For this post I wanted to test the inefficiency of inverters when powering an LCD TV. It is stated by many companies that inverters are about 10% inefficient when converting from 12 volts DC to 120 volts AC.
This can be true when running them at max output and with inductive loads but is far from true when powering items such as computers & LCD TV's. These efficiency losses are obviously not all from the inverter but stem from operating devices that normally take 120 volts and then convert it to DC voltage inside the unit, or in the AC cord with an in-line converter. If your device already runs internally on DC then on a boat you're converting from DC to AC then back to DC again. By doing this you are only adding to whatever inefficiencies your inverter already has.
To accomplish this test I used our 19" Polaroid TV that runs on either 12 volts or 120 volts. What I really wanted was less "lab" or "theoretical" numbers and more "real world" on a device that can operate on both DC and AC and one that would give a steady output from which to measure. Please be aware that not all devices that internally run on 12V can run on variable 12V meaning they may do okay on 12.00V but may toast themselves when fed 14.6V. Please be sure your 12V internal voltage device can be run on a wide voltage range at least 10.5V to 15.5V, before using it on a boats DC system fed directly off the 12V system.
To make sure this TV was consuming a fixed amperage I loaded a DVD into it and then paused it at exactly the same spot in the "Elmo" disc of my daughters.
The on screen shot is showing the TV paused and in this case it is running off of 12 volts DC. A little known fact is that many items you would choose to use on a boat, such as an LCD TV or a laptop computer, already run on DC internally. By using an inverter and the "wall wort" or AC/DC converter box, that usually resides in the middle of the power cord, you are getting horrible inefficiencies because you are converting from DC to AC then back to DC again. Many devices will already run on 12 DC without an inverter and the AC/DC wall wort. You can simply read the output specs of the "wall wort", or AC/DC converter, to determine if it is a 12v output.