Laser Tube power ratings, what do they mean?

[mikest]

I'm a bit confused about various numbers I've seen stamped on the sides of laser tubes and laser power supplies.

I have a couple of large tubes for my laser cutter that are 40kV rated. That's pretty high, if I'm not mistaken. The machine came with a pair of power supplies (one was supposedly broken...) The first power supply is rated at 400W/20kV/25mA, and the second at 750W/40kV/35mA. Unfortunately, the working power supply is the lower of the two. It also has a funky interfacing cable on a DB9 (serial) style connector.

What do those numbers mean, and how does one pick the right power supply for a tube? For example, a tube stamped 40kV, is that trigger voltage or operating voltage? I'm using a power supply with a 20kV rating on a 40kV tube at the moment, it seems to work fine, but is it running half power?

I'm also trying to pick a PWM frequency. The original controller system used a 100kHz. Most systems I see use 10kHz. Does it matter up around those frequencies? Is it a dependency of the power supply or the laser tube?

Thanks!

[baccus61]

The laser tubes are just like big fluoro tubes and the longer they are the more power (voltage) you need to start the ionization process. Some power supplies will work for different length tubes but the biggest killer of a tube is the amperage that the high voltage works at.
All lasers should come with a max power setting or should be available from the manufacturers or suppliers. My 100 watt laser is rated at 32mA BUT the manufacturers say I am not supposed to go over 30mA for extended periods of time or the electrodes will discolour and reduce the operating life significantly. You can tell when a tube has been run too high for too long as the electrodes will be a blue or purplish colour.
My guess, like yours, is it's the triggering voltage.
I set my laser Max power to 80% so I can get an extended life from my tube or around 28mA. I can engrave on paper at 150mm/sec and the power set to 5% and I get a very light burn that just marks it. That's really controllable for a 100 watt laser.

Most glass laser tubes run well at 20KHz for most jobs. Some materials cut/engrave better at different frequencies than this and the settings can be 5KHz or up to your 100KHz. This is up to you to find the right settings.
I haven't found a good source for different frequencies yet but I do have a .jpg somewhere showing the frequency curve of Universal lasers. These are RF types.

I'm not sure how you can tell whether you are running at 1/2 power or not as it is also dependent on whether your tube is old and near dead or depleted. There is a test you can do to heat up water for a set period of time to test the power output but I can't remember the equation at the moment.
Rich.