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Old 09-08-2008, 09:11 AM #1
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Default a question on 18x long open can ld

Hi mates, I'm new to the forum, *it's the best I've found looking around the internet!
As the title says, here's the question:
what is the "safe" current for a 18x long open can WITHOUT special cooling?
The LD comes from a LG GSA-H58N DVD burner.
I'm asking 'cause I just got a freaking overpriced LED (my fault) and I don't' wan't to repeat the experience.
I'm using the DDL driver with 6 1.2v batteries, the output voltage was ~2.9v max
Max current with a 4.7 ohm resistor and a 100 ohm pot *should be around 260 mA (measured with a cheap DMM).

the Ld started laseing , but looked a little underpowered compared to my previous 16x.
After some tests the "dot" was shining less than before and ultimately "ledded" (ld->led)
The cooling was provided only by the custom aluminium casing holding the diode and the lens.
Searching the forum I found that someone feeded the 18x LD with ~250-300 mA with no problem.
So, do I need some sort of active o better passive cooling for <250 mA?
At the same current shouldn't the 18x output more than a 16x? (or it's just me that should study some more?)

Please forgive my english, I'm Italian, and a noob about lasers!

Have fun and good luck!
Andrea


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Old 09-09-2008, 12:07 AM #2
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Default Re: a question on 18x long open can ld

Welcome to LPF,
Now that you made your own "test load" out of your diode,
you can use it to measure the current of your DDL driver.
Quote:
Max current with a 4.7 ohm resistor and a 100 ohm pot should be around 260 mA (measured with a cheap DMM).
The 18x LD should have been able to handle that current.
Quote:
The cooling was provided only by the custom aluminium casing holding the diode and the lens.
Is the diode properly mounted in an Aixis or similar module? If so, &
encased by aluminum housing, that should suffice for cooling when run
under short cycle, (less than 60 seconds).

Heres some good reading to advance your knowledge,
Pro Tips w/ Spyderz: Building Your First DIY Laser
http://www.laserpointerforums.com/fo...num=1218324818
Quote:
Please forgive my english, I'm Italian, and a noob about lasers!
English......A+




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Old 09-09-2008, 12:21 AM #3
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Default Re: a question on 18x long open can ld

Andrea ---

I'm not familiar with that diode but in that power family, 2.9 volts should be about 260 mA. * Note that the curves at the top of the graph are not linear and 0.05 volts can go much higher.

Your heatsinking should have held for several minutes with out over heating.

Is it possible that a clip lead came loose and the driver lost regulation? Is there a capacitor in the circuit? *This has happened to me too many times *> * *

Mike
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Old 09-09-2008, 07:38 AM #4
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Default Re: a question on 18x long open can ld

hi mates, and thank you for answering !

@ moond0ggie

lol, "test load" is surely better than "cooked LD"! *



Quote:
Is the diode properly mounted in an Aixis or similar module? If so, &
encased by aluminum housing, that should suffice for cooling when run
under short cycle, (less than 60 seconds).
I just remembered that before the LD died I was turning the pot with the LD on, 'cause I wanted to check the current with the DMM, could this cause a failure?

I'll try to have better cooling with some thermal paste. In the meantime I've ordered 3 5mW modules from DealExtreme, until then I'll use EXTREME caution *

I'll read the link you provided , I'm slowly sorting through the forum to collect all the informations needed.

(WOW!! A+ * *)

@ Mike

all leads and components are soldered, the circuit is the basic daedal driver with a 47 microfarad capacitor, maybe the contact surface between the LD and the heatsink wasn't enough and the LD overheated and eventually died.

As I said, I'll wait for my modules from DX and I'll try again, in the meantime I've a 16x LD to play (carefully) with *

thank you very much for your time and have a nice day!
andrea

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Old 09-09-2008, 05:20 PM #5
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Default Re: a question on 18x long open can ld

I think it may have died because you were messing with the pot, you are best off just picking a current and sticking to it.

Your English is fine, it doesn't require 3 reads before you understand it.

Good luck with your future laser builds

-Adam
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Old 09-09-2008, 06:16 PM #6
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Default Re: a question on 18x long open can ld

^^^^^^yeah, like Diachi said,
You shouldn't adjust the pot with your &quot;good&quot; diode powered, the tiny potintiometers can be very touchy &amp; provide unpredictable changes while pushing in &amp; turning.
Now that you made a &quot;custom&quot; test load you can use it to load your circuit
while making &amp; measuring your adjustments.
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Old 09-16-2008, 02:52 PM #7
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Default Re: a question on 18x long open can ld

Yay! I finally received my red dot focusable modules from DX!

they were wrapped in plastic, but hey, free shipping,so as long as they work, who cares about the ugly packaging.
Tomorrow I'm going to install the 16x LD and mount the thing in my &quot;custom&quot; case (erm.. a broken Hard disk).
Hope to get the thing working!

Have fun!
andrea
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