I made a heatsink for Dorcy 1W (w/pics)

Crux

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Nov 4, 2003
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Mentor, Ohio
This Dorcy 1W has been sitting disassembled on my workbench for months now. Its an OK light, but because it is direct drive by transistor, I feel it needs help dissipating the heat it can generate. Lacking a lathe, its taken me a while to think of how to do this. Its far from ideal but its a step in the right direction.

PICT0718s.JPG

PICT0721s.JPG

PICT0725s.jpg


I peened over the edge of a 3/4" copper pipe, then cut it to the same length as the split plastic ring in the original setup (0.236"). The pipe O.D. is a little too large so a small segment was removed (~0.080") and then squeezed into a smaller circle with pliers.

The copper ring is soldered directly to the Star after unsoldering the anode lead. I stuck a circle of copper foil tape over kapton tape on the back of the Star and ran a wire from here to the anode lead. Brought out the cathode connection similarly and began reassembly.

The slip-fit way that the ground rings connect to the switch board concerned me, so I soldered them to help lower overall circuit resistance. This may have been a mistake...

While testing the light for about 15 seconds, it failed! Opening it revealed the acrid smell of "letting the smoke out". The output transistor had smoked. A check of the LED - no shorts there. Maybe soldering to the Star was a mistake, lowered the Vf increasing current draw?

I'm stumped. Has any one else fried a transistor in their Dorcy?
 

udaman

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Feb 13, 2004
Messages
381
[ QUOTE ]
Crux said:
This Dorcy 1W has been sitting disassembled on my workbench for months now. Its an OK light, but because it is direct drive by transistor, I feel it needs help dissipating the heat it can generate. Lacking a lathe, its taken me a while to think of how to do this. Its far from ideal but its a step in the right direction.

Maybe soldering to the Star was a mistake, lowered the Vf increasing current draw?

I'm stumped. Has any one else fried a transistor in their Dorcy?

[/ QUOTE ]

[ QUOTE ]
This Dorcy 1W has been sitting disassembled on my workbench for months now.


Hehe, Crux I see we both have that kind of predicament /ubbthreads/images/graemlins/wink.gif, stuff lying around we intend to get around to one of these days when more time can be found. I'm still intending a follow up to your comments on the DMM thread /ubbthreads/images/graemlins/smile.gif

I know practically nothing about LED electronics, but there are plenty here on CPF who have devised heatsinks, that will hopefully chime in with recommendations. Dorcy LED's are popular mods, so someone may have touched on this before last year with a similar mod, IIRC? You have tried searching back more than a year?

So why does, assuming you have lowered resistance by soldering directly to copper sink, lower the Vf---which you then assumed caused an increase in current draw, which you attribute frying the transistor to(could be something else, but I'd let those with more experience come up with a guess)?

BTW, your 2nd picture does not display for me. Perhaps it is my slow internet connection acting up again?

"Not Found

The requested URL /crux2/PICT0721s.JPG was not found on this server"
 

Crux

Newly Enlightened
Joined
Nov 4, 2003
Messages
160
Location
Mentor, Ohio
I found the problem why the transistor blew...

I didn't realize how far the reflector comes over the Lux. When I screwed the reflector on it pushed down the anode connection shorting it to the heatsink ring. Duh...

Well I fixed that and replaced the FET and all works well. I need to try this idea on something a little better than the stock circuit.
 
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