) when it was still a polytechnic in 1997. I came to Coventry forthe work in September 19…

The idea for this project came from a friend. He had taken his family on a camping holiday, like he had done for quite a few years since his children became old enough to enjoy it. Well, last year at the end of the holiday they all piled back into the car and on the way back he noticed the consumption figure had drastically dropped from the 37MPG he had got it up to, it was now more like 27! Not only that, 1/4 of the fuel had magically "disappeared". Well, his son fessed up ... he had been calling and texting his girl friend but his phone had run out of charge he "borrowed" the car keys and settled down to charge his phone ...he'd made sure the car was in neutral (manual gear box/stick shift), started the engine and got his phone charging ...well, he had the heater on so he was nice and toasty, and the radio on his favorite music, up nice and loud ... but he'd done it every day!

So, my friend asked if I could make something to charge phones when away from the mains, which could be used one-handed, whilst using the phone with the other. This got me thinking and messing about with magnets and coils to no avail, I couldn't get enough oscillation to generate the necessary power.

...Then another friend got a job managing a local "Middle Class" D.I.Y. store, and they had these wind-up torches, which occasionally came back as not working. He gave me a three to investigate...

Step 1: Failure Modes - Like You Are Interested???

...if you are not interested, skip this section, but remember it is here in case one of your friends ever asks you to mend one...

The first problem I located was that because the alternator (generator) was pushing out about 4-5 volts it was damaging the batteries. Well, it was the middle battery in all three cases - 3 1.2V NiCds wired in series, the middle one tended to go short. Having opened the pack up and resurrected* them a few times I found a second failure mode ...

The third image shows the inside of the alternator - the rotor is a fixed magnet, the stator being the coils. Cranking the handle operates the dog which flies out and engages into the rotor to spin it, when the handle reaches the extent of travel the legs are then knocked off the ratchet teeth so the rotor continues to spin. Well, on one the dog had "jumped up" slightly so the legs were facing the wrong way, hence the alternator was not generating very much...

And the next failure was the loose magnet which needed gluing back on...

and those fine wires, one of which had come adrift ....

*If you know how to resurrect NiCds fine ... if not, you probably should not ask... (but I'll do an Instructible if you do ask nicely!)

Anyhow, the two streams came together in my head and I though, what if I could use the alternator from a broken torch to charge a mobile phone...

Step 2: Tools and Stuff I Started With..

As you can see I had a soldering iron, flat screw driver, a Phillips head (cross-head) screw driver, cutters, pliers and a test meter.

I also splashed out on some BIG 1.0F (yes, One Farad) capacitors, a USB socket, a 5V regulator, two 0.1uF capacitors

... and I had those broken torches

I wired the USB socket, then set about mounting it onto the torch before sorting out getting the alternator to charge the big capacitor. Hey, please see calamity corner later (!!!)

So, as the images in the previous step show, the torch breaks down into a load of bits. Having had the "fun" of re-assembly several times, I super-glued the switch actuator to the switch toggle. I also glued the lens to the reflector (actually I held them together an applied glue to the outside to try to stop the vapour fogging the lens!)

Step 3: And What I Ended With...

Having mounted the USB as a quick test I wired in the large capacitor (the 1F) in place of the cell pack, as shown in the first image, and tried cranking the alternator ... hmmm ... it just about made it to 0.2 volts with 10 minutes of work. (Just as well, it was too big to fit in the torch body anyhow)

So I tried a 0.22F capacitor although it got up to 1.1 volts that still was not right.

I ended up using a 33uF capacitor - whey it seemed to almost get there. Given the way these were frying batteries I expected it to get to 5V with ease. So I tried a different torch and it almost made 5 volts! (As the photo shows, actually 4.92) With the plus point that the capacitor was physically smaller. I was worried in case the device may have generated more than 5 volts, but it didn't, so this meant I didn't need the 5V regulator or the 0.1uF capacitors, simplifying the make considerably.

So, in summary, all I needed to do was to mount the USB socket then replace the battery pack with a physically small capacitor then simply put it all back together.

Step 4: Testing

I re-assembled the torch then connected the test meter via a "sacrificial" USB lead. As the first video clip shows it readily generated 4.92 volts with vigorous cranking. I then verified I had wired the USB socket correctly (!!) then connected my phone and took a deep breath ... and started cranking. As you can see from the second clip it does require vigorous cranking to develop enough power to charge a phone.

The last job, when I can get some black Sugru, will be to fashion a dome over the USB socket to protect it and make the torch more durable.

But hey, there you have it, take a broken torch and with two components make it into a mobile phone charger to take on your next camping trip. I told my friend I just need to make a pretty one for his son ...he told me that actually this year they will be taking his son's girlfriend with them ... but he would still like one to save his fuel consumption!

Step 5: Calamity Corner

As promised, a few of the things that did not work out (so well)...

1) Plan A was to make a "power bulge" in the torch case to house the USB socket. ... A soldering iron was not hot enough - well, it didn't generate a diffuse heat to melt the case. So, I borrowed the Coventry Makerspace turbo-nutter crafting hot-air machine - no it is not one of those poncy Blue or Black ones, it is turbo pink! Well, as you can see, it made a grand job of doming, but unfortunately warped the whole torch back. D'Oh!

(...the design previously presented shows the socket heat welded to the outside with the wires fed through holes in the case - plan B)

2) Plan was to use a large capacitor to hold the charge ... but the first ones obtained were too large - both physically and electrically!

3) The torches kept "exploding", i.e. just as I got one bit back in, another would fly off. That's why I glued as much as I could.

4) Plan was to present a nice design with a nice 5 volt regulator, nicely decoupled with small capacitors... hmmm...can I take them back to the shop and get my money back?

Step 6: Trouble Shooting

Well, the above images pretty much sum up all the things that may be wrong.


The dog legs may pop off or pop backwards, make sure that when it spins (anti-clockwise) the legs open out to engage in the ratchet teeth.

Make sure the magnet is firmly affixed to the rotor.


Check all the joints on the little circuit board, make sure the alternator leads are well soldered to the board and the diode connections are clean and bright. The board in the image above clearly needed some attention.

Make sure the connections to the new capacitor are soldered nicely, and do make sure the capacitor is soldered the right way round! (Fortunately, the torch manufacturer used red wires for the positive and black for the negative.)


When cranking, use your best hand (!!), as you can see from the videos I am left handed...

Do not operate under water or near heavy electrical machinery, or near any thing which may stab, cut, kill or bite you... will the noise upset your dog?

Thank you for reading my Instructable, I hope it has given you a lot of good ideas and you will remix it and make your own.

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