Hi Norm,
The theory about resistive losses increasing by 4X when the load is increased
by 2X seems plausible for a specific Inverter design. (ie: if FET's are used
for switching semiconductors) Actually the losses may increase more than 4X
because both the wiring resistance as well as the FET channel resistance
increases with temperature at higher loads so the IsquaredR losses may increase
by 8X (ie: Squaring the current and as much as doubling the resistance when
hot) Therefore the efficiency will definitely deteriorate with increased load
as shown in your graph.
Higher power Inverters that use bipolar transistors or IGBT's don't behave like
this because these semiconductors do not have characteristics like a resistor
but more like a diode, (The device saturation voltage stays the same or becomes
even lower at high temperature) so the Efficieny tends to be lower than FET
designs at low loads and increase with higher loads up to a sweet spot. The
power factor loads makes the equation even more complicated.
Actually the original subject was about a blog that unjustly blamed false
advertisement for the efficiency of an Inverter. The relative testing the
author used may show more power consumed (compared to powering the TV directly
from 12Vdc) even if an ideal inverter (with 100% efficiency) could be found and
used.
http://www.pbase.com/mainecruising/boat_projects
Ahmet
S/V 8827
Lying on the drawing board waiting for retirement.
> From: [email protected]
> To: [email protected]
> Date: Mon, 30 Mar 2009 09:57:13 -0400
> Subject: [Liveaboard] Inverter Efficiencies with Attachment
>
>
> Attached find efficiency curves for my Trace inverter. Note that the first
> two numbers of each model number (SW=sine wave) is the rated power in
> hundreds of watts, and the second two figures is the nominal DC input
> voltage.
>
> Notice the steep curve at the start. This is because of the idling current,
> which on my SW2512 is stated to be 1.0A while search mode is 0.08A.
>
> I hope this will clarify the issues somewhat.
>
>
> Norm
> S/V Bandersnatch
> Lying Julington Creek
> 30 07.695N 081 38.484W
>
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