Laser starting bright but dimming

[Kyle445]

Hello all, This is my second laser build. I am fairly new to lasers, but not new to electronics and other dangerous diy devices.

Anyway, I have a 2w m140 diode at 445 nm running off an x-drive powered by a 2 cell lipo pack. At first it was able to light paper on fire and was intensely bright even with glasses. Soon, however, it would start intensely bright but grow dimmer than a flashlight. the diode is fine, as it was well heat sinked. when testing current draw however, it only drew about 850 mA. I retried with fresh cells and even a fixed power supply to the driver but it would always start bright but grow dim. Any ideas as to what might be the cause?
Thank you for the help, I wont screw with the laser anymore until I get some more experienced feedback.

 

[VisibleGreen]

Is it an Xdrive or an Xboost? Also could you show us some pics of the set up?

 

[Kyle445]

It is the x Drive buck to be precise. I dont have it in a housing yet, de-wired it when it wasnt working test pieces individually but here are the components used:
http://www.amazon.com/1-8A-X-Drive-...&qid=1445926371&sr=8-1&keywords=x+drive+laser

http://www.amazon.com/445nm-Diode-C...id=1445926407&sr=8-1&keywords=2w+445+nm+diode

the power source is a home made two cell lipo pack, each cell has its own over charge/discharge protection board.
Sorry i am still trying to figure out how to get pics online, it wont accept what i try to upload :cryyy:

parts come from dtr laser shop

 

[Lifetime17]

Hi,
Your pics should be taken first in a smaller file size 600x800.
Your driver might be the problem, if you had a PSU to test the diode separately to eliminate that it is the diode failing. Then you can rule out the driver, if you can test with two lithium ion cells.

Rich

 

[Kyle445]

I'm at college for an electrical engineering degree now so luckily I have access to a full lab of professional equipment. Also I have never run a diode from a lab power supply, how exactly do I go about that without frying the diode? I think the driver may have been bad so I will definitely try it, also would lithium polymer vs lithium ion make a difference?

 

[Lifetime17]

Ok make sure your diode is in its copper module, then put that into a larger heat sink that fits a 12mm module.
Now turn on the PSU make sure the voltage and the amper knobs are turned down to Zero.
Now turn the voltage is set to 3.7V, then attach the +pros to the correct diode pin
Then attach the - neg to the correct diode pin. Make sure they don't touch important !!!
Now turn the Amps up slow , now turn the voltage up slow, your Amps should start to climb don't go past 1.8A that's max for the M140 at 4.7 Volts .
When your done turn both A and V knobs down first disconnect the - neg then the + post shut down PSU.

 

[Kyle445]

Ok so when testing, it gets brightest at 1.5 to 1.6 amps at around 4.2 volts an gets slightly dimmer after that, but when I turn the power back down its instantly brighter and can cut nicely. So it seems that it doesn't want the full 1.8 amps at 4.7 volts, and if the driver put that out,maybe that's the issue?

 

[VisibleGreen]

Ok so when testing, it gets brightest at 1.5 to 1.6 amps at around 4.2 volts an gets slightly dimmer after that, but when I turn the power back down its instantly brighter and can cut nicely. So it seems that it doesn't want the full 1.8 amps at 4.7 volts, and if the driver put that out,maybe that's the issue?

Yeah sounds like you're pushing past the max current that particular diode can handle. That almost always happens when testing them. The diode will get to it's maximum output and when pushed harder it will begin to drop output until it eventually fries.
I think you're lucky that your diode didn't pop so I would just run it at 1.5a from now on.

 

[Kyle445]

Thank you for the help! Ill just get a driver that outputs 1.5 amps modify it myself to do so and it should work fine.

 

[VisibleGreen]

Thank you for the help! Ill just get a driver that outputs 1.5 amps modify it myself to do so and it should work fine.

You could probably send the driver back to lazeerer and he can set it to 1.5a for you. I'd pm him about it.
Hey glad we could help out.

 

[Lifetime17]

Ok so when testing, it gets brightest at 1.5 to 1.6 amps at around 4.2 volts an gets slightly dimmer after that, but when I turn the power back down its instantly brighter and can cut nicely. So it seems that it doesn't want the full 1.8 amps at 4.7 volts, and if the driver put that out,maybe that's the issue?

Hi, great the diodes telling you how much it can handle efficiently wise. Then set the new driver to the Amp that the diode is satisfied with. With diodes it's luck of the draw.Sometimes you get a freak and at times you don't. Now you found out how to test a diode for efficiency. I'm glad you made it happen great job.

 

[Lifetime17]

Thank you for the help! Ill just get a driver that outputs 1.5 amps modify it myself to do so and it should work fine.

Hi,
Get your self a test load and get an adjustable Xdrive and set it yourself. Just a suggestion Pal. This way you know what everything you put in it is doing.

Rich

 

[Benm]

Hello all, This is my second laser build. I am fairly new to lasers, but not new to electronics and other dangerous diy devices.

Anyway, I have a 2w m140 diode at 445 nm running off an x-drive powered by a 2 cell lipo pack. At first it was able to light paper on fire and was intensely bright even with glasses. Soon, however, it would start intensely bright but grow dimmer than a flashlight. the diode is fine, as it was well heat sinked. when testing current draw however, it only drew about 850 mA. I retried with fresh cells and even a fixed power supply to the driver but it would always start bright but grow dim. Any ideas as to what might be the cause?
Thank you for the help, I wont screw with the laser anymore until I get some more experienced feedback.

I guess there might be two things at play here: There is the optimum current for the diode itself, which you established to be at 1.5 amps or so. This is fairly normal, and driving these diodes harder than that generally doesn't improve output power much or even decreases it.

This does not exlpain why the current from the batteries/driver drops all the way down to 850 mA after a while though. I'd carefully speculate that the driver regulates the current down to prevent itself from overheating. Your laser diode may be well heatsinked, but how about the driver? Thermal protection of the driver itself may reduce current which would result in what you describre: good power initially that drops down after the time for the driver to overheat.

Setting the driver to a lower current may solve both issues though: the laser diode will be more efficient (not more powerful, but more mw output for mw input) and the driver will dissipate less power remaining cooler.

 

[Kyle445]

Ok, I will have the driver only putting out 1.5 amps and will get thermal paste for the driver. Hopefully it will work

 

[VisibleGreen]

I guess there might be two things at play here: There is the optimum current for the diode itself, which you established to be at 1.5 amps or so. This is fairly normal, and driving these diodes harder than that generally doesn't improve output power much or even decreases it.

This does not exlpain why the current from the batteries/driver drops all the way down to 850 mA after a while though. I'd carefully speculate that the driver regulates the current down to prevent itself from overheating. Your laser diode may be well heatsinked, but how about the driver? Thermal protection of the driver itself may reduce current which would result in what you describre: good power initially that drops down after the time for the driver to overheat.

Setting the driver to a lower current may solve both issues though: the laser diode will be more efficient (not more powerful, but more mw output for mw input) and the driver will dissipate less power remaining cooler.

Good point Benm I had forgotten about driver heatsinking. This is definitely the problem.
Wow I've been out of it for too long. I should have known this.

 

[Benm]

No problem. Perhaps you can add some heatsinking to the driver and see if that improves things a bit. Often it doesn't have to be much since the thermal conductivity of these IC packages is very poor and mostly relies on having a decent amount of copper clad pcb material around it. In small boards you don't really have that option, so glueing on a small heatsnink you help you out more easily.