Another of many questions about inverters

Discussion in 'General Electronics Chat' started by Atton, Jan 31, 2016.

  1. Atton

    Thread Starter New Member

    Aug 30, 2015
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    Recently I did a bit of research and I learned that most inverters use a high frequency switching system. This system from what I know produces several hundred volts which is rectified into dc. After that there is some kind of weird switching system which turns it into AC, which did get me thinking a little bit. How would someone build a switching system like that. I do know that there is no transformer involved and the circuit runs at mains voltage. So how could you make a sign-wave switched circuit like the ones in high power inverters, where you could change the frequency. Also is this even possible to actually do?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    You're saying that a high power inverter changes DC to AC to DC to AC. That sounds like an inefficient approach, especially the part about the "weird switching system", which sounds like a very precise description of how to do things in the most inefficient way possible. To bring you back to reality, there is a simple relationship which applies to all such devices.

    Power Out is ALWAYS less than Power In; sometime it is much less. Assuming that each of your conversions above was 85% efficient, the result would waste nearly 40% of the input power and be hardly worth doing. If one was to say that producing AC at 50-60 Hz. is "oh so difficult", I would be inclined to agree. IMHO there are better ways to get portable AC power.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Hello Atton. You raise several points but I am unsure what they are pointing to unless you link to the article or articles you are reading.

    There are many ways to skin this cat with new techniques coming faster and faster. Also the terms such as "inverter" are not really specific, that term can mean a simple 1 transistor circuit up to a mega watt power station.

    I do know you can make sine wave inverters with a variable frequency: I have several in my shop. I don't know what is inside any of them as they are tool to me. But they do exist.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    One of the things you see repeatedly is the notion that amplification implies an increase in power. The only way to amplify "power" is to have a power supply that will meet your needs.
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    What you are describing is a "modified sine" inverter. Yes, they do up convert 12 volts to 200 volts DC and then use high voltage switches to alternate it. This is cheapest method and produces a crude waveform. There are better modified sine inverters that produce an additional switching voltage to improve shape of the waveform.
    The pure sine wave models are completely different.
     
  6. Lestraveled

    Well-Known Member

    May 19, 2014
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    Here is the waveform for the cheaper modified sine inverter.
    [​IMG]




    And here is the waveform for a better modified sine inverter.
    [​IMG]
     
  7. Atton

    Thread Starter New Member

    Aug 30, 2015
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    I see that is a far more complex issue.
    But for those who asked this is one of the video I watched on the subject.
     
  8. Atton

    Thread Starter New Member

    Aug 30, 2015
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    Also this
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    The pace was horrendously slow and the video made me dizzy. One of the worst that I've forced myself to (partially) watch...

    Does he ever get around to saying anything useful?
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    When it comes to inverters it can be really hard to distinguish between what you need, what you want, and what you can afford to pay for. AFAIK you risk a good deal hooking up expensive electronics to a modified sinewave inverter, especially one from China. You want to do it, that's your business. You want to learn how to design one, well there is a path for that. You want to learn how to fix 'em for big bucks there is a path for that. Getting an inverter to replace the power company, is just not going to happen anytime soon.
     
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