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compatable MOSFETs for a Chinese Plasma Cutter

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by webacraft, Jan 28, 2010.

  1. webacraft

    webacraft New Member

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    Hi All,
    I am a 62 yr old A&P-IA and work as a machine designer in a factory that mfgs hydraulic cylinders. I design and build the machines we use to make the cylinders. My actual degree is in journalism but life experience has led me to my present job. I am fairly well versed in electrical but weak in electronics. Glad I found this site.

    A buddy gave me two Cut50D plasma cutters. One works but has a minor issue, the other has some blown MOSFETs. (WFW20N50)

    These plasma cutters are notorious for blowing the MOSFETs and they have 12 of them.

    I found thru internet research that 20N50 are used in most and Toshiba 2SK2837 are used in the better ones.

    My Question:
    I can get the 2SK2837 or 2SK2611 toshibas pretty cheap. the 2611 is rated at 900 Vdss but I have no idea what all that means. Would the 2611 work and if so could I just replace the three blown ones or should I replace all.

    Thanks in advance.
    Bill
     
  2. BrownOut

    BrownOut Banned

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    The 900 Volt VDS rating is simply a maximun voltage that may be connected to the MOSFET without damaging the device. There is typically no reason to replace working components, just replace the ones that are blown. Unless, that is, you think the 2611's are better FET's, and less likely to blow.

    Wow! You job sound pretty interesting. I'd like to see some of these macines :)
     
    Last edited: Jan 28, 2010
  3. webacraft

    webacraft New Member

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    Tell me how to attach a photo and I will send you some photos or email me at "webacraft (at)msn(dot)com"
    really like to post photo of a semi robotic "port welder" and some robot welder fixtures I designed and built.
    Thanks,
    Bill
     
  4. dave

    Dave New Member

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  5. BrownOut

    BrownOut Banned

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    Click the "Go Advanced" button, the use the paper clip at the top of the text window to start the app to insert a file. Browse to the one you want and hit "upload"
     
  6. webacraft

    webacraft New Member

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    Automated Port Welder

    This is a "port welder" I designed and built that welds the ports where the hoses attach to a hydraulic cylinder. It is programable to make multiple passes, overlap, and return to "zero" when done.
    I uses any hand held mig gun.
    It is controlled by a cheap programmable electronic counter ,Red Lion Legend, and Red Lion optical encoder.
    Bill
     

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  7. BrownOut

    BrownOut Banned

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    That's awesome Bill.
     
  8. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I work on plasma cutters as part of my business so I am familiar with your wanting to get rid of cheaper parts when rebuilding. When changing out power Mosfets IGBT's are a good replacement choice. They are far more forgiving than Mosfets when used in switching power supplies.
    I have done many power supply rebuilds with IGBT's. I prefer the International Rectifier Brand devices for most of the smaller stuff but any of the bigger manufacturing brands devices are good.

    What you would look for is a IGBT with a higher working voltage and current rating than what your Mosfets have. Then use ones designed for high speed switching. The IRF warp speed devices have always worked well for me as drop in replacements for older cheaper Mosfet systems.
    When rebuilding a power supply always change out all of the Mosfets in the switching banks.

    If each bank has three then replace all three. If there is room for more then add them as well being more switch capacity doesn't hurt anything. I have found a number of low end plasma cutter power supplies that had three or four switching devices on a bank but the circuit boards where made to hold four to six devices. I always add the extras if there is room. I also recomend building up all the switching banks to equal capacity.
     
  9. webacraft

    webacraft New Member

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    TCMTECH

    Thanks so much for the help.

    Would this one work? It is a to-247 like my wfw20N50.

    International Rectifier
    Manufacturer Part No. IRG4PC50UPBF
    UltraFast Insulated Gate Bipolar Transistor

    Marked on part: G4PC50U

    G4PC50U Specifications
    Input Type: Standard
    Voltage - Collector Emitter Breakdown (Max): 600V
    Current - Collector (Ic) (Max): 55A
    Vce(on) (Max) @ Vge, Ic: 2V @ 15V, 27A
    Power - Max: 200W
    Mounting Type: Through Hole
    Package / Case: TO-247-3 (TO-247AC, Straight Leads)
    Lead Free Status: Lead Free
    RoHS Status: RoHS Compliant

    Would I just unsolder my MOSFETs and replace with these? Do I just replace the 12 on the top board or also the ones on the bottom?

    Bill
     
  10. webacraft

    webacraft New Member

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    Point Gap On Cut50D

    I just opened the case on the other CUT50D. The one that cuts but gets OC fault. It does have the toshiba K2837 MOSFETs and none are blown.
    There are no obvious burnt areas. I did notice that it is very similar to the Simadre with basically the same boards except the Simadre has a digital read out.

    Somewhere I read that the point gap could cause issues. The point gap on the somewhat working machine is much wider than on the blown one.

    I have an older century high frequency unit and know the points have to be adjusted.

    Anyone know the correct point gap on a Cut50D?

    Thanks,
    Bill
     
  11. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Those will probably work just fine if your power supply is works at a frequency within the working ranges of those IGBT's.
    I wont give it a 100% yes they will work but in all probability they should work!
    Without actually having worked on the power supply myself I can only take an educated guess and assume that if the voltage, amperage, and frequency ratings are compatible they should not have any problems working.

    I use the IRG4PC30W IGBT's for rebuilding power supplies that use the TO-247 style devices that have 500 volt or less and 20 amp or less ratings. Generally the frequency of plasma cutter power supplies are in the 30 - 50 Khz range so they are a direct and improved drop in for what I have worked on. I have also found that the power supply heat sinks that the switching devices are mounted to also tend to run noticeably cooler with IGBT's as well.

    Yes I would change out all of the switching devices if possible. If you blow out another set of the old ones you will have to take the machine apart again anyway. Plus you run the chance of the new IGBT's getting damaged if the other old ones went bad.

    The spark gap on a Cut50D might be around .015' - 025" I think.
    All though some will work better with wider or narrower gaps due to poorly matched parts in the high voltage circuits. Its sort of a tune it to work best set up. Cheap equipment tends to have that problem fairly often.
     
    Last edited: Jan 29, 2010
  12. WoodGas

    WoodGas New Member

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    I have the same issue. Did you ever get this to work with IGBTs?
     
  13. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Welcome to ETO!
    You have just resurrected a long-dead thread. Chances of a reply are slim :(.
     
  14. ClydeCrashKop

    ClydeCrashKop Well-Known Member

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    Thanks for resurrecting this thread.
    I have a Cut50 and now I know what to do if it quits.
     
  15. jak

    jak New Member

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    i also have plasma cutter with a blown Q12 mosfet k2837 when it shorted out it also took out the resistor R12 in the circuit trying to repair it not sure of the value of the resistor R12 the only thing on it is 6rb not familiar with that style of resistor. the mosfet next to it Q11 and R11 reads approximately 7.2 ohms. the resistor looks like a flat waffer style no color codes on it. i can supply a photo on the damaged mosfet circuit
    any help would be appreciated i am old school electronic repair person not familiar with new style circuits and components
     

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