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Golf Challenge:

Discussion in 'General Electronics Chat' started by Beau Schwabe, Mar 6, 2018.

  1. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Having been a professional service engineer for over 45 years I'm also 'less than happy' about the three resistors in parallel, but on the basis of poor reliability. I've seen such design choices MANY times (either series or parallel) in commercial equipment, and it's one of the most common cause of faults that are 'designed in' from the beginning.

    The reasons for doing it are obvious, as you've already explained (to some extent) - but the real reason is cost - it's cheaper for a manufacturer to fit multiple small resistors rather than one large one. However, this makes for an unreliable design, and a single larger wattage resistor would be far more reliable. There's also the added bonus that higher wattage resistors are rated for a higher voltage than smaller ones.

    As an engineer, it makes many repairs simple to find - one of the first things to look for are series or parallel resistors in 'at risk' areas, and check those. I've even pointed out the design flaw on manufacturers courses, and pretty well always a couple of years down the line they will start to fail.

    I've never been able to find out if this type of poor design choice comes from the actual designer, or the bean counters on the production line - I've certainly seen a few 'cost saving' measures implemented, where it was obviously not designed that way.
     
  2. Beau Schwabe

    Beau Schwabe Member

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    .... No it is correct, your schematic is not.

    ... Any failure here would be due to thermal stress and possible cracking or cold solder joint of the SMT resistor. In this application I'm not terribly concerned.
     
    Last edited: Mar 11, 2018
  3. kinarfi

    kinarfi Well-Known Member

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    As my mother once said," there are more ways to kill a cat than kissing it to death" I think the same is true with electronics. Is there anything wrong with this modification of what you did? Untitled.png
     
  4. dave miyares

    Dave New Member

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  5. kinarfi

    kinarfi Well-Known Member

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    This simms also

    Untitled.png
     
  6. Beau Schwabe

    Beau Schwabe Member

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    Kinarfi,

    They might simulate, but check your currents and Wattages !!

    In the first circuit ...

    The 4.7k resistor is in parallel with the three 330k resistors

    at 120V...
    ... the 4.7K will need to dissipate 2.3 Watts of heat
    ... the Zener will need to dissipate 450mW of heat
    ... the b-e junction of the transistor will see 103V

    at 240V...
    ... the 4.7K will need to dissipate 10.6 Watts of heat
    ... the Zener will need to dissipate 1.3 Watts of heat
    ... the b-e junction of the transistor will see 222V


    In the second circuit ...

    The 250 Ohm resistor will glow ...
    at 120V... the 250 Ohm will need to dissipate 176 Watts as heat
    at 240V... the 250 Ohm will need to dissipate 756 Watts as heat
     
  7. tomizett

    tomizett Active Member

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    I'll just add that I think this type of "design competition" - set a specification and then compare the different ways people have solved it - certainly has the potential to be fun and improve our design skills.... as long as we can keep good-natured about it (as we have here). It's pretty brave to throw your design out there any have people pull it apart. Perhaps these "challenges" should have their own sub-forum?
     
  8. dave miyares

    Dave New Member

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  9. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Already working on it. Defining the generalized scope of rules/requirements seems to be the present stumbling block to take on.

    Too little rules and requirements definition and people are confused. Too many and people are confused again.

    https://www.electro-tech-online.com/threads/the-great-circuit-challenge.153223/
     
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  10. gophert

    gophert Active Member

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    .ƚʇɘl oƚ ƚʜǫiɿ moɿʇ nɘƚƚiɿw ƚiuɔɿiɔ ɘlqmiƨ ɒ ʇʇo woʜƨ oƚ ɘmoɔ bnɒ ƚnɘmnǫiƨƨɒ ɘʜƚ ob yɘʜƚ mɘʜƚ ʜƚiw ƨɔiƚɒmɘʜɔƨ nwɒɿb ylɿɘqoɿq lɒɿɘvɘƨ ǫniwɘivɘɿ ,ƨɔiƚɒmɘʜɔƨ ǫniwɒɿb ʇo ƨɘluɿ bɿɒbnɒƚƨ ɘʜƚ llɒ mɘʜƚ ǫniʜɔɒɘƚ ɿɘƚʇA .ɔiƚɒmɘʜɔƨ ƨbɿɒwʞɔɒ-ƨƨɒd ɒ ʜƚiw qu woʜƨ ƨƚnɘbuƚƨ nɘʜw ɘƚɒʜ I
     
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