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Thread: Simple Workings of a Transformer

  1. #16
    Rancher
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    Quote Originally Posted by DJhandy
    I personally don't understand when u bench test an item and have 7.5 out of each lead and if you connect one leg to ground that 7.5v ends up in the positive leg giving 14 v. I've read and read about transformers. Can someone explain this in layman's terms??
    AC transformers are spec'd at their full load current (or 80%, I forget) so if you bought a 1 Amp, 12 Volt CT (center tapped) transformer, the open circuit voltage could well be 15 volts as you have discovered, or 14 volts under load, or 12 volts under full load that the transformer was spec'd at.

    Rancher

  2. #17
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by geniescience
    Transformers keep AC as AC
    and DC, DC.

    David

    nd DC, DC. ??????????

    Have you learned how to transform DC?

  3. #18
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    Quote Originally Posted by jwelectric
    nd DC, DC. ??????????

    Have you learned how to transform DC?
    Sure you can transform DC, 12 Volts DC into one side of the transformer, 0 Volts DC out the other side.

    Rancher

  4. #19
    DIY Senior Member abikerboy's Avatar
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    Quote Originally Posted by jwelectric
    nd DC, DC. ??????????

    Have you learned how to transform DC?
    Yea...it's called an "inverter"...lol!!! In the early days of electronics, it was called a "vibrating coil"... it was used to synthesise ac voltace out of a dc input by creating a chopped sign wave. Sorry guys, I just couldnt resist!

  5. #20
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by abikerboy
    Yea...it's called an "inverter"...lol!!! In the early days of electronics, it was called a "vibrating coil"... it was used to synthesise ac voltace out of a dc input by creating a chopped sign wave. Sorry guys, I just couldnt resist!
    Does not an inverter work by reversing the polarity of the DC voltage applied to the transformer or in other words by alternating the polarity of the DC voltage.
    Last edited by jwelectric; 08-30-2007 at 12:47 PM.

  6. #21
    Retired Defense Industry Engineer jadnashua's Avatar
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    The better inverters make an actual nice, clean a/c signal. Mid-range ones make a stepped square wave, and the cheapest just make a noisey square wave. Most of them are nasty, though, and some things won't work well with the power they provide. They also tend to make a huge amount of electrical noise and rf. None that I"m familiar with reverse polarity to generate the wave, though.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #22
    Homeowner geniescience's Avatar
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    Default Invertor. DC-to-AC.

    Quote Originally Posted by jadnashua
    The better inverters make an actual nice, clean a/c signal. Mid-range ones make a stepped square wave, and the cheapest just make a noisey square wave. Most of them are nasty, though, and some things won't work well with the power they provide. They also tend to make a huge amount of electrical noise and rf. None that I"m familiar with reverse polarity to generate the wave, though.
    off-topic, I'm wondering if a cheap invertor made for car lighter plugs can be used to charge a new Nokia cell phone without damage (to the Nokia).

    David
    p.s. also off-topic.
    Quote Originally Posted by jwelectric
    ....Have you learned how to transform DC?
    Huh? clarity please, if you want to ask a direct question instead of addressing the subject as a subject matter expert. Or, just be a subject matter expert and share what you know, gently.

  8. #23
    Retired Defense Industry Engineer jadnashua's Avatar
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    For the cost of an inverter, (while maybe useful for various things), I think you'd be better off with their car charger cord. I'm lusting after their new N95...maybe when a carrier picks it up to subsidize (ATT listening?).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #24
    Homeowner geniescience's Avatar
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    i have a 1st generation invertor but I'm wary about using it on a new Nokia. Unless I hear that new devices can handle a dirty wave signal.

    david

  10. #25
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by geniescience
    Quote Originally Posted by jwelectric
    Have you learned how to transform DC?
    p.s. also off-topic. Huh? clarity please, if you want to ask a direct question instead of addressing the subject as a subject matter expert. Or, just be a subject matter expert and share what you know, gently.
    I did clarify the question here
    Quote Originally Posted by jwelectric
    Quote Originally Posted by abikerboy
    Yea...it's called an "inverter"...lol!!! In the early days of electronics, it was called a "vibrating coil"... it was used to synthesise ac voltace out of a dc input by creating a chopped sign wave. Sorry guys, I just couldnt resist!
    Does not an inverter work by reversing the polarity of the DC voltage applied to the transformer or in other words by alternating the polarity of the DC voltage.

  11. #26
    DIY Senior Member abikerboy's Avatar
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    Quote Originally Posted by jwelectric
    Does not an inverter work by reversing the polarity of the DC voltage applied to the transformer or in other words by alternating the polarity of the DC voltage.
    Im not sure about the newer ones, or the ones made in recent years. The older ones would just "chop" the wave...you could actually measure a positive and a negative voltage at the 110 volt output. The old ones even up through the 1970's and I think some even up into the 80's (unsure about this though) used the vibrating coil, then the "chopped" 12 volt feed was sent through a step up transformer to increase the voltage to 110 volt. There was no positive or negative on the input. Both wires are black with alligator clips to attach them to a battery. The vibrating coil is not electronic, so it doesnt care which way you feed it. The voltage was never stable, and the frequency would vary quite a bit as you put more load on it. I have a very old one here...it belonged to my uncle that died in 1975 if that gives you any idea of its age...when you put power on it, it buzzes loudly from the vibrating coil, and it gets very hot even with no load on it. Its only rated for 75 watts, so all Ive ever used it for was to charge an electric razor, or to run a small lamp on it when camping out. Im not brave enough to plug anything electronic into it.
    Last edited by abikerboy; 08-30-2007 at 10:37 PM.

  12. #27
    DIY Senior Member abikerboy's Avatar
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    Quote Originally Posted by geniescience
    i have a 1st generation invertor but I'm wary about using it on a new Nokia. Unless I hear that new devices can handle a dirty wave signal.

    david
    I wouldnt be brave enough to try it myself, though it actually might work. If it were me, Id just go to Wally world and buy the car cord that fits the phone for about $8 If you find out that it will or will not work, I would be curious to know.

  13. #28
    Plumber jimbo's Avatar
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    An inverter takes the car's DC battery voltage and outputs an AC waveform. Most commonly sold inverters take the 12VDC and output 120VAC. We should stop talking about polarity with an AC wave because it is not relevant.

    Your charging cube for the phone takes a regular household 120 VAC and makes a much lower voltage, DC, to charge the battery. Why would you start with a car battery, invert it up to 120 AC, then "wall wart" it back to low voltage DC???? Why not just plug the phone in directly with a car adapter?

  14. #29
    Homeowner geniescience's Avatar
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    it's a new phone, and the battery is so good they don't give you a car charger with it. Recently I did need to charge it, once, while in my car fro several hours. I later found an AC plug instead of using that old "toy" invertor. I had left the phone uncharged and out of service for a few hours.

    ((I have never used this inverter, although when I got it in 2004 I thought it would be good for a laptop, but then that just never happened either.))

    Maybe one day someone who knows Nokia well might be able to say whether their phones can take a craggy AC wave.

    david

  15. #30
    Homeowner geniescience's Avatar
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    ok, got it.

    The inverter hopping back and forth from positive to negative is what you are talking about, and that is what i figured.

    When you asked it to me, i thought it had something to do with my short statement about transformers keeping a current's wave pattern.

    Later, it looks like the other meaning of reverse polarity got picked up, i.e. two reversed-polarity AC waves. Also not relevant now.

    David

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