"Roger Long" wrote in
:

Say, how much more battery draw is there on something like a laptop
being run on a small inverter vs being hot wired directly to the 12 V
system as I was discussing earlier?

Does anyone have any solid info on whether Vista will crash if it
doesn't contact Micro$oft via the Internet occasionally?



It depends on the inverter. Plugging a laptop into a 4000 watt Heart
beast, whos no-load battery current is more than the laptop's power
drain, isn't going to be very efficient.

So, what we do is to leave the 4000 watt Heart OFF and plug the laptop
power supply into the smallest little inverter that can safely handle the
laptop's maximum load, when it's battery is dead and charging at full
power, its display is on full brightness and its processor/harddrives are
trying to decode high definition TV and save it to a converted-on-the-fly
Divx file...about the most intensive load my laptop has ever performed.
Just playing HDTV from the Hauppauge DTV USB dongle eats the extended
battery in 40 minutes and makes the processor fan run full blast like a
furnace!

Luckily, the power supply brick that came with the laptop has taken all
this into account to save us some time. READ ITS LABEL. If it tells you
its AC power input in watts, that's what we're looking for. If it tells
you it puts out 19VDC at 2500ma, then we multiply the 19V x 2.5A = 47.5
watts. We buy the AC inverter that is just double that need....around
100 watts. If Wally World has the 75 watt on sale at 40% off, we buy
that one, which is still plenty of margin, but can't also charge the
cellphone at the same time.

Practically speaking, I like a small inverter that plugs into a cigarette
lighter, that can handle my small loads; laptop charging, cellphone
charging, any small AC-only gadgets I like to use; simultaneously. Just
add up all their small power drains. If it comes to 148 watts, I buy the
175W inverter Wally sells cheap.

Now, from actual measurement, the unloaded 175w inverter draws about .3A
just sitting there running, including it's fancy blue LED lighting.
Charging the 50W laptop, you may assume it is around 98% efficient, if it
was purchased in the last 5 years. They've gotten so good the 750 watt
inverter in my stepvan shop, a Black and Decker/Vector sinewave inverter
from Wally World, even shuts down its fan when the load is under about 90
watts. Loaded to 250 watts, the case hardly gets warm and the fan runs
on low speed! How warm it gets (or how hot the air is coming out of it
under load), is an indication of how much wasted power it wastes.

The little 175W or my 80W (which is built right into the cigarette
lighter plug, itself) don't even get warm to the touch. The cost of
power conversion using these little units powered from a decent house
battery is totally insignificant and CERTAINLY not worth endangering a
$1500 laptop by plugging it directly into boat batteries to save 1AH/day!

Just don't hook them to the Beast-in-the-Bilge and leave it buzzing....
(c;

Larry
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