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Thread: Miggy Got 'Capped'!

  1. #1
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    Miggy Got 'Capped'!

    Working on a fairly big job last weekend (job completed today and I'll post that thread later) that involved a ton of preparation and more welding than I've done in awhile. Wasn't really pushing the MM200 too hard even though I was running in globular transfer all Sunday afternoon. Had about 12" of weld left and heard what sounded like a ruptured air hose except it stopped. I flipped my hood up just in time to see a puff of smoke from the back of the unit (1st generation MM200 - no fan on demand). Rectifier diodes usually go 'POP' and I figured one of the capacitors blew so I pulled the trigger to see if it would still lay down a bead - which it did but no GT this time only short circuit even though the settings didn't change. Finished up what little welding was left, pulled the shelves off the top of the machine and pulled the wrapper to find capacitor electrolyte on the base of the unit.

    Pulled the cap bank assembly and found the blown unit.
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    I removed the remnants from the ruptured safety plug (yellow arrow) before snapping the shot but you can see the bubbled top of the 29 year old capacitor (black arrow).
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    Now, the parts break-down of my 1st generation MM200 shows the six PN 031728 capacitors to be 9000mfd, 35v but when checking my favorite Miller parts source, the same PN shows up as 20000mfd, 35v. So I looked at a later generation parts break-down and found that they include eight 15000mfd, 45v caps for the same combined total of 120000mfd as six of the 'new' 20000mfd units. Trouble is, I didn't really like the almost $32 a copy price and knew a better deal could be had. Found 20000mfd, 40v Mallory units at tedss.com but they didn't have six so I went with a 50v version at $16.50 each.
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    All banked up, reinstalled and ready to be fired up with drive rolls disengaged.
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    First few 'charges' demonstrated the new caps not only held a charge a little longer than the old ones (small spark when wire touched to work piece after releasing gun trigger) but a stronger charge as well. A quick check of the OCV on HIGH-6 before running the first bead.
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    HOLY SPARKLERS BATMAN!!! It's like a new machine. It has always welded nice in the past but there was a marked improvement in its performance with the new capacitor bank - most likely due to a more stable output voltage but I don't have any before & after of that. I guess I know why Miller made the change.
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  2. #2
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    Re: Miggy Got 'Capped'!

    So you will have to start keeping an eye on it in about 25 years?

  3. #3
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    Re: Miggy Got 'Capped'!

    Glad to see you were able to get some new "smoke " to reinstall in the machine. I hate when that stuff leaks out!
    .



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    Re: Miggy Got 'Capped'!

    I had a 48 volt capacitor fill the room with smoke one night on duty. There was only visibility in the first 2 - 3 feet from the floor and it stunk like .... fried skunk.
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    Re: Miggy Got 'Capped'!

    Nice fix duane,ill keep that capacitor info on file in case mine fry someday.
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    Re: Miggy Got 'Capped'!

    After 29 years, you got your moneys worth.
    BTW, you see the differance one cap makes. I added a cap to my mig and increased the current 50%.

  7. #7
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    Re: Miggy Got 'Capped'!

    That looks like a easy fix,unscrew each old capacitor,replace and yer done,great thread duane!
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  8. #8
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    Re: Miggy Got 'Capped'!

    Quote Originally Posted by Bluewelders View Post
    So you will have to start keeping an eye on it in about 25 years?
    At least. Maybe 30.


    Quote Originally Posted by DSW View Post
    Glad to see you were able to get some new "smoke " to reinstall in the machine. I hate when that stuff leaks out!
    Yeah, I didn't have a can of replacement smoke so I had to wait until Friday for the new caps to arrive. Didn't matter as I didn't have time nights after work all week to finish anyhow.


    Quote Originally Posted by tanglediver View Post
    I had a 48 volt capacitor fill the room with smoke one night on duty. There was only visibility in the first 2 - 3 feet from the floor and it stunk like .... fried skunk.
    I can't recall the last time we had fried skunk Danny but I can imagine it was quite the aroma.


    Quote Originally Posted by Felonyass Monk View Post
    Nice fix duane,ill keep that capacitor info on file in case mine fry someday.
    Felon
    You may want to consider an upgrade Felon if you come across an extra $100 if your earlier 200 still has the lesser capacity 9000mfd caps. I'm having to adjust my settings down from the previous normal which I'm sure is due to the new caps maintaining a more consistent, higher output weld voltage than the old ones. I'm serious - it's like a new machine.


    Quote Originally Posted by transit View Post
    After 29 years, you got your moneys worth.
    BTW, you see the differance one cap makes. I added a cap to my mig and increased the current 50%.
    Definately - on both points.

    And I find it interesting that the original caps were relied on to operate within the 'surge' voltage buffer range for the upper OCV settings. Miller obviously changed that with later generations of the MM200 but still. . .
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    Re: Miggy Got 'Capped'!

    Good job!
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    Re: Miggy Got 'Capped'!

    I built a Magnetizer/DeMagnetizer for speaker reconing a while back. It had 24, 8000 ufd, 475 volt caps in it. A few of the caps came from Ebay, and the third time I used it, (out in the garage) I let the voltage climb to about 480 volts. Caps are usually rated for about 20% tolerance, and 25% overage. Well, one of them didn't cut the mustard. The explosion was identical to a 12 gauge shotgun. Thank god I built the caps inside a metal case.

    Regarding electrolytic capacitors, the electrolyte in them is usually a paste, and can dry out over time. 25 years will usually show about a 50% drop in capacitive efficiency, depending on climate, usage, and the type of circuit. Those mallory's should do a great job for you. I have a few vintage Fender amps with original mallory's from the 60's that are still kicking, and test within 10% of original spec.

    Thanks for the pics Duane!! Great job!
    -andy-

  11. #11
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    Re: Miggy Got 'Capped'!

    Duane,

    Thanks for the write up. The new caps look very nice.
    That may be the only "maintenance" you'll ever need to do on your welder.

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    Re: Miggy Got 'Capped'!

    Old Mallorys will often show a little bubble at the end before they go. Moisture inside with heat maybe? They can last longer but it let's U know something is going to happen. Replacement with a little more Voltage/mfd capacity is usually a good idea.
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    Re: Miggy Got 'Capped'!

    I looked at my 200 and it has eight 15000mfd 45v capacitors in it.

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    Re: Miggy Got 'Capped'!

    Quote Originally Posted by Michaeljp86 View Post
    I looked at my 200 and it has eight 15000mfd 45v capacitors in it.
    That's correct - for the later generation MM200s. 8 X 15,000 = 120,000mfd total capacity. The replacements for the first generation MM200 are 6 x 20,000 for the same 120,000mfd total capacity whereas original mfd value on the 'six pack' was 9000 each for a total of 56,000.
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    Re: Miggy Got 'Capped'!

    So is more better? I noticed my machine is all set up to add 2 more.

  16. #16
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    Re: Miggy Got 'Capped'!

    They will drop in capacitance as they age and there is a large variance in the actual capacitance.
    In theory you need about 40,000 mfd per hundred amps of output, so 120,000 mfd should be plenty for 200a.

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    Re: Miggy Got 'Capped'!

    I would like to bring this back up.

    I have a MM200. Awesome machine. I use it for hobby projects mostly. Well my last project had about 20+ hours of weld time. I was doing it in 5 hour welding blocks.





    Anyway I started a new project and I noticed something was off. My favorite setting is low/6.
    I can normally lay a pretty good bead with that setting. But now the bead just stands up like the wire speed is to fast or the heat is too low.

    Should I look at the caps or diodes?

    Gif

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    Re: Miggy Got 'Capped'!

    The diodes failing usually cause a welder to suddenly be unusable.
    Capacitors can fail in several ways,sometimes shorted,but usually they cause the power and weld quality to change.
    If it is a either capacitor or diode guess.
    So I would guess that some of your capacitors have dried up.

  19. #19
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    Re: Miggy Got 'Capped'!

    Agreed. It's easy enough to check the diodes too.

    The capacitors can be checked for opens, shorts, charging and discharging but actual capacitance (overall performance factor) requires a capacitor tester that most folks just don't have.

    If an output diode fails, its like partner typically isn't far behind at which point you won't have any output.
    Last edited by duaneb55; 04-24-2011 at 11:25 PM.
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    Re: Miggy Got 'Capped'!

    My mm200 has been used and abused, Im sure Im going to have to change out some of these one of these days.

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    Re: Miggy Got 'Capped'!

    Quote Originally Posted by duaneb55 View Post
    Agreed. It's easy enough to check the diodes too.
    If an output diode fails, its like partner typically isn't far behind at which point you won't have any output.
    This was my guess too. I have seen this before on a MM35. I just wondered if they would react the same. The MM35 wire speed was affected because of the bad Diode also.

    I will pull them and check them tomorrow.

    I will check the caps too just because.

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    Re: Miggy Got 'Capped'!

    Nice fix Duane! I love it when someone fixes one of the oldies but goodies! Last time I discussed a customer fixing an older unit on this forum, I got told from somebody that they would have thrown the unit away, and bought a new chicom unit.

    No doubt you just bought yourself many more years of trouble free service!

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    Re: Miggy Got 'Capped'!

    Quote Originally Posted by jeepgif View Post
    This was my guess too. I have seen this before on a MM35. I just wondered if they would react the same. The MM35 wire speed was affected because of the bad Diode also.

    I will pull them and check them tomorrow.

    I will check the caps too just because.

    Gif
    Would it be possible for you to post a few pics? Might help some of us out in the future.

  24. #24
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    Re: Miggy Got 'Capped'!

    Problem solved.

    Turns out I got a bad mix of gas.

    I was talking about my welder at work and one of the guys mentioned he got a bad mix of welding gas once. So I borrowed a tank from a friend and "WOW" that was it!

    It never occurred to me. In 20+ years this is the first!

    I will post up some pics of the welds. bad tank vs good tank. No other changes.

    So, I will bookmark this page for future reference.

    Thanks to all.

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  25. #25
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    Re: Miggy Got 'Capped'!

    Well that's good to hear and I have to admit I wouldn't have thought about gas with the given information.

    Did you just change tanks? I can understand how you may not have thought about it either given you've never run into it in 20+ years.

    Thanks for the follow up.
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