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re: a special thanks
10 may 2002
george l ghio   wrote:

>> so far, we've seen that two inverters have (5%?) lower efficiency near
>> max output than at say, 20% of the max.
>
>which two would that be?

the graph on your site (for which manufacturer?) and
the one on the trace site, eg p 59 of the sw4048 manual... 

>>does it make any difference in longevity?
>
>oh yes. 

how much? i'd say it's "insignificant," a priori.

>the max continuous rating is largly the point where the
>inverter will run without overheating and shuting down.

that's irrelevant. shutting down is not the same as failing early.

>heat is not good for electronics.

neither are vibration, overvoltage, component flaws, cold solder joints,
moisture, fretting corrosion in connectors, lightning, metal migration,
ozone, and many other failure modes that don't depend much on heat. those
that do depend on heat don't do so in a linear way. they have different
wearout and failure modes with different arrhenius activation energies.
you might correctly say "this capacitor will eventually fail," but that
may be unimportant if something else is likely to fail first.

>if you choose an inverter that will run at its best efficiency at your
>load it will run cooler and last longer than an inverter that runs at
>its max contiuous rating to meet your load. 

maybe. maybe not. that depends on the circuit details. it looks like
a trace 4048 would be most efficient at about 200 w, 5% of the max
output spec. would you use a 4048 for every 200 w load? how much would
that reduce its failure rate? as a system, consider that you have 20x
more stuff to fail, and a 20x larger investment... 

>i have the stat. sheets for all the trace inverters and the ones that
>show efficiency vs load all seem to be in the range of a 10% to 30%
>drop in efficiency  at their max rating.    

looks to me that the max efficiency is about 95% at 200 w, falling off
to 90% at 4 kw. you might (wrongly) call that a 50% drop in efficiency.
 
>> >if you have a load of say 700 watts and you buy a 700 w inverter then
>> >the chances are that the inverter will fail in a short time.
>> 
>> >if on the other hand you buy a 1500 w inverter then not only will the
>> >inverter last many times longer but you will get your 700w at the
>> >inverters best efficiency.

bullshit.

nick




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