inverter output questions

trkarl Solar Expert Posts: 33
I have been using an SW4048 for about two years and it has been fine. However, I have wanted a bigger inverter and settled on a sunny island 5048u. The main reason being that I only want/need to run 1 inverter and the 5048 has a generous overload capability for short durations of time. I installed it Saturday morning and had a few questions.

I know the SW is ancient technology compared to the 5048 or the new XW or Outback stuff but I am not too keen on the workings of the inverters and how they manage their output.

I noticed a few differences between the two when running loads and thought maybe someone could give me an explaination in laymans terms.

For instance the refrigerator is definitely quieter than before. Is this because the SW puts out "dirtier" power?

My computer speakers don't have a buzz with the 5048.

When turning on the coffee pot or the microwave there is barely any perceptible dimming of the lights where as before you could definitely tell something turned on. Even when the fridge turned on.

Measuring the voltage coming out of the SW when the coffee pot or microwave was on there was 120 but at the plug in the house there was about 111.
With the 5048 there is 120 coming out also under load but the voltage at the plug inside is about 117. Why the difference?

Both inverters also put out a steady 60hz no matter what though.

I know the SW has a "stepped sine wave" so maybe this is what causes the buzz but why the sag in voltage at the plug end when they both put out the same at the inverter under the same load?

Another question is the voltage coming from the grid is generally between 123 and 126 no matter when I test it. Since the 5048 has user adjustable output would there be a benefit to raising it from the 120 it is default set at to 123 or so?


  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: inverter output questions
    I know the SW is ancient technology compared to the 5048 or the new XW or Outback
    I run a SW4024 only when there is a power outage and I can't tell the difference from utility power except when my 1/2 horse well pump kicks on there is a bit of momentary dimming. No noise in speakers or radio, TV ect. When I run my tractor driven PTO generator, there is all kinds of hash on the AC that affects florescent lights well as radios etc. I wonder is your old SW may have a malfunction in one of its three circuits that makes the stepped waveform.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: inverter output questions

    The Trace SW series use three transformers to stack voltage for output sinewave. This yields a maximum of 27 steps from negative to positive peak voltage of sinewave. Since these steps must cover min battery voltage and max grid voltage the typical number of steps is about 20-22. Each step is about 12-18 volts along the output 120vac sinewave. This creates the rough sinewave.

    Newer inverters use high frequency pulse width modulation to create a quality sinewave.

    The SW changed steps at about 240 Hz rate. New inverters run 10-30 kHz PWM.

    The down side of high freq PWM, caused by high freq switching of MOSFET's, is they will generally have higher low load idle current drain from batteries. Some of the more expensive model inverters get around this by 'furlowing' some of the parallel MOSFET's at low output loads.

    I know the SW has taken over when I hear a low audible buzz in my Hunter ceiling fans. This way I know when the grid has gone down. ;)