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SCR Welder amperage controller circuit

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  • #16
    Jok3R-x, I have aquired all the parts for a similar project. The SCR I'm planning on using is the IXYS # MCC56-16 (101B) module. The gates and cathodes signal pinouts (4,5,6,7)are in a different order but schematic is on the side of the module for easy identification. My plan was to use Mike W.'s diagram but yours is more simplistic. Can you look up my SCR and see if it looks like a good candidate for the project. Thanks. Uncrichie.

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    • #17
      Ohmthis, I think its a typo, maybe a 600 watt dimmer as thats what most of them are classified as? I'm hoping JOK3R-x pops up to let us know. Make sure you get one that says it has built in RFI suppression, most do now a days. It'll help keep SWMBO out of the garage yelling, "your messing up the TV again"! Uncrichie.

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      • #18
        uncrichie - Yes I did mean 600 watt, sorry bout that! The MCC56-16101B looks good to me... As long as it's not some monster welder that requires a 100 amp circuit or something..

        ohmthis - I am looking at the schematics for the HF-251D-1, I will let you know what I come up with. Been kinda busy, sorry.

        What I came up with was really just to give you control over the primary windings on a standard AC or AC/DC stick welder. Not sure with different HF boxes in the mix, haven't tested it with that.

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        • #19
          Thanks Jok3R-X for popping back in. The welder I'm using is an ancient Miller Thunderbolt would only draw 50 amps on the primary at full bore which would hardly be ever.

          If anyone is interested there are several (I believe compatable) SCR's on E-Bay right now at an excellent price. Item #130354620328 and #140369966886. I have no relationship to that auction on E-Bay so as always bid at your own risk!

          Uncrichie.

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          • #20
            Hey all, Yea I put two and three together and figured it was a 600w dimmer. I also figured out how to incorporate the dimmers pot into my foot pedal. I do have 1 last question though. Instead of the 600pf capacitor, can I use a 680pf? It's the only one I found with a 2k Volt rating. If all goes well I'll be wiring this up next week.....I'll let all know how it does. I'll also take pictures as I go to.

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            • #21
              Originally posted by ohmthis View Post
              Hey all, Yea I put two and three together and figured it was a 600w dimmer. I also figured out how to incorporate the dimmers pot into my foot pedal. I do have 1 last question though. Instead of the 600pf capacitor, can I use a 680pf? It's the only one I found with a 2k Volt rating. If all goes well I'll be wiring this up next week.....I'll let all know how it does. I'll also take pictures as I go to.
              Yes, that will be fine.

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              • #22
                Originally posted by J0K3R-X View Post
                Yes, that will be fine.
                Cool, thought so I already ordered it. Thanks everyone!!!

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                • #23
                  What are you guys measuring for voltage spikes at the electrode holder due to switching the input side of the transformer on/off? The transformer is basically a large inductor so the peak input voltage is V = L (dI/dT). The peak out voltage will probably be about 1/2 to 1/3 because of the step down.

                  I am curious because I don't see any type of snubber across the SCR. I wonder how much the voltage spikes are going back into the wall outlet.

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                  • #24
                    Junkweld, great question. I have transient voltage suppression at my service entrance and smaller units inside outlet boxes where I have sensitive radio receivers. Would these help prevent a problem even though they are designed for incoming problems, not necessarily spikes internal to the system? Uncrichie.

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                    • #25
                      Originally posted by junkweld View Post
                      What are you guys measuring for voltage spikes at the electrode holder due to switching the input side of the transformer on/off? The transformer is basically a large inductor so the peak input voltage is V = L (dI/dT). The peak out voltage will probably be about 1/2 to 1/3 because of the step down.

                      I am curious because I don't see any type of snubber across the SCR. I wonder how much the voltage spikes are going back into the wall outlet.
                      That is basically what the 2kv 600pF cap across pins 5 and 7 are for. If you look at the pinout for the SCR you will see that pins 5 and 7 are directly connected to the 1 and 2 screws on top of the SCR. You could put the cap between 1 and 2 and it would be the same.

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                      • #26
                        A snubber with just a capacitor and no current limiting? it would be a good idea to run some simulations on that ckt. It may not be functioning as you might expect.

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                        • #27
                          Originally posted by junkweld View Post
                          A snubber with just a capacitor and no current limiting? it would be a good idea to run some simulations on that ckt. It may not be functioning as you might expect.
                          junkweld - Any suggestions are welcome!

                          A capacitor takes time to charge, It also keeps the voltage from too rapidly rising across the leads of the SCR module. This is important because noise or spikes of voltage here will cause the SCR module to trigger when it shouldn't. So the 2kv 600pF cap across pins 5 and 7 limits the rate of rise, or dv/dt across the SCR.

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                          • #28
                            okay i know im bringing this back from the dead but, i tried this on my lincoln tombstone with an irkt91 module and it doesnt appear to affect the current very much if any. im using a 680 pF 2kV cap and a 150 ohm 600 watt dimmer. there is a bumping sound when the welder is running with no load. why does it seen like the current isn't changing?

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                            • #29
                              welder scr input controll circuit

                              Originally posted by J0K3R-X View Post
                              Hope this helps?
                              Hello JOK3R-X
                              I'm not quite sure if I'm doing this replying thing the right way but here goes. I would very much like to get a little additional help on the SCR input control circuit, posted. What is the name and description of those main components, besides the SCRs, shown in your drawing and in Ohmits photos? Thanks for any help here!
                              Gary

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                              • #30
                                SCR power control TIG

                                Hi All!
                                I am putting together the SCR controller as per JOJ3R-X . Can someone tell me which 600W light dimmer to use or will any work with those specs? Has anyone got this circuit working well?
                                Thanks,
                                Techtalk

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