8X Diode Murder fund

[IgorT]

Yep... I've got an 8X in a tiny Pocket Mini and it's fine.

The Pocket Mini is actually not that tiny, that i would be worried.. I was mostly worried about keychains, where the body is the only heatsink, or the heatsink is small...

I would not put a 12x in a keychain host, however if a duty cycle is observed, it can still be done, because in 1-2 min, it would not overheat...
The reason i'm thinking about heat and host size is that i don't like observing the duty cycle.. :evil:

There are plenty of kits with a much more massive heatsink than a Pocket Mini. The 12 X can't be that much more heat.

A 12x and heat... Let's say we power a 12x for 650mW.. I'm gonna have to guess some numbers, but it'll come out close, besides it'll vary by 12x diode efficiency anyway, and it's the diodes efficiency that will impact the calculation the most.


So, assuming similar slope efficiency as a high efficiency 8x for a good 12x diode, it will take 410mA after the threshold current to reach 650mW... Let's say Ith = 40mA since it's a higher power diode.. It'll probably be a little less tho, between 35 and 39mA i'm guessing.

Anyway, 410 + 40mA = 450mA for 650mW. If the Vf stays in normal ranges, 0.45A x 5.6V = 2.52W of electrical power going from the driver into the diode...

Since 650mW comes out of the laser, 2.52W - 0.65W = 1.87W.. The diode will produce 1.87W of heat.

If it is powered by a ~90% efficiency driver, the driver will create some heat as well. 2.52W is coming OUT of the driver, if it's 90% efficient, this means 2.52W is 90% of the power going INTO the driver..

2.52W = 90/100 x Pin => Pin = 2.52W/90 x 100 = 2.8W - a 90% efficient driver needs 2.8W to feed 2.52W to the diode.

Since it's 90% efficient, 10% of 2.8W gets converted to heat, meaning the driver creates 0.28W of heat.

The 650mW 12x laser as a whole creates 1.87W + 0.28W = 2.15W of heat... (Well actually a little more if we consider that the Li-Ion warms up some from the high current draw..)

It's not like were going to run them for 10 minutes at a time.

Umm... I might?
Actually, it's very likelly. I'd say it's almost certain.... :angel:

Igor's got an efficient blu-ray driver that will not be a heat issue for the driver, and Dr. Lava is working on one as well...

Actually Lava's existing FlexDrives were always a couple of percent more efficient than my driver, cos they work in a slightly different way. He uses a synchronous switching IC, which rectifies the output with MOSFETs, while my driver uses a Schottky diode to rectify the output, which introduces slightly higher losses, due to the higher voltage drop across the diode.

The reason i prefer my own driver for 405nm diodess is not the efficiency (which is very high with both), but the fact that i don't have to worry about driver's current and voltage output limits when powering BluRays (and the little extra stability it offers due to the very simple circuit).



Switching drivers, when used correctly, are all very efficient. Especially in comparison to linear drivers, which often produce as much heat as the diode itself, and in some combinations almost twice as much!

In comparison a DC/DC converter driver from the example i used above, the 90% efficient driver creates only 11.1% as much heat as the diode, or 13% of the lasers total heat...

 

[IgorT]

My experience on heat dissipation is from hundreds of LED lights that I have built.

I am not doubting your experience, i was just trying to figure out why it is different than mine.. Like i said, i'll try to replicate 2W heat dissipation in a small host and see what happens.

I'll try to record a temperature graph. Or rather two - a graph of the diode temperature and another of the hosts external temperature. In a good build, the difference should not be too big.

Obviously, we cannot expect good life at these temp levels if we are driving the diodes at 2X or 3X these power levels.

What operating temperature at the diode, do you think is acceptable for 10 minutes of continuous use ?

Well, as long as a diode does not go too far above body temperature, i am not worried. So usually i define the outer duty cycle limit with the time it takes a diode to come close to 40°C.

I'm just trying to caution people from long operating cycles with small hosts.

Understandable. I was trying to say the same thing, but then i remembered that everyone already uses a short duty cycle, even when it's not needed.

But if a build is good, you can feel the heat outside. Even more so since the hosts are made from metal. Due to the metals high thermal conductivity, a laser at body temperature will feel hot to us (seems like more than body temp, even when it's not)....

So even if a person forgets about the duty cycle, they would notice the laser is starting to get warm.
It will feel hot to us much sooner than to the diode, which is made to operate at 80°C as you said...


It is of course possible that in some designs there is poor thermal conductivity between the heatsink and a host. In those cases the heat is trapped inside, and it really could get dangerous to the diode, especially now that we have 8x's and 12x's.

But this is easy to check for if you have an LPM. If the laser doesn't feel warm outside, but the power is dropping fast, there is something wrong!


If the power doesn't drop by more than a few mW during a certain time period, there is nothing to worry about on the other hand
Perhaps i should try to figure out how much the power (or rather diode efficiency) depends on heat preciselly (to find the approx number of mW the power has to drop for it to become dangerous to the diode)..

 

[IgorT]

Is the V5 flexdrive going to be adequate as a driver?

The v5 is nearly identical to the v4, still using the same switching IC as v1, the only difference to v4 is the input polarity protection, achieved with a MOSFET (same method Rkcstr has been using) it's better than a diode in series due to lower losses, and better than a diode in reverse, as it poses no risk to the batteries, while protecting the driver against reversed polarity 100%.


I'd say with v5 the FlexDrive has become completelly fool-proof, only danger now comes from not being careful with the pot, or the soldering iron.


Once diodes start requiring higher currents (12x's?), Lava will have to move to a new chip. But he's been working on completelly new driver designs for several months by now...

He told me the specs once, and they were very impressive, when it comes to the currents it can produce, and i think the upper voltage limit should no longer be a problem either...

 

[jayrob]

The Pocket Mini is actually not that tiny, that i would be worried.. I was mostly worried about keychains, where the body is the only heatsink, or the heatsink is small...

I would not put a 12x in a keychain host, however if a duty cycle is observed, it can still be done, because in 1-2 min, it would not overheat...
The reason i'm thinking about heat and host size is that i don't like observing the duty cycle.. :evil:

Fair enough... I personally would put a 12X in a Key Chain CR2 host even if I only get a 1 or 2 minute duty cycle just because of how small and awesome the host is! (I just got some 3.6/4.2 CR2's that should handle it)

I'm used to a duty cycle from hand held green's anyway...

It's not like were going to run them for 10 minutes at a time.

Umm... I might?
Actually, it's very likelly. I'd say it's almost certain.... :angel:

I'll also have some builds that can handle some longer duty cycles too!

But for sure I'll have a tiny build if I can get 1 or 2 minutes of on time safely!

I don't see myself running a class 4 hand held blu-ray for 10 minutes though!

I wonder what kind of a current draw a 12X at 450mA's will have?? We're talking boost circuits, so I would imaging quite a lot of current draw. (probably be better off with an 18650 supply for a 'long run time' build, just to watch out for the heavy discharging)

 

[jayrob]

Hey don't do that yet!

That's what this whole thread is about...

So Igor can test the diodes for us!

 

[IgorT]

Fair enough... I personally would put a 12X in a Key Chain CR2 host even if I only get a 1 or 2 minute duty cycle just because of how small and awesome the host is!

I'm used to a duty cycle from hand held green's anyway...

I'm not saying anyone shouldn't... I said that since 99.99% of all people here use their lasers with a short duty cycle anyway, it really doesn't matter... In fact, for once the duty cycle will finally actually start making sense!

I'll also have some builds that can handle some longer duty cycles too! But for sure I'll have a tiny build if I can get 1 or 2 minutes of on time safely!

You know where i'd love to put an 8x in?

Your first Keychain host - the tiny one!

It would be awesome having 400mW of power from that! :drool:
If of course 400mW should turn out to give a decent enough lifetime, that is.


And if you machine it for me so it's a tight press fit for AixiZ, i wouldn't be worried about the diode, since i'd feel the heat outside before it could get dangerous. That host has some wicked heatsinking for it's size!

I'm just not sure if the tiny Li-Ion would manage not to explode... I guess i'll have to try.
A 12x in there is not likelly tho, altho mostly due to the battery.

Obviously i'm putting a LOC at 525mA in first... :angel:
(Keep in mind, when sending my package back, include one of these kits, the 10280 Keychain Host - AixiZ press fit please :evil: Hmm, i should probably make a new list for you!)

I don't see myself running a class 4 hand held blu-ray for 10 minutes though!

Well, it's not like i do that every time i pick up a laser. :yabbem:
But i like to be able to!

Like, sometimes i will use a laser, and it'll be ON not continuously, but for the majority of 15-20 minutes. Every so often it'll be OFF, however not to please the Duty Cycle Monster, but just cos i'm looking for a new "target" or whatever. It'll be OFF for a few seconds, or maybe longer, but not for a predetermined amount of time.. Basically, i just don't like restrictions, i guess..


But the 10-15 minute runs happen mostly just when i'm taking beamshots..
For example, when i try to align multiple lasers into a nice formation for the photo which takes a while by itself, and then take multiple pictures from different angles, adjusting the alignments, and so on, 10 or even 15 minutes can be over before you know it!


Another reason i like to have a laser capable of keeping a diode cool up to an hour straight (well, tested with a LOC at 450mA, not sure about an 8x yet) is, that if it can keep the diode cool (or rather safe) for that long, the power will be VERY stable during normal use! Maybe it'll change by a mW or two in 2 minutes. (I once left a 6x - my first one - at 200mW ON for 20 minutes, the power dropped by 3mW and then remained a flat line for the remainder of the graph! As if the laser was capable of dissipating the created heat into air and whatever it was holding it during the test)

But a host that actually REQUIRES a 2 minute duty cycle, there the power will drop considerably in that same amount of time...

I wonder what kind of a current draw a 12X at 450mA's will have?? We're talking boost circuits, so I would imaging quite a lot of current draw. (probably be better off with an 18650 supply for the 'long run time' build, just to watch out for discharging at over 2C)

Hmm, i wouldn't be worried about AA or CR123 size Li-Ions. It would be no worse for them, than a 6x at 200mA is to the 10280.

Otherwise, with a 6x at 200mA in the tiny Keychain, the draw on the 10280 is over 2C! I just measured it as 3C on a nearly full battery, but it gets much worse as the battery goes empty! It probably gets close to 4C, but except faster aging of the battery, i'm not worried yet. My micro heli draws 10C, altho that's a special Li-Ion...


As for 12x's and battery current draw, I can calculate from the numbers i guesstimated in the heat dissipation calculation above. Just need to check them first.



EDIT: Ok, if you find a 12x that produces 650mW after glass at 450mA and had a 5.6V Vf there (and you actually set it to that current), the driver would need 2.8W from the battery to power it....

A full Li-Ion under the high current draw it will be exposed to, will probably sag to 3.8V immediatelly, if not lower.

So it's a simple calculation. P = U x I => I = P / U = 2.8W / 3.8V = 737mA out of the battery...
As the Li-Ion goes empty, and drops to 2.8V, the current draw would climb to 1A....

Since the Li-Ion shuts down just under 2.8V, the current would probably not go above 1A. I'm know AA Li-Ions can handle that, because i've drawn more than 1.3A from them to power a CREE LED...


But i'm guessing we won't be pushing 12x's to 450mA, so the actual current draw will be less..

 

[jayrob]

Igor, that's the thing about the Key Chain 10280... (the smaller in diameter one - it is the same length as my CR2 Key Chain)

The 10280 battery is only 200mAh capacity, so if we want to be nice to the battery, we wouldn't want to push too much past the rule of thumb of a 2C discharge rate for Li-Ion's. Maybe 400mA's or 500mA's wouldn't you say?

I measured, with my high efficiency (freak) GGW 6X blu-ray set at 183mA's, and putting out 268mW's! (405-G-1) - 288mA's battery current draw.

That's with a fresh charged 10280, and as you know, as the battery will start to discharge and drop in voltage, the current demand will increase, as the driver will need to boost more voltage...

With that in mind, that's why I found the Key Chain CR2 host!




Slipstream, aren't you worried that the diode might die? Let's let Igor test these first!

 

[Slipstream]

but doesnt a flex drive change that? it draws more from the batt anyways?

 

[jayrob]

but doesnt a flex drive change that? it draws more from the batt anyways?

The fresh charged 10280 battery takes 288mA's to run the GGW 6X diode at 183mA's with a single battery/FlexDrive build...

That's because the driver must use extra current to boost the voltage to what the diode is asking for.

As the battery drains, the voltage drops. As the voltage drops, the FlexDrive will use more and more current to give the diode what it asks for.

So the demand on the battery gets larger, as it drains...

Keep listening to Igor, he's the one who explained this to me some time back!

 

[Slipstream]

thats exactly what im saying.. even though the batt has a max discharge rate the flex will pull more as the voltage drops, until the batt has no more.. regardless of the host.. its the batt that detemines the max output "time"

so when you say " With that in mind, that's why I found the Key Chain CR2 host" i think its dependent on the batt , not the host.

but i do love the fact that its a click and not a twist on host.

"Slipstream, aren't you worried that the diode might die? Let's let Igor test these first! "

Naw im a monster.. !! i eat 8x's for lunch

 

[jayrob]

thats exactly what im saying.. even though the batt has a max discharge rate the flex will pull more as the voltage drops, until the batt has no more.. regardless of the host.. its the batt that detemines the max output "time"

so when you say " With that in mind, that's why I found the Key Chain CR2 host" i think its dependent on the batt , not the host.

Yes, but the host will only take a certain battery...

The Key Chain CR2 host takes a different battery with a higher capacity. A 3.6/4.2 UltraFire CR2 rechargeable (the ones the I just got today), have a 'stated' capacity of 600mAh's.

That means that at a 2C discharge rate, you can safely draw 1200mA's from the battery for a thousand cycles or so. (probably)

Even if the capacity is not really 600mAh's as they claim, I'm sure we can draw at least an Amp from them safely.

A 10280 on the other hand, is only 200mAh's. That's the difference in hosts. The battery used...

 

[bryce007]

Slipstream, aren't you worried that the diode might die? Let's let Igor test these first!

If he's not worried about that diode, then I sure am. 12 minutes straight in a host that small (does look great BTW, just saying) with a current setting that high, that scares me. Hopefully there's nothing to be scared of, but we'll see when the results are in!

 

[Slipstream]

so when you say " With that in mind, that's why I found the Key Chain CR2 host" i think its dependent on the batt , not the host. QUOTE]


Yes of course...



i didnt quote mylsef correctly... oops

 

[IgorT]

Gah!


As i mentioned, itw3ak's diode arrived a day or so ago, and today i decided to take a closer look at his "diode with kink", and suddenly wanted to plot it.

But as i looked inside the module, while replacing the lens, i did what i always do. I looked at the diode window. I kept changing the angle, until i caught the reflection of a light in it. But something was off. Slightly strange. Couldn't figure it out, so i repeated a couple of times, and then it hit me... I checked it under a better light, and realized what had happened.

The diode did not develope a kink. It "developed" a broken diode window.
And i don't just mean loose and still in one piece, but broken into two pieces, with one piece still bonded to the can, and the other, larger piece, lost somewhere inside the can. :undecided:

itw3ak originally called it "Diode with fractures in the beam"... Only after i showed him the photo of HemlockMike's diode with kink, and itw3ak said it was the same, did i decide it had a kink, but in fact, itw3ak's description was closer to the truth... :yabbem:


I immediatelly turned it upside down, in a way that might have minimized the risk of the broken shard damaging anything it hasn't damaged already, and got excited about the possibility of decanning and "reviving it"..


Unfortunatelly, the diode was not placed upside down inside a gyroscope, to keep it in this position during shipping, where a package is thrown around in every way possible at least ten times a day...

The shard already did all the damage it could, and by the time it got here, the diode was an open circuit.. One of the hair thin golden wires must have snapped off the die. :cryyy:


So it would seem there will be no plot of an 8x with a kink, unless one of the test subjects degrades in this way..


The only thing i can't figure out is HOW the diode managed to "develope" a broken window! :thinking:

 

[IgorT]

well its hot i just touched the host.. but mw havent dropped.. in fact its at 480mw now..

ok ill stop the torture.. its a trooper !!
after 12 min... it just got better!!

dont get me wrong , its hot/ warm! but its still burning!!

I don't understand what you're trying to say..
Could you describe better what your setup is, what you're doing and what happened exactly?



EDIT:

well i just placed my pocket mini x8 @ 365ma, LG diode for a 5 min duty cycle 476mw reading on a kenometer. .

.. 5 min later the heatsink is defintely warm .. i have arctive silver paste between the heatink and the aixiz module.

475mw...............
474..................

so ends my experiment... after 6 minutes the host is warm . . and the diode is still alive..

peace

after this im going to let it go until the battery dies..

Sorry, i missed this part somehow. I see now..
Don't do that. Oh, too late.

Anyway, all you'd achieve with that test is shorten the diode's life by as long as the battery can keep it ON... And at 365mA it's life is short enough as it is!

You're pushing it to the limit of what these can take for any amount of time, and your diode is not a high efficiency one either.


If i were to push a diode THAT far, i would not be leaving it ON for any more than i'd "have" to use it myself..

Otherwise, the 2mW power increase... Did you turn the laser OFF to check if the meter goes back to zero with everything around it still in the same place (your hands included if they were close)?


Sometimes diodes can climb in power as they get warm, but this cases are rare, and usually happen either because of:
1. A diode being in a kink, or
2. A driver issue or an unsuitable driver...


There is one factor which could influence a FlexDrive. As a diode gets hot, it's Vf drops. Depending on how hot it gets, the Vf could drop quite a bit!

I know from testing, that a FlexDrives output current changes slightly with input voltage AND output voltage or rather the load's Vf..
But i find it hard to believe it could change enough for the current to climb far enough to both offset the power drop from the heat AND add 2mW on top! :thinking:


It is however possible that your kenometer was measuring the IR coming from the hot diode and host...

Because otherwise, so far the ONLY diodes that ever climbed in power as they warmed up were PHRs set into a kink.. They would climb out as they warmed up, and the power appeared to be climbing for no reason.


It is of course also possible that you found an 8x with a kink that exists without the diode having to be abused for a while. These diodes were never made to put out that much power, not even pulsed.. A kink at >400mW would not affect their operation in drives...


But somehow i my first suspicion is that your meter measured the host's heat on top? :thinking:
How close to the meter was the laser?



Otherwise, an example of an unsuitable driver would be a constant voltage source. Since the diode's Vf drops as it heats up, a constant voltage would result in more current through the diode... That could easily raise a laser's power as it would get hot.

But just for that reason a constant voltage source is not good for laser diodes...

 

[IgorT]

im gonna have one of Ehgemus's custom RPL style hosts for the host/heatsink, then as Igor is doing the build for me he is going to use one of his drivers...cant wait...

Hey!

So is it your host that just arrived then (are you H.G.E.)? :angel:

hopefuly goin to use one of IgorT's lenses also...

Working on that.

The lens is in an express multipack to California, so Jay will have it in a few days.

While there is a whole list of things i want him to machine for me, i asked for the prototype lens-nut to be made first, and i'll pay for priority shipping back to me, so i can start CNC lens nut production sooner. The shop i use can make a batch in a week or less. :yh:

But they don't want to do it for less than 50pcs... :undecided: