I think I know just enough to be dangerous... NEWBIE help please

Heres the backstory... I Just finished my XY table for my homebrew CNC yay me for the Z axis I wanted to use a laser to engrave into light things like plastic, scorch wood, or burn paper. So what I did was a little research (probably not enough) and then I went on Ebay and bought a 1W 808nm laser, the data sheet that came with it says:

CW output power: 1000mW
Peak wavelength: 808+/-10nm
Spectral width: <5nm
Threshold current: >300mA
Operating current: >1400mA
Operating voltage: >2.2V
Slope efficiency: >10WA
Wavelength temperature coefficiency 03nm/Deg C
Beam Divergency: 12/40
Emitting area: 100:1
Serial resistance: >0.50
Lifetime: 10000 hours
Package: T05

While I was waiting for it to arrive I built the driver from:
Laser driver - It can be done

The only modifications were I added a second LM317 in front of the current driver to adjust the voltage, as in the datasheet http://www.national.com/ds/LM/LM117.pdf

I added a third 10ohm resistor to bring the "safety resistor" down to 3.3ohm

And I installed a 25ohm pot instead of the 100ohm

I didn't have a 7.2V power source, but I had a 12v 1500mA wall wart, so I figured I could use a LM317 to step down the voltage to 7.2V and feed that to the driver

It came in and I hooked it all up, I set the first LM317 to 7.2v and when it comes out of the driver it's at 6.9v (no load) I placed an ammeter between the driver and LD and flipped it on... 340mA 4.4v

It's IR so I cant comment on the brightness other than on the cellphone camera the reflection from the electrical tape I was trying to cut was the brightest light in the room...

Here's my problem, (I'm welcoming opinions) I've seen 300mW lasers on youtube pop balloons from 15'+ away... My LD is capable of being 3x more powerful, and It barely nicks vinyl electric tape, millimeters away.

I believe my problem is #1 I don't have a collimating lens and #2 I don't think I'm pushing it hard enough to get to the 1400mA operating current.

To fix #1 I guess I have to find the right lens off ebay, the one I did order was for a 5.6mm LD and the LD I have outer diameter is 9mm, I'm trying to modify it, but I'm not sure I have a steady enough hand.

To fix #2 I think I need more current, but I am honestly afraid I don't know how to do it, reference the unknown maximums. I don't know if I should add more "safety resistors" to lower the resistance, or take them out all together. I could add more voltage .... as per the LD data sheet the 12V 1500mA wall wart connected directly to the LD would be acceptable as it is " >2.2V " in operating voltage, and " >1400mA " in operating current. I wouldn't do that, but that is what I mean in "unknown maximums"

Again I am welcoming opinions, anything that can help me get the laser "full power" without "blowing it"

Thanks,
Newbie Matt

Wouldn't you want tonuse like a 60 or 100 watt co2 tube so you can actually cut stuff ith yr fancy cnc setup?


Probably both... If your focus is off your not going to get alot out of it... If it's spread out it's like shining a 1 watt light at it which isn't much..

your driver from the "it can be done" site can handle the 12v no problem. just heat sink it. you are complicating an already easy set up.

and one thing with ir is that obviously it is invisible. so focusing will be a pain. but your project sounds cool.... you should post some pix. we love pix here!!!!


do you have any lens at all or is you laser just blasting away. YOU NEED A LENS.

1400ma is close to the max of the lm317 driver so make sure you use good wattage resisitors and heatsink the regulator.


michael.

UPDATE

In trying to find the source of the current problem I connected 7 D Alkaline batteries in series for a total of 7.7 volts, I fed that to the driver, it outputted 7.2V (no load) and 4.2V at 140mA ... this tells me I have more avail amperage from the first LM317 than the 7 D batteries.

chipdouglas said:

your driver from the "it can be done" site can handle the 12v no problem.

Click to expand...

I am worried about the maximum voltage of the diode. The driver's output voltage seems to be close to input voltage. I realize Laser Diodes run off current, but I'm worried about a maximum that I don't know about. The datasheet was of no help, it's half of an 8.5 x 11 piece of paper and what I posted above is all that it had on it.

Thank you chip I will start heat sinking as soon as I hit submit.

the diy driver you are referring to feeds the proper amount of voltage to the laser diode. all extra voltage gets turned into heat. hence why i said use a heat sink.

The driver tutorial you followed mentions using a pot for variable control. I'm sure thats just to make the driver more versatile in regards to making it work on more diodes.

According to the LM317 calculator, to get the 1400mA you need for your diode, you must use a .9 ohm resistor. If you want to go for convenience (and heat safety), grab a 1 ohm resistor from radio shack. Make sure it's at least 1.5 watts or higher.

For the LM317? just need the 1. Put a heatsink on it because it will get burning hot if you try and drive a laser of that power.

Here is my own drawing of the circuit I use.

I think I figured the power problem out, I ended up with 12 10ohm resistors in parallel, with a total of 1.2 ohms (I know the math doesn't add up), I put them in, turned it on and turned the pot down, my test load showed 1.05A, When I connected the LD it started at about 1.05A then after about 5 minutes, It started down to about .85A I turned it off and let it cool, It is sitting in a 2" x 2" PC heatsink I drilled and it sits snugly.

As a test, it works well. It burned a hole in a mardigras cup, so not too shabby.

I'll shine it close to the xy table and see what kind of damage it can do without a lens. Will post soon with pictures. Thank you all.