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Miller 330 A/BP build date

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  • #31
    You the man, Wayne!

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    • #32
      Ref. to my post #26 in this thread---Need to add some info on the "How to Test A Diode Bridge" I posted there. I say in there that the forward voltage drop measured by the multimeter in diode test mode will be a few tenths of a volt. That is true for most, generally smaller, diodes, but if you look at the specs on the bridges I posted, some of them are up to a bit over 1 volt forward drop. I should have noted that before--standard diode drop is the lower voltage I stated, but higher current, higher voltage power diodes (like the ones in these bridges) are often a bit higher.

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      • #33
        Since I seem to be the only one who has the big one, does that mean I win? Perhaps that means it is the oldest machine on this forum.
        G-ManBart, thanks for the offer, sent you a PM.

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        • #34
          Yep, you must be the winner. If you want to go ahead with replacing the big one, some more investigation is needed. I am really handicapped in that area since I don't have a machine to look at. Would be great if someone with electronics knowledge was also the owner of one of these and was able to help with physical mounting issues, etc.

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          • #35
            That main selenium power rectifier takes up so much room, that there should be no problem mounting one of those 400amp silicon bridge rectifiers on a large finned heat sink. Taking a guess that the diodes in those silicon bridges are electrically isolated from the mounting base, and if this is the case, the heat sink may not have to be mounted on insulated standoffs. I have a couple of large heatsinks that were used by 100amp triac switches, they may be large enough to do the job, especially if the fan pulls enough air thru the fins.

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            • #36
              You know, I'm so old, I didn't even think about a single 400 Amp bridge rectifier--anything that handled that much current had to be made up from 4 high current diodes mounted on a couple of heat sinks back in my day. Need some younger guys around to poke us old codgers into today's reality!

              You are absolutely correct. There are 400 amp, 600 volt bridges available on ebay and Amazon for very reasonable prices, and I agree that they probably do not have any terminals connected to their mounts. I would definitely use thermal compound when mounting them to the heat sink. Interesting that I got no hits on anything that large at Mouser or Digikey, but then they are not generally in the power electronics business. I think you are on the right track, and this may not be hard at all. I think I'd get a 400-600 amp bridge, rated at least 600 volts just to be safe, put it on a very large heat sink with perhaps even an extra fan to blow over it if the main fan doesn't provide a strong flow, and you will have it. As cheap as those bridges are, I agree--I think I would try one of the heat sinks you have, start welding, and have someone monitor how hot the rectifier gets with an IR thermometer--add additional cooling or a bigger heat sink if necessary. I love simple fixes!

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              • #37
                I just ordered a 400a 1600v Bridge rectifier, and some 50a 1000v bridge rectifiers. That should work to replace the selenium ones in the welder. The big one will be mounted on one of these heat sinks. Click image for larger version

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                • #38
                  I don't know about earlier or later models -- nor where the rectifiers are in relation to the fan, yet -- but the fan in my 1978 330A/BP seems strong enough to run a wind tunnel. It moves a lot of air!

                  07wingnut, please let us know how you make out with changing the rectifiers in yours.

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                  • #39
                    I will, but don't hold your breath because the rectifiers won't be here till June. In the meantime I'll see if we can destroy those selenium ones with some welding. If they let the smoke out before the new ones come in, there's always the mickey mouse wire feed mig welder. Cheers.

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                    • #40
                      Looks great! I cannot imagine those heat sinks wouldn't be more than adequate, especially with good airflow. We'll be waiting for an update.

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                      • #41
                        The fan on that machine pulls air in from the bottom and exhausts it at the top on the back. It moves so much air that I think you could hang a radiator off the back and run a water cooled torch. That’s actually a project on my list to be honest. Just have to find the time as that job is pretty far down the priorities list.

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                        • #42
                          Lots of good info here! Y'all are making me think I should be upgrading my '63 Airco 300. It works great now, but I'd hate to have it fry due to losing one of those antique selenium units. Thanks Aeronca!

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                          • #43
                            I was just looking at the wiring diagram for how the main power rectifiers were connected. From what I can see, a bridge rectifier will not work. It looks like its going to take stud mounted individual diodes to do the job. However, I could sure use some reassurance that I'm not screwing up by going out and ordering these. There is already a power bridge on the way that apparently will not work for this. Click image for larger version

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                            • #44
                              I'm so tired right now my mind is not functioning clearly, but I think I see what you mean--seems you can't get the polarity switching done with a bridge. However, right off the top of my head, I think you could use two of those bridges and just leave two terminals on each unconnected But I'm not coherent enough right now to think it through. I learned long ago to wait until morning--will take a look then. :-) I'm guessing two Chinese bridges might still be cheaper than four individual diodes, but not sure without looking it up.

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                              • #45
                                Sorry--busy day--no time today.

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