Hi All,
It was a hot summer, and I found that my 50W laser's power would drop over the course of a few hours run due to temperature rise of the cooling water. It seemed to struggle to get through the same 6mm ply that was cutting like butter when it started, and was highly dependent on the temperature of the cooling water. I'd like someday to determine power vs temperature, but I don't have the ability to do it now.
For a few months, I used ice or blue ice blocks in the 4 gallon reservoir to cool it down. Worked great at keeping the power up but was tedious in swapping out blocks or adding ice. A chiller was needed - and not a radiative like the '3000, because my work area was also pretty hot. I needed an actual compressor chiller. I could not find clear advice on sizing, etc, so I looked up the calculations and here are my notes from reading up on chillers, and my own estimates of chiller sizing. If nothing else, it will be useful to me to have written down somewhere.
At full power, I see ~500W used by the laser. Probably 400-450W to the tube supply, and the other 50W to the fan, motors, etc. At 85% efficiency I estimate ~375-400W is delivered to the tube, of which 300-350W is heat and the rest as laser output.
Let's call it 350W heat that must be removed. At 0.293 Watts per BTU/H, this means that I need about 1200BTU/h cooling capacity to keep the water at a constant temp. More BTU's and I can make it colder, less and the temperature will still climb but will climb slower than having no chiller at all.
This puts me above the 1/10HP (~900-1000 BTU) range, but below the 1/4 HP range (~2300-2500 BTU/hr). But as luck would have it, I found a "new" Active-Aqua 1/4HP chiller and figured what the hell. I bought it. Sadly, the unit was a lemon as shown by a simple test, so it's going back to the seller. But.. I learned some valuable information that may be useful to you guys while checking it.
With water circulating, and laser off I ran the chiller for about a half hour while using a meter to plot the temperature in the 4 gallon reservoir every minute. Here's what I got. Sorry for Fahrenheit scale, US chillers are all in BTU which relies on degrees F.
Attachment 293516
The water is cooling consistently at about 0.6F/minute, or 36F/hr. The reservoir size is 4 gallons, which equals 4 * 8.33 => 33.3 pounds of water. So 33.3 pounds of water * 36F/hr => about 1200BTU/hr cooling capability. This is far below the rating for a 1/4HP unit! I should have been dropping the temperature of 4 gallons of water at about twice the rate that I did. An actual 2300BTU/hr chiller would have given me -1.15F/min without the external heat load of the laser tube. This chiller would barely keep up with the laser's heat output, when it should be able to do nearly double the cooling that it is doing.
So valuable lesson, folks. It might be worthwhile to check your chiller to see if it's in spec! I probably just got a bum unit, but had I never sat down and mathed it out I would have never known. I will replace this one with a 2000 BTU/hr unit and see how that goes.