Dave Plowman (News) wrote:

But a laptop will be nothing like 100 watts otherwise it wouldn't last for
minutes on its internal batteries.

But......
Probably most overlooked is the fact that laptops (when I were a lad)
were set as default to offer no power saving features when plugged into
a 240v supply.
i.e. Set as default to "maimum performance" compared to "maimum
battery life" when on internal battery.

So unless these default settings are modified to offer the same economy
of energy when on both battery and mains there will be a significant
increase in power usage.

I would guess.



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Dave Plowman (News) ) gurgled happily, sounding much
like they were saying :

Thus the wattage drawn by the invertor will be the same as its load,
but increased by the efficiency figure of the invertor. So if that's
say 80%, the load of 40 watts will draw 50 watts from the battery.

Plus the inefficiency of the laptop power supply, which may be another
20%, or maybe 60-65W

The 40 watts was just following on from ab's post - not meant to be an
actual figure for a laptop.

60-65 watts might be closer when it's charging the laptop battery - the
actual running current will be very much less.

Depends on the laptop.

Mine (big widescreen) whinges if it's on a 65w psu, and came with a 90w.
Others come with a 45w psu.

I've never come across a laptop psu that wasn't clearly labelled, though...

"The Natural Philosopher" wrote in message
...
aussie bongo wrote:
"Lobster" wrote in message
...
I'm thinking of buying an 12V - 240V for the car, to enable me to
charge/run devices such as a laptop / mobile phone(s) / AA batteries for
gameboys & camera etc etc while on the road (one at a time!); they seem
to be as cheap as chips these days and this would enable me to use the
standard mains chargers for all the above devices rather than buying
separate low voltage kit to connect each of them up to the cigar
lighter.

Sounds good in theory, but are there any gotchas? Eg, safety? Does it
run a car battery down more to power up a laptop via a 240V inverter
than directly to the cigar lighter? etc etc

Can't help feeling an inverter would be much better if wired or plugged
into the car some other way than via the god-awful universal
cigar-lighter plug...

Thanks
David

i dont know about power usage on a laptop, but,
i do know that 100w drawn from an inverter at 240v, will give you less
than 1/2hours usage.

Car bateries are 40-70Ah, and at a nominal 12v, that is 480-840Wh.

Giving and expected uptime at npominal 80% eficiency of say 4-8hrs
roughly.

one thing to remember if you get one, is that you have to make sure it
is turned off with no power going into it whilst starting the car as to
do so will damege the inverter.

Total ******** as well.



yea total ********, then buy one and read the instructions, i have had two
in the past, and damaged them by keep starting the car without turning them
off.

aussie bongo wrote:
read the instructions, i have had two in the past, and damaged them


Now why doesn't that surprise me..?

"Adrian" wrote in message
. 244.170...
Dave Plowman (News) ) gurgled happily, sounding much
like they were saying :

Thus the wattage drawn by the invertor will be the same as its load,
but increased by the efficiency figure of the invertor. So if that's
say 80%, the load of 40 watts will draw 50 watts from the battery.

Plus the inefficiency of the laptop power supply, which may be another
20%, or maybe 60-65W

The 40 watts was just following on from ab's post - not meant to be an
actual figure for a laptop.

60-65 watts might be closer when it's charging the laptop battery - the
actual running current will be very much less.

Depends on the laptop.

Mine (big widescreen) whinges if it's on a 65w psu, and came with a 90w.
Others come with a 45w psu.

I've never come across a laptop psu that wasn't clearly labelled,
though...




just looked at my psu and it is rated at 1.6amp at 240v input and 3.5amp at
18.5v output

In message , aussie bongo
writes

Indeed, and my point that he completely missed the point that asking
"Was it 40W at 18V or 240V", is obviously referring to the conversion
efficiency.

the current drawn at 40w on 18v is around 2.222222222222-amps // but 40w
at 240v is about 6-amps
this do not include the extra power that the inverter needs just to run
its self,

also if you draw 40w at 18v then the inverter will need more than 6-amps
input




sorry the 6-amps should read 0.6-amps
(puts head under jumper in shame)


And only a tit would say "around 2.222222222222-amps"

that's an extremely precise, practically unmeasureable value

--
geoff

In uk.rec.cars.maintenance raden wrote:
snip
And only a tit would say "around 2.222222222222-amps"

that's an extremely precise, practically unmeasureable value

I'm pretty sure it's not actually measurable at the moment.
8.5 digit multimeters are around the $10000 mark.

"Ian Stirling" wrote in message
...
In uk.rec.cars.maintenance raden wrote:
snip
And only a tit would say "around 2.222222222222-amps"

that's an extremely precise, practically unmeasureable value

I'm pretty sure it's not actually measurable at the moment.
8.5 digit multimeters are around the $10000 mark.


well with the watts and voltage and a calcalator = amps

On Mon, 15 May 2006 18:27:43 +0100, The Natural Philosopher wrote:

aussie bongo wrote:
"Lobster" wrote in message
...
I'm thinking of buying an 12V - 240V for the car, to enable me to
charge/run devices such as a laptop / mobile phone(s) / AA batteries
for gameboys & camera etc etc while on the road (one at a time!); they
seem to be as cheap as chips these days and this would enable me to
use the standard mains chargers for all the above devices rather than
buying separate low voltage kit to connect each of them up to the
cigar lighter.

Sounds good in theory, but are there any gotchas? Eg, safety? Does it
run a car battery down more to power up a laptop via a 240V inverter
than directly to the cigar lighter? etc etc

Can't help feeling an inverter would be much better if wired or
plugged into the car some other way than via the god-awful universal
cigar-lighter plug...

Thanks
David
i dont know about power usage on a laptop, but,
i do know that 100w drawn from an inverter at 240v, will give you less
than 1/2hours usage.

Car bateries are 40-70Ah, and at a nominal 12v, that is 480-840Wh.

Giving and expected uptime at npominal 80% eficiency of say 4-8hrs
roughly.

one thing to remember if you get one, is that you have to make sure it
is turned off with no power going into it whilst starting the car as to
do so will damege the inverter.

Total ******** as well.



You're failing to take into account quite how badly designed most "cheap"
invereters are, they're realy easy to break. Might would have been better
than will though.

Duncanwood wrote:
On Mon, 15 May 2006 18:27:43 +0100, The Natural Philosopher wrote:

aussie bongo wrote:
"Lobster" wrote in message
...
I'm thinking of buying an 12V - 240V for the car, to enable me to
charge/run devices such as a laptop / mobile phone(s) / AA batteries
for gameboys & camera etc etc while on the road (one at a time!);
they seem to be as cheap as chips these days and this would enable
me to use the standard mains chargers for all the above devices
rather than buying separate low voltage kit to connect each of them
up to the cigar lighter.

Sounds good in theory, but are there any gotchas? Eg, safety? Does
it run a car battery down more to power up a laptop via a 240V
inverter than directly to the cigar lighter? etc etc

Can't help feeling an inverter would be much better if wired or
plugged into the car some other way than via the god-awful universal
cigar-lighter plug...

Thanks
David
i dont know about power usage on a laptop, but,
i do know that 100w drawn from an inverter at 240v, will give you
less than 1/2hours usage.

Car bateries are 40-70Ah, and at a nominal 12v, that is 480-840Wh.

Giving and expected uptime at npominal 80% eficiency of say 4-8hrs
roughly.

one thing to remember if you get one, is that you have to make sure
it is turned off with no power going into it whilst starting the car
as to do so will damege the inverter.

Total ******** as well.



You're failing to take into account quite how badly designed most
"cheap" invereters are, they're realy easy to break. Might would have
been better than will though.

Mmm.

One upon a time, I took a trip in a plane...and being of that bent,
inquired as to what the whining was that I could hear as the pilot
prepared to take off "its the rotary converters spinning up: They supply
all the various voltages we need for the equipment". (it was a plane
decdicated to radar testing and full of equipment racks) I nodded sagely
and said 'surely it would be lighter to put in solid state inverters'...
"Mmm..." the pilot said "Until you watch what happens to the battery
voltage when we pull the undercarriage up and roll the flaps back in"

The inertia of the rotary converters acted like a ****ing great
capacitor apparently...

In article ,
The Natural Philosopher wrote:
One upon a time, I took a trip in a plane...and being of that bent,
inquired as to what the whining was that I could hear as the pilot
prepared to take off "its the rotary converters spinning up: They supply
all the various voltages we need for the equipment". (it was a plane
decdicated to radar testing and full of equipment racks) I nodded sagely
and said 'surely it would be lighter to put in solid state inverters'...
"Mmm..." the pilot said "Until you watch what happens to the battery
voltage when we pull the undercarriage up and roll the flaps back in"

The inertia of the rotary converters acted like a ****ing great
capacitor apparently...

What was it 'rotary converting' from? Thought many planes used an aux jet
engine for power, or one of the main ones. And wouldn't the undercarriage
be powered off the hydraulics?

--
*Some days you're the dog, some days the hydrant.

Dave Plowman London SW
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