Old 11-02-2014, 06:41 AM #1
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Default How much is too much current for C-Mount IR?

Hello,

Has anyone here taken a C-mount 808nm laser diode and overdriven it much? I have one rated to 4.4 amps 4 watts CW and want to push it to 6 amps. Would that likely kill it or substantially shorten its normal life?



Why? Mo-green power! Sharing the story for those who might have dead high power pointers and want to do something similar:

I recently took a 250mw 532nm laser pointer I've had for three years which was advertised on aliexpress to be 2 watts (I think I paid 250 for it):



50000mw green laser pen on Aliexpress.com | China laser sellers often LIE stating outputs several times higher than reality

...and put the battery in backwards, killing it, stupid to design it that way, a blocking diode would have prevented the problem - Moving forward after murdering my pointer and checking its C-mount 808nm laser diode, I found it was still good, but the driver toast, the parts for it wiped of identifying markings. Instead of trying to find another high current driver to fit or toil trying to determine the unmarked parts to fix it, I modified it some (extreme understatement), removed the 2.5 watt (output measured at 2 VDC) IR diode and replaced it with a FAC lensed C-mount 4 watt laser diode, remounting it in one of these:



808nm Housing Case Mount for Laser Diode C Mount Good Cooling | eBay

Fortunately, the part of the laser pointers head (inside part, now removed) which has the vandate and ktp crystal inside it had the right OD size to fit into the above laser host so it could take heat away from it. However I couldn't use the original section of the pointer which contained the C-Mount laser diode because it's OD didn't match the new host, but the new hosts C-mount section fit together with it fine.

After putting the thing together the new hosts lens wasn't right (expected), I couldn't focus, so I had to remove the concave-concave expander lens from the output of the laser module to reduce the beam width to something easier to adapt to the optics I had on hand. However, after removing the concave lens I was pleased to find I didn't need to find another collimating lens because the one which came with it would then make a tight enough beam, but at increased divergence, a problem I intended to solve using a telescope.

Testing, I pushed the IR diode above its 4.4 rating to 5 amps and was able to get about 550mw out, now I'm cooking with green ...maybe risking the laser crystals inside but no failure yet! Adding a 8X beam expander I recently bought on ebay (thank you electronic badger for the link) the divergence was then taimed and what a beautiful beam it puts out, the divergence appears to be low now and I can put a bright green spot on the underside of clouds at night

Expander:



However, not willing to leave good enough alone, I'm wondering, how hard can a 808nm laser diode rated for 4.4 amps of CW output be driven without shortening it's life too much? I mean, I probably won't put a whole lot of time on this laser pointer over the years, so if it's life is reduced to 50 hours, that's probably more than 2 life times worth for me. Any idea if I can drive it to 6 amps very safely? Next, I will be crying I fried my ktp crystal, I know, but wondering.

Oh, I might as well add, I'm now driving the unit with a pack of size C alkaline batteries and this voltage regulator:

http://www.ebay.com/itm/LED-DISPLAY-...-/161051476129

It is not constant current, but I can watch the amount of current draw to keep an eye on it, so far, the diode is behaving and not drawing additional current when it warms up (very little, anyway).

My 550mw ghetto pointer:



Nevermind the 2.4 volts shown on the regulator, the power leads to the diode are small, a bit of voltage drop there.

Next is to have a host built so that everything can fit into it and a constant current regulator.


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Attention new brothers of the collimated light!

Newbie advice: Please take the time to first make an introduction in the Welcome section before posting questions.


Divergence to spot size calc: - 1 mRad is about .057 degrees which expands to be very roughly ~10% the diameter of the moon or sun at their distances.

Divergence Calculator: pseudonomen137's JScript mRad Calculator - Measure your lasers beam dia. at 1 foot & then 20'.

Online calc. to determine spot intensity at different mRad's & powers: http://tinyurl.com/divergence-calculator

Laser Power Density Calculator: Laser Power Density Calculator - Ophir

Build a beam expander to reduce divergence: http://tinyurl.com/BeamExpander

University YAG Project The Professor's Homebuilt Lasers Site - YAG Lasers

YAG Power Calc. Laser Peak Power Calculator - Ophir

Angular Size Calculator; use with diode angle of radiation spec. for lens dia. at FL: Angular Size Calculator

RHD's Calc: http://lsrtools.1apps.com/RelativeBr...&useRaleigh=on

High Current Pulse Drivers: https://tinyurl.com/ya7whuk3

Last edited by Alaskan; 11-03-2014 at 04:35 AM.
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Old 02-03-2015, 05:02 PM #2
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Default Re: How much is too much current for C-Mount IR?

Hey,

Awesome ghetto pointer! I cannot believe no one has responded to this! I will chip in my $0.02 for what it's worth. I haven't done very much experimentation with C-mount diodes, I've only worked with a 500mW rated 808nm C-mount. The beauty of these IR C-mounts is their fairly large to massive emitter sizes. This is very bad when it comes to collimation (and requires an FAC to do so apparently), but is a blessing in disguise when overdriving. I personally think your C-mount will easily handle 6 amps for a few reasons. Since the diode's design current is already 4.4A, you're only increasing the current by 36%. Compared to most other overdriving scenarios(which can sometimes exceed 200%), this will most likely be a walk in the park for your diode. The other reason is the emitter size, it has a lot more area to be pumping out that 808nm, so you are less likely to see a catastrophic optical destruction occur, especially for such a small current increase. (Keep in mind, it was MEANT to run 4.4 amps for potentially hours on end)

I know it has been a while since you've posted, but I just wanted to chip in just in case the ghetto saber is waiting to be awoken. I'll be doing some more C-mount testing soon, and see just how far these 808 diodes can go.

--Max
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Old 02-21-2015, 07:27 AM #3
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Default Re: How much is too much current for C-Mount IR?

Don't cross the streams with that. Could be dangerous
How much is too much current for C-Mount IR?-str2_cn_2404_ghostbusters_a.jpg
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