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Liberty Torch powered by a single 18650

danq

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This is my new red burner. It powers an Optnext hl6545mg diode from a group buy at Photonlexicon using a single rechargeable lithium cell (18650 size) in a modified DX Romisen RC-M4 flashlight. To get current regulation with very low overhead I used a circuit posted by Phenol.

The name "Liberty Torch" comes from my heat-sink. I wanted a good one... Jayrob makes nice heatsinks, but they don't fit my hardware... so I improvised. Rather than replacing the reflector cone with a heatsink, I used coins and washers of various diameters to fill the space inside the reflector. Looking for something that fit exactly for the last/outside layer, I found that a dollar coin is exactly the right size - and I thought Liberty with her torch was appropriate. Here's how it looks:



The various metals in the heat-sink don't conduct heat as well as a solid block of Al would, but they have a much higher heat-absorbing capacity; and the space around and between the washers is filled with heat-sink compound. This thing takes quite a while to heat up, even though I'm driving it with 300mA.

I put the circuit on 2 boards: one replaces the flashlight's original board and doubles as the battery contact holder; the second board has only the output stage and is placed on the backside of where the Cree LED was originally. Surface-mount components were used to keep the size down. The current is adjusted with a tiny 10-K pot (the original circuit called for 20K); it's placed in the center of the board and is adjusted through a hole in the back of the board (via the center of the positive battery spring terminal).

The circuit board came out a bit rough because I heated the etchant, and then got distracted playing with my dog so left the board in too long - there were a lot of pits and rough edges. The photo below shows the bare boards, not yet cut and trimmed. All the rough copper outside the circles is where I used a black marker pen to mask unused areas, to save etchant. The big pads for battery and heatsink contacts on the reverse side of the boards are visible as shadows through the thin etched board.



The boards with all components:


Mounted on the flashlight parts:


Nitpicky component details that vary from Phenol's:
  • sense resistor: 3.0 ohm
  • dual op-amp: TLC252CPWR in TSSOP-8 package
  • P-channel power MOSFET: FDT434P
  • voltage reference: little green LED with Vf=2.0V
Lastly, there were a couple of errors in my pc board - like for example I transposed the FET source and drain, and made the IC pads for a much larger package. Both were worked around without re-doing the board though...

One unfinished piece: I'm going to add an "overdrive" switch to push it up to 400mA. That will be implemented with one of the magnetic reed switches mounted inside the head. Attaching a magnet in the proper spot will connect a resistor in parallel with the reference voltage adjuster.

:)
DanQ
 



toked323

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very nice i made mine in an mxdl with 360ma running to it on rcr123's i like these diode i hope he sells more soon, unless you want to sell one didnt you buy 10? lol
 

danq

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yes, I bought 10 - killed 1 already, and 7 are reserved for a 7-beam-combined project. So I have 1 left, sort of. ;)
 

toked323

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i love them though i i guess i can say that they can match up to DDL's phasor's
 

drlava

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nice job on the home-made circular PCBs! what is the efficiency of the unit?
 

danq

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drlava said:
nice job on the home-made circular PCBs! what is the efficiency of the unit?
you mean the diode? there's a datasheet here

Other than that, I don't really know... but since the LD operating voltage is given as 2.45 - 3.0, and the circuit is running with 3.6V or so input, there's not too much waste there. Probably losing more in the non-glass lense?

re: the boards - it's a wonder how round you can make something with a tiny cutoff wheel and a Dremel and some time ;-)... I used Diptrace to do the pc layout, and the toner transfer paper method. If you look closely at the populated board you'd see a lot of microscopic balls of solder, which is trash from the use of solder paste from DX - I couldn't do all that fine soldering without it.

DanQ
 

toked323

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yea i am using this in my mxdl thats forsale, but Danq, if you gonna try combing 7 beams you can get 1400mw if you run them at 200mw each thats crazy
 

danq

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toked323 said:
yea i am using this in my mxdl thats forsale, but Danq, if you gonna try combing 7 beams you can get 1400mw if you run them at 200mw each thats crazy
Yes it is crazy [smiley=evil.gif]

but I'm not the only one doing it - I wonder how the Hex DIY Red Laser project is doing?

My big one may need more than passive heat sinking to run for more than a few seconds. I already have a nice finned body for it - a big power resistor - and a mini fan that fits inside. Only problem is getting the innards out of it! Anyone know something that dissolves or softens old heat-sink compound? It's either that or drilling through the cement-like interior (maybe I'll post that question on a separate thread).

Now to design a 7- regulator board...

:)
DanQ
 

danq

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hey, that's a great idea - I didn't think of acid.. just need to keep it off the aluminum I guess.
thanks!

:)
DanQ
 

toked323

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yea home depot sells 2 gallons for 9.99$ mix it with a bit of peroxide it may help i use it fo pcb etching
 




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