how inverters output a steady 240

ws9876ws9876 Solar Expert Posts: 414 ✭✭✭
I have asked this on electronics forums but never got an understandable answer.
I am familiar how an inverter switches a DC signal thru a center tap transformer
and filters out the associated harmonics,leaving a sine wave.Here is question 1...
what is in a low pass filter that doesnt allow some freq. to pass. Is it just a capacitor?
Here is the main question and the important one....
How does the out put stay at 240 if (in the case of SMA inverters) the input DC is variable,from 130-400 volts DC.
I know that alternators in cars output a steady voltage by using a circuit that allows more or less current to pass thru a valve transistor and stoke the coil under the electro
magnets. Less current lowers the output volts and more current stokes the electromagnets and makes a higher voltage.
Is this what is going on in a SMA true sine wave inverter???
Or do they use a big industrial Zener Diode that outputs 240 when its used in reverse,..
like the 7805 little voltage regulator..??
Or does switching at a certain speed just produce a certain voltage ..because?????
An experienced Electrical Engineer might be good at this one.....


  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: how inverters output a steady 240

    best guess:
    They use a transformer (or measure directly) and a control circuit varys the power duration fed into the system, so that the output is limited to the factory preset limit.

    heres a page with several ideas & schematics.
    your mileage may vary, and smoke may come out of your wires if you attempt these.

    Search the web - that's what I did
    120VAC inverter schematic theory
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    gen: ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: how inverters output a steady 240

    nowadays, it's pwm technology that is allowing the wider ranges. the filter for these becomes simpler than trying to filter a 120vac square wave. both inductance and capacitance can help achieve this, but one must realize that for power square waves you are dealing with passing higher power levels and components must meet the requirements. in other words unless you know what you are doing, don't try this at home kids.
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