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My laser diode's specs are one thing and the input is another...

The Purple Death

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Hi guys,
I'm a laser newbie and after doing a fair amount of reading here, and asking a few questions on ebay, I purchased a few lasers from ebay and waited an eternity for them to arrive (no surprises).
Now I've tested them and am uncertain what to make of them. I don't intend a return or refund, it's just that though they work and are the correct color, they are not preforming to spec.
I want to know how I might determine what exactly these laser diode's specs are.
I understand that you're giving advice and if I burn the house down it's my fault.
EDIT: I did read https://laserpointerforums.com/threads/list-of-diodes.100402/ to see if what I was experiencing could be quickly identified without success.
Here's what I've got (official specs):

980nm 1.6V 50mw
780nm 80mw
650nm 3/5V <40mA <5mW
405nm 10mW @ Ith=26mA (spec'ed by other sellers as being 5mW-20mW)

And now here's how they preform (measured with an ancient analog multimeter since my digital one places too much resistance in the circuit):

980nm 10mA@1.6v/31mA@1.8v
780nm 34mA@2v
650nm 8mA@3v/24mA@5v
405nm 58mA@5v/40mA@4.5v/20mA@4v (The 405nm would not start at 3v or below.)

The 780nm laser I guessed the values on and got pretty close to what the seller said, but the others are way out of spec.
980nm laser is drawing 16mW when it should be drawing 50mW (and 55.8mW at 1.8v), so is the voltage wrong or what?
780nm is running at 68mW when it should be using 80mW.
650nm is runnig at 120mW@5v and 20mW@3mW! It's rated for 5mW!
405nm is rated for 20mW max and it's drawing 80mW@4v and 290mW@5v!

So, am I burning these out? What's going on? How can I determine the true specs of these laser diodes? Is there a happy medium in the event that I've no idea what any given laser diode is spec'ed at?
 
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paul1598419

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This is a perfect example of a little knowledge being a hinderance to you. Laser diodes are driven by the current instead of voltage because they decrease in resistance as they heat up. For this reason you always look to the amount of current you allow one to draw. Also, the power rating is for the output power, not the power it consumes. You can only measure this with a calibrated laser power meter. So, you are not looking at these diodes correctly.
 
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The Purple Death

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Thanks, that really helps, but my main concern was and still is how much electrical power should I be feeding into these diodes? Obviously, they can't produce a higher wattage beam then the amount of wattage I put into them. Perhaps this cannot be determined without a LPM to check output power against?
 

paul1598419

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Forget about the power consumed by the diode. This will not help you in determining how to drive the diode. Most of the consumed power is dissipated as heat, so this will not be of use to you. Driver current is the most useful parameter that you will find for laser diodes. Also, the initial forward voltage can be useful as they can be fairly high on some diodes.
 

The Purple Death

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Ok, how do I determine what the drive current and normal operating voltage should be?
I know how to determine the initial forward voltage.
I'm ready to RTFM, point me to it.
Thanks!
 

paul1598419

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For diodes like the LPC836 or LPC840, which are both 650nm diodes, the drive current is 360 mA or 400 mA and will give you ~380 to 400 mW with a G1 or G2 lens. I would need parts numbers for other diodes to give you their drive currents. The lenses used will also give you different output powers.
 
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