Hey John,
I'd be interested in the answer to this question as well. If you're running the PWM power supply from lightobject (
http://www.lightobject.com/40W-PWM-CO2- ... y-P71.aspx), the specs are as follows:
Power: 40Watt
Triggering Voltage: 25KV
Operating Voltage: 22KV
Current: 18~20mA
according to the specs for the replacement lightobject sells, the tube specs for the k40 are:
Power: 40W (45W peak)
Triggering Voltage: 20KV
Operating Voltage: 15KV
Current: 16~18mA.
It seems to me that the power supply is not designed for a 40w laser, per se. It falls into the correct power output range for one, and therefore is appropriate to use, but can, if set incorrectly, overpower the tube.
If the power supply puts out 18-20mA, 90% would never be over 18mA. However, 90% puts it at about 19.8KV operating voltage, and the tube is rated at only 15KV operating voltage, but in that particular set up we still only have aprox. 34 watts. We've set ours to 68% max (15KV is 68% of 22KV), just to stay safe. The problem with this set up is that we're actually only getting 19.5 watts out of a 40 watt machine.
This is the part I have no real understanding of. I can do the math and figure out what the numbers are, but I don't really know what they mean. My knowledge of electronics is pretty limited. So maybe someone can take the info I've put out and make a good analysis of it and what it means for adjusting the power to operate safely and get the best performance out of the machine.