billbolton wrote:WNJ wrote:I gave a brief explanation for the basis for my assertion.
You chose to omit this in the quote you plucked from my reply. Clever.
You produced nothing of substance regarding contemporary inverter design which provides any support at all to your
assertion. Not clever!
I gave concrete examples of good quality, moderately-priced 120-volt output inverters available in the USA, which claim "peak efficiencies" of less than 90%. I have seen
no credible claims of efficiency
in excess of 90% for inexpensive small 120-volt inverters (120-volt models being the only ones of use in the USA, where most of the readers of this forum reside) a standard which you claim is commonplace.
I’m not sure how “low end” this inverter may be compared to low-end inverters available in the USA. From what I can tell, it is for producing 240 VAC (Europe/Australia, I presume) from 12 VDC.
In any event, the table on the web page shows efficiencies varying from 93.2% (loss of 6.8%) at about half load, to 85.7 (loss of 14.3%) at its rated capacity, to 81.4% (loss of 18.6%) at the maximum measured load.
To my mind, losses ranging from 6.8% to 14.3% to 18.6% represents something more than “very little” variation.
billbolton wrote:See this FAQ on typical inverter efficencies....
DC Inverter FAQ
This web page is focused on inverters for solar power and selling AC back to the grid. Again, I’m not sure of its relevance for low-end inverters of the type most people would consider for powering a CPAP from a battery.
I would note its reference, however, to waveform inefficiencies of modified sine wave inverters:
“However, there is more to the story. Efficiency ratings are usually given into a resistive load (basically something like a light bulb or electric heater). When running such things as motors, the efficiency actually breaks down into two parts - the efficiency of the inverter, and the efficiency of the waveform. Waveform efficiency means that most motors and many electronic appliances run better and use less power with a sine wave. Typically, an electric motor (such as a pump or refrigerator) will use
from 15% to 20% more power with a modified sine wave than with a true sine wave.” (emphasis added)
I’ve seen references which give higher figures, 20% to 30%, for losses due to waveform inefficiencies with a modified sine wave inverter using other than a resistive load.
The description of the smallest model notes that it is quasi sine wave (modified sine wave). In quickly scanning the others, I did not see where any of them stipulated quasi/modified sine or pure/true sine.
In any event, I see their output is rated at 240 VAC, which I take to be
single phase AC. Again, I’m not sure what direct relevance this has for those of us in the USA who are accustomed to using 120 VAC
split phase power for most of our needs. We use 240 VAC single phase for powering things like water heaters, electric ranges, whole-house air conditioning, etc.
This is a page of Xantrex inverters for producing power to be sold back to the grid. Input 600 VDC, output 208 VAC,
three-phase power. (Three-phase power is generally used only by commercial enterprises. It is almost never seen in homes in the USA, unless maybe the owner has some monster woodworking machines or similar. You will recognize it by the four wires, not three, on the power drop.) The sizes of these inverters range from 10,000 watts to 225,000 watts.
I’m confident that the coal-fired generators at the power plant are similarly more efficient than my little gasoline-powered generator that I use for charging the RV batteries when camping.
Where is the relevance?
Wayne