24-SEP-2008
Inverter Tested on My 12 Volt / 120 Volt TV
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. 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.
To make sure my 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.
24-SEP-2008
Amp Consumption At 12 Volts DC
This photo is of the TV on pause while plugged into the boats 12 volts system.
The TV when running the DVD, paused, on 12 volts, consumes 3.9 amp hours per hour of use. It should be noted that I left it paused for over 5 minutes and the voltage never fluctuated nor did the amperage up or down from 3.9 amps so I was getting good steady readings.
24-SEP-2008
TV Plugged Into A 1200 Watt Inverter
This photo shows the DVD paused in almost the exact same spot though this time it's running on 120 volts AC through my larger 1200 watt inverter. Take a look at the next photo to see how inefficient it is compared to 12 volts DC.
24-SEP-2008
TV Running On A 1200 Watt Inverter
There is no trickery here and the Xantrex battery monitor is not lying. Running this same exact TV on 120 volts AC through a 1200 watt inverter uses 5.8 amp hours per hour of run time.
When compared to running this SAME EXACT TV on 12 volts DC the inverter is 32.8% less efficient or a far cry from what many would assume is a 10% inverter inefficiency.
Keep in mind that some of this efficiency loss comes from the conversions from DC, to AC and back to DC through the TV's "wall wart".
24-SEP-2008
TV Running On A 400 Watt Inverter
Yes, if you're wondering, I do have a lot of gadgets on the boat. It does make for some interesting experiments though.
For this test I used my smaller 400 watt inverter that I power my laptop with. My reason for doing this test is to show that an inverter sized closer to the load can sometimes be slightly more efficient.
24-SEP-2008
TV Running On A 400 Watt Inverter
So maybe it's not that much more efficient but 6 tenths of an amp is nothing to snub your nose at. The 400 watt inverter ran the TV using only 5.2 amp hours per hour of run time and was a mere 25% inefficient. Again this is a far cry from the 10% claimed by most manufacturers, and believed by boaters.
This certainly was not a very scientific experiment but rather a real world experiment designed to show what one item, a TV, designed to run on both 120 volts AC and 12 volts DC, will do run both ways.
It is clear to me that if you have the option to buy a device that will run on 12 volts DC vs. 120 volts AC, you should buy it. Inverting power from 12 volts DC to 120 volts AC, then back to DC again is a terribly inefficient way to power devices off your boats house bank of batteries..
