Welder Electronics - 3 phase Bridge Module/Thyristor Question
Close
Login to Your Account
Likes Likes:  0
Results 1 to 3 of 3
  1. #1
    Join Date
    Apr 2007
    Country
    UNITED STATES
    State/Province
    West Virginia
    Posts
    1,248
    Post Thanks / Like
    Likes (Given)
    779
    Likes (Received)
    550

    Default Welder Electronics - 3 phase Bridge Module/Thyristor Question

    I suppose this is not quite Transformers/Phase converters etc but I know some folks with quite a bit of power electronics experience hang here so I thought I would give it a try. I will pose the main question with the rest of the story after it.

    I am testing a Sanrex CVM75BB160 3 phase rectifier module with thyristor (schematic below). Currently trying to test the thyristor which is part the module. I put some voltage across the thyristor and triggered it by connecting the gate to the Anode. When I connect the gate it does turn the thing on but it doesn't stay on (latch) when I remove the jumper from the gate. For power across the thyristor I initially used a multimeter in diode test mode. Then I used a bench power supply set at about 20v and current limited to .5a or so. I triggered the gate with a 500 ohm resistor. I changed to the power supply because I thought maybe the multimeter current was not enough to keep the thyristor latched on. Is there such a thing as a thyristor (I think this is an scr) that doesn't latch?

    The rest of the story is that I bought a Miller Pipepro 304 engine driven welder/generator. It's an interesting machine. It has a Kubota engine, 12kw generator 1 and 3 phase, and an inverter welder built in. It has between 2 and 3k hours so not so bad there. The generator works and the welder does not. I was able to buy a technical manual for it on ebay. This I think was a lucky snag since it seems Miller likes to keep all this info a secret. It is very detailed including trouble shooting and pc board schematics.

    I like Miller stuff a lot but it seems really stupid to me that they leave the thing full of pretty big holes so mice can get in. Needless to say the inverter welder became a big mouse nest.

    Last night I pulled the inverter out of it and set it on the bench. The inverter is functionally the same as an XMT 304 but the design is completely different.

    The 3 phase rectifier module w/thyristor that is used to charge some big capacitors. What I see so far is that there is a fried power resistor (which had a dead mouse below it-clue?). The power resistor seems to be for gate drive current limiting on the thyristor on the rectifier module. I think they use it so shut the power off in certain situations. I want to try to make sure the rectifier module is good. The other issue is that I can't see what the resistance of the power resistor was since the writing is burned off of it. I think I can come up with one that will work. Gate drive current is 70ma max so I am thinking about 20k ohm.

    sanrex-cvm75bb160.jpg

  2. #2
    Join Date
    Nov 2004
    Location
    Webster Groves, MO
    Posts
    7,865
    Post Thanks / Like
    Likes (Given)
    2040
    Likes (Received)
    3821

    Default

    If that is the circuit used in the welder, a typical SCR would not unlatch until the three phase power was turned off or the capacitors charged close enough to the peak voltage of the AC that there would be a brief reverse voltage on the thyristor. If you can look up the part number, you may find that it is a gate turn off type.

    Bill

  3. #3
    Join Date
    Apr 2007
    Country
    UNITED STATES
    State/Province
    West Virginia
    Posts
    1,248
    Post Thanks / Like
    Likes (Given)
    779
    Likes (Received)
    550

    Default

    Bill: Thanks for the response. I was not aware of gate turn off thyristors. I read up a little on them. I looked at the data sheet again and it doesn't mention either way. It just says it has a thyristor. Anyway, since it does switch I guess I will assume the module is good and continue looking for other problems before replacing the resistor and doing a smoke test.

    There is a safety sticker in there that says beware of exploding components! Quite a few high voltage/high current components.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •