Duty cycle on Blu-rays.....?

[Schrecken_Licht]

As of now, I have two blu-ray lasers - one a module that's supposed to be putting out 90-100mw (no way to test it - just going by the seller's description - but a reliable seller so it's believable) and one doing 140mw (a pointer I just purchased from Daguin). So, in general, what sort of duty cycle should be observed for 405nm lasers?

I did notice the module was getting a little warm after a minute or so, but that was back in the summer time and now I have it mounted on a strip of aluminum, which I think helps to dissipate the heat + it's of course cooler in winter. The pointer, I will have to ask Daguin as he built it, but in general - what's a good rule of thumb for blu-rays?

 

[digital_blue]

I usually run mine till they get slightly warm to the touch... Haven't fried one yet with this method...

 

[daguin]

As of now, I have two blu-ray lasers - one a module that's supposed to be putting out 90-100mw (no way to test it  - just going by the seller's description - but a reliable seller so it's believable) and one doing 140mw (a pointer I just purchased from Daguin).   So, in general, what sort of duty cycle should be observed for 405nm lasers?
I did notice the module was getting a little warm after a minute or so, but that was back in the summer time and now I have it mounted on a strip of aluminum, which I think helps to dissipate the heat + it's of course cooler in winter.  The pointer, I will have to ask Daguin as he built it, but in general - what's a good rule of thumb for blu-rays?

As long as the module is not getting warm, there is really not a "duty cycle" associated with the "heat" of the diodes. Once the diode is being driven toward the upper limits of the diode then heat may become a factor (although that is not really clear yet). With the PHR diode that limit is about 150mA. As long as you are below that threshold (and assuming "normal" heat sinking), the diode really doesn't generate enough heat to do damage. Unless something else influences the life of the diode (a current/voltage spike, ESD, significant impact, etc.) the major factor in the life of the diode is simply time "on." Utilizing a duty cycle lengthens the effective life of the diode by limiting the amount of "on" time. The life is also effected by the number of on/off cycles.

Peace,
dave

 

[davidgdg]

"The life is also affected by the number of on/off cycles."

So would that mean all things being equal, it is better to power on for 10 minutes without a break than to power on-of-on-of etc for a total of 10 minutes on? Rather like running a car or a neon tube light?

 

[Razako]

I've left my 140mw blu-ray on for periods of around 10 minutes without killing the diode. Imo as long as you have them heatsinked properly and they aren't too badly overdriven they don't really have a duty cycle.

 

[suiraM]

Duty cycle is a myth as far as anything with remotely decent heat sinking is concerned. It may be an issue with certain greenies, where the crystal and diode are both dealing with a much larger amount of power, frequently with very limited heat sinking. Or, to be precise, the surface area is too small to dissipate the heat faster than it is generated. That is not the case for BR diodes.

Power on and off, however, cause thermal stresses that will adversely affect the lifespan of the diodes, so operating them periodically will give a shorter life than operating them continuously.

 

[Benm]

I agree with the above, duty cycle is only applicable to lasers constructed so badly that the heatsinking doesnt cut it. With proper heatsinking your diode should reach more than 10 degrees over ambient running at 100 mW or so.

One exeption might be running it just in the aixiz module - those are so small that heat does become a problem after a minute or so. Additional heatsinking is the way to go, not blinking it on and off.

 

[Schrecken_Licht]

That makes sense....since red diode lasers generally can run for long periods of time unless they are very powerful. Just wasn't sure about the blu-ray, though.

 

[nvmextc]

I try not to leave any laser pointers on for more than 2 minutes. But the other day I thought I'd start experimenting since I don't have much to do (I have spare diodes so will just give me something to do when I break this one). I have a 803t MXDL with a jayrob heatsink running a flexidrive v2 @ 185ma. To start, ambient temperature was about 25C and output was 136mW. After 8 minutes the heatsink got warm to touch and output rose to 140mW. I'm going to keep running it in this cycle once or twice a day to see how long it can last. At 185ma I don't think it will last long but will be good to see.

 

[suiraM]

For my red, I just screwed the AixiZ head into a CPU heatsink (the sort you'll find in older computers- just a finned piece of aluminium with enough thickness to hold it). That is more than adequate, and I don't expect to ever notice any heating. It's been holding steady at 28°C temperature for the diode whenever I've used it, regardless of how long it's on. The driver reaches 33°C, which is okay, since it's getting significantly less cooling (regular RAM chip cooler). Heatsinks are cheap.