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Making sense of watts, amps and volts -- a typo?

Discussion in 'Electronic Basics' started by W. eWatson, Apr 8, 2012.

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  1. W. eWatson

    W. eWatson Guest

    Could the following be a typo. Written by someone to me on inverters (DC
    to AC).

    Volts x Amps = Watts so as the voltage goes down, the amperage goes up
    to maintain the same number of watts.

    1000 watts at 120VAC is about 8.3 amps.
    1000 watts at12VDC is about 83 amps. <--typo? Shouldn't it still be 8.3?
  2. Guest

    This isn't strictly true for AC.
    Do you have a calculator?

    1000/12 = ~83 on mine.

    There is also a little thing of efficiency, in here. The inverter is going to
    get hot.
  3. Jamie

    Jamie Guest

    The assertion is correct. That is (83 amps) is the correct answer.

    Get out your Ohms law book on Power calculations and do your
    home work! :)

  4. W. eWatson

    W. eWatson Guest

    My book are sooo old it wouldn't help. Actually I see what happened. Ah,
    nuts. I read both as 12, and didn't notice the 120. So, yes, it's
    correct. BTW, either Ohm's Law or Kirchoff's Law was discovered by
    Cavendish. Not only was he severely anit-social, he often offered up
    some of his discoveries to various scientists.
  5. W. eWatson

    W. eWatson Guest

    What I did was mis-read it, as explained by my post to Jamie.

    Here's how the paragraph began to the two sentences above that followed:

    Make sure cables between the batteries and the inverter are short, fat,
    well-crimped and screwed down tight on both ends. They will be handling
    ten times as much current as the AC side of the inverter.

    He's basically telling me that I'm going to need some fat wire on one side.
  6. Jamie

    Jamie Guest

    Well, then he would fit right in here for the most part, as far as the
    anti-social goes :)

  7. Guest

    PF, dumbass.
  8. Fred Abse

    Fred Abse Guest


    Do the math:

    Volts x Amps = Watts
    Therefore Amps = Watts / Volts
    1000/120 = 8.3 (approx)
    1000/12 = 83
  9. Guest

    But, as any first-year engineering student knows, I * V <> W, where AC is
    concerned. Go back to your 555s.

    You're as dumb as DimBulb.
  10. Fred Abse

    Fred Abse Guest

    But ain't always Volt-Amperes.
  11. Jamie

    Jamie Guest

    When I see the term "VA", I know we're dealing with "REACTIVE" power.

    PF (Power Factors) denotes the difference between "REACTIVE" and
    "RESISTIVE (True power)" So, using the term VA is assumed power.

    Having AC in the equation has nothing to do with it actually, I can
    put AC into a purely non reactive load and it would simply power.. There
    difference being is, you need to take measurements along the vectors to
    come with a sum of power with in a time frame. Normally, with a clean
    sinusoidal wave, we just assume RMS power.

    if you look at this formula.

    P = I+V*Cos(x), you'll notice that "I" is used as "Amperes" here.
    This is a AC power formula but you don't see any distinction here with
    the use of "VA" as would be in case of "REACTIVE" power.

  12. Guest

    Absolute nonsense. to be expected from dumbass Myers.
  13. Guest

    Moron, reading between the lines, anyone with as much as half a brain, would
    understand that he was talking about an INVERTER, which is *NOT* resistive.
    What a dumbass.
    Like I said, you're as dumb as AlwaysWrong. Keep proving it.
    Like AlwaysWrong, you insist on proving that you're *always* wrong. I have
    nothing against the 555, just one-trick-ponies, like you.
  14. Guest

    He didn't. You know, that pot and kettle diversion.
  15. Guest

    No, he was talking about volts and amps. You can't get to watts from there.
  16. Guest

    No, when you se "VA" you simply don't know "W"; not enough information given.
    With an inverter you can *bet* the power factor is not unity.
    What? Did you really mean to write that nonsense?
    You've just specified the PF by stating a resistive load, so no, you're still
    wrong. Without the PF explicitly stated you *cannot* get there from here.
    Your "COS(X)" *is* the power factor, which is only true for sine waves.
    WTF, is the COS(X) term, if not to cover reactive power? Jamie, go back to
    your ham shack.
  17. Jamie

    Jamie Guest

    Oh really..

    Well excuse me, I slipped with the keyboard. I hope you really don't
    think I intended it to be that way ? If so, you are naive.
    And if you want to start punching at the bit, from what I can see with
    your last assertion, It seems that It's you that has a problem with
    understanding this. Maybe you should brush up on Kirchoffs laws a little
    on this subject.

    nuff said, And btw, there is such things as RMS power. How much in
    the dark you are.

    You know, I tried to actually help you but it seems obvious you have a
    one way street and much of which have people going the wrong way, except
    for you of course.

  18. Guest

    It shows.
  19. Guest

    I first encountered it in college in calc class and then in second semester
    physics. ...both first year.
  20. Guest

    Joining the AlwaysWrong brigade?
    You don't have to tell us about your Saturday night. Really.
    Sorry, but you failed EE-101, as usual, Maynard.
    You *certainly* don't show it here. You're wrong about just about everything.
    "Engineering level work" tells it all. Like Fields (and DimBulb), you *aren't*
    an engineer, and it show. Loudly.

    You even sound like AlwaysWrong; "I worked for". "I worked on". "I worked
    with". Not "I Did".
    I believe you! Really, I do!
    I don't drink, dimwit. You really are slow.
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