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Thread: Sudden drop in power/milliamps

  1. #1

    Sudden drop in power/milliamps

    Here's a baffling one. I have an 80 watt Gweike LC6090. I have had it for a number of years and replaced the power supply once along the way. In that instance I saw a gradual drop in power output over time.

    This weekend however I had the laser up and running and it was performing just fine however the main door/top was out of alignment, the hinges had loosened over time and the door was scraping against the one inner side when I tried to shut it. I stopped to remove the door and re-align the hinges and then put the door back on. The door/lid now opens and closes just fine, problem solved.
    However, when I start the machine back up, all of a sudden the power output has dropped by a half. I usually cut with it running at 20 milliamps however when I started to run a file that had been running just fine a half hour earlier the output is down to 10 milliamps. Running a few tests I can see that I can get the power up by doubling the power setting in the software but clearly I don't want to run it that way, something is still very wrong.
    I am at a loss as to how these two events could be related, fixing the door and the power drop and yet the timing of the two is so related that I am struggling to pass it off as coincidence as well. I am open to any suggestions as to what may have happened.
    Also, if anyone knows of any good tutorials on debugging power issues I'd be grateful for a link.

    Cheers
    Greg

  2. #2

    Debugging

    Thought I'd try to debug possible issues in the power chain. Following this rudimentary but helpful sequence: https://www.youtube.com/watch?v=zwXY7Yy_sV0 I got to the step of testing the power supply output with the big resistor in place of the tube:
    IMG_8123.jpg
    IMG_8124.jpg
    IMG_8122.jpg
    As you can see in the third image I am getting 15 mA which I believe is about half of what it should be. This is consistent with what I am seeing when I run a file, the power setting assigned in the job which usually gets 20 mA of power to the cut is only getting 10 mA.
    Anyone have any idea of what could cause the power to drop suddenly by half? I've seen a slow decline before with a gradually failing power supply but not such a sudden drop.
    This is the second power supply that I have gone through with pretty light usage of the machine (I am not a professional). Any idea what could be causing this? Should I be looking at a better PS, the two I have used were the two that came with the cutter upon purchase.
    Last edited by Greg Fowler; 08-20-2021 at 12:19 PM.

  3. #3
    I know jack about Chinese DC-laser power supplies, but I AM aware of the fact that RF "metal" laser power supplies, the ones incorporated as part of the laser tube itself, have 2 capacitors that supply power to the laser, and that should one of these capacitors go bad, the laser WILL continue to fire, but at half the power. My BIL who works for me has his own Gravograph LS800 40w laser, and he blew one of the capacitors several years ago. The laser to this day continues to work fine, but his max output was measured by our machine rep at 21 watts, exactly half what it should be-

    I'm not sure WHY an RF laser uses 2 capacitors, but it may be that these Chinese power supplies do too, and it would explain the exactly-half output you're getting...
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
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  4. #4
    Thanks Kev, that explanation certainly fits the "exact half" behaviour I am seeing. I've ordered a new power supply to get things up and running but it seems worth it to also crack the old one open and see if there are a pair of capacitors in there that I can take a measurement off of. If I can repair it I'd keep it as a backup.

    Still can figure out how fixing the door fits into the equation...

  5. #5
    coincidence

    example: years ago decided to change the carburetor on my '56 Ford pickup truck. The truck ran like crap. I proceeded to adjust, several times, the fueling of the 'new' carb (from a boat). Ran the same, or got worse. Several days later I decided to give up and put the old carb back on. And it still ran like crap...?? After a few days of 'hunt-n-peck' troubleshooting I eventually changed out the spark plug wires. Voila! Ran perfectly!

    Don't ask me why the spark plug wires decided to go south at the exact same time I changed the carbs, but this is just one of MANY such incidences in my life where fixing one thing 'caused' something else to go bad-but in reality it didn't-has happened. For a long time now I've given 'the coincidence theory' top priority when such stuff happens

    Probably an offshoot of the 'everything happens in three's' theory
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  6. #6
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    I would check ALL of the connections. Sounds like you might have a loose connection somewhere. And it might be inside the power supply. I'd bet you dropped the lid, banged on it a bit and something came loose. Might be solder connection that was really poorly done and it just gave way. Ain't a coincidence, those don't happen. Kev probably pulled on one of those plug wires and broke it.
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  7. #7
    The plot thickens. Received my new power supply and hooked it up and... the exact problem persists.
    So, what I think I know so far:
    1) I removed the tube from the signal chain using the large resistor that came with my cutter and I tested, the problem persisted so I reason that the problem is not the tube.
    2) I changed out the power supply and the problem persists (both with the tube in the circuit and with the big resistor in the circuit) so I reason that the problem is not the power supply.
    3) I have opened all panels and done a visual inspection of wired connections and cannot see anything obvious. Still, could be this.
    So what else is in the laser power circuit? I noticed that the controller readout panel has a few lines missing from the text:
    IMG_8243.jpg
    Would it make any sense for this problem to be coming from a compromised controller?

  8. #8
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    No telling about your controller, but your test resister showed only half output. And the controller isn't being used. So it still seems like controller, but it isn't. Could it be wiring between power supply and the laser tube? Check that wiring well.
    Woodworking, Old Tools and Shooting
    Ray Fine RF-1390 Laser Ray Fine 20watt Fiber Laser
    SFX 50 Watt Fiber Laser
    PM2000, Delta BS, Delta sander, Powermatic 50 jointer,
    Powermatic 100-12 planer, Rockwell 15-126 radial drill press
    Rockwell 46-450 lathe, and 2 Walker Turner RA1100 radial saws
    Jet JWS18, bandsaw Carbide Create CNC, RIA 22TCM 1911s and others

  9. #9
    Have you considered the possibility that the problem is your mA meter-?
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  10. #10
    No, not even for a moment. What I am seeing on the meter is reflecting the power drop that I am seeing in terms of the laser output power. Are you saying that a faulty meter could actually be knocking the laser power down? I wasnít imagining that it would be able to do that (but i canít say i understand the laser circuit enough to say otherwise).

  11. #11
    I haven't a clue to be honest, but I've seen stranger things when the flow of electricity is involved, and the meter IS in the loop...
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


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