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250A portable test set, 850 amps into copper braid

Discussion in 'Electronic Design' started by P E Schoen, Dec 30, 2012.

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  1. P E Schoen

    P E Schoen Guest

    Seems about time to get away from political discussions and global warming
    arguments, and back on topic of electronics design. I just made a short
    video clip of my latest design: a portable (36 pound) high current test set
    which has a 250A 3V output tap (as well as 6V, 24V, and 120V at 750 VA). I
    have two parallel copper braids on the output and when I separate them and
    run 850 amps through them, they move together (as expected, of course).

    All of the processing and control is performed by a Microchip PIC18F4455,
    which includes USB (although that is not used in this version). It performs
    real time true-RMS calculation on 1200 samples per second and reads the
    current through a PCB-mounted 1000:1 CT. It uses a load resistor of 2 ohms
    and provides 8 ranges from 5 amps to 1000 amps full scale, at 1% rated

    This is the final production prototype, after a previous design that used
    two four digit 7-segment LED displays:


  2. Jon Kirwan

    Jon Kirwan Guest

    Now that would make a really nice LED driver for the next gen

  3. Nico Coesel

    Nico Coesel Guest

    None of the Youtube links work... What is the use for this device?
    Earth bonding testing?
  4. P E Schoen

    P E Schoen Guest

    "Nico Coesel" wrote in message
    I don't know why the links don't work for you.

    This device can be used for earth bonding testing, or even as a general
    purpose AC voltage source, but probably its most prevalent use is for
    testing small circuit breakers and motor overloads. Here is a video of a
    typical test of a 60 ampere molded case breaker (MCB):

    I hope the link works for you.

  5. P E Schoen

    P E Schoen Guest

    "Jon Kirwan" wrote in message
    But you need DC. Here is a video of a 4000A DC test set providing a current
    of 20,000 amperes. That's probably enough to make a bank of Crees emit
    photon torpedoes!

    You can see the guts of this test set and others here:


  6. Jon Kirwan

    Jon Kirwan Guest

    Thanks, Paul. Very interesting to me. I design and program
    devices used to monitor the oil temperatures (there are
    multiple points of such measurement) inside power
    transformers in the multi-MVA rating category. It's normally
    a difficult measurement, but it uses fiber optics that are
    placed inside during the transformer's assembly process --
    enough fibers so that some breakage can be tolerated later.
    No conductors of any kind are used for the sensor. The fibers
    are brought outside and run over some distance away where the
    device exists. The core temperature is a key element in
    keeping track of the remaining lifetime of the transformer.
    Kind of an engine-hour thing.

  7. Jon Kirwan

    Jon Kirwan Guest

    Not for a Cockroft-Walton Multiplier, you don't!


    Higher frequency would be nice, though.

    Anyway, lots of fun. The above link feeds into other systems
    used to perform experiments exposing interesting quantum


    Hmm. Not to OP, but instead to George H: Need one of these in
    the product line? (Have you read his book?)

  8. P E Schoen

    P E Schoen Guest

    "Jon Kirwan" wrote in message
    But LEDs don't need such high voltages. And you can always add rectifiers to
    get high current DC, although there are lots of losses through diode
    junctions. Schottky helps, but synchronous rectifiers might be more
    efficient. For 20,000 amps, however, you need lots of parallel MOSFETs with
    ON resistance of 50 uOhms to match the 1 volt Vf of silicon diodes, and
    that's still 20kW of heat!

    My next project may be an insulation test set that will need to generate up
    to 5 kV. I might use one of the modules from this company:

  9. Jon Kirwan

    Jon Kirwan Guest

    Of course... But I was on to a different subject, now. You
    just need to keep up!


  10. P E Schoen

    P E Schoen Guest

    "Jan Panteltje" wrote in message
    Insulation resistance test sets (sometimes called Meggers) are usually DC,
    and it is fairly easy to generate HVDC using ferrite core transformers such
    as TV flybacks. Sometimes substantial current is needed, because the
    insulation is capacitive, and may be significant for testing large
    transformers or motors, or a 500 foot length of high voltage cable. I bought
    this a while ago:

    This is interesting as well:

    There are also insulation breakdown testers, usually called Hipots, and they
    may be DC or AC.

    And there are complete insulation analyzers, which use various techniques:

    For other purposes, AC is required, at line frequency. When I worked at EIL,
    they manufactured an OG-100 which was an oil/glove test set. It had a large
    plexiglass cylinder into which a lineman's glove could be placed, and water
    filled the cylinder and the glove. Then up to 20 kV AC was applied, and
    there was expected to be some current (from capacitance), but insulation
    breakdown and pinholes would trip a breaker. It also had an oil test cup
    into which transformer oil was placed, and a pair of electrodes could be
    adjusted to a specific distance. Then the voltage was adjusted per
    specification. As the oil aged and deteriorated, higher currents were seen,
    and sometimes breakdown would occur.

    (Glove tester - I have done work

    (Oil tester)

    At, we often encounter high voltage test gear up to 200 kV or
    so. But at Phenix Technologies, they have manufactured high voltage devices
    well into the megavolts. When I worked at EIL, they were in Sparks, MD. And
    Phenix Technologies (originally American High Voltage), is in Accident, MD!

    See some of their stuff here:

  11. P E Schoen

    P E Schoen Guest

    Another interesting video of Phenix Technologies:

    and other videos from the same guy:


    Happy Gnu Year!

  12. why are the knobs marked "vernier"?
  13. Ok, so it would make perfect sense to anybody that uses these test sets.

    I noticed in your videos of breaker testers from other companies that they
    all have the same general appearance, down to the crash-bars or handles
    for trying to move the things around so preserving operator panel legends
    would make sense. do these all trace back to one company ages ago?
  14. P E Schoen

    P E Schoen Guest

    "Cydrome Leader" wrote in message
    AFAIK the first such test sets were manufactured by a company called
    Multi-Amp around 1971. At that time they were in Camden, NJ, and then moved
    to Dallas, TX, probably around 1975. They later changed their name to AVO,
    and now they have merged with Biddle and call themselves Megger. But
    apparently they go back even further, to 1963, when the Multi-Amp Institute
    was established, and the following article says they had been making
    equipment since 1902, or earlier, (as Megger):

    Another company that has made high current test sets (but mostly high
    voltage equipment) is:
    They have been associated with major industry names Hubbell, Peschel, and

    I think the Multi-Amp circuit breaker test sets date back only to about
    1971, however. Their product model numbers generally consist of a two-digit
    year of introduction and a two digit representation of output current or
    power, so their CB7140 was a 40kA test set designed in 1971. I have
    encountered some rather old circuit breaker test sets made by GE and
    Westinghouse, some of which used a matrix of transformer taps (like an old
    telephone switchboard) to adjust output current.

    Here is an article I wrote about Circuit Breaker Testing Technology:
    and another less serious article:

  15. Fred Abse

    Fred Abse Guest

    AVO, Limited are/were a UK company, founded some time before WWII, maybe
    before WWI, I don't know.

    They originally were called the "Automatic Coil Winder and Electrical
    Equipment Co. Ltd", (ACWEECO). with headquarters at Kingsway, London.

    "AVO" was their trade name for their range of multimeters, built like
    battleship, with a patented overload trip, operated by the needle hitting
    an end stop, which mechanically tripped a circuit breaker. Name derived
    from "Amps Volts Ohms". I have one of those, still working and within spec
    last time I checked it. I bought it on a working sojourn in the UK in the
    1970s, since it was far more rugged than the Simpsons we had back home.

    Their coil winders were branded "Douglas".

    Sometime after WWII, they changed their name to AVO, Ltd, and moved to
    Dover, England.

    "Megger" was originally the trade name of Evershed & Vignoles, for their
    range of hand-cranked insulation testers, which incorporated a dual-coil,
    voltage-current,"dynamometer" type movement, without hairsprings, and
    were, consequently, insensitive to variations in voltage.

    AVO and Megger merged sometime in the 1970s (I think).
  16. Fred Abse

    Fred Abse Guest

  17. that's a great idea.

    they apparently still make "the" simpson analog meter, so yes, point to
    point wiring is technically still is use.
  18. I don't know that book! Thanks Jon
    (I just ordered it!)

    Any favorite experiments?

    George H.
  19. Jon Kirwan

    Jon Kirwan Guest

    Oh, cripes. They are ALL my favorites, since I haven't
    actually built any of them, yet.

    But I'm particularly interested in playing around with the
    experiments requiring a vacuum pump. Actually making my own
    evacuated systems is a lot different that using "store
    bought" products that are already done and sealed and only
    usable for one or two experiments. This would develop and
    refine new skills I don't currently have and teach me a lot
    about practical problems along the way that I'd like to
    learn. It would open doors to new things for me and I like
    that. I'm more interested in this that the next one below
    because it's more achievable for me, I think.

    Obviously, I'd like to test Bell's inequality myself. That's
    later in the book. I'm not sufficiently convinced that his
    design is up to the real challenges, though. I think there
    are sources of error that are too large and that he "got
    lucky" in finding approximately the right values that he
    reported. So I really think that when I get more into it, it
    will wind up costing more than I really imagine in getting
    the right parts. And that trying to avoid that cost and
    building them myself won't make it any better. I just don't
    have the right infrastructure here and getting enough of it
    will set me back too much money. So before I dig into that
    area, I have MORE reading to do and hopefully more study
    about the details so that perhaps I can either convince
    myself his approach is good enough or that I can come up with
    something else that takes really good ideas from several

    Another book I'm finding some recent joy with is:

    It also includes laboratories for exploring ideas.


    P.S. Here is an interestingly easy approach to a fluxgate

    I like the basic concept, though it's clear to me he author
    is still struggling with the final implementation details.

    As I've told you before, I am VERY interested in developing a
    series of science project/tools that are targeted at high
    school level students who could afford to create them and
    take them home as their own. This means it cannot cost a lot
    of money. The paper-box spectrometer using a DVD that I laid
    out and have tested is one such example. It costs them
    Elmer's glue, a sheet of colored cardstock paper, access to a
    laser or ink jet printer to print the cutout design on it,
    and a DVD-RW. Scissors and perhaps an exacto or razor blade
    helps. I'd like to do the same for a device to measure the
    velocity of balls rolling down inclined planes; etc. The
    whole idea is that the parts are cheap enough and the
    instructions easy enough that almost anyone can make it and
    get reasonable results and that it is theirs to keep when
    they are done. Putting hands on and making your own equipment
    goes a long way in deepening the ideas so they are retained
    better. And tools that one has only one-time experience with
    and cannot take home make it all the more forgettable.
  20. Oh I'm interested in vacuum too! There's this nice technique using
    molecular sieve and liquid nitrogen. It won't pump He, H2 or Ne so
    you have to purge the system first with N2 gas or something.
    Ahh I saw the reference to Kiko(sp) at Colgate. A collegue has done
    that experiment too. (But I've not done it.) The expensive parts are
    the two single photon avalanche photodiodes. Seems if we could get
    access to the right photodiode we could build our own.
    Hmm, do you know the ZAP book that came out of MIT in the 80's(?)
    maybe the 70's. It was take home electronics projects for MIT
    freshman to do.

    George H.

    - Hide quoted text -
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