Warm outside, but getting several minute Duty cycle

[Richie89]

It's funny because I've been trying new ideas because I don't have large heat sinks.
I wanted to fire my laser directly straight up into the clouds and just sit there and admire it's beauty without worrying about rushing to shut it off every 45-60 sec. so I was thinking that if I could figure out how to keep that head/heatsink/module cool or around 45-55 degrees Fahrenheit than I'll triple my D cycle. So I threw a relatively small hand towel in the freezer making sure it was a tad damp and not soaked, let it near Freeze and wrap it around the head with a rubber band. I did this and went outside leaving it on for several minutes maybe 5 minutes and after turning it off I used my IR thermometer and found that the module was only sittin about 15 degrees hotter than usual. I doubt this same thing would work for a laser pushing over 3 amps and an output of over 4 watts, the one I used for this experiment was only a 1.2 watt 445.
Anyways I felt I had to share this with you all.

 

[BobMc]

Inventive, as long as it worked. The idea is sound, just keeping the heat sink heat sinking. A small breeze would probably increase it even more, or a small fan even. Sure you thought of these, but can't argue with successs.

 

[paul1598419]

I guess the best thing you can do is buy hosts with large heat sinks to begin with. Fins will also help, but are not always practical. Remember that copper has about 160% better thermal conductivity than aluminum. Aluminum with a copper core is also a good alternative.

 

[Richie89]

Inventive, as long as it worked. The idea is sound, just keeping the heat sink heat sinking. A small breeze would probably increase it even more, or a small fan even. Sure you thought of these, but can't argue with successs.

Thanks, I always thought of using a small fan like you said. I probably wouldn't do it if I was using a G2 just in case the moisture gets on the lens then heats up and leaves a water spot when evaporates. Acrylics are much cheaper funny how I'm a little shocked that I'm getting 1220mw out of my Sci-fi 501b with an acrylic.

I guess the best thing you can do is buy hosts with large heat sinks to begin with. Fins will also help, but are not always practical. Remember that copper has about 160% better thermal conductivity than aluminum. Aluminum with a copper core is also a good alternative.

You're definitely right, I should have been using larger heatsinks to begins with, I have already decided that my next blue build I'll have lifetime make me a bigger copper HS, and may ultimately end up using Thermal compound as well, like I should have done from the start. I learned my lesson when I build that pltb450b laser and didn't use any compound or copper at all, it gets warm fast!

 

[GSS]

Richie, good point on avoiding moister on the lens
Did you put the acrylic lens on the Sci Fi build? It can't be holding up to 5 minutes?

 

[BobMc]

Thanks, I always thought of using a small fan like you said. I probably wouldn't do it if I was using a G2 just in case the moisture gets on the lens then heats up and leaves a water spot when evaporates. Acrylics are much cheaper funny how I'm a little shocked that I'm getting 1220mw out of my Sci-fi 501b with an acrylic.

Yes, good call about the moisture. But curious, would the heat in the beam keep the moisture away from the lens? It's a question I wouldn't want to take a chance on. Just curious. Better safe than sorry though.

1220 out of a acrylic, not bad. what are you getting out of it with the g2?

 

[Benm]

I guess the best thing you can do is buy hosts with large heat sinks to begin with. Fins will also help, but are not always practical. Remember that copper has about 160% better thermal conductivity than aluminum. Aluminum with a copper core is also a good alternative.

The thermal conductivity is only relevant when it is the limiting factor.

When heatsinking hobby lasers the limiting factor usually is coupling between the unit itself and the air around it, where the fins, fans and such come in.

Using copper can be useful around the diode itself, for example by using an copper 'aixiz module' to mount the laser, and then fit that into a heatsink. After that it makes little difference if the actual big heatsink is copper or aluminium, apart from some electrochemical problems in damp environments.

The reason things like copper heat spreaders and heatpipes are used on things like cpu's and gpu's is that the heat comes from a very small area, and you want to transfer that to a large area efficiently.

Something similar happens in high power laser diodes in small packages (5.6mm or even smaller).

One other thing to be noticed is that copper is superior for heatsinking if you count it by volume. If you count it by volume, aluminium is superior. That's to say that if you had to keep the weight for a heatsink too 100 grams, it would be better to construct it out of aluminium as it would be much bigger and hav a larger surface area.

 

[paul1598419]

We're not talking about heat sinks so large on handheld lasers that weight becomes a limiting factor either. In every case, copper is superior to aluminum in this respect. Adding fans and other active cooling devices to handheld lasers is also not practical. This leaves fins as your only real option. That is where I believe I've said that a copper core inside an aluminum heat sink is a good alternative. If you live in an area where the outside temperature reaches over 105 degrees F, you will have to learn to deal with it. I did make some small pocket 532nm lasers that ran off a single Li-ion battery and had a fan to actively move heat away, but that was several years ago and even though they had an unlimited duty cycle, it wouldn't be practical for the high power diodes we use today.

 

[RedCowboy]

These commercial round finned sinks I buy and repurpose often have additional surface area multiplication in the form or little triangles that increase the length of the surface area because every bit of area is a heat vehicle to the surrounding air, there are also calculations as to fin spacing and what is most efficient for stationary air or moving air so it's easy to buy the ones made for stationary air use.

A larger heat sink finned or not is worth it if you enjoy runtime, it doesn't have to be huge, the hosts that eughmeus used to make from solid bar stock would be really nice.

 

[Benm]

There is quite a bit of science in heatsinking really.

If cost nor weight are of any concern, and you just want to get the lowest K/W figure for a given size, using copper is probably the best way to go - provided you put a good emissive layer on that copper.

In reality this is fairly different. For one the emissive coating on aluminium can be done by anodisation, yielding a very durable black layer.

Look any consumer product that has a heatsink: it always is aluminium. Even in things that could easily sell for a price using a copper heatsink, the bulk of the heatsink is aluminium. Even in things that are very expensive like premium laptop computers the acutal heatsink is aluminium, though copper walled heatpipes are used to spread the heat from cpu and gpu to that heatsink.

This has to do with weight concerns: An equallt size heatsink made from copper is 3 times heaver that that made of aluminium.

You could do something like a macbook with full copper heatsinking in copper instead of aluminium, which would run a few percent faster, but weights a fuckton or two extra for that performance gain. Such a product will not sell.

 

[GSS]

I'm still curious if you are sure your using a acrylic lens?
5 minutes run at one point.

 

[Richie89]

Richie, good point on avoiding moister on the lens
Did you put the acrylic lens on the Sci Fi build? It can't be holding up to 5 minutes?

Yeah I actually put the Acrylic on the sci-fi because I wanted to use the 3 Element for something else, it's actually my fault I don't have many lenses because everytime I buy a diode in module from DTR I always opt for no lens to save a little money, but I can't do that forever, definitely don't wanna have 20 laser builds and only like 3 or 4 lenses lol! But yeah somehow the lens held up it's actually just the surrounding area around the lens that the spring touches that melted a tad bit. If I do this again outside I'll probably end up puting the 3E back on it.
I'll see if I can't get a picture of the actual lens, as far as I know it's acrylic, is that the one that comes with DTRs no lens option?

Yes, good call about the moisture. But curious, would the heat in the beam keep the moisture away from the lens? It's a question I wouldn't want to take a chance on. Just curious. Better safe than sorry though.

1220 out of a acrylic, not bad. what are you getting out of it with the g2?

You're probably right to be honest, I imagine it won't since I think the beam itself doesn't actually carry thermal heat, I believe since water vapor doesn't absorb energy very well since it's transparent than the water or moisture will just fall onto the lens. This was an experiment I tried a long time ago to show that laser beams itself only carry energy in the form of Electromagnetic Radiation at high concentration not actually thermal energy, the test I did was that I have two lasers almost very close in output 638nm and 445nm and the blue 445nm will burn you very bad if your hand stays in the beam for a couple seconds, but when you put your hand in the beam of a 638nm at almost the same power for the same time no burn at all. In fact you could almost leave your hand there all day and it won't really burn. So my conclusion was that if laser beams actually carried Thermal heat than you wouldn't be able to do this because they would both burn your hand equally.
I also haven't tried a G2 yet

These commercial round finned sinks I buy and repurpose often have additional surface area multiplication in the form or little triangles that increase the length of the surface area because every bit of area is a heat vehicle to the surrounding air, there are also calculations as to fin spacing and what is most efficient for stationary air or moving air so it's easy to buy the ones made for stationary air use.

A larger heat sink finned or not is worth it if you enjoy runtime, it doesn't have to be huge, the hosts that eughmeus used to make from solid bar stock would be really nice.

Whoa! Yeah that definitely makes sense. Nice fins though.

 

[BobMc]

You're probably right to be honest, I imagine it won't since I think the beam itself doesn't actually carry thermal heat, I believe since water vapor doesn't absorb energy very well since it's transparent than the water or moisture will just fall onto the lens. This was an experiment I tried a long time ago to show that laser beams itself only carry energy in the form of Electromagnetic Radiation at high concentration not actually thermal energy, the test I did was that I have two lasers almost very close in output 638nm and 445nm and the blue 445nm will burn you very bad if your hand stays in the beam for a couple seconds, but when you put your hand in the beam of a 638nm at almost the same power for the same time no burn at all. In fact you could almost leave your hand there all day and it won't really burn. So my conclusion was that if laser beams actually carried Thermal heat than you wouldn't be able to do this because they would both burn your hand equally.
I also haven't tried a G2 yet?

Now you got me really scratching my head. If the beam itself doesn't carry thermo energy. How come it doesn't matter ( within reason ) how far the laser is away from the thermo sensor of a LPM. I mean you can get a reading at 2" to 12" even more. So the energy would have to be in the beam itself. :thinking:

The 638nm is inherently weaker at the same power level as a 445nm because as far as I know the lower (smaller) the wavelength is the better burner it is. That's why a 1watt 405 is one of the best burner pre wattage there is. Please correct me if I'm mistaken? Thanks

 

[RedCowboy]

You have more bandwidth, that is more wave fronts per given unit of measure with 405nm than 660nm, the number you know is the distance between waves, so like an impact hammer the 405 is running faster than the 660, the 405 is the higher frequency even though it's a lower number.

I calculated how many waves per second that is and it's a number with an exponent, just incredible.

Air consumes some energy, it's not like a vacuum, the beam you see is energy that won't get to the target.

On a foggy night or in heavy smoke a visible laser beam can be mostly consumed before it reaches even a close target 50 feet away.

 

[paul1598419]

Actually, when talking about the power of a laser a watt is a watt, regardless of the wavelength, period. If you feel one over the other it is most likely because the two have very different profiles. The smaller the profile in the same power, the greater the energy density of the beam. This is independent of the wavelength.

 

[BobMc]

You have more bandwidth, that is more wave fronts per given unit of measure with 405nm than 660nm, the number you know is the distance between waves, so like an impact hammer the 405 is running faster than the 660, the 405 is the higher frequency even though it's a lower number.

I calculated how many waves per second that is and it's a number with an exponent, just incredible.

Air consumes some energy, it's not like a vacuum, the beam you see is energy that won't get to the target.

On a foggy night or in heavy smoke a visible laser beam can be mostly consumed before it reaches even a close target 50 feet away.

Actually, when talking about the power of a laser a watt is a watt, regardless of the wavelength, period. If you feel one over the other it is most likely because the two have very different profiles. The smaller the profile in the same power, the greater the energy density of the beam. This is independent of the wavelength.

Thanks for the explanations. Does that mean that it is correct, that the shorter or lower wavelengths burn better because of that reason?