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Old 07-12-2016, 03:29 AM #1
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Default How to cool a 40W CO2 laser?

I intend to buy a tube, PSU etc. and build my laser cutter.
But how do I cool it???


1) How many watts will I have to deal?
In other words: a 40W CO2 laser tube is like a electric water heater of [___] watts.
Surely much more than 40W...


2) How many liters/hour should I pump?


3) How temperature affects laser performance?


4) What temperature will cause damage?


5) What coolant should I use? I heard it should be Deionized / Demineralized Water, like car battery water.
Iīm considering using a peristaltic pump. And also a heat exchanger.

6) Flow direction matters?


Thanks


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Old 07-12-2016, 05:06 AM #2
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Default Re: How to cool a 40W CO2 laser?

1) CO2 lasers are somewhere in the order of 20% efficient. That means about 200W in and 40W out, giving 160 watts of heat. Maybe round up to 200W

2) You don't need much at 200W. We can run some calculations for this. 200W for 1 hour is 720kJ. "Water has to absorb 4.184 Joules of heat for the temperature of one gram of water to increase 1 degree celsius." This tiny aquarium pump claims a flow of 300 liters per hour. 300 liters is of course 300000 grams, and 720kJ / 4.184 / 300,000 is 0.57C. This means that with a flow rate of 300l/m, the temperature difference between the inlet and the outlet will be 0.57C, or ~1F. If a tiny aquarium pump is good enough, just about anything is.

3) colder water will result in slightly higher output. I run mine at 20-40C water temp. I wouldn't go much over 40C - just a personal preference. I think closer to 5-10C is ideal, but probably not necessary.

4) Not sure.

5) Distilled water is okay. Grocery stores here carry gallon jugs of it for 80 cents.

6) Given the difference from input temp to output temp is nearly zero, I don't see flow direction would matter in the slightest.
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Old 07-14-2016, 11:49 PM #3
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Default Re: How to cool a 40W CO2 laser?

Now thatīs an engineering approach...

Unfortunately, Iīm about to give up my CO2 laser - itīs too big to mess around.
Fortunately, I think Iīll switch to diode laser; Iīve seen some 5W, 10W diodes. Hopefully they will fit my needs for 1/10th of the space.

Actually, I think they cost almost the same...
I saw an ad in eBay for a 40W diode laser at U$200. You need a 45Amp constant current power supply (at 2V....) which turns out to be 90W of heat produced by the laser, instead of the 200W.
And you still need some fancy lens, īcause the beam canīt be really round.
Coherent 40W 808nm Laser Diode Bar DPSS Pump Tested and Guaranteed | eBay

Well, Iīll be around in other parts of the forum.. thanks for the info!
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Old 07-15-2016, 12:00 AM #4
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Default Re: How to cool a 40W CO2 laser?

Quote:
Originally Posted by ambr View Post
Now thatīs an engineering approach...

Unfortunately, Iīm about to give up my CO2 laser - itīs too big to mess around.
Fortunately, I think Iīll switch to diode laser; Iīve seen some 5W, 10W diodes. Hopefully they will fit my needs for 1/10th of the space.

Actually, I think they cost almost the same...
I saw an ad in eBay for a 40W diode laser at U$200. You need a 45Amp constant current power supply (at 2V....) which turns out to be 90W of heat produced by the laser, instead of the 200W.
And you still need some fancy lens, īcause the beam canīt be really round.
Coherent 40W 808nm Laser Diode Bar DPSS Pump Tested and Guaranteed | eBay

Well, Iīll be around in other parts of the forum.. thanks for the info!
That diode isn't going to be good for a laser cutter. For diode lasers like that you need it to be fibre coupled - which isn't really something you can do at home either. Those bar diodes aren't single diodes (more correctly, emitters) - they usually have 19 or so emitters placed next to each other. They have their uses but you should go with something else for a laser cutter. CO2 is actually one of the better options.


Dissipating 200W of heat with water cooling isn't really difficult - with a big enough water reservoir you don't even need a radiator.

If you want to go for a diode laser - you want something more like this:



That's a FAP (Fibre Array Package) diode from Coherent.
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Last edited by diachi; 07-15-2016 at 12:02 AM.
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Old 07-16-2016, 04:19 AM #5
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Default Re: How to cool a 40W CO2 laser?

Diode lasers NEED cold water if you want them to live more than a few hours, whereas CO2 lasers don't care too much. Constant current at 45 amps is hard to come by, especially with modulation capability. When you add the large power supply and the water chiller, a diode setup may end up being larger and more power hungry than an equivalently powered CO2 laser.

Oh, and as mentioned above, they're useless in a cutter to begin with.
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