Luxar Cooling Optics Gallery

Cooling

Again, ebay comes to the rescue. I have secured a device that was orginally made by Bernard. See: this link

It has the following specs: 

Stainless Steel Coolant Circulator 115/230v operation.
Seamless Stainless Steel Tank 
10,000 BTU/Hour 
1.8 gpm @50 psi. 
2 Gallon Capacity Standard Vane Type pump.
This is good because 10000 BTU/hour = 2,900 watts which should be more than sufficient for the laser.
Here is a diagram (pdf) of the cooler.

Regarding the cooler. Go to Home Depot and buy the necesary connections. In the air compressor section of HD I found an air compressor hose with threaded ends. I bought some other parts that I'll describe.

Connection to the cooler. Remove the brass ends that come with the cooler. Cut the air hose from HD in half, this leaves two hoses each with a male threaded end and one with a cut end. Attach to the male threaded end of the hose a fitting a female counter part that then goes to an end that fits inside of the cooler hose. Connect to cooler hose using a beloved hose clamp.

Connection to laser. See picture. I drew the hose clamps really badly and it doesn show that the stainless tubes can still just sit in there mounting plate but there is a plate that holds down the stainless steel tubing on the laser that is held on with phillups screws and thermal grease. Take out the screws, and gently pry the plate away from laser housing. This allows you to remove the plastic hoosy jiggies from the open ends of the stainless tubes. Leave the u-turn side of the stainless steel cooling unit alone, leave the plastic hoosy jiggies on that side alone. Cut 5 inch lengths of hose from your air hose, and attach with hose clamps to open side of laser cooling stainless steel tubes. Then plunk sections of copper tubing into the ends of the hose, attach with hose clamps. These are useful so you can "quick" disconnect the laser, and avoid having really long hoses connected directly to that unit.

If doing it again I would also not get an air compressor hose. I later found nylon reinforced tubing in the plumbing section of HD that would have worked just as well.

While at HD I also bought two digital outdoor thermometers. These have detectors on wires, I electrical taped one sensor to each copper tube coming off the laser. These served to monitor the temperature of the laser which was really helpful.

I fired up the cooler, checked for leaks, avoided spraying my power supply with water, that sort of thing.

The laser was connected to a 24 volt power supply and pointed at a brick. The laser produced a bright white spot on the laser where you are essentially making a little spot of glass on the brick.

The temp of the system started at 20 degrees (all measurements in celsius) which was below ambient temp because I filled it with cold water from the tap. As it ran for a while the temp went to 25 degrees the intensity of the beam clearly went down. The problem is that after 10 minutes the laser gets up to about 35 degrees and then the power goes to nearly zero.The temperature difference on the input and output ends of the cooling system was never greater than 1 degree. This is great and indicates that the laser is not heating the hell out of the water.

Applying Cold Plates

Hooking up the cooling blocks. I purchased cold plates that were manufactured by www.lytron.com. Here's some other stuff that's at their site.
The blocks originally were 3.5 inches wide, and I cut them narrower so I'd be able to wrap them around the laser head. They were applied to the block using large 4 inch diameter hose clamps. This modification required that I remove the old power supply and place it on a plate that occupies a single side of the head. I filled a trash can with 65 pounds of ice. The pump from the Bernard cooler was disconnected from its resevoir and the pump was used circulate the ice water.

This is your laser: This is your laser on cooling:
How'd it perform. A themperature probe was mounted on the side of the laser head. I circulated the icewater prior to starting. It read 6.2 degrees C. The laser was pointed at a thermocouple from a high temperature oven. When the laser was first fired up there was a way hot white light visible using the brickometer, and the meter connected to the thermocouple read 610 degrees. The laser ran for about 10 minutes and the temp went up to 10.9 degrees. At this stage the laser beam power dimished to about 50% according to the brickometer. When I pointed it at the thermocouple it read a dissappointing 350 degrees. After I shut the laser down and left the chiller on, the temperature of the laser head went to 6 degrees.

Idle speculation Who freakin' knows? It may not be that the machine is getting too hot, per se, me thinks the laser head is bending due to inequal thermal expansion. The are three sides of the laser head that're getting cool, but one side that has the power supply gets pretty warm. Life'd be fine if when the laser starts running its at 40 watts and then when all elements reach equilibrium its runs at 20, but this seems pretty unlikely. I think what would be swell idea would be too send this thing to the landfill and start over.

Another approach

Its called pulse width modulation. Like duh, thats what the board on the luxar is for. I hung a signal generator on the input of the laser, set it on 1200 hertz. I used the stock cooling pipes on the laser and ran cold water in from the house plumbing. I pointed the laser at the brickometer and let it run for 50 minutes. The system seemed to be cooking along, but dropped maybe down to 50% of the original intensity. After ten minutes. The good news is it looks like it can run at the lower level continuously.



Here's a circuit diagram that'll make a PWM circuit. It has a huge white border so its really hard to read, but if you put it in software that allows you to blow it up its readable.