Degradation of M140

Well, few mouths ago I made some very simple build with M140 diode, that consisted of diode pressed into a massive round aluminum heatsink i found on radioshack and external power supply with custom linear driver and 2 Turingy lipo batteries of 1200mah & 15C discharge rate (those appeared to be great for feeding powerfull lasers).
Diode performed excellent, getting ~1.6A, sometimes if fed it with up to 2A for a very short periods of time with a bench PSU, but always monitored the temperature and took safety measures. Had great times with it until last few days.
Brightness decreased dramaticly with no obvious reason - no more than 1.6A fed through it. with same battery condition and current measurments. Bench test seemed quite strange for me - diode increases it's power proportionally with current until 1.4A point, after wich it goes dimmer with every current increase.
So diode have a peak power at 1400mA, performing close to a normal diode at same current (sorry, I don't have an LPM yet, can't take exact measurment). At 1.8A it is probably 50% of it's power on 1.4A. Further is worse. So it's just an interest, has anyone faced similar behaviour with any kind of laser diodes?

Thanks for any kind of participation.
And sorry for no pics or videos, I'll post later if needed.

I think you should have it sent to someone on this forum to test it properly with a lpm because its hard to estimate the output of a laser without one

I'm guessing the 2A was too much for the diode to handle. Even if the temperature did not increase that much, the wires inside the diode may have melted.

A picture of your setup would be nice.

Cheers! :beer:

Here's a video, where brightness loss can be seen (I hope). Just disassembled driver and connected the diode directly to PSU.

http://laserpointerforums.com/attachment.php?attachmentid=39039&d=1343646774

The heatsink itself (looks oldschool )

Man you need to push that module into that sink more... the diode is in the part not being sinked. Sure some wicking is occuring not what needs to be, if you have been running it that way it is prolly toast. order another and cool it off right.

It's top part of Aixiz screwed in, plus brass nut fitted tightly, to maximize thermal contact, all filled with CPU-grade thermal compound, I'm not sure overheating was the main reason for power loss, but i agree this is not best design however..

New 9mm diode will be great to go more serious with laser build

like jander said you needed heatsinking. i bet that aixiz got hot as hell.

I know I'm a massive noobie around here but that just seems like way too little direct contact from the module. If that is your only option to run it sticking out like that you might want to consider at least a copper module. It might help a little. You could also grab a generic heatsink from another build and attach it to the module and put thermal paste between it and the main heatsink.

Thanks everyone for help, that was my first one, anyways i'll defenitely take heatsinking issue into consideration :beer:

I think it's really good and nice of you to have such a setup to begin with

Your deff on the right track.

I hope one day to have a bench PSU and all the little wires and stuff to test and build lasers

The only thing i've havn't looked into yet is how on earth you press a diode in a heatsink, and how you get it out again ^^

Maybe tomorrow i'm buying a bench PSU and getting things started.

Cheers,Sm.

Thanks! For better diode in/out pushing I, for example, made axiz "diode holder" about 0.1mm wider for ease.

sorry, double post

Hi,
Probably a bit late now, but one idea I just had for making a better A140 heatsink.
Get a copper Aixiz, mask off the front and sides then fit diode and install ESD protection + cables onto the wires.
Then once working, Epoxy drop over the bare wires adding coils to ensure good solid encapsulation.
Once done, electroplate copper over everything else so the diode is embedded in the copper.
As long as you don't let the electrolyte get into the front part of the Aixiz this should work very well indeed, and if the diode ever does fail you just use the duff block as a source of copper for plating.

Comments?

For diode removal, Flaminpyro sells a press that threads into the same pace you normally put your lens and it just pushes the diode (intact and unharmed) back out. Check it out Here:

http://laserpointerforums.com/f64/diode-press-sale-pushes-out-diode-42614.html

As for the epoxy and copper plating, in theory it seems like it would improve things but I believe it was tested and shown not to do much if I am remembering correctly. You may be better off (suggestion given to me by Flaminpyro) cutting the rear normally unused aixiz housing about a quarter inch out and threading that onto the module. After you solder up your diode you fill the back area you made with electrically insulating and non-capacitive thermal epoxy to make a rather large pool of it filling over the back of the diode and making contact with the module and the cut off housing. The epoxy, once dried will add thermal mass to the module and can increase thermal conduction by pulling heat out the back of the diode for maximum conduction area. I plan to use this method on my new 9mm 445nm diode from DTR that is in the mail right now. I am hoping to close in on the 3W output mark with that baby. I am thinking that the back of a 9mm diode will give a ton of area for this epoxy method to work even better.

No offense to your suggestion conundrum, but this method would be a tiny fraction of the effort, time, and money.

Filling anything with thermal paste/epoxy won't make any difference, in fact it'll probably make it worse and just harder to service if you ever need to.

Thermal compound becomes basically useless after a couple of mm, because it has a relatively high thermal resistance. With small gaps this is not an issue, as the heat can be dissipated quickly to the other side.

The whole purpose of it is to assist the heatsink by filling small gaps that would otherwise not make contact, not become a heatsink itself

You might have misunderstood my suggestion. It would be replacing air altogether and thermal epoxy is more thermally conductive than air. There is usually nothing more than air touching the back of a diode. Add thermal epoxy and now you have a conduit for heat transfer out the back also. While it may not be super efficient, it will be better than nothing. Also, obviously you wouldn't do this in any situation where you may need to service the parts. Its not like a 12m aixiz module is expansive anyway though, even if the diode blew out eventually.