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Modified sine - mains LED?

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  • 19-02-2018 4:24pm
    #1
    Iderown
    Registered Users Posts: 233 ✭✭


    Interested to know how mains voltage LED lamp would perform (if at all!) when powered by a modified sine wave inverter.
    Test is now under way.


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    #2
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    Iderown wrote: »
    Interested to know how mains voltage LED lamp would perform (if at all!) when powered by a modified sine wave inverter.
    Test is now under way.

    That depends on the nature of the modification.


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    #3
    Iderown
    Registered Users Posts: 233 ✭✭Iderown


    I guess so. Unfortunately, I don't have access to an oscilloscope to examine the inverted mains waveform. To be honest, I'm  really only interested in the performance with this particular inverter. It's a cheap 12V, 150W output item.
    The test on a 12W led is still under way. No obvious problems. Have lower rated LEDs still to test.


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    #4
    Iderown
    Registered Users Posts: 233 ✭✭Iderown


    I powered three mains LED lamps: 13W, 9.5W and 6W each for one hour using the modified sine wave inverter. They were supermarket "own brand" types. Then repeated each for one hour powered by mains. They all survived and seemed to get about equally warm during running with inverter and mains power.
    Happy user here.
    Some day, I must take a saw to one of these items to see just what sort of electronics is inside. I hope that it is a bit more sophisticated than bridge rectifier, reservoir capacitor and series resistor.


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    #5
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    That depends on the nature of the modification.

    Id say that modified in this case means the type of inverter.

    Modified v pure. Modified being a rough 3 step output or similar, although pure is just a higher resolution rather than being a true sine wave probably.

    Modified are good for resistive loads.


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    #6
    Iderown
    Registered Users Posts: 233 ✭✭Iderown


    The booklet which came along with the inverter includes a crude diagram of the output waveform:
    2.5ms 0,    5ms +V,    5ms 0,    5ms -V,    2.5ms 0
    Total time 20ms = 50Hz frequency
    A very crude approximation to a sine wave. I hope that the V is about 325V to result in an rms value of 230V.
    I assume that the zero times are adjusted so that the rms value remains at 230V when the peak-to-peak output voltage gets reduced by an increased load. I really need an oscilloscope.
    For your interest, the drive system in a 12V ac/dc led can be quite complex. An example of part of such a drive system is described here. http://www.circuitstoday.com/led-driver-ic

    As I said: seems good enough for this type of load.


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    #7
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Iderown wrote: »
    The booklet which came along with the inverter includes a crude diagram of the output waveform:
    2.5ms 0,    5ms +V,    5ms 0,    5ms -V,    2.5ms 0
    Total time 20ms = 50Hz frequency
    A very crude approximation to a sine wave. I hope that the V is about 325V to result in an rms value of 230V.
    I assume that the zero times are adjusted so that the rms value remains at 230V when the peak-to-peak output voltage gets reduced by an increased load. I really need an oscilloscope.
    For your interest, the drive system in a 12V ac/dc led can be quite complex. An example of part of such a drive system is described here. http://www.circuitstoday.com/led-driver-ic

    As I said: seems good enough for this type of load.

    It sounds like a square wave.

    Anyway, it doesnt work the same way as an RMS of sine wave peak, as the voltage all along the sine wave is the voltage being driven so is varying up and down in real time, but a square wave is just on or off, so the voltage seen is the voltage of the magnitude or thereabouts. The power output is based on duty cycle though, like pwm dimming a LED for example.


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    #8
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    They wouldn't sell so many but modified square wave would be a more apt description.
    LEDs won't care they're extra low voltage DC with onboard rectifiers.
    You'll get problems with appliances using principles of electromagnetic induction, anything with a transformer, ac motor, induction cookers, microwaves etc...

    Pure sine isn't pure it's still stepped but the steps are very, very small. It's close enough for most things not to notice.
    Old skool inverter; brushed motor coupled to an alternator, now that was true sine ...bit loud and inefficient though.


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