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Calling all FAPpers - FAP800 - precautions and driving advice

Junkers

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So I've been doing some digging on these forums and elsewhere, learning that these units are VERY susceptible to static. My laser has arrived but I'm reluctant to even remove it from the box knowing that I could potentially kill it. How do you guys go about handling these units? Do you always wear a static strap while handling these?

I also have another question that's sort of on the same wavelength. I have been reading over the docs regarding these and found an older application note for the LB series. On the third page is states that transients as low as 25uA can destroy the unit. Wow. I'm guessing this is why people favour linear supplies. On the other hand, I stumbled across this video where the guy appears to be powering his unit using $4 buck drivers off Aliexpress. I imagine those would be extremely noisy under load and therefore think I might be misinterpreting something here. Do any people here use a SMPS to power their FAP800? I almost bought this unit but now I'm unsure.

Also, does anyone know the thermistor plot/scale for these?
 
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Alaskan

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I've mistreated a used surplus low priced FAP800 terribly, and it hasn't failed "yet". My understanding is they normally operate around 20-25 C, as high as 30 C for case temperature. See this: https://edge.coherent.com/assets/pdf/COHR_FAP800Series_DS_0917_1.pdf#page=3

What I've done wrong: Direct connection to 2.0 VDC Cyclon battery with no driver, being careful not to zap it with static by handling it properly, but do not have static protection or a device across the input terminal to shunt static or voltage spikes.

Would I treat a new or expensive FAP800 that way used or not? Hell no. I'm daring this one to die, trying to see if it can take this kind of abuse, so far, so good. I have a dozen of these devices, so if this one dies, it will be for a good cause, exploring the limits.

Edit: How much power output is your FAP rated for? Without knowing that, I can't suggest a proper driver for it. What value of thermistor are you wanting to know the resistance vs temperature for? 10K?

Google:

Thermistors are available in two types: those with Negative Temperature Coefficients (NTC thermistors) and those with Positive Temperature Coefficients (PTC thermistors). NTC thermistors’ resistance decreases as their temperature increases, while PTC thermistors’ resistance increases as their temperature increases. Only NTC thermistors are commonly used in temperature measurement.

Thermistors are composed of materials with known resistance. As the temperature increases, an NTC thermistor’s resistance will increase in a non-linear fashion, following a particular “curve.” The shape of this resistance vs. temperature curve is determined by the properties of the materials that make up the thermistor.

Thermistors are available with a variety of base resistances and resistance vs. temperature curves. Low-temperature applications (-55 to approx. 70°C) generally use lower resistance thermistors 2252 to 10,000Ω). Higher temperature applications generally use higher resistance thermistors (above 10,000Ω). Some materials provide better stability than others. Resistances are normally specified at 25°C (77°F). Thermistors are accurate to approximately ± 0.2°C within their specified temperature range. They’re generally durable, long-lasting, and inexpensive.
 
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Junkers

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The unit I have is 40W. Now that I have it I can see the thermistor is an aftermarket addition (it sits in one of the bolt holes and looks to be held in with something like silicon). I thought they may come with them given their tight temperature tolerance. I also see that the specified temperatures reference the case temperature rather than something like junction temperature so that makes more sense.

I ordered some of the DC-DC power supplies that Endurance Lasers used in the aforementioned video. I have a sizeable capacitor here and will do some load tests before I connect everything together. I just need to figure out how I will control 3 SMPS in parallel. They appear to have both current and voltage control which is a bonus. That'll make balancing the load much easier.

On a bit of a tangent, which safety glasses do you use? I have been eyeing up a pair from Thorlabs but at 180 USD + 120 USD shipping + whatever customs tax I have to pay, the price is eye watering. They are almost more expensive than the entire project thus far. I know my eyesight is invaluable but sheesh... Reputable lower tier manufacturers (recommended by this forum) don't really seem to focus on the 808nm band so I guess I'm left with little choice unless someone can recommend me a better alternative.

All text and no pictures makes Junkers a dull poster

20190621_221131.jpg


20190621_221230.jpg
 

Alaskan

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I would be nervous putting a cheap switching power supply regulator on that diode, they can be noisy with transient voltage spikes riding on the output as well as have huge voltage spikes when first powering them on, or if there were a short interruption to the input the same thing; zap, dead diode, I've done it a few times, but not with a FAP.

I see that big capacitor, maybe you intended on putting that across the output to help smooth out ripples but I'd use one closer to the DC voltage you are using as it will be far smaller for the same amount of capacitance. I don't think this is the right way to power this and not sure putting a capacitor across the laser diode like that is a good idea, maybe it is and I just don't know, but I haven't seen that done before. With three of these regulators in parallel I am concerned things can go haywire fairly fast, that said, I did the same thing for some high power 100 watt RGB LED arrays, but eight of them and it worked for me using isolation diodes between each PS output. But, they weren't sensitive laser diodes either.

Also, my experience with these cheap CC regulators has been poor, I had to try several until I could find a model which would produce enough current because they rate them at an amount of current capacity, but only when having the lowest voltage drop, if they are regulating a higher voltage down to a low voltage, not so good, or if a step up, from a lower voltage to a higher voltage, the current capacity is always far lower than the power handling ability they advertise.

I would stay away from cheap switching regulators at this kind of current level all together and use something else, unless a laboratory design power supply, but that won't guarantee they won't also behave the same way, I have an expensive one which does the same thing when powered on. The fix for this is simply to make sure the wires to the diode are disconnected when powering on, or turning off the power supply. If you don't, too often they produce a huge spike when powering on which will kill that laser diode (that and pray you don't have a blip to your AC power when hooked up to a diode). This problem can also happen to regular non-switching supplies too, it's a challenge to find one which won't do that.

Optlasers makes high current regulators which can run a FAP, that would be a better way to go, but not cheap for a 40 watt FAP. I know, I told you I powered one of my FAP's straight off a 2.0 VDC lead acid battery, but it is a FAP I don't care about, if I had a newer FAP which had lots of life left in it, and all of the fibers good inside that bundle, I wouldn't treat it that way. If you can find a DC power supply designed to run FAP laser diodes that would be ideal, but I haven't found them cheap.

Optlasers high current laser diode drivers:


If you want to try using that cheap regulator, check it out to make sure you won't have the problems I mentioned. If you want to parallel the outputs of the regulators, some will allow that without an isolation diode between them, some won't. You might need to add that diode and then of course, factor in the voltage drop through that diode. Do you have an O'scope to check the output of that regulator?

Oh, on that FAP thermistor, it looks like a standard unit to me, something Coherent supplied with it. Here's one I just received in the mail this week which came from Coherent this way:



You probably have searched the forum and found this thread by now, but just in case you haven't, this may be of interest:


Here is a link to a data sheet for the Texas Instruments 50 amp regulator Mike was trying to use with his FAP: ptv08t250w, but I don't think he found a way to control the current yet. I also have this same document saved here:


These TI regulators have built-in over current protection, just get one of the models which is designed to run close to the current you want to run (which is still below the maximum current rating of your FAP) and let it fold back (or perhaps stop output) to prevent over current and don't worry about trying to make an adjustable current set point, just make sure the voltage is set low enough the diode won't reach fold back or interruption current limiting, unless the diode gets so hot it starts pulling more current, you probably won't reach it. However, you will need to investigate this idea to be sure my reasoning is sound regarding how it functions, but I believe it will protect the diode from over current that way.

Edit: I found this information regarding overcurrent loads:

Overcurrent Protection:

For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that exceeds the regulator's overcurrent threshold causes the regulated output to shutdown. Following shutdown, a module periodically attempts tor ecover by initiating a soft-start power-up. This is described as a hiccup mode of operation, whereby the module continues in a cycle of successive shutdown and powerup until the load fault is removed. During this period, the average currentf lowing into the fault is significantly reduced. Once the fault is removed, the module automatically recovers and returns to normal operation.


The way I read this, when an over current situation occurs the output is shut down but keeps trying, or "hiccuping" an output until the FAP cools enough to have a higher impedance, or lower current draw, but to reach overcurrent with the 50A module it is far too high at 85 amps to safely run the FAP that way. Choosing a lower current rated TI module which has close to a 50 amp overcurrent threshold (depending upon which FAP you have) such as the PTH08T210W rated for 30 amps continuous appears to be the way to handle this, but perhaps 50 amps is too high for your unit. There are several versions of the TI regulators to choose from, so you probably can find a suitable one with a lower threshold. if running the FAP in intermittent duty cycle, this ought to work out for us, but I wouldn't try it for 100% duty cycle as the module would probably heat up too much.

Here are some 30 amp units on ebay cheap right now: https://www.ebay.com/itm/5-NEW-Texas-Instruments-PTH08T210WAH-MODULE-PIP-7-3-6V-30A-HORZ-T-H/162926589289 - Unfortunately, the drop-out voltage of this regulator is fairly high, so you would need to run a few volts higher into the regulator than you might want to use, if using batteries. The good news is 96% efficiency, so you wouldn't waste enough battery capacity doing so to worry about, just that your pack would need to be larger. I'm assuming you want to run off of batteries though, you probably don't, I'm projecting a bit there, as I do.

One of the things these regulators could be useful for is as a high current pre-regulator to hang another regulator off of, their efficiency is uber high and depending upon what you are using, could be far more efficient to reduce a few volts using one of them first ahead of your adjustable CC regulator.

Download PDF for the 30 amp TI regulator here:
Enough ideas from me now? I've given you everything I've come to see as a poor mans solution as well as good practice, that is, if you use optlasers drivers. Only thing I've left out is collimation.
[/COLOR]
 
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Hemlock_Mike

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I am using the TI PTH08T250 supply. It is rated for 50 Amps but I've limited it to 30 Amp MAX for now.
I am using 3 18650-25R cells to light it up but I can regulate the current from 0 to 30 Amps with a small pot.
For basic lens testing, I run it just above threshold because my cooling is rather minimal for now. I haven't had
time to work on it recently trying to get that damn beam under control.
I damaged my first module by burning something to close to the unprotected output and COOKED the fiber end off!
Mike
 

Alaskan

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Mike, long time no see, glad to see you post. Where did you insert that pot to control the current with that module? I'd like to do the same.
 

Hemlock_Mike

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I'll have to find my schematic I drew up. I thought I sent you a copy of it.
I simply followed the data sheet for that. There was a resistor for MAX current
and an adjustable pin too as I recall
Mike
 

Alaskan

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You may have, been a long time, what, 2-3 years maybe. If you did, I've lost it, but my interest in FAP has returned.
 

Hemlock_Mike

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Hey Desert guy! I can't find my schematic I drew up - But - I downloaded pages 3 & 4 of the data sheet.
It sorta come back. Remember, this is a "stable voltage" regulator.
1. Pins 4 & 18 set the max voltage output. I forget the module voltage for 40 Watts.
2. Here's the magic ---- Pin 20 is an analog tracking input. Read about it on page 4.
I put a 5 volt supply on the board (LM78L05) and fed that to a resistive divider which includes the
adjustment pot.
This gives you an adjustable range with the top end clamped at your Max voltage setting. I never
noticed any current drift in my short on times.
3. Pin 21 is used for my beam on/off switch.

Read the 43 pages of data sheet! --- Mike
 

Alaskan

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Mike, good info :) If the duty cycle is so short the FAP cannot heat up enough to start pulling more current, then no problem. That is the same thing I observed with my own FAP without a regulator, but my on time was 20+ minutes on a fairly massive but passive heat sink using a lead acid battery which was draining at such a fast rate for its capacity, the input voltage was continually trailing lower and lower.

From what I've read, these Texas Instruments voltage regulators will trip out if the current is beyond their design and then immediately auto reset. The way I see it, this function isn't true current limiting, only a current trip-out limit. I imagine the unit would cycle on and off repeatedly if over-current is reached which wouldn't be bad, as long as the voltage output doesn't spike.

I imagine, if the diode is used too long (for the amount of heat sink) and starts pulling more current, exceeding the regulator design limit, that behavior may end up duty cycle modulating the IR output into some kind of oscillation which may be acceptable as an over current protection mode.
 
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styropyro

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I've powered a Coherent FAP with a stack of LM338s in parallel (+ ceramic and electrolytic filter caps.) Extremely easy, effective, but not very efficient and it generates a lot of waste heat in the driver.

More recently I bought a 25W 975nm laser diode array (not a FAP but similar) and since I needed to make it portable, I couldn't have the poor efficiency of a linear driver. So I did a bunch of reading and experimenting and I eventually came across this video where the guy built a 40A CC driver for IR laser diode arrays:
(the schematic is in the vid somewhere)

I built it with a few minor mods and it was certainly effective. Compact too and produces very little waste heat (at least on the run times I was using). I made a cool IR laser gun with it.
65253
 

paul1598419

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I haven't had any experience with these fiber array packages, but this thread has become fairly interesting to read. Thanks to all who have contributed.
 

RedCowboy

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I have driven my FAP's and other fiber coupled modules with a bench top power supply and have had no trouble, they do need to be kept cool.
 

Alaskan

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Paul, searching for information on these fiber array packages/FAP's is what brought me to this forum to begin with, it's only a small group of members who have much interest in them, so I was happy to see another individual join who wants to talk FAP. These units can produce more power than anything else I can afford on the surplus market and sometimes I find them new old stock for a good price, like this last one I posted the photo of above. That one won't be used for burning, it was built as a pump for DPSS, I have some crystals I'd like to try to make some green with, quite a challenge though, have been collecting parts for too long towards that end, when I can find them cheap enough.

I'd like to see pyro's unit in operation and see what choice he made for the battery pack which isn't shown in his photo. Interested in duty cycle information before the unit gets too hot.

Mike, all of the photo's in your Portable FAP thread no longer work, can you repost some to this thread?

Here's a photo of the output of one of the FAP's I found on ebay cheap, you can see why it was on ebay, one of the fibers is dark. That's the massive passive heat sink I used on it which would allow the unit to run for so long without getting too hot. Although very warm, and I am sure above recommended temperature for long life.



Above, the bottom half of this photo shows what the beam pattern looked like on a wall about 15 feet distant. The camera used had the IR cut filter removed.



Above and below: Danger Will Robinson, don't do this, too much power to be shooting around on objects and god forbid, cross onto someone. This photo was taken with the output reduced to a minimum, but showed up nicely in the photo as a sky shot above, tree shot below.



Above, the beam pattern on a tree about 100 feet distant, the divergence with this small 12.7 mm PCX collimation lens is about 16 mRad.
 
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RedCowboy

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Does anyone here have an active fiber laser ?
I understand that the beam specs can be incredibly good.
They have been out of my budget so far but in time as they get replaced I hope to find some used units with a bit of life left at a good price.
 

paul1598419

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If I were to buy one, it would be to drive a Nd:Yag/KTP or Nd: YVO4/KTP crystal to get 532nm out. I wouldn't be interested in it for burning purposes. Seems like it would be great for end pumping.
 




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