...Other battery brands are available.
I first came across the Joule Thief from Big Clive (I'm not responsible for the content of external sites, some inherently risky stuff there) and then again reminded of it by MAKE/EMS.
Having been hoarding dead batteries since then and my hall having it's light switch at the oposite end to my bathroom and bed room has been all the catalyst I need to get round to it. (one too many stubbed toes/ times falling over the junk I have left in there on the way to take a leak in the night) (If the thought of a sleepy and dishevelled man going arse over apex as he's forgotten the big bag of caving gear outside his bed room door dosent make you smile, nothing will).
Circuit digram by Windel Oskay and Bre Pettis (via Evil Mad Scientist)
The transformer is a custom hand wound ferrite, and the transistor is somewhat interchangeable so I started off with a reclaimed ferrite and a BFY 50 transistor (I brought a massive (aprox. 2 cubic feet) "lucky bag" of components from a car boot sale a while back). To start with I had little luck, I tried different coils and transistors got nothing, things were getting frustrating.
Eventually I thought I was might as well go with what I know works and brought a reel of magnet wire and small ferrite beads from maplin (ala Big Clive) as well as a pre wound ferrite in the hope that it would have better properties. I also went over to a PN2222a that I had brought in for another project and had seen extensively in the EMS Comments.
On my second attempt to get it working i find:
The the current flow in the two windings needs to be in oposite directions! (oops)
(that is to say if wrap both coils together you need the start of one coil and the end of the other connected to +V)
I must have missed this simple point the first time around. Both Big Clive and EMS point this out and it's shown in the circuit diagram by the Dot Convetion.
Now it works pretty much (more on this later) whatever transistor or coil...DOH!
With success on the bread board I went in to production.
I had had the idea of a device that can sit on top of the battery (mostly AAs from friends caving lamps) as it is stood on end with a wire to a common ground plane almost like electric candles.
It just so happens that AAs fit nicely into 15mm pluming fittings!
I can haz hat?
So these 15mm end caps became the base of the build. To be able to attach these (with their high thermal mass) to the circuit board I first soldered a piece of paper clip (the round end bit) bent at a right angle to give two leads to attach the board.
\m/etal end cap rocks out!
I soldered these with a 30W iron without too much difficulty altho they do take about a miniute to reach temperature. My tesco paperclips solder really quite well, I was surprised, wonder what they are made of/plated with.
Next on goes the board:
The cable tie and hole are used to restrain the small ferrite transformer. This picture also shows where I have broken the tracks on the strip board.
On goes the ferrite:
How the transformer is held.
I have black permanent markered the vero board to make it look better, why they make it in such a horrible brown I do not know. (plus black boards are all the rage)
The rest of the components just solder in, here is a no expense spent plan view.
The strange thing in top right is the unclipped LED leg wich provides a convenient attachment fot the negative lead
The transformer is wound to Big Clive's spec. using 38swg (0.15mm) enamelled wire (e.g. YN91Y) on small ferrite beads (Aprox. 3.5m OD 1.5mm ID and 5mm long) (e.g.N88CU). While fiddly you dont need to be too careful most of mine have at least a couple of crossed turns.
I used BC107 transistors as I had lots (that big "lucky bag" again) and they are in a fairly small TO-18 packages.
This gives the final result of:
The unclipped LED leg is soldered to a 9" length of the same 38swg wire this then enters a "earthing screw terminal" (a JL99H in fact, I really like the knurled top on this terminal post, not seen them elce where) on a plate of blank copper pcb. I initially tried 7/0.2 (aprox. 1.2mm dia.) hookup wire but it was so springy it kept knocking the battery over.
Hi-tech Candles
I'm really pleased with how this came out. About the only downside is they don't have quite enough weight to ensure a good connection particularly on slightly corroded terminals (wich ex-caving batteries often have). So I have to sand the battery terminals a bit and even then it sometimes takes a couple of goes before the run continuous.
This setup will take AA, C and D cells. AAAs are to scrawny to stand on end, this is unfortunate as I have collected quite a few, may have to make an adaptor.
I probably dont need 5 going at once (I made 7!). One is adequate to give me enough light to dodge the obstacles in the hall, but then again I have plenty of fuel at the moment:
All the Energy!
However I will doubtless be nabbing dead batteries off family and friends to feed to my vampire candles.
