Variac condition unknown

Discussion in 'General Electronics Chat' started by Gdrumm, Nov 15, 2013.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    This variac has some kind of residue between the wires.

    Would you advise to buy it or not?

    I've never seen one with this residue, and I am hesitant to purchase it.

    It's under $50.00

    Thanks,
    Gary
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I will be on the enameled wire , so it should not affect the performance unless its acidic and burnt the enamel, the main concern is the terminals where the wiper connects to the copper wire is functioning.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It looks to me like a previous hot-spot that has burned the enamel some, it may be OK or recoverable, but that should be reflected in the price?
    Max.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks guys.
    Gary
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I noticed what appears to be a couple of darker turns to the right, it may be an indication that someone started upping the fuse size in order to get a little more out of it? ;)
    Max.
     
  6. PackratKing

    Well-Known Member

    Jul 13, 2008
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    I am assuming that this is a one-layer coil ? If so, if the wires can be shifted one at a time by a sharp-edge piece of plastic,
    then brush off any detritus with a toothbrush, and soak it with either heavy varnish, or something on the order of Corona Dope...
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The burned spot could indicate a shorted turn, which would make the unit inoperable. You then would need to try what PackratKing suggested.
     
  8. Duane P Wetick

    Active Member

    Apr 23, 2009
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    Use your nose first...if the dark area smells of a burn, its probably a case of shorted turns. Sometimes you can spread the turns using a nylon drift and re-coat with electrical varnish. The unit may be salvageable.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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  10. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I would see about buying it as-is for the listed price, but make a deal with the seller that he or she will need to cover the cost of any repairs. I did that with a 'scope once, paid an initial $50 for it but ended up getting a $25 refund for the repairs I had to make to one of the boards. I think that'd be worth a shot.

    Matt

    EDIT: Or spend a bit more for an encased one like GopherT suggested.
     
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I actually bought one very similar to the one shown. I drilled a lage hole in the bottoms of a 3-pound coffee can and smaller holes for the mounting screws. I then put two single-gang switch boxes (one on each side). It is not pretty but I consider it safe and functional.

    The one shown looks a bit big for a coffee can but there are always bigger cans and plastic buckets.

    I wished I spent $10 more on an enclosed one.
     
    Last edited: Nov 16, 2013
  12. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Heck, Gopher... That looks great !!
     
    GopherT likes this.
  13. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I bought it, and recieved it last night.
    I looks pretty desent, but the bakelite box for the attachment of the wires is "busted up".

    What would be a suitable material to build a new wiring box?

    Could I use part of the casement of an old power strip? Are there any heat issues with the box when it's under a load?

    Also, a piece of carbon that looks like it contacts the coiled wire as the dial is turned is broken and partially missing. Can I use a DC motor brush to replace that?

    Looks really cool. I'm thinking of making a nice looking wooden cabinet.

    Thanks,
    Gary
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Traditionally they come in a metal case with a couple of louvers for cooling.
    Didn't someone make a case from a coffee can (post #12)?
    They have large mass and plenty of copper so it takes quite a bit to heat them up, unless you over drive them as it seems yours was!
    I sort of suspected that the brush had suffered when you posted the picture.
    The nature of the brush and copper content is important, you may be able to source one at Helwig Carbon, but I would look for high copper content.
    Max.
     
  15. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Thanks for the insight.
     
  16. PackratKing

    Well-Known Member

    Jul 13, 2008
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    The type of brush as used in an automotive starter, copper impregnated...or I believe they refer to it as sintered copper/carbon... or a piece of the positive electrode from a D cell battery might be less abrasive on the coils
     
  17. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I found a terminal strip to replace the broken box.
    I filed away the broken brush and cemented in a custom sized replacement.
    Now I'm looking to wire it up to power.

    Please see the attached .bmp.
    I need to understand where to wire my inputs, common and hot, and my outputs.

    I am also curious about the reversable dial (referred to in the .bmp.

    Many thanks.
    Gary
     
  18. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    How exactly did you "cement in a custom sized replacement"? If the "cement" is separating the two parts, there will be no electrical contact and it will not work at all. What kind of "cement" did you use? How did you glue it in place?
     
  19. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    As mentioned, I filed down a brush to custom fit it into the brush housing (which is made of brass).
    I pressed the brush into the housing, then tapped it in with a piece of wood and a small hammer, until I was sure it had bottomed out.
    Then I mixed some two part epoxy, and applied it to the outer edges, like what I saw when I removed the old brush.
    I'm certain it has good conductivity, and I trust the epoxy will hold.

    Any insight on the wireing?
    On Youtube, I saw a similar one, where 1 is common, and 3 is hot.
    If so, how do I wire the outputs?
    Is there an unused wire?
    Or are two of the wires joined together?

    Thanks for the feedback.
     
  20. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Normally, the brushes are on a spring to keep pressure on the irregular surface. The brushes 'brush' over the coils as you turn the dial.

    Ifi remember correctly, the reversible dial is because, voltages in any given place may range from 110 to 120 and this dial can be more accurate if you measure your voltsge and then flip the dial for wich ever is closest to calibrate your Variac. Normally the common is shared. The live and neutral go in one side, the secondary and neutral go out the other side.
     
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