Cheap Chinese Laser Power Supply Replacement Issues

[Jason Loman]

Hello everyone! I found this forum several months ago and I found it pretty helpful after I bought my chinese laser. However I haven't seen any posts that pertain to the issue i'm having. Hopefully someone here has had this experience and knows what to do.

1. My wife and I purchased our cheap chinese 60w CO2 laser off ebay in April of 2017. We've used it for all kinds of things, metal marking, wood and acrylic engraving, its really been a fun tool.
2. About 2 weeks ago the power supply blew an internal fuse and the power supply fan would not run. At first I hoped it was just a fuse so I ordered those.
3. A job came in that I really wanted to complete, to speed things up i jumpered the fuse with a single strand of small gauge speaker wire. Instant sparks. The power supply was definitely bad.
4. I ordered a 60w CO2 laser power supply off of ebay for $130 and it arrived yesterday. After I installed it i turned on the laser and fired a test pulse. All was good, or so i thought.
5. I immediately (my mistake) began to work on a job i had waiting and the laser did some funny things. The jobs sequences were all in scan mode, keep that in mind as you read the symptoms please:
a. the scanning reserse interval (in RDworks) appeared to be way off, but the compensation factors had not changed. Why would a new power supply change the overrun compensation factors?
6. I immediately began to troubleshoot the issue. I changed the pulse frequency from 20khz (factory setting) to 1khz hoping that maybe the old power supply died because of an excessive frequency setting and perhaps the new power supply simply wouldn't tolerate the high frequency. This didn't change anything.
6. At less than 80% power the laser would not fire at the job speed rate (500 mm/sec).
7. When switching to cut (vector) mode the laser seems to work fine, no issues. In fact it seems to be working too fine. With the last power supply the laser required 2mm/sec and 100% power to cut through this particular piece of acrylic (.250" cast sheet). Now it will happily cut through the same piece of acrylic at 5mm/sec, perhaps faster (i haven't tried yet).
8. At low scan speeds the power supply appears to function fine (albeit with the messed up overrun compensation factors).

My theory is that for some reason there is a delay between the point the software tells the power supply to energize, and the point the tube fires, but I don't understand why a new power supply would do this.
I can't reconcile my theory with the cut operation. If the power supply isn't firing the tube in a timely manner, why does the cut operation work fine?
I have not adjusted any settings on the power supply, perhaps I need to but i'm unsure how. Has anyone seen symptoms like this? What did you do to fix it?

Thanks,
Jason

[Bill George]

Memo, stop shopping on Ebay If your planning to run a business. Lots of USA venders with support. It could be as simple as do you have the PS set to 120 volts or do you have another bad PS or the wrong one?

[Dave Sheldrake]

6. I immediately began to troubleshoot the issue. I changed the pulse frequency from 20khz (factory setting) to 1khz hoping that maybe the old power supply died because of an excessive frequency setting and perhaps the new power supply simply wouldn't tolerate the high frequency. This didn't change anything.

baaaaaaadddddd move, leave the frequency setting alone pretty complex reasoning behind it but it never ends well messing with DC tube base frequencies unless you have the right system and tubes to do so.

Check the residual current at the negative end of the tube with an inline ammeter (set to mA) you may very well be cooking your tube with that new PSU unless you know it is firing within a safe margin

[Jeff Body]

60 watt ebay laser really means a 40 watt tube and power supply that can peak at 60 watts for a fraction of a second.

If you ended up buying a real 60 watt PS then you're throwing alot more power at your tube. That could be the reason you're cutting fast. Good news is you'll cut faster - Bad news is you'll cook your tube alot faster.

[Clark Pace]

My goto is lightobject for severl parts

[Bill George]

60 watt ebay laser really means a 40 watt tube and power supply that can peak at 60 watts for a fraction of a second.

If you ended up buying a real 60 watt PS then you're throwing alot more power at your tube. That could be the reason you're cutting fast. Good news is you'll cut faster - Bad news is you'll cook your tube alot faster.

A quick way to find out for the OP is measure the Installed tube and convert into mm if needed. Dave Sheldrake posted here and other published reliable sources have the information to tell you some many mm's equal X watts.

[Mike Lysov]

What you need to do is to check how much current is going to your tube. It may be that the new PS is going with more/less current than it should be and all your previous tube power percentage is way off for the new PS.

[Jason Loman]

Thanks for the advice guys. I'll measure the tube and figure out how many watts its supposed to be. I'm still a little confused though. Why would the cut parameters work like normal and the scan parameters don't though? The power supply should just switch on and off according to the program. Its ramp rate should be constant, shouldn't it?

[Jason Loman]

i'm getting 22 mA at 99.9%. From what I understand it should be set at 30 mA, correct?

[Dave Sheldrake]

22mA is going to fry a real 60 watt tube

Try 15 MAX, 22 is the top line for a narrow body 80 watt, given your 60 is likely to be a long 40-45 even more so,

at 50/55mm diameter tubes run

40 watt 850mm
50 watt 1050mm
60 watt 1240mm
80 watt 1450mm

30mA is the typical run current for a 150 watt wide body

[Bill George]

IF the OP really wants to solve his problem, go to either LightObject dot com or Rabbit Laser USA and get the proper tube and matching power supply. Yes you will pay 2x or so more for one that Works.... key word Works. Why will it not engrave now but cut just fine? Its more than likely the cheap power supply can not cycle fast enough to engrave and/or your tube is now bad.

[Jason Loman]

The tube diameter is 50mm and the length is 810mm (or there abouts, i couldn't find my tape measure so I had to use a ruler end to end). It would appear this is not a 60 watt tube. Should I tune the power supply down to 15 mA, or even further?

[Bill George]

The tube diameter is 50mm and the length is 810mm (or there abouts, i couldn't find my tape measure so I had to use a ruler end to end). It would appear this is not a 60 watt tube. Should I tune the power supply down to 15 mA, or even further?

Its more than likely a 30 or 40 watt tube that had been over fired perhaps to the point it damaged the both tube and power supply. What was the part number of the old power supply?

[Dave Sheldrake]

@ 810mm its a 35 watt, no more than 12-13 mA for that