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Millermatic 200 - Big spark without trigger being pulled

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  • #16
    Originally posted by ryanjones2150 View Post
    That part number 085 002 shows as a stocked item at miller4less. There’s also a bunch of abbreviations next to it that tell me nothing but be a clue to you guys about it being the correct part. Might not even be what you’re looking for, but worth a try.

    Also, some old components can have an updated p/n from miller. In the past I’ve obtained that information by calling miller tech support and/or parts department. This could also be worth a shot.
    That part number does not appear to be a contactor. The correct number for the Miller part shown in the manual for that serial number welder is 032786. There might be a newer number, but I doubt its 085002. Here's a link to ebay for one that will work (you may have to fudge the mounting a bit) for $25 plus 8 bucks shipping. As Franz points out, it is probably not rated for DC loads, and will not last forever, but for the price, I'd change it every few years if necessary.

    https://www.ebay.com/itm/Gould-EBA73...b3c1d12580ef6e

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    • #17
      Originally posted by ryanjones2150 View Post
      That part number 085 002 shows as a stocked item at miller4less. There’s also a bunch of abbreviations next to it that tell me nothing but be a clue to you guys about it being the correct part. Might not even be what you’re looking for, but worth a try.

      Also, some old components can have an updated p/n from miller. In the past I’ve obtained that information by calling miller tech support and/or parts department. This could also be worth a shot.
      I found that and guessed that it was not the part - looks like it might be a polo shirt?

      I'll give Miller a call tomorrow and see what they have to say about a newer/updated part number with the same functionality.

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      • #18
        Originally posted by Aeronca41 View Post

        That part number does not appear to be a contactor. The correct number for the Miller part shown in the manual for that serial number welder is 032786. There might be a newer number, but I doubt its 085002. Here's a link to ebay for one that will work (you may have to fudge the mounting a bit) for $25 plus 8 bucks shipping. As Franz points out, it is probably not rated for DC loads, and will not last forever, but for the price, I'd change it every few years if necessary.

        https://www.ebay.com/itm/Gould-EBA73...b3c1d12580ef6e

        Thanks for the ebay link - I'm sure that will work fine...

        How did you come up with that part number? I just double checked that I got the correct manual for the serial number - screen shots below from said manual?

        How does the contactor differ between an AC and DC load? Assuming RMS current for AC and steady state for DC - is there that much difference? Not to mention they're trippled up so the 75A is really 225A, however I'm guessing it's not the steady state current, but the transients of charging/discharging the capacitor bank and the inductive spikes that generate the high voltages when the circuit is broken? Not sure if you could put a flyback diode around the contacts (have not analyzed it that much )?


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        • #19
          You're right on the part number--I clicked on the wrong serial number manual. Sorry about that.

          I don't know what is different about the contacts in switching devices rated for AC vs DC--I assume it's a difference in the material. I know in the world of avionics with which I am somewhat familiar, you MUST always use the appropriate switch/circuit breaker relay rated for the type of current to maintain FAA certification. And while I've been typing this, something has cropped up in my mind's dusty recesses about the spring tension in the over-center mechanism in the switch being stronger for one than the other, but I can't remember which. I think I could make a good argument either way. Stronger for AC because it has to deal with peak voltage rather than the RMS we always talk about, or stronger for DC because there are no zero-crossings to break the arc. I'm tending to the latter. Good item for internet research some snowy night this winter.

          I have to say that I have used AC rated switches on cars, trucks, and tractors for years without ever having a failure, but obviously would never do it on an airplane. A welder? Yep.

          I also thought about adding snubber diodes across the contacts, but when you change the polarity (which you may never do if you don't ever run flux core, so it wouldn't matter) they would be backwards. Just off the top of my head and not digging into the books, I have thought about just adding an R-C snubber to my MM200, maybe adding something in the range of a 0.01-0.1 mfd cap (whatever I can find in my junk box) in series with a couple of hundred ohms of resistance, in parallel with the contacts. I'd want a good high voltage rating on the cap--maybe 400-500 volts or more--1 KV if I could find one in the box--to account for inductive spikes, and I would use a ceramic. If I used a diode, I'd go for 1KV PIV rating. And probably add a couple of hundred ohms of resistance in series with the diode to protect it. But, all of that said, maybe I'm just being too geeky--hundreds, probably thousands, of MM200s have been running without snubbers for years. At my age, if the W contactor in mine isn't shot by now, it will probably outlast me.

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          • #20
            ""How does the contactor differ between an AC and DC load? Assuming RMS current for AC and steady state for DC - is there that much difference? Not to mention they're trippled up so the 75A is really 225A, however I'm guessing it's not the steady state current, but the transients of charging/discharging the capacitor bank and the inductive spikes that generate the high voltages when the circuit is broken? Not sure if you could put a flyback diode around the contacts (have not analyzed it that much )?""

            Can you accept you really don't want to know and I don't have that number of keystrokes left in me?
            When that machine was built, there were 4 types of contactors, AC, DC, Motor Starting and LIGHTING. You want to watch fun watch what happens when a contractor substitutes motor contactors for lighting contactors in a baseball stadium cause he's sure nobody will notice since the HID lighting is really an inductive load.
            From memory of the day I learned from the Square D factory Rep, "If they were interchangeable we'd only build one class"

            Just dealing with DC, you get a thing called multipathing, and microarcing on closing, increased contact erosion in comparison to the same load on AC, and easily established arc on opening that either gets compensated by opening speed or by an arc interruptor, unless the contacts are immersed in oil. Once you get wrapped around that, there is the matter of the FOUR (4) stages of a switch. On, Off, on going to Off and Off going to On.

            Honestly, just use the ebay contactor and put healthy arc suppression diodes across the contacts. Personally I always thunk welder manufacturers cheated by not putting a suppression diode across the microswitch on the trigger, so I put diodes there when I got the machine. I also opine sufficient time elapses in a welder between trigger and arc load established to ignore half of the problems. Some day I gotta meter that.

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            • #21
              Thank you, Franz. That is good stuff. The part about opening speed is consistent with my faint memory of different over-center designs for DC. The stadium lighting thing sounds like someone may have learned a financially painful lesson.

              Metering the action of the contactor is interesting. I have a reasonably high speed digital storage scope that might capture some interesting pictures. As my wife always said, Whether i’d ever get around to actually doing it is obviously in question, but I’m definitely interested. I’ll be looking up info on Micropathing and microarcing.

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              • #22
                Miller says that 085 002 75A 3 Pole contactor has been discontinued and the recommended replacement is a 252 907 which is a 60A 3 Pole and seems to be available for "reasonable" money ($200-300 - which is still pretty darn expensive in my opinion for what it is...).

                Interestingly, the ratings on it are all for A/C motors... Hmmm, I started looking at the schematic to see if I could put in a flyback diode across the contactor and realized that we're all overthinking this too much

                Contactor W is on the AC side of the circuit, so you can't use a flyback diode and all this discussion about AC vs DC contactors, while interesting, is moot.

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                • #23
                  That makes the eBay ones all the more appropriate. No way I would be spending 200 bucks.

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                  • #24
                    $205.73 on miller 4 less.

                    One on eBay for $195.

                    Maybe you can find something else, or just spend he money and have it fixed.

                    Hopefully.

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                    • #25
                      Here's a new one that looks similar for $46.50 - https://www.automationdirect.com/adc...)/wdp60-3l-120

                      It is 9.3VA on the coil vs 7.6 on the Hartland Controls one that Miller recommends as their replacement, however the inrush is only 47VA on the Automation Direct one vs 76 on the Hartland Controls. Likely lower resistance (bigger wire) but higher inductance (more turns) on the Automation Direct one?

                      Automation Direct is a bit "Wal-Mart" like so there's that to consider...

                      I can get a 25 ohm, 50 watt resistor for ~$8 at Mouser
                      https://www.mouser.com/ProductDetail...imSduYlJpgA%3D

                      Looks like DigiKey has both items available though the contactor will be $80-100.

                      Lots of options - The contactor still works, but I'd like to get another one so if/when it fails, we're not down for any significant length of time. The resistor I will get on my next order from any of the electrical vendors.

                      Thanks everyone for your comments and thoughts. When I get the resistor installed, I'll update on how it works.

                      Thanks again

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                      • #26
                        Take it loose from the machine and look at the mounting surface for a manufacturer name. Pretty sure it ain't Square D, but I recall those contacts just can't say whose they are. Might be Allen Bradley or even furnas.

                        Once you have the 411 you can probably find replacement contacts cheap someplace.

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                        • #27
                          No problem putting a new set of contacts in - if I can find them...Any suggestions?

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                          • #28
                            Looks like a bunch of them on eBay for cheap.

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                            • #29
                              Lots of Furnas 42EE "stuff" on eBay - didn't find any contacts, but did find a few complete contactors that seem close...

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                              • #30
                                https://www.repcoinc.com/contacts/series.asp

                                I got a hunch it'll be cheaper to buy a replacement off ePay, but Repco has an 800 # so fasten seatbelt and call.

                                "Definite purpose" translates to 'designed to work in air conditioning equipment' usually either as the compressor controller or electric heat controller.
                                Lot of those items tend to head for China as recycle.
                                If you know somebody in the HVAC business you might get to save one from the ocean trip for a few bucks.

                                Also http://www.electricalcontactkits.com/furnas.asp

                                or www.galco.com

                                Looks like there are many suppliers
                                http://www.southlandelectrical.com/items.asp?cc=CK_FRN is a surplus dealer with 800 number so they might have good pricing.

                                ONE THING that I wonder about, there are multiple references to this style contactor being "vertical pull in". Some "engineer" may have ignored that in designing the machine and caused excessive wear.

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