Minimum power needed to fire laser increasing

Hi experts,

I recently received my Chinese RedSail 100W CO2 laser, with RuiDa RDC6445G controller. It’s hooked up to a CW5000 chiller.

The day I unpacked it I tested it with the POWER and PULSE buttons and it needed 11% power to make a mark on wood. As I was doing my first material tests a couple of days later I noticed it needed a minimum of 14% power to make a mark. Now a week later I notice the minimum power required is 24%.

I’ve always used it with the chiller connected and running. I’ve never exceeded 24mA to the tube (which is around 65%).

Can someone suggest to me what might be going wrong? Am I doing something I shouldn’t be, or do I need to chase this up with the seller in China?

Cheers all,


Hi Mark,

have you checked that your mirrors and lens are clean? Usually if that happens to me it is a reminder to myself to check my mirrors and my lens if they got some dirt on them.

Furthermore the circumstances of your tests are important as well. A fresh tube that hasn’t been used for a couple of hours has more power for the first few minutes. Especially the cheap china ones. So if you have run your tube for quite awhile and do your test shots afterwards without granting your tube some time to rest then it is quite normal that you would need more power to get the same mark as before. But that would only be within a very small range and certainly not between 11% and 24%.

Good luck and cheers,

Thanks for that Brian. It’s a brand new machine, but even so I’ve waved some acetone at the optics for good measure.

On closer inspection I noticed that the HV PSU is smaller than visually similar 100W power supplies on eBay. I wriggled my phone camera underneath and, lo and behold, my 100W tube is being driven by an 80W PSU.

My best guess is that the PSU is being overdriven to provide the ignition voltage for the tube. That would probably explain why all was good until I started doing engraving tests with multiple ignition strikes per second. I can’t find a spec sheet for the PSU, though, so I don’t know for sure.

Have you had any experience with mismatched HV PSUs and tubes? I don’t mind so much if the PSU is cooked, but I’m going to be upset if the tube is damaged.

I have a red and black 60 watt that had a 50 watt supply in it. It fried several months after I received it, and I replaced it with a 60 watt supply of better quality. It has been working fine ever since.

It sounds sad and understandable to mount a PSU that is 20% below the required value. I will advertise immediately and make it very clear to the seller that I expect to be sent the correct power supply as soon as possible.
good luck