I obtained a little Ryobi 150 W inverter with the idea of using it to run a table lamp or two in the event of a power outage. I thought that if an LED bulb uses 7 to 9 W it could run for quite a long time on a 4 Ah battery.
However, I've noticed that while these bulbs do indeed draw the rated power from the mains according to my power measuring device (a Kill A Watt clone), they draw twice as much at the input of the inverter, giving an overall efficiency of 50% or less. Since my measuring device doesn't work properly on the output of the inverter, I cannot tell where all the extra power is going. Is it wasted in the bulb, or is it wasted in the inverter?
(I am measuring the efficiency by running the inverter off a DC power supply and measuring the input current at a fixed 20 V.)
Some LED bulbs don't work at all on the inverter, and I have heard stories of other LED bulbs failing prematurely.
For comparison, incandescent bulbs of a similar 6 - 25 W power rating run the inverter at a reasonable efficiency approaching 90%, but this is not helpful when the total power draw is so much higher.
I have one 14 W CFL that draws 17 W at the inverter input, and although that's a reasonable efficiency it is still 17 W.
Questions:
- Does anyone know what's the deal with modified sine wave inverters and LED bulbs, and why they don't work efficiently?
- Does anyone have experience of Kill A Watt devices on MSW outputs, and knows of one that works correctly and gives proper readings?