Electrical Power for Laptops

Yes, I meant 'my laptop is 0.37 ampere AC, at 220 Volts'. And it's a worse
case scenario. But I always assume 'worse case', when I am somewhere in the
Fench Alpes. Do't want to end up with a dead battery when I am under
excellent skies 1200 kilometers from home.

Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/



"Jon Isaacs" schreef in bericht
...
A 17AH 12V battery with an inverter is a good solution, but I think the
17
AH battery will be empty too soon. My laptop is 0.37 Ampere DC.

I think you meant to write AC and 220 volt at that.

It can be
easily calculated that it will run 2.2 hours max. with a 17AH

I am curious if you have actually measured this or if this is just a
calculated
number.

The stated current draw of the transformer is a maximum value and I
suspect
that it is only that high when the laptops own battery is being charged.
The
operational needs are likely much less.

Something to consider...

Most laptop batteries are around 4000ma-hr and something around 10-12
volts and
will power the laptop for 2 hours or so. I would seem that if one could
get
the DC from the battery directly to the lap top rather than going through
the
DC-AC-DC conversions that there would be more than enough to run the
laptop for
many hours.

It is also difficult to believe that the DC-AC-DC conversion is so
inefficient
that a 17 amp-hour battery will only run the laptop for the same amount of
time
that its own 4000ma-hr would.

Something else to consider for Alan if he is brave and knowledgeable...

If one is handy with wires and meters and such...

If they laptop is essentially disposable, the 15 volt requirement is
actually
close enough to the 12.6 volts that a 12 volt battery produces that you
might
get away with operating directly off the 12 volt battery. Some laptops
though
actually operate on AC and have the rectifiers built in to the laptop.

My guess is that the 15 volts is actually there to provide a bit of
headroom
for the charging regulator and that the laptop actually operates on
something
signficantly less.

Another possibility if one is handy is to wire the battery external
battery
directly to battery terminals of the laptop itself, replacing the battery.
This would take some investigation to see if it were possible and might
require
some external circuitry.

Personally I just use an inverter plugged into the motorhome's second
battery
which is 106 amp-hours or so...

But mostly I avoid such things and use my Palm with Planetarium which runs
for
a month or so on two AAA cells.

jon

Jan van gastel wrote:

Yes, I meant 'my laptop is 0.37 ampere AC, at 220 Volts'. And it's a worse
case scenario.

That's about 80-watts but the efficiency of the laptop's power supply
(transformer) is less than 100%, so the laptop would actually use
considerably less power if you could bypass the 220-V AC power input and
run it directly on DC with a high capacity external battery. Does it
have a DC power input jack?


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That's about 80-watts but the efficiency of the laptop's power supply
(transformer) is less than 100%, so the laptop would actually use
considerably less power if you could bypass the 220-V AC power input and run
it directly on DC with a high capacity external battery.

A point of reference: I have a 75 watt inverter that seems to have no problem
running my Laptop...

jon