Chris Crowley
Member
See my web page on how to do this at http://web.onetel.net.uk/~chriscrowley
Convert your Oldham headset into a 3W LED lamp for about ?25
- Thread starter Chris Crowley
- Start date
beardedboy
Member
Hi Chris,
I'm not an electronics expert or anything, however, i have played with and botched quite a few caving lights using various LEDs and have some constructive comments.
As I understand it, when using a standard bulb, the resistance across the element actually increases as it gets hotter. This stops the bulb from burning itself out immediately. However, with LEDs the resistance actually decreases, which allows it to draw more current, which in turn makes the LED just burn itself out, quite quickly. (I'm REALLY surprised yours has not done this, if not i'm sure you will notice that the colour of the LED has changed, and the light output has decreased, signs that the LED is killing itself.)
Therefore, it is standard practice to put a resistor in the circuit, which limits the current that the LED will draw. Here is a calculator to work out what size you need. LED resistor calculator
When using this calculator you also need to take into account that a fully charged battery will be closer to 1.5v, rather than 1.2v, giving you an initial 9v ish, rather than 7.2v.
Also as you said, these LEDs get REALLY hot, so i personally would not run them at 800ma, because the heat build up on such a small heatsink would lead to it burning out after a small amount of time. Personally i would go for something closer to 350-400ma.
The problem running the LEDs like this is that the light output will decrease quite quickly (but it would be much more reliable than your setup). These high power LEDs really do prefer a constant current source, which as you said, requires some circuitry.
Here is an inexpensive circuit (20 of them costs ?9, so share them!). They would provide the 350ma constant current required, easily fit into the headset and would only require 3AA batteries rather than the 6AAs you are using. Also you could play with them so that your light used both switch positions in the oldham. One position to power one if these, giving 350ma to the LED and in the other position, two of these could be used to give the LED 700ma. However, doing this you do loose your backup bulb, but if done properly it shouldn't be as important as if you were using halogen bulbs. :-\
I hope that helped.
I'm not an electronics expert or anything, however, i have played with and botched quite a few caving lights using various LEDs and have some constructive comments.
As I understand it, when using a standard bulb, the resistance across the element actually increases as it gets hotter. This stops the bulb from burning itself out immediately. However, with LEDs the resistance actually decreases, which allows it to draw more current, which in turn makes the LED just burn itself out, quite quickly. (I'm REALLY surprised yours has not done this, if not i'm sure you will notice that the colour of the LED has changed, and the light output has decreased, signs that the LED is killing itself.)
Therefore, it is standard practice to put a resistor in the circuit, which limits the current that the LED will draw. Here is a calculator to work out what size you need. LED resistor calculator
When using this calculator you also need to take into account that a fully charged battery will be closer to 1.5v, rather than 1.2v, giving you an initial 9v ish, rather than 7.2v.
Also as you said, these LEDs get REALLY hot, so i personally would not run them at 800ma, because the heat build up on such a small heatsink would lead to it burning out after a small amount of time. Personally i would go for something closer to 350-400ma.
The problem running the LEDs like this is that the light output will decrease quite quickly (but it would be much more reliable than your setup). These high power LEDs really do prefer a constant current source, which as you said, requires some circuitry.
Here is an inexpensive circuit (20 of them costs ?9, so share them!). They would provide the 350ma constant current required, easily fit into the headset and would only require 3AA batteries rather than the 6AAs you are using. Also you could play with them so that your light used both switch positions in the oldham. One position to power one if these, giving 350ma to the LED and in the other position, two of these could be used to give the LED 700ma. However, doing this you do loose your backup bulb, but if done properly it shouldn't be as important as if you were using halogen bulbs. :-\
I hope that helped.
beardedboy
Member
beardedboy said:
Apologies, i've just noticed that you said that the battery packs should be connected in parallel, however, the fact that it will initially be closer to a 4.5v pack rather than 3.6v still stands.
A
Agrophobic
Guest
Having converted an old zoom in a similar way i can vouch for its simplicity and brightness. however mine is not totally waterproof but still works fine with water in it.
I used a luxeon 3w LED and four rechargeable AA cells, you definately need a resistor to limit the current but it gets pretty hot too so several in parrallel helps get rid of the heat as long as you maintain the right overall resistance.
I used a fair size heatsink to mount the led and resistors on.
Hope this helps chris.
I used a luxeon 3w LED and four rechargeable AA cells, you definately need a resistor to limit the current but it gets pretty hot too so several in parrallel helps get rid of the heat as long as you maintain the right overall resistance.
I used a fair size heatsink to mount the led and resistors on.
Hope this helps chris.
A
Annette
Guest
Hello Cavers,
Well, I recently went caving with Chris who was wearing his converted Oldham headset with the 3W LED lamp and it worked brilliantly. We did a five hour trip into Carno Adit and Chris's lamp was eye burningly bright for the whole trip. Well done Chris.
Here is Chris at the end of our caving trip, as you can see his brilliantly bright lamp is still working just as well at the end of the trip as it did at the beginning.
And here is the lamp itself, photographed later in the evening when we were back at the Croyden Caving Club Cottage in Ystradfellte, that lovely little cottage we CCC members call home, in the Brecon Beacons.
As you can see these are sharp pictures showing what Chris's converted lamp actually looks like.
Annette
Well, I recently went caving with Chris who was wearing his converted Oldham headset with the 3W LED lamp and it worked brilliantly. We did a five hour trip into Carno Adit and Chris's lamp was eye burningly bright for the whole trip. Well done Chris.
Here is Chris at the end of our caving trip, as you can see his brilliantly bright lamp is still working just as well at the end of the trip as it did at the beginning.
And here is the lamp itself, photographed later in the evening when we were back at the Croyden Caving Club Cottage in Ystradfellte, that lovely little cottage we CCC members call home, in the Brecon Beacons.
As you can see these are sharp pictures showing what Chris's converted lamp actually looks like.
Annette
Peter Burgess
New member
Can you try to post links to those pictures again, please?
A
Annette
Guest
Hi Sam, Pete,
Sorry the pictures aren't there, I seem to be having problems putting them into a post - I'm probably just too tired to think straight, it is quite late now. I've put the pictures onto a web page, I hope that works instead....
Here's the link:
http://www.h2ophotography.co.uk/chriscrowley.html
Best wishes
Annette
Sorry the pictures aren't there, I seem to be having problems putting them into a post - I'm probably just too tired to think straight, it is quite late now. I've put the pictures onto a web page, I hope that works instead....
Here's the link:
http://www.h2ophotography.co.uk/chriscrowley.html
Best wishes
Annette
D
darkplaces
Guest
A very high quality image of the inside showing normal LED soldered to a screw base and the main LED mounted on a small heat sink.
Code:
[IMG]http://www.h2ophotography.co.uk/Resources/Carno%20113.jpg[/IMG]
vanoord
Member
There's quite an interesting paper here: www.mine-explorer.co.uk/open-pdf-white-paper.asp?id=10
It gives a bit of an in-depth conversion of a Youle headset to a Q5, which seems to work quite well.
And some sort of Oldham conversion with a Q5 LED: http://www.mine-explorer.co.uk/bbs/forums/thread-view.asp?tid=818&start=1
It gives a bit of an in-depth conversion of a Youle headset to a Q5, which seems to work quite well.
And some sort of Oldham conversion with a Q5 LED: http://www.mine-explorer.co.uk/bbs/forums/thread-view.asp?tid=818&start=1
Chris,
If you did want to play around with a few of the AMC7135 circuits that beardedboy mentioned, drop me a PM and I'll mail you some - I bought a pack of 20 and have plenty of spares.
I doubt they'd be particularly sensitive to dampness if your headset did leak, and since you'd be running a couple in parallel, they shouldn't impact reliability since there'd be some redundancy built-in.
They aren't large, especially if chopped down to remove some of the empty area of the boards.
If you did want to play around with a few of the AMC7135 circuits that beardedboy mentioned, drop me a PM and I'll mail you some - I bought a pack of 20 and have plenty of spares.
I doubt they'd be particularly sensitive to dampness if your headset did leak, and since you'd be running a couple in parallel, they shouldn't impact reliability since there'd be some redundancy built-in.
They aren't large, especially if chopped down to remove some of the empty area of the boards.
