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Bridge rectifier and polarity 'oops'

Discussion in 'Hobby Electronics' started by Wayne., Oct 13, 2008.

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  1. Wayne.

    Wayne. Guest

    I plugged into LTSpice the schematic for a bridge rectifier to test if
    it could negotiate the change in DC polarity - which it did.

    How much wear will the bridge endure before failing?

    Along the train tracks, as it is now it is still in development, I have
    segments that have reduced voltage and different polarity depending on
    the function of the segment.

    At this stage, I am only testing over a 3m section of track.
     
  2. That depends on a lot of factors, all of which you have not told us.
    Generally, in a properly designed system with suitable margins, they
    won't (or shouldn't) fail.
    Your post really doesn't make any sense.
    What are you trying to do here?

    Dave.
     
  3. Phil Allison

    Phil Allison Guest

    "Wayne Kerr"

    ** Will miracles never cease ......


    ** We might well ask - how much can a Koala bear ????

    Toooot, toooot ...............




    ........ phil
     
  4. Cosmic Ray

    Cosmic Ray Guest



    If you are talking about a small model train set........

    You need to know how much current the train(s) draw - I'd guess a small toy
    train would draw < 2A, probably 300mA+ when running. Try something like a
    W04 bridge. Be aware that a bridge will lose arount 2 x 0.7V. Your trains
    may not run at full speed with the bridge in circuit.
     
  5. kreed

    kreed Guest

    Well, if the change in polarity is happening across the AC or ~
    terminals, and the voltage current ratings are followed, and the
    frequency isnt high (you need a fast recovery type if so) the thing
    shouldnt wear out for a long long time - possibly decades even.
     
  6. Eeyore

    Eeyore Guest

    What is that supposed to mean ?

    You're a student ? It's time you got back to doing bench work instead of
    fucking about with wanky simulations that give you no feel for REAL
    engineering.

    Sorry, but it's true. Current graduates are almost worse than useless. In
    fact I've seen (and rescued) an example where a new graduate nearly
    completely wrote off a major project for a major UK plc. I understood the
    main problem in under 30 seconds. Bet you never did electronics as a hobby
    either. That's where the competent designers come from.

    Graham
     
  7. Eeyore

    Eeyore Guest

    That's modern education for you ! We're producing a generation of clowns,
    idiots and know-nothings. And many are functionally quite illiterate and
    innumerate too.

    Graham
     
  8. Eeyore

    Eeyore Guest

    MORON ! 0.7V is a small signal current Vf for typical silcon diodes.

    Power bridges are more in the region of 1V per diode at rated If.

    Sigh !

    Graham
     
  9. Eeyore

    Eeyore Guest

    Uh ?

    How did you understand his 'question' ?

    Graham
     
  10. Jasen Betts

    Jasen Betts Guest

    the bridge should be rated for the stall current, when the motor is
    running at full speed there will be less drop.

    Bye.
    Jasen
     
  11. Ross Vumbaca

    Ross Vumbaca Guest

    Hi,
    They gave a new graduate so much responsibility that he could write off
    a major project? Sounds like the 'major UK plc' was a bit naive too.

    Regards,

    Ross..
     
  12. It's possible, and you don't need much responsibility at all. I worked
    on a project once that was worth around $10M that could be ruined if
    you blew the one and only high end PCB prototype. All it would have
    taken was one curious and/or careless grad to poke around and screw
    something up.

    Dave.
     
  13. Guest

    Had a graduate recently apply for a job who could not calculate a
    circuit with 1 zener, 1 battery and 1 resistor!
     
  14. I've interviewed grads who couldn't tell me what the beta of a
    transistor was.

    One recent grad I interviewed (2 years industry experience) was
    supposedly a "microcontroller specialist" but he couldn't name two
    brands of micros. He also bought in his thesis documentation so I
    asked him a question from it. You guessed it, he couldn't even tell me
    what a particular part of the circuit did, even when it was described
    in his own text underneath it.

    Simple questions sort out the morons quick smart.
    I also like to give them a loaded board and say "tell me anything you
    can about it"

    Dave.
     
  15. Phil Allison

    Phil Allison Guest

    "David L. Jones"

    ** Old hat - everything is MOS these days.

    Might as well ask them what the "mu factor " of a valve is.


    ** You mean there is ANOTHER brand besides PIC ??


    ** Most students "outsource" their theses, these days.

    Many will even "sub contract " sitting for exams.

    Good business sense - really.


    ** To be fair, even a supposedly "simple question " must not suffer from
    ambiguity in the way it is presented - plus YOU must know all the possible
    correct replies to it.


    ** ..... errr, its all covered in SMD, sir.



    ...... Phil
     
  16. I would have settled for that!
    Apparently.
    He hadn't even heard of PIC.
    Yep, they'll be able to climb that corporate ladder in no time.
    Straight to the big-bickies for them.
    I try to pick questions where an exact answer isn't required, or there
    are many answers.
    And I'm always happy to restate the question in different ways if they
    don't understand, but never let the little buggers off the hook.
    The idea is to find out if they have some general knowledge, or are
    completely clueless. It's always easy to spot which after a few
    minutes.

    Phone and video conference interviews are harder.
    "What *type* of SMD packages son?"
    With some of the grads I've interviewed, I would have been impressed
    if they knew what SMD was.

    Dave.
     
  17. kreed

    kreed Guest

    I didnt really, just made guesses :)
     
  18. Eeyore

    Eeyore Guest

    LOL !

    Graham
     
  19. MisterE

    MisterE Guest

    I've interviewed grads who couldn't tell me what the beta of a
    I graduated a few years back now. Electronic engeering needed an OP of 15 to
    get in, so many useless people went in and dropped out. Austrlaian uni's
    have a pass at 50%. Which means you can get a degree and only learn 1/2 the
    stuff you really should know. Its not like america where anything below
    about 80% is a fail. I graduated with about 90ish percent, the average was
    56 (considering 50 in is the minimum pass you can see how low most were -
    something like 90% of people from 50 to 55). Was pretty easy to get $80k job
    after a year or so but all the graduate jobs started at $35-45k because the
    skill level was so poor. Many people I know from my course now work at
    jaycar or dicksmith shops. One is now an electricians apprentice. Others I
    know work for $15/hour usually to companies that have won military
    contracts.

    Personally I blame the univerities, not so much the students (though many
    are lazy). You simply are not taught most things anymore about circuit
    design. A 4 year electronics degree probably only has 1 year of work that is
    specialiased to electronics, the rest is general science, physics, and
    mostly computer programming. You would be surprised how many couldn't tell
    you what the beta of a transistor is, but how many could tell you have to
    the pipeline in a pentium works. Its all about digital electronic circuit
    design these days.
     
  20. Wayne.

    Wayne. Guest

    I read through an article using a 6v dolphin battery and an LED. To
    overcome the polarity in the dark, the author used a bridge rectifier.

    What I am wondering, can this be relied upon when the train tracks
    change polarity through a turn-out loop?

    Oh, and no I am not a student. Just someone who want to do something
    fancy with a train set that I am resurrecting after 20 years of sitting
    idol.
     
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