Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

Another LD to an early grave

a_pyro_is

New member
Joined
Aug 15, 2007
Messages
790
Likes
3
Points
0
I'm sure most have read the suggestion that in order to check current through the LD, one should use a small shunt resistor. And for ease of calculations the most common value used is a 1 Ohm resistor. When places in series with the load on your constant current supply it will not change the current or voltage to the load, will only draw a few millivolts more from the power supply, and most importantly will give you a safe place to test the current to the load.

Well, sometimes people know the right answer, but do not put it in practice. Today that person was me. :-[

I had just adjusted my regulator to 300mA and wanted to test it out. I didn't have a 1 Ohm resistor handy, so I placed my meter in series with the LD, (I think you know the story from here) I saw but one second of beautiful red trying with all it's might to burn through my beamstop (a flat black painted 1"x6") When what would you know, but the test lead slipped out of my hand :eek: I then saw the all too familiar red lines of COD :'(

While this is indeed a sad story, it is my desire that others may learn from my grievous mistakes and perhaps some LD somewhere will live a few moments longer.
 

S

SenKat

Guest
a_pyro_is : Can you do a HUGE favor.....there are some folks on here that are uncertain about WHERE or HOW the shunt resistor is to be used...and of course WHERE to take the measurements. Can you do a fast and sloppy drawing, or picture, and indicate WHERE the readins need to be taken ? I think that would help out some of the folks on here that do not want to ask the question :p Thanks ! Sorry to hear about your diode going to worse place :( I KNOW it was already in a good place ! :)
 

a_pyro_is

New member
Joined
Aug 15, 2007
Messages
790
Likes
3
Points
0
Gladly SenKat, and good call.

I usually use a 1 Ohm resistor as when measuring the voltage across it there is no conversion to do. 1Ohm / 1mV =1mA

But if you’re a little tight on voltage, i.e. running on battery power, 2% tolerance .2 Ohm resistors can often be found inside a dead multimeter. Just look where the test lead plugs in to measure current and you’ll prob see what looks like a small metal block.

But in that case the conversion is .2 Ohm / 1mV = 5mA
 

Attachments

rog8811

New member
Joined
Jul 24, 2007
Messages
2,749
Likes
38
Points
0
That is a point so worth making A-P-I....With my first builds I was lucky placing the meter in the circuit, but I have seen so many sob stories about the clips falling off or shorting out resulting in a dead LD.

Every build now gets the 1 ohm resistor treatment.

*stick in stickies time maybe?*

Regards rog8811
 

Daedal

New member
Joined
May 23, 2007
Messages
2,277
Likes
8
Points
0
Well... in an effort to keep the stickies organized, we resorted to shrinking the stickied list down to a single thread of links...

Some people ignore the list and go straight to the building... ::)

--DDL
 

a_pyro_is

New member
Joined
Aug 15, 2007
Messages
790
Likes
3
Points
0
^ As Mike says, nothing like repeating info to hold up progress. :-[ sorry...well, except for my drawing. I kinda like that one. :D
 

JohnnyBra

New member
Joined
Sep 13, 2007
Messages
25
Likes
0
Points
0
This was completely new news to me. Still working thru the "teach yourself electronics from what you find on the net" class I've been taking :)

I figured the cap protection would be enough to keep the diode safe from any sort of surge that would result from a accidental clip disconnect. It's always good to learn these things BEFORE letting the magic smoke out of my electronic bits.
 




Top