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USA mains voltage.

Discussion in 'Electronic Design' started by Geoff, Aug 15, 2011.

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  1. Geoff

    Geoff Guest


    I am making a line of products to ship to the US. Since my
    preferred voltage selector selector has only 3 positions, I
    would like to have only 1 position for the USA. Currently I have
    a choice of 110 volts or 120 volts. Practically, is 117 the
    closest nominal so I can choose 120 volts setting for the USA?
    It is a 50/60Hz transformer input.
  2. You would do well to reconsider your design. Messing around with
    a voltage selector switch is not the thing to be doing in todays world
    with the technology that is available. Most products today use designs
    with efficient switching power supplies that accept a wide input range
    of 90 to 260 VAC at 50 or 60 Hz.
  3. Reconsideration of the design is not simply one of replacing the power
    supply. Instead it has to be a system level thing and in the case you
    called out the fans would typically be changed out to be low voltage DC
    powered fans.
  4. Martin Brown

    Martin Brown Guest

    I still remember discovering how a Ronson electric razor was actually
    *supposed* to work the first time I visited the USA. It relied on a 60Hz
    mechanical resonance to work properly and tended to jam on a UK 50Hz
    supply. They were widely advertised in the UK as suitable Christmas
    presents for men by some nutter who bought the company.

    I swapped to a properly engineered Braun shaver soon afterwards.

    The most extreme example I can recall was a US brand of early multisync
    monitor that included a small proportion that in the UK would under some
    unfortunate circumstances spontaneously catch fire if left on power for
    more than a few days at a stretch. The fault was that on some of them
    the flyback transformer was going into saturation on UK video refresh
    rates. We swapped to NEC after that and never looked back.

    Martin Brown
  5. Phil Allison

    Phil Allison Guest


    ** The most common arrangement is a split primary transformer - each half
    rated at 120 volts and 50 Hz.

    Wired in parallel, it is fine for the USA and Canada.

    Most of the rest of the world is then covered by the series connection -
    pay attention to correct phase.

    Japan is the really odd one out - with a nominal AC supply of 100 volts and
    either 50 or 60 Hz depending on which part of the country.

    ..... Phil
  6. Uwe Hercksen

    Uwe Hercksen Guest


    a transformer designed for 50 Hz will operate with 60 Hz also, so what
    is the problem? You only have to avoid using a transformer designed for
    60 Hz only with no reserve in iron weight.

  7. Phil Allison

    Phil Allison Guest

    "Uwe Hercksen"
    ** Helps if you read the whole of a post and don't snip it and forget.

    ** The most common arrangement is a split primary transformer - each half
    rated at 120 volts and 50 Hz.

    Wired in parallel, it is fine for the USA and Canada.

    Most of the rest of the world is then covered by the series connection -
    pay attention to correct phase.

    Japan is the really odd one out - with a nominal AC supply of 100 volts and
    either 50 or 60 Hz depending on which part of the country.
  8. +/-5% _at the mains plug_ is very optimistic. Better to design for
    +10/-15% or wider (especially momentarily on the low side).
  9. Phil Allison

    Phil Allison Guest

    "John Fields"
    ** The latter is not true.

    Japan local market products all use 50Hz rated transformers so can take an
    extra 20% in voltage if used at 60 Hz.

    For a give level of core saturation ( Imag), input voltage and frequency are
    in simple proportion.

    .... Phil
  10. Rich Grise

    Rich Grise Guest

    Ignore the noise on the thread. Just stamp it 120, albeit I know
    you know to design it to take about 95~125V. They still call that

    Have Fun!
  11. Jamie

    Jamie Guest


  12. Geoff

    Geoff Guest

    Thats the sort of info I was after. Is that USA wide? One of
    the posters said his local supply drops to 98V in summer. That
    would be an outlier in that case. As a lad most hobby stuff I
    read about the USA stated 117V as the nominal. I know some
    areas of north Japan use 100V, but that market may be non-
    existant for this product and I may be able to handle that
    eventuality by choosing the 100V tap only for that area. My
    customer knows where his overseas customers are located.
  13. Geoff

    Geoff Guest

    "Phil Allison"
    The transformer I have is a single multitapped one and is made
    to order by SES in Melbourne. I can change it as I like but
    need to make a few more batches of 10 or so to use up stock. I
    will consider doing this in conjunction with choosing an inlet
    selector/IEC module which does not require a rear panel
    metalwork or artwork change (no small deal).

    The 120V sounds like an appropriate choice. There is a fair
    overhead on the secondary voltages, I might do a variac check
    on the next one as a check.
  14. Phil Allison

    Phil Allison Guest

    "John Fields"

    ** The Chinese and others are still making huge numbers of iron core
    transformers - for small AC adaptors mostly plus toroidal and R-core
    types in all sizes.

    SMPSs only shine when you need regulation of the DC voltage.

    My Westinghouse ( 5 yo) gas oven has 300VA auto-transformer for the SiC
    igniter that only comes in 120VAC rating.

    Very few audio power amps and no tube guitar amps use SMPSs.

    ..... Phil
  15. Geoff

    Geoff Guest

    A valid point but this is a low volume specialised product
    with not much complexity and a reputation for reliability. The
    voltage is preset to the end customers country. Plus, my
    customer is paranoid about design changes and previous bad
    experience with switch-mode designs.
  16. Geoff

    Geoff Guest

    No single off the shelf switchmode will give 600V 30mA, 9V 7A,
    and +/- 15V low noise.
  17. Geoff

    Geoff Guest

    I agree with that philosophy where products are available.
    Except in this particular case the 600V and 9V supply wil
    probably add up to more than the cost of transformer+selector
  18. Phil Allison

    Phil Allison Guest


    ** JL is talking out his arse as usual.

    For your app a custom wound tranny is ideal.

    " ... 600V 30mA, 9V 7A, and +/- 15V low noise. "

    You simply have 3 secondary windings done to your specs on one tranny of
    about 120 VA - quite compact and light if a toroidal is used.

    Efficiency of such a tranny is about 92% at full load, much better at lower

    Reliability is NOT an issue at all - unlike with all SMPSs.

    And BTW - PFC at such low power is a wank.

    ..... Phil
  19. Geoff

    Geoff Guest

    Exactly. It's not a toroid but nevertheless it is less than
    $100, has excellent isolation and failure rate of this
    manufacturer is known to be about 1 in 2000 IME. I can't do
    anything about the secondary requirements. They are defined by
    the load which is not modifiable. Good point about the
    reliability. That is important since I would have to bear the
    warrantee costs. Thanks for reading the requirements.
  20. PeterD

    PeterD Guest

    Yes, but realize that each 'drop' can vary somewhat. But the goal of the
    utility company is that the customer get 120/240 volts.
    That is *very* unusual, and I suspect that the 'customer' should contact
    the local utility and see about having the pole transformer upgraded. It
    is NOT acceptable to drop to under 100 volts.
    Many years ago 115, 117, 110 and some other voltages were 'local'
    standards. As the years progressed, it was realized that a national
    standard was needed, and 120 was chosen.
    Yep, Japan's standard is 100 volts--the only country that I know of with
    that voltage! How'd that happen? Got me!
    I find it difficult to imagine any electronic device that won't handle a
    spread from 110 to 130 without any problems at all. If it doesn't handle
    that spread then I'd call that a design flaw. Ideally you should be able
    to handle 100 to 140 volts without serious impairment to functionality,
    though that may be a bit idealistic.
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