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Thread: Reactor in a portable Miller Big 40 welder?

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    DIY Junior Member inillinois2's Avatar
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    Default Reactor in a portable Miller Big 40 welder?

    I am looking for some info on a "reactor" that is in a potrtable welder. This reactor is basically a transformer, I believe, and the welding current is controlled by the windings. I would just like to confirm that this is my problem. The welder runs fine except for the fact that the weld power cannot be adjusted to lower settings, is always putting out too much power no matter where the switch is set. Does someone know how to positively check this "reactor" as a new one is quite expensive. I am a maintenance electrician but just have never dealt with this particular unit. Thanks in advance for any assistance......
    Last edited by inillinois2; 10-27-2009 at 08:37 PM. Reason: Link to schematic

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by inillinois2 View Post
    I am looking for some info on a "reactor" that is in a potrtable welder. This reactor is basically a transformer, I believe, and the welding current is controlled by the windings. I would just like to confirm that this is my problem. The welder runs fine except for the fact that the weld power cannot be adjusted to lower settings, is always putting out too much power no matter where the switch is set. Does someone know how to positively check this "reactor" as a new one is quite expensive. I am a maintenance electrician but just have never dealt with this particular unit. Thanks in advance for any assistance......
    It could be a "saturable reactor". You post schematic, we troubleshoot.

    http://www.freepatentsonline.com/3833849.html
    Last edited by Thatguy; 10-27-2009 at 06:06 PM.

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    Plumber jimbo's Avatar
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    http://www.tpub.com/content/neets/14.../14180_135.htm

    There is a lot in the circuit besides the reactor ( transformer ) itself. If the reactor was bad, it likely would actually show burned. If it is an open winding, that could be determined with an ohmeter, using the schematic.

    Beyond the basic open/shorted resistance measurements, this type of device could only actually be tested in a laboratory environment. However, you should be able to arrive at a decision short of that. Basic VISUAL troubleshooting always is first, and will solve half the cases. Then basic voltage tests on the other components involved. Remember that high voltages are involved, and beyond the visual and ohm readings, this job might best be left to factory service. Of course they will replace major components and send you a large bill!

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by inillinois2 View Post
    Give me a day or so to reverse engineer this thing. . .

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by inillinois2 View Post
    putting out too much power no matter where the switch is set.
    Do you mean the 5 position range switch (I assume this is Z1 on the diagram on pg. 24) or the voltage/current adjustment?
    Is CT1 on the diagram the reactor you referred to? To me it seems to be a current transformer that outputs a signal to PC1.

    I can't find the 300w 34 ohm fine adjustment rheostat (R1) on this diagram. Scratch that, it is in the upper left corner and varies the gen. field current.

    Basically it looks like a 3Φ weld generator in series with a tapped current limiting inductor Z1 feeding a 3 phase diode bridge. A current transformer CT1 feeds back signals to PC1 and RC1 (which goes who knows where?)

    For troubleshooting you might need to simulate a very steady arc, unless you can weld and troubleshoot at the same time. 40v @ 80A is 3200W at 0.5 ohm. You can get a half ohm using a few yards of skinny copper or iron wire but to prevent melting it would have to be submerged in 3 gals. of water or oil.
    That's a problem yet to be solved.

    What options did you get, if any?
    Last edited by Thatguy; 10-28-2009 at 10:24 AM.

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    Figure 2-4 in your link tells me that the impedance of each of the three sections of Z1 should be 3 ohms at the low welding current setting.

    Power off the welder.
    Set Z1 to lowest current setting.
    Disconnect Z1 and hook a section to a 24 vac transformer (assuming the welder runs at 60 Hz from the generator).
    Measure the voltage across and the current through that section.
    V/I should equal ~3.
    With a 40 VA 'former the output V will probably drop to ~17 vac. Don't leave it on too long.
    Repeat for the other two sections.
    Last edited by Thatguy; 10-28-2009 at 05:38 PM.

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    DIY Junior Member inillinois2's Avatar
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    I really have not yet gotten a chance to work on this but did turn welder on myself today. I am confident the reactor is not the problem as i did a visual and i sure did not smell coils burnt. What is going on is that if i have the welder turned all the way down i can still strike an arc. I talked to another of the guys at work and he told me he was using it last week and the welding rod "burnt up".
    Tells me it turned a cherry red. I am assuming the welder shorted out. I have a load tester and the generator responds as it should as i ramp up the power, just too much current. I also did a check and the generator is putting out 48 volts phase to phase vice the 42 the print says it should. I do have a Fluke Scopemeter and am as of now going to assume that the welder has blown diodes. Am I on the right track?

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by inillinois2 View Post
    I am confident the reactor is not the problem as i did a visual and i sure did not smell coils burnt.

    I'd check with an ohmmeter; you might read 1.5 ohms but check for consistency between Z1 coils.

    What is going on is that if i have the welder turned all the way down i can still strike an arc.

    How much voltage does that take?

    I talked to another of the guys at work and he told me he was using it last week and the welding rod "burnt up".
    Tells me it turned a cherry red.

    I assume from excess current. What metal is it and what diameter?


    I am assuming the welder shorted out. I have a load tester and the generator responds as it should as i ramp up the power, just too much current. I also did a check and the generator is putting out 48 volts phase to phase vice the 42 the print says it should.

    That depends on the amps load.

    I do have a Fluke Scopemeter and am as of now going to assume that the welder has blown diodes. Am I on the right track?
    It could be shorted SR3 diodes. If so, you should see some AC on the welder output with the scope, instead of 3 phase full-wave-rectified DC.
    http://wpcontent.answers.com/wikiped...fication_2.png

    Note that VR1/R4 may clip the tops of the waveform if there is no load on the welder.

    To check a 275A 300 PIV diode, hook it in series with the 48 vac from your welder and an assembly of a few 100w incandescent lamps in parallel. With the scope you should see half-wave-rectified DC with a peak value of about 67v. You could also use 120vac from your house but with a 300 PIV diode you might be pushing your luck.
    The incand. lamps provide current limiting.

    A similar diode has a forward voltage drop of 1.3v maximum at rated current and about 1 mA reverse current at 200vdc.

    If it is a bad diode, I assume it failed for internal causes and not 'cause it was overstressed, but who knows? These power levels are enormous.

    You'll need heat sink compound if you mount a new diode.

    Can you post a link to your load tester?
    Last edited by Thatguy; 10-29-2009 at 06:05 PM.

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