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Question about wiring wall cubes in series to get 30v.

Discussion in 'Electronic Repair' started by Charlie Wilkes, Feb 6, 2005.

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  1. Today I bought a well-used HP DJ 697c to print from DOS apps.

    It came with no adapter. The label specifies 30 volts at 400ma.

    I took an old plustek scanner 24v/600ma cube and a radioshack 3-12v
    adjustable cube and wired them in series. I got 36v with no load, so
    I figured that was probably about right. The printer powered up, but
    after a few minutes the plustek power cube failed. The rshack cube is
    still fine.

    This group's FAQ reassured me that I wasn't doing anything too crazy,
    but it mentioned a rectifier, which I don't have. I didn't get the
    impression the rectifier was really essential, but I don't know much
    about electronics.

    Any ideas why this setup would fail?

    Charlie
     
  2. James Sweet

    James Sweet Guest

    Were the power adapters AC or DC output? If they're DC then they already
    have a rectifier built in. Wiring wall warts in series is generally a bad
    idea, particularly if you don't know the details of the output. 24v should
    run the printer just fine, no need to muck around with the two adapters.
     
  3. NSM

    NSM Guest

    You might find one in a thrift or

    http://www.allelectronics.com/cgi-bin/category.cgi?category=480&item=PS-2416&type=store

    might be close enough.
     
  4. Without knowing the details, it's hard to say what went wrong. What
    were the exact ratings of the adjustable wall adapter? Many of those
    are poorly constructed with limited current capability.
    Jameco usually has a pretty good assortment. www.jameco.com

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
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    Note: These links are hopefully temporary until we can sort out the excessive
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    Important: Anything sent to the email address in the message header above is
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    contact me via the Feedback Form in the FAQs.
     
  5. The requirement was 30v 400ma. All the cubes were rated at 600ma.

    I felt wantonly destructive that night so I repeated the experiment,
    this time with the surviving (3-12v adjustable) cube and two others
    like it. I set two of them at 9v and one at 12v. Then I twisted and
    I taped and I plugged it in and it works! I've had it going for a
    couple of days now, printing away like a brand-new HP printer, which
    is the price I paid for it with new cartridges. I just hope I don't
    end up burning down another house.

    Charlie
     
  6. Jerry G.

    Jerry G. Guest

    As long as their current rating is high enough, it should be very safe. The
    total current output will be of the lowest rated one. The voltage output
    will be the sum of all that are in series.

    I personally would go around to the various electronic suppliers and try to
    get a 30 Volt supply, that is rated to at least 500 ma or more. This way
    only one outlet will be used, and it is a more practical way to supply your
    unit.

    --

    Jerry G.
    =====

    The requirement was 30v 400ma. All the cubes were rated at 600ma.

    I felt wantonly destructive that night so I repeated the experiment,
    this time with the surviving (3-12v adjustable) cube and two others
    like it. I set two of them at 9v and one at 12v. Then I twisted and
    I taped and I plugged it in and it works! I've had it going for a
    couple of days now, printing away like a brand-new HP printer, which
    is the price I paid for it with new cartridges. I just hope I don't
    end up burning down another house.

    Charlie
     
  7. jakdedert

    jakdedert Guest

    There is no info given as to the nature of the voltage: AC or DC. Two
    adaptors in series? The adjustable wall wart would have to be AC to pass
    any current at all through the second one, but I've never seen an adjustable
    *AC* wall wart. I suppose they could exist, but every one I've seen was DC.

    If it's the case that the OP needs 30 volts *AC* then a simple transformer
    should suffice. Finding a ~30v transformer might be difficult, but I'll bet
    the tolerance is not all that close. If the unit accepts AC, then there's a
    complete power supply inside which probably includes some degree of
    regulation.

    I certainly wouldn't mess around with cascading wall warts....

    jak
     
  8. Asimov

    Asimov Guest

    "jakdedert" bravely wrote to "All" (08 Feb 05 10:41:45)
    --- on the heady topic of "Re: Question about wiring wall cubes in series to
    get 30v."

    ja> From: "jakdedert" <>
    ja> Xref: aeinews sci.electronics.repair:9852

    ja> There is no info given as to the nature of the voltage: AC or DC. Two
    ja> adaptors in series? The adjustable wall wart would have to be AC to
    ja> pass any current at all through the second one, but I've never seen an
    ja> adjustable *AC* wall wart. I suppose they could exist, but every one
    ja> I've seen was DC.
    ja> If it's the case that the OP needs 30 volts *AC* then a simple
    ja> transformer should suffice. Finding a ~30v transformer might be
    ja> difficult, but I'll bet the tolerance is not all that close. If the
    ja> unit accepts AC, then there's a complete power supply inside which
    ja> probably includes some degree of regulation.

    ja> I certainly wouldn't mess around with cascading wall warts....


    jak,

    A device that requires 30 VAC might still work with DC if it contains
    its own rectifiers. However recall that 30 VAC is actually about 42V
    peak, so the supplied input DC should really have this higher value.

    The problem is if 30V DC is too little voltage for any internal
    regulation to function properly. If it is a switching supply then it
    might not be a problem other than it getting a bit warmer due to the
    inceased duty cycle.

    A*s*i*m*o*v

    .... If plugging it in doesn't help, turn it on.
     
  9. Huh? Think: two DC power supplies in series.

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name is included in the subject line. Or, you can
    contact me via the Feedback Form in the FAQs.
     
  10. jakdedert

    jakdedert Guest

    Okay, I finally get what the OP was talking about when he said 'series'. If
    I understand, what he actually did was commoned one leg of the OUTPUT of
    each device and used the two remaining leads as the output....

    I agree with James. Try it on 24 volts (one adaptor: unfortunately, the one
    he blew out), or else obtain a suitable supply (or buy a transformer and
    build one). While what he's doing is not cascading supplies, it still
    sounds like a recipe for disaster...not a huge disaster, to be sure, but....

    At the very least, I wouldn't leave this kludge plugged in when not
    attended.

    jak
     
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