Announcement

Collapse
No announcement yet.

Another laser, this one is a little crunchy.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Another laser, this one is a little crunchy.

    I picked up a Rofin CO2 laser condition unknown today. Its a 300W unit that has a head and a separate power supply. the head is connected to the power supply with a big 7/16 style RF cable and a DB25 for signals and control. Looking at the manual I saw that the power supply is composed of three individual 48v power supplies which are in series so thinking I could rewire it to run off single phase, just parallel the power supplies.

    So I took off the back cover when the smell hit me in the face, a strong chlorine smell. And then I noticed that the insides where covered with a brown stain. NOT GOOD

    IMG_1583 by Jerry Biehler, on Flickr

    I disconnected the in and out leads and slid the power supply out. Top cover has more of the staining so ti was definite coming from there. I popped off the cover to find this:

    IMG_1589 by Jerry Biehler, on Flickr

    IMG_1587 by Jerry Biehler, on Flickr

    One of the output inductors is totally fried. So two things I notice, one, it is not three individual power supply like the manual shows, it is one giant 48v power supply with rep output transformers with he primaries in series and the secondaries in parallel after rectification. All driven by a mosfet h-bridge. The mosfet drive board can be seen at the top center above with the fan which has seen better days. Second thing is that other than the smoke the damage is limited to the output inductor, the hall current sensor, and the fan.

    But why only one inductor fry? The transformers are in series so if one dies they both will die so the load can't become uneven that way, if the RF power supply had an issue the whole unit should have faulted out since the current sensor is on the output. I pulled the buss bar off the output of the diodes and checked them and they are all fine and also the transformers which appear to be fine, I need to grab my 34401A with the kelvin clips to check them out for sure, it is too low to measure with my hand held. Maybe a bad connection on the inductor cause a runaway heating event and just killed it?

    I think its repairable, The ferrite itself won't care about the heat, I can rewind it with suitable wire and make it match the existing one with my old LCR meter. The current sensor turns out to be a Chinese knockoff of a LEM125-P which is about $30. And the little fan is a generic 12v 40mm fan, I probably have one of those lying around someplace.

    So first thing I am going to try and clean off some of the boards, the mosfet driver is the worst since it just sucked the smoke through. Get that back together and then check out the current sensor, easy enough to test, I need to get a new connector for the ribbon cable, it melted.

    A couple more pics of the carnage, the first one is the inside of the top cover, you can see how the little fan circulated the smoke.

    IMG_1597 by Jerry Biehler, on Flickr

    Current sensor:
    IMG_1594 by Jerry Biehler, on Flickr

    Mosfet h-bridge board.

    IMG_1599 by Jerry Biehler, on Flickr

    This thing smells sooo bad.

  • #2
    Yes, curious that one of the inductors fried but not the other. Also, I'm wondering that there was not something in place to shut it down completely before things got as far as they did? For sure, a mere fuse is not a smoke detector or temperature sensor, but...
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

    Comment


    • #3
      Yeah. I just can’t understand why.

      There are temp and current sensors. There is a current sensor on the primary side so if it saw an over current condition it should have shut down.

      No temp sensors on the inductors. If I can get it to work again I might as some thermal fuses to the inductors in series with the rest of the temp interlock.

      There is someone seelling a few of these supplies on eBay. Only $3500. Lol

      one option may to be to try and rig up an external 48v supply in the place of the one in the box and interface it to the control circuitry in the PSU. I don’t think it would be too hard. I have some power supplies that would handle it.

      Comment


      • #4
        Maccona, I would look VERY carefully for a fracture in the ferrite core of the output inductor. It would be very uncommon, but it easily could cause the heating shown. Do you know the approximate frequency the inductor is filtering? The only other cause I could think of you already mentioned as being a bad connection leading to a cascade heating failure. Looking at your pictures I do not think this is likely. The reason for my thoughts is that every connection heating failure shows obvious increased damage at the end near the connection failure. Yours seems very uniform. Much more like an RF inductor failure caused by high standing wave or termination impedance issues. Disclaimer!!! I know nothing about lasers!! If I had a question I would ask YOU!! Let us know what you figure out 😀.
        Robin

        Happily working on my second million Gave up on the first

        Comment


        • #5
          Yeah. I just unwound it and there is a crack in it. I have no idea what frequency it runs at. I’m going to pull the other one out and put it on my LCR meter and see what it reads as.

          Comment


          • #6
            Long ago I had a career in laser shows, worked with big argon/krypton lasers al the time.
            The power supplies were just big DC constant current sources. Typically a 4w full color KrAr mixed gas laser was around [email protected] As the tube burned the gas the voltage would go down, then more gas was added from the attached reservoir to get back to the optimum volts vs. amps for the best color balance and power output.

            I would contact the laser tube manufacturer and find out what the operating specs are then adjust your repair hacking accordingly.

            Comment


            • #7
              This part of the power supply is just a 48v switcher, probably somewhere around 100A out, the current sensor is limited to 125a.

              The good inductor is 46uh and 110 ohms at 1khz and 5 milliohms at 10 or 100hz. I found a toroid that matches the dimensions of the old one pretty much exactly when you factor in the burnt off epoxy. I would need the 60u version to match based on the calculators.

              https://www.tme.com/Document/06fb668...S-300014-2.pdf

              I measured the wires that the inductors are wound with, 8 pieces of wire .0625" (1.6mm) thick. Works out to be about 6 awg. So I think my plan will to be get the core and some 6 awg wire and wrap it until I get the same readings.

              Comment


              • #8
                Originally posted by eric_h View Post
                Long ago I had a career in laser shows, worked with big argon/krypton lasers al the time.
                The power supplies were just big DC constant current sources. Typically a 4w full color KrAr mixed gas laser was around [email protected] As the tube burned the gas the voltage would go down, then more gas was added from the attached reservoir to get back to the optimum volts vs. amps for the best color balance and power output.

                I would contact the laser tube manufacturer and find out what the operating specs are then adjust your repair hacking accordingly.
                CO2 lasers are a bit different than ion lasers, where ion lasers have a filament and a relatively low tube voltage and high current, CO2 lasers when DC driven will run in the 10kv range and in the 10's of ma depending on design. In the case of this laser, it is RF excited. This power supply provides 48v to the RF power supply as well as handles some other power supply voltages and some IO, but I am not sure what.

                The company that made this laser, Rofin, was going out of business so Coherent bought them, then the DOJ said no and now Rofin is no more. So no support available now, i am on my own.

                Comment


                • #9
                  Does this unit have an L-C filter on the output as would be normal? The physical arrangement makes it a bit unclear. But it appears that the inductors feed the filter board, and that the third connection visible goes to the output.

                  In that case, the inductor would drop in inductance if the core cracks, and would then tend to carry a high ripple current, the power would essentially be diverted from the load to cooking the inductor. That might very seriously overheat it.

                  Depending on the protection, it's location, and the mode the SMPS is operating in, it might have worked fine, holding the current to the set level, even though the power was no longer going to the intended load.

                  How do the capacitors look? That would likely mean a lot of current through them.
                  4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                  Keep eye on ball.
                  Hashim Khan

                  Everything not impossible is compulsory

                  "There's no pleasing these serpents"......Lewis Carroll

                  Comment


                  • #10
                    Yes, the inductors are the L part of the filter, the capacitors are under that board with the resistors on standoff. The caps all look fine. There are 10 33uf foil caps in parallel, checked with my LCR and together they read 354uf. So within tolerance. In parallel with the caps are 10, 3.9k resistors, all of which I am replacing.

                    I cleaned up the Hall effect current sensor board and powered that up. One of the tag tant caps was reading 3uf instead of 10, so I will be replacing both of those, the sensor works perfectly following the current mode on one of my bench power supplies.

                    Untitled by Jerry Biehler, on Flickr

                    Comment


                    • #11
                      I think you most likely found the problem with the cracked core. It is very unusual, but it does happen. Another thing will be cleaning all the smoke out of the circuitry and off the PCB's. Grab gloves and a mask and a long playlist of good tunes 😂.
                      Robin

                      Happily working on my second million Gave up on the first

                      Comment


                      • #12
                        Those film type caps tend to have quite high current capacity (I have used similar ones that were rated at 25A each, IIRC), so I am not surprised they are OK.
                        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        "There's no pleasing these serpents"......Lewis Carroll

                        Comment


                        • #13
                          Hah, I ordered some parts cleaning brushes from amazon and will clean the board up when it arrives. I tried IPA and flux remover to get rid of the residue but it woudnt touch it. Mineral spirits does, not surprising with the vaporized PVC, epoxy, and polyolefin from the heat shrink around the inductor wiring. All the hardware will go into mineral spirits in the ultrasonic.

                          Comment


                          • #14
                            When I read the posts made by you electronic guys I am in awe! Really. You guys know ****! Macona my Polaris Ranger EV has two 48v banks of batteries. I was thinking we could mount this laser on my buggy and when unwanted bike riders come on my property I could use the laser and cut their bikes into pieces. More modern than a .50 caliber machine gun. A VR helmet for aiming and I would be good to go.

                            If you have a problem you could send your unit to A.K. Boomer. He is a pit bull when it comes to finding problems.
                            Location: The Black Forest in Germany

                            How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                            Comment


                            • #15
                              Lol. The problem is you still need 3 phase to run the power supply since it also powers stuff in the head and seems to do some io stuff. That’s why I am really hoping this fixes it.

                              I have another 150w coherent that does run off of straight 48v at 50A. But both of them are water cooled so you are going to need to bring a heat exchanger capable of handling a few kW of heat.

                              I always thought a stationary turret would be great to deal with wildlife incursions of the domesticated sort.

                              Comment

                              Working...
                              X