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Difference in Amperage matter much?

Discussion in 'Electronic Basics' started by Mike, Jan 26, 2004.

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  1. Mike

    Mike Guest

    Hi, I am trying to replace a DC adaptor:

    Original adaptor from U.S.:
    input 110v AC
    Cycles????? unknown

    output 5.8v DC with 1amp(1000ma)

    I own a current DC adaptor which is for Japan:
    input 100v AC 11VA Cycles 50-60Hz
    output 5.8v DC 730ma

    Is the difference in amps going to be a big problem?
    The think is basically only charging 1.2recharge batteries.

  2. The replacement has two strikes against it. It may be 37% overloaded
    on current and have its core overloaded with 20 % excess voltage. It
    may survive, but you have no compliant is it catches fire or melts its
    thermal overload switch. What happened to the original?
  3. JeB

    JeB Guest

    you also must pay attention to the polarity of the plug.
  4. Don Bruder

    Don Bruder Guest

    The part above is of no meaning. The input side is a non-issue, aside
    from considerations about what kind of socket it will be plugged into.
    Obviously, an adapter made to work in the USA, with 110-120 volts at the
    socket, isn't going to be happy if plugged into a 220 volts outlet, but
    that's not particularly important.
    THAT is the critical information. Regardless of what goes in, what comes
    out *MUST* be 5.8 volts of DC, at 1 amp. It doesn't matter if the input
    is designed for 110, 220, or 500KVolts - the output side is the critical
    Perhaps not a *BIG* problem, but it will definitely be a problem. Exact
    how much of one is something that I can't predict without a whole lot
    more information than what you've offered. (information that you're
    probably not going to be able to supply from the other side of an ocean
    What it's doing with the juice is irrelevant. The only important factors
    are the voltage/current/polarity the device wants. Everything else is
    distraction that has no bearing on your question. No, that's not a
    "chewing out" - just an attempt at education.

    Now, having covere those preliminaries...

    The 730 mA one you have will probably cook itself in fairly short order.

    Your application needs (or at least, your old adapter supplied) 1 amp at
    5.8 volts. When looking for a replacement, you *MUST* match or exceed
    the amperage rating of the original. Using a supply with a lower output
    will almost certainly burn it up, and may do so quite quickly, and with
    a large amount of damge to the surrounding area. If you're lucky, it
    will "hold you over" until you can get a proper one in place, but don't
    count on it lasting any significant amount of time. Find an adapter
    wired for your location's (Japan, US, Britain, whatever) AC system that
    puts out 5.8 volts of DC at 1 amp or more, with a plug that puts the
    proper polarity on the proper terminal of your device. Only then will
    you have the "right" adapter.

    Anything else is, at best, going to "smoke-test" itself as it tries
    valiantly (but in vain) to supply what your device wants. At worst, it
    will not only burn itself up, but possibly take along you, your
    house/apartment building, maybe your wife and kids and/or neighbors, etc.
  5. Mike

    Mike Guest


    The original is a 110v DC adaptor for the U.S.
    I can't use that original in JAPAN since the it's 100V here.
    I'm not sure what cycles is in JAPAN or if that matters much,
    except it seems the cylces are 50-60hz(my existing Japan DC adaptors
    are showing that).

    SO, I need to find an adaptor in Japan that will push out the same as
    the original, which is 5.8v and 1amps

    I would like to know why the replacement I suggested would be a bad
    The replacement I currently have is a 100V(FOR JAPAN), pushing out
    5.8v and 730ma.
    How could the adaptor be overloaded since it can't supply enough
    ampherage that the device requires in the first place?
  6. Mike

    Mike Guest

    I don't think I was clear.

    I live in Japan, Yet the product I bought has ONLY a DC adaptor for US

    So I need to find a DC adaptor in Japan that will push out the same as
    the original US adaptor.

    Japan is 100v system
    So I currently have a DC adaptor in Japan that works FINE with
    Japanese voltage, and this adaptor pushes out 5.8v and 730ma

    My concern is: providing a bit lower amperage(730MA) to the product
    that's expecting a higher amperage(1000MA) will big a big problem?

    Thanks again
  7. I missed the fact that you are in Japan. My previous post was based
    on the assumption that you were using a 100 volt supply in the US.

    So disregard my comment about the excess voltage causing trouble. But
    you may still have problems when your load draws 1000 ma from a supply
    rated for only 730. This will produce almost twice the internal heat
    compared to what the supply was designed for, unless the load just
    happens to use only a fraction of the 1000 ma capability of the
    original supply.
  8. (Mike) wrote...
    Well first off, "wall-wort" type adapters do not "push out" anything.
    Instead they provide a output voltage and the load (the device powered
    by the wall-wort) pulls whatever current it needs for whatever it is
    it does. The product designer knows what types of current the device
    uses so they then pick a Wall-wort that meets or exceeds those specs
    for the current.

    As an example, if I had a product that draws roughly a half-amp, then
    I wouldn't pick a wall-wort that has a max rating of just a half-amp
    since I would then be drawing the max rated current all the time.
    Instead I would like some head room. So I might decide that if I want
    to draw 0.5A most of the time, then to give me a little head room, I
    might decide that 0.5A is no more than 80% of the max rating of my
    wall-wort. So I would need a wall-wort that has a current rating of
    625mA (aka 0.625A). Looking in my ACME Wall-wort catalog I might find
    they make one model in my voltage output that puts out 0.5 amps, then
    the next size up is 0.75A. So I then simply pick the 0.75A model and
    away I go.

    The whole point of that is whatever you are supplying power to with
    your wall wort is not likely to be drawing 1000ma (1A), but something
    less. The question is how much less?

    Since we can assume your product is not really drawing 1A, but instead
    something less, you MIGHT be able to use the wall wort you have rated
    for 0.73A. If your battery charger draws around that 0.7A or less,
    then you are ok. If you are worried, check out other wall-worts made
    for the Japanese market with the 5.8V rating and find one rated for 1A
    or higher. Even if you get one rated for 100A, if your device only
    draws 0.8A it will draw that same current regardless of the max output
    rating of your wall wort.

    However, if it was me and since it is just a battery charger and your
    alternate wall-wort is pretty close, I might just go for it and give
    it a try, at least for batteries that are not overly expensive to
    replace (AA NiMHs for example). I might not be so keen to attempt it
    for a charger that charges a $100+ laptop battery for example.

  9. John Fields

    John Fields Guest

  10. Mike

    Mike Guest

    Hi John,

    Well I'm hearing the if one can't find a match on amperage, that it's
    better to have more than less(as long as voltage is correct), is that

    I don't know how much load this device will cause on the DC adaptor.
    I only know at this point that the original adaptor pushes out what I
    said before.

    If I can't find an EXACT match for a DC adapter, in your opinion, what
    is the tolerance level that I can safely use and adaptor as a

    Meaning, If I had a 6.0V DC adaptor with 1000MA, would that be
    better than a 5.8V DC adaptor with 730MA? Or is voltage more
    important to match versus amperage or vice versa. Of course it's just
    best to find an exact match, however if I can't.. I'm wondering just
    how far and in which direction I can have a difference in amperage and
    or voltage.

  11. Yes. Unused capacity is better than over taxed capacity.
    Without knowing a lot of details about your load it is hard to say
    what variations would be best tolerated. But I suspect that having .2
    volts extra with all the current capacity that is needed is better
    than having only 73% of the capacity required.
  12. Mike

    Mike Guest

    Ok, well obviously I'm not expert on this but understand what you're
    I don't have any mean readily availble to determine the exact
    requirements of my device, so therefore I just don't know if 730ma
    will cut it or not.

    I'm wondering what will happen though if my device is expecting 1000ma
    and the wall-wart can only provide 730ma what will happen then?

    Thanks for the advice
  13. The voltage will sag. (Drop)
    | __O Thomas C. Sefranek
    |_-\<,_ Amateur Radio Operator: WA1RHP
    (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz
  14. The output voltage will not be as high as the nameplate specifies and
    the unit will get hotter than it was designed to stand. This second
    effect takes a little time, so it might work long enough to measure
    the output voltage under load to see if it stays within spec. If it
    passes this test, then you can run it longer and check it often for
    heat of burnt smell.
  15. Mike

    Mike Guest

    Well, as luck would have it.... I can't find anywhere a DC adaptor
    with 5.8v and 1000ma.... I see plenty of multi-volt adaptors... and
    6v DC seems to be the closest I can come to voltage.
    Now I'm wondering just how much damange an extra .2 volts will do to
    my product, because it seems like I have no other choice..
  16. There is no way to know, without more information about the load. But
    I will bet you a dollar that it will work. 0.2 volts is just not a
    very big % extra. If the original was a regulated supply, not a raw
    supply, then, who knows. But if the original was just a transformer,
    rectifier and capacitor, then the output would vary more than 0.2
    volts just from load swings and line voltage changes.
  17. Mike

    Mike Guest

    Thanks John. I'll give it a shot and keep my fingers crossed!
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