Re: FS: >110mW Blu-Rays - available
You mean heat
sink...
The aluminum heatsink/module is 18mm in diameter and 27mm long. The bottom part has threads on the outside, allowing it to screw directly into the head, and form thermal pathways into the host, which is by itself quite massive aluminum.
It's more than enough for the PHR diode, because it doesn't create much heat by itself.
And i have to be sure of it, as i give a warranty on the diode as well...
I set my personal/experimental lasers much higher, than the >110mW units. I did many tests at 160mA and even at 190mA, and it takes the laser 60 minutes to reach body temperature.
People usually use the laser for two minutes at a time, but five is fine as well.. Even if you get so hypnotised by the beam, that you forget about time, and leave it on for 10 minutes, it wouldn't be bad. The diode never even gets close to it's rated operating temperature.
At the power levels i usually set them to, they don't even get luke warm during normal use. After about 15-20 minutes you could start feeling a hint of warmth. But they are usually not used that long..
The same build can easily keep cool an open can at 420mA! My 6x diode at 197mA creates almost as much heat as an open can, but doesn't overheat, even when i use it for up to 15 minutes at once at night. If there wasn't enough heatsinking, i wouldn't dare put such an expensive diode into this build (it cost me $350).
There is one thing people usually don't realize about heatsinking.
In the usual approach with a linear driver, the diode is not the only source of heat. It's not even the main source of heat. The heatsink has to be so big, not because of the diode, but more so, because you need to prevent the driver from overheating the diode. You need over three times as much heatsinking when using a linear driver, as you would, if you only had to cool the diode.
Let me give you an example..
- An open can diode, with a 317 driver, set to do 300mW:
You have to give the driver two Li-Ions, which is 8.4V when full. The laser will draw 420mA. So you have power going into the driver = 8.4V x 0.42A = 3.53W
The open can only gets ~3V and 420mA from the driver, which makes power coming out of the driver = 3V x 0.42A = 1.26W.
What this means is, when the batteries are full, the driver pulls 3.53W, but puts out only 1.26W.. The difference is converted to heat. 2.27W of heat, before the power ever even comes to the diode!
The diode itself gets 1.26W and puts out 300mW in the form of light. 0.3W comes out, so the difference - 0.96W - is converted to heat.
The total heat of the system is 0.96W + 2.27W = 3.23W.... The diode is creating less than one third of the total heat in a red laser driven by a 317 driver! 29.7% to be precise..
This is the worst case scenario on full batteries, and as their voltage drops, it slowly gets a little better, but you have to take the worst case into account, otherwise you cook the diode a little, every time you recharge the batteries.
I use a high efficiency constant current boost driver for my blu rays.. It operates at almost 90% efficiency, so it doesn't really contribute much to the total heat. It never even gets warm by itself. The diode is pretty much the only source of heat in such a setup.
For example..
- The same open can with a highly efficient buck/boost driver:
The diode converts 0.96W to heat (calculated above).
The driver puts out 1.26W, and since it operates at 90% efficiency, this means it pulls 1.4W from the battery. The difference is 0.14W, which gets converted to heat..
The total heat created by the system in this case, is only 1.1W. That's slightly over a third of what it would create with a linear driver.. 34% to be precise.
If you compare just the drivers, the high efficiency driver creates only 6-7% of the heat a linear driver produces!
To compare this with the blu rays...
- A 6x blu ray writer diode at 197mA, doing 203mW:
The diode gets 1W and puts out 200mW, so it converts 0.8W to heat. The driver creates 0.11W, so the total heat is 0.91W.
- A PHR blu ray diode at 160mA: The laser creates 0.82W of heat together with the driver.
- A PHR diode set to the usual power level (>110mW): Only 0.626W of power converted to heat.
Basically, what this means is, if you replace a linear driver with a high efficiency switching driver, you can get the same results with one third of the heatsinking, because then, you only have to take care of the diode.
To test the heatsinking under harder conditions, i made a red laser in the same size host but with slightly less heatsinking (thinner host).
I used two 1/2AA size Li-Ions, and a linear driver. It is set to 350mA and puts out 220mW. The total power converted to heat by the laser is 2.72W (slightly over four times the heat created by a >110mW blu ray)..
It takes it 3.5 minutes, to reach body temperature. This means, that the heatsinking is actually still sufficient for 2-3 minutes of use, even in such a low efficiency setup, but it takes a while for it to cool down afterwards.
So, as you can see, the heatsinking on my blu rays has a quite large safety margin. You don't really have to worry about a duty cycle, when using it.
It probably shouldn't be left on unattended, but you also don't have to look at a stop watch, while using it..
