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  • Have a bag of 10 bridge rectifiers in hand rated at 1000piv and 50amps that will be replacing the smaller 4 selenium bridges. If those ratings don't meet Miller spec I'll eat my hat. On second thought, maybe not, I only have the one hat.

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    • Originally posted by 07wingnut View Post
      Have a bag of 10 bridge rectifiers in hand rated at 1000piv and 50amps that will be replacing the smaller 4 selenium bridges. If those ratings don't meet Miller spec I'll eat my hat. On second thought, maybe not, I only have the one hat.
      Those are exactly the specs for the rectifiers I was telling Ryan would work--cannot IMAGINE those won't handle anything one of those old seleniums could. And they're really easy to mount. I'm right with you, wingnut, and came close to posting the part number today. But I don't like to post a "99.9% sure" and find out I was the sole person who made up the "0.1% stupid" class later--thus a call to Miller tomorrow before posting. I have ended up in that class a time or two over the years. :-)

      Comment


      • Well-no need to call Miller tomorrow. I was reading back through this thread and according a post I made on April 25 (post # 26), I had found a later manual with specs on the small seleniums. Quote from post 26 follows:

        "I took a look at a later 300AB/P manual--all 4 of the selenium rectifiers (except the one in the main welding current path) were replaced by Miller part number 035914 (which is obviously no longer a valid part number after all these years). The good news is the parts list has the specs--30 amps, 400 volts--quantity 4 used per machine."

        I did find yet some other manuals that showed some of the bridges with different part numbers--but the ones wingnut has are plenty big enough to handle all 4 applications if the same part number was used for all applications at one point in time.


        So, those 50 amp 1000 volt rated bridges are WAY overrated and should last forever. Like hiring a tractor trailer to bring two bags of groceries home.
        The manufacturer's part number for the ones I found is KBPC50-10. You can get them at Mouser.com or Digikey.com for less than 5 bucks each. One alternate source is surplus components dealer MPJA.com. They have them for $1.95, 200 in stock, under their part number
        "31094 BR". I have bought components from MPJA for at least 15 years, and never got anything bad. In fact, I have some of these bridges in my stock that I bought a few months ago just because they were so versatile and cheap. MPJA buys up stock from companies going out of business or reducing inventory, and resells at lower prices. But, if you want a "traceable to the manufacturer" part, it's only a few bucks more to go with one of the first two vendors--or any other distributor like Allied, Hamilton, TEDSS, etc.

        Just be careful to get the right wires on the right terminals!

        Comment


        • TRYING A REPOST--LAST ATTEMPT TURNED GREEN AND SAID "UNAPPROVED"

          Well-no need to call Miller tomorrow. I was reading back through this thread and according a post I made on April 25 (post # 26), I had found a later manual with specs on the small seleniums. Quote from post 26 follows:

          "I took a look at a later 300AB/P manual--all 4 of the selenium rectifiers (except the one in the main welding current path) were replaced by Miller part number 035914 (which is obviously no longer a valid part number after all these years). The good news is the parts list has the specs--30 amps, 400 volts--quantity 4 used per machine."

          I did find yet some other manuals that showed some of the bridges with different part numbers--but the ones wingnut has are plenty big enough to handle all 4 applications if the same part number was used for all applications at one point in time.


          So, those 50 amp 1000 volt rated bridges are WAY overrated and should last forever. Like hiring a tractor trailer to bring two bags of groceries home.
          The manufacturer's part number for the ones I found is KBPC50-10. You can get them at Mouser.com or Digikey.com for less than 5 bucks each. One alternate source is surplus components dealer MPJA.com. They have them for $1.95, 200 in stock, under their part number
          "31094 BR". I have bought components from MPJA for at least 15 years, and never got anything bad. In fact, I have some of these bridges in my stock that I bought a few months ago just because they were so versatile and cheap. MPJA buys up stock from companies going out of business or reducing inventory, and resells at lower prices. But, if you want a "traceable to the manufacturer" part, it's only a few bucks more to go with one of the first two vendors--or any other distributor like Allied, Hamilton, TEDSS, etc.

          Just be careful to get the right wires on the right terminals!

          Comment


          • I discovered last night my post #26 in this thread on April 25 while reading back through this long discussion. I had forgotten, but I found cross references that show the bridges wingnut has will work fine. Attempted to post last night but it kicked me out and said I was "unapproved". Tried again, same results. Anyway, I'm hoping a moderator will get at least one of those (duplicate) posts up today. Part numbers and sources for a single part to replace all 4 seleniums are in there.

            Comment


            • Today I got everything physically installed but have not yet verified that all the connections are correct. Last thing needed is to turn it on and let out some massive smoke cloud as multiple rectifiers go to semiconductor ****.
              First is the replacement of the main rectifier SR1 which handles the largest current.
              This is the original selenium rectifier


              Click image for larger version

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              It was replaced by power rectifers, two to a heatsink, with the heatsinks electrically isolated from each other.

              Click image for larger version

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              Click image for larger version

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              Click image for larger version

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              Click image for larger version

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              If you look closely, you can see the bypass capacitors, and the larger bypass capacitor that spans the two heatsinks. |There is also a thermal fuse that must be attached to one of the heatsinks to guard against overheating.


              Comment


              • I will post this in stages, since a max of 5 pics are allowed per post.
                Next was the replacement of SR2 and SR4. The originals are shown below

                Click image for larger version  Name:	Sr3.jpg Views:	16 Size:	277.1 KB ID:	615571
                and its replace with these small silicon bridge rectifiers. Don't let the small size fool you, these are good for 1000v and 50amps if properly heatsinked.


                Click image for larger version  Name:	Nr3.jpg Views:	11 Size:	277.0 KB ID:	615572

                The last rectifiers were SR3 and SR5 on the right side of the welder. The old ones shown below

                Click image for larger version  Name:	Sr2.jpg Views:	11 Size:	360.7 KB ID:	615574

                were replaced by these silicon bridges, the heatsink being used because the one they replaced seemed capable of handling more power than SR2 and SR4.

                Click image for larger version  Name:	Nr2.jpg Views:	11 Size:	347.5 KB ID:	615573

                Click image for larger version  Name:	Nr1.jpg Views:	11 Size:	391.9 KB ID:	615575

                and that concludes the selenium rectifier saga.
                As mentioned in a previous post, the BIG one was well on its way out. The smaller ones have yet to be tested.




                Last edited by 07wingnut; 06-24-2021, 11:25 AM.

                Comment


                • Lookin' good. Nice heat sink for the replacements for the two bigger ones.

                  Comment


                  • I’m on the path of replacing the two smaller ones on the right side and then that doubled up looking doofloppy kind of in the center-ish at the top. I’m just going to need guidance on which wire goes to where. These pictures are the ones I’ll be replacing.
                    Attached Files

                    Comment


                    • OK. Let's do the black ones in the second picture first.

                      Looks like the black one on the left (SR4) has wire 64 going to its left and right terminals--two connections (2 wires numbered 64), but tied together by the rod at the back bottom of the rectifier. You will have to connect those two wires together somehow, and then put the single result to the MINUS (-) terminal on the new bridge. Wire 63 goes to the PLUS (+) terminal. Wires 4 and 21 go to the AC terminals, doesn't matter which one goes where on the AC terminals.

                      For the black on the right, (SR2) wire 37 to PLUS, 35 to MINUS, and wires 36 and 3 to AC.

                      For the two big orange ones:

                      First replacement (SR5):
                      Wires 44 and 43 to MINUS and PLUS, respectively.
                      Wires 42 and 41 to AC

                      Second replacement (SR3) :

                      Wires 45 and 24 to MINUS and PLUS, respectively.
                      Wires 32 and 47 to AC

                      Comment


                      • Make sure all four of your new bridges are firmly attached to clean metal (I'd scrape off the paint and smooth the contact area of the sheet metal with sandpaper or scotchbrite to improve heat transfer) using machine screws, nuts, and lock washers. I would also use heat sink thermal grease since I have it, but I really don't think it's essential. Do not use regular grease--it does not conduct heat well. Sheet metal screws are not the best for long-term holding of torque for thermal conductivity.

                        Comment


                        • And the parts you sent me that link for is what I need? I’ll order those today if so. Seems pretty straight forward, provided I can keep the operator error variable out of this equation!

                          Comment


                          • Originally posted by 07wingnut View Post
                            Have a bag of 10 bridge rectifiers in hand rated at 1000piv and 50amps that will be replacing the smaller 4 selenium bridges. If those ratings don't meet Miller spec I'll eat my hat. On second thought, maybe not, I only have the one hat.
                            Here's the info I tried posting the other night when I got kicked out, for anyone who is interested.

                            Those 50 amp 1000 volt rated bridges are WAY overrated and should last forever. Like hiring a tractor trailer to bring two bags of groceries home.

                            The manufacturer's part number for the ones I found is KBPC50-10. You can get them at Mouser.com or Digikey.com for less than 5 bucks each. One alternate source is surplus components dealer MPJA.com. They have them for $1.95, 200 in stock, under their part number "31094 BR". I have bought components from MPJA for at least 15 years, and never got anything bad. In fact, I have some of these bridges in my stock that I bought a few months ago just because they were so versatile and cheap. If you want a "traceable to the manufacturer" part, it's only a few bucks more to go with one of the first two vendors--or any other distributor like Allied, Hamilton, TEDSS, etc.



                            Comment


                            • Originally posted by 07wingnut View Post
                              Have a bag of 10 bridge rectifiers in hand rated at 1000piv and 50amps that will be replacing the smaller 4 selenium bridges. If those ratings don't meet Miller spec I'll eat my hat. On second thought, maybe not, I only have the one hat.
                              For others who may be looking to replace selenium rectifiers, those are far overrated for this application, and should last forever. Excellent choice. Like hiring a tractor trailer to haul two bags of groceries home! :-)

                              The manufacturer's part number for the ones I found is KBPC50-10. You can get them at Mouser.com or Digikey.com for less than 5 bucks each. And one alternate source is MPJA.com--surplus dealer that I have bought a lot of stuff from over 15 years or so and never got a bad part. In fact, I bought a few of those bridges from them a while back just to put in my stock since they are so versatile and so cheap.. If you want the "traceable to manufacturer" parts, it's only a few bucks more from the big vendors listed above, or likely also available from Allied, Hamilton, TEDSS, etc.

                              Comment


                              • This site, for whatever reason, REFUSES to let me post those rectifier part numbers. Keeps saying "UNAPPROVED".

                                One more try. Bridge Rectifiers KBPC50-10. I will keep adding additional info in baby steps in following posts to find out what is causing the problem.

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