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

"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.

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.

"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...

Only thing I can think of is they do (or mine does) get rather (read heater
in winter) warm in operation.

I have never used mine without the engine running, but I suppose the main
issue will be current drawn. mines only 150 watt, so I wouldn't put much
more than a charger into mine. but it has already paid for itself in the
amount I have saved buying car chargers for camera's, mobiles, etc etc.

My only annoyance is its recommended not to plug anything else in to car
socket at the same time as the inverter (no socket doublers/tripplers) so
mines hardly used now I have a PDA sat nav always plugged in.

loopy



--
Posted via NewsDemon.com - Premium Uncensored Newsgroup Service
-------http://www.NewsDemon.com------
Unlimited Access, Anonymous Accounts, Uncensored Broadband Access

On Sun, 14 May 2006 10:23:38 GMT, Lobster
wrote:

|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

Yes! assume your invertor is 80% efficient.

|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...

Be careful that there is enough charge available to start the car.

There are two sorts of invertor Modified sine wave output as below

|---|
--| |--| |--
|--|

These are quite cheap but electronics do not like sharp edges anywhere near
them. You should *check* that they will work *your* laptop. I was warned
off using one of these with a TV Set Top Box by Bill Wright on
uk.tech.digital-tv

Others are pure(ish) sine wave which cost 3 times as much and should be OK.

For myself I would buy a laptop which will run off 12V, which I did with
the STB.
--
Dave Fawthrop dave hyphenologist co uk Google Groups is IME the *worst*
method of accessing usenet. GG subscribers would be well advised get a
newsreader, say Agent, and a newsserver, say news.individual.net. These
will allow them: to see only *new* posts, a killfile, and other goodies.

In uk.d-i-y Dave Fawthrop wrote:
On Sun, 14 May 2006 10:23:38 GMT, Lobster
wrote:

|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

Yes! assume your invertor is 80% efficient.

|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...

Be careful that there is enough charge available to start the car.

There are two sorts of invertor Modified sine wave output as below
snip
These are quite cheap but electronics do not like sharp edges anywhere near
them. You should *check* that they will work *your* laptop. I was warned
off using one of these with a TV Set Top Box by Bill Wright on
uk.tech.digital-tv

FWIW, I've never had a problem running any of ~12 power supplies on MSW
inverters, including laptops, scopes, ...

In practice, there is relatively little difference in stress between
proper sine waves, and MSW inverters.
The diodes typically get slightly hotter, but that's it.
(IME)

In uk.d-i-y 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.
snip
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.

YLMV.

And 100W can never give any meaningful amount of run time without
specifying how long.

My laptop - admittedly a subnote - uses about 40W when charging, and
about 15W running normally.

This runs on a standard car battery for around a day, from an inverter.

In article ,
Lobster wrote:
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

I've got a 150W one from www.tlc-direct.co.uk and I've used it for a
few years now. It's got a standard 13A socket on the side of it. It's
supposed to cut-out if the input voltage goes bbelow 10.5V, but I've
never had to test it...

It produces a "modified sine wave" output, which does tend to make some
battery chargers buzz a little and mayby run a little hotter than when
on the mains at home, but otherwise I've not had a problem with it.

I used to use it when out & about to test & install various wireless
networking equipment. Not had much use for it recently though, but
it's handy for charging various batteries which I don't have a separate
adapter for.

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...

Very probably - my last car had the socket powered at all times, but my
current car needs the keys in & the ignition on to make it work )-:

Gordon

"Ian Stirling" wrote in message
...
In uk.d-i-y 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.
snip
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.

YLMV.

And 100W can never give any meaningful amount of run time without
specifying how long.

My laptop - admittedly a subnote - uses about 40W when charging, and
about 15W running normally.

This runs on a standard car battery for around a day, from an inverter.

but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance

Dave Fawthrop wrote:
On Sun, 14 May 2006 10:23:38 GMT, Lobster
wrote:

|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?

safety is ok, though you've got none of the protective devices found in
houses, eg rcd, mcb. And you need to ensure you dont connect an output
line firmly to earth, otherwise your car might end up live. Lower
standards yes, but it seems to work ok in practice.


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

Yes! assume your invertor is 80% efficient.

every conversion loses power, so yes.


|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...

Battery clips are less convenient. A cig plug limits power throughput.
Some cars have built in power connectors, though not many. Might be
worth a look in the glovebox for a 2 pin socket.


Be careful that there is enough charge available to start the car.

yup! Or park on a hill.


There are two sorts of invertor Modified sine wave output as below

These are quite cheap but electronics do not like sharp edges anywhere near
them.

electronic SMPSU supplies will behave fine on square or msw waves.
There is one type of supply that cant tolerate these waveforms, and
thats a CR supply. CR supplies are only used for tiny power outputs
with no external power connection, eg plugin timers, killawatt meters
and so on. Laptops are always smpsu.


For myself I would buy a laptop which will run off 12V, which I did with
the STB.

thats best, but if yours doesnt, it doesnt.


NT

In article ,
aussie bongo wrote:
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.

A reasonable sized car battery will be around 70 amp/hour at the 20 amp
rate. 20 amps at 12 volts is 120 watts, so it would be reasonable to
expect something like 3 hours use at 100 watts 240 volts.

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

--
*Who is this General Failure chap anyway - and why is he reading my HD? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Lobster wrote:
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...

Only small ones work off the lighter socket - this is restricted to a max
of 10 amps. Larger ones have crock clips for direct connection to the
battery. But nothing to stop you using custom wiring and a suitable
plug/socket for connection inside the car.

TLC have rather good prices on modified sine wave invertors. You'll see
the identical ones elsewhere at more than twice the price.

--
*Husbands should come with instructions

Dave Plowman London SW
To e-mail, change noise into sound.

In article .com,
wrote:
Be careful that there is enough charge available to start the car.

yup! Or park on a hill.

But mine's an auto...

--
*Husband and cat lost -- reward for cat

Dave Plowman London SW
To e-mail, change noise into sound.

"aussie bongo" wrote in message
...

"Ian Stirling" wrote in message
...
In uk.d-i-y 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.
snip
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.

YLMV.

And 100W can never give any meaningful amount of run time without
specifying how long.

My laptop - admittedly a subnote - uses about 40W when charging, and
about 15W running normally.

This runs on a standard car battery for around a day, from an inverter.

but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

In uk.d-i-y aussie bongo wrote:

"Ian Stirling" wrote in message
...
In uk.d-i-y 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.
snip

My laptop - admittedly a subnote - uses about 40W when charging, and
about 15W running normally.

This runs on a standard car battery for around a day, from an inverter.

but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance

About the wattage at teh plug.
The figures from 15V are 2A (sticker - I've never seen it past 1.5A) and
about 12W.

"Dave Plowman (News)" wrote in message
...
In article ,
aussie bongo wrote:
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.

A reasonable sized car battery will be around 70 amp/hour at the 20 amp
rate.

? where did 20A come from?


20 amps at 12 volts is 120 watts,

Not when I went to skool


so it would be reasonable to
expect something like 3 hours use at 100 watts 240 volts.

WTF?


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

I'll give that a tick



--
*Who is this General Failure chap anyway - and why is he reading my HD? *

Dave Plowman London SW
To e-mail, change noise into sound.

In uk.rec.cars.maintenance Slurp wrote:

"Dave Plowman (News)" wrote in message
...
In article ,
aussie bongo wrote:
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.

A reasonable sized car battery will be around 70 amp/hour at the 20 amp
rate.

? where did 20A come from?


He means 20 hour.
Battery capacity is typically expressed as how much current it can
supply when discharged in 20 hours.
Discharge it faster, and you get less out.

snip
so it would be reasonable to
expect something like 3 hours use at 100 watts 240 volts.

WTF?

100W/12 = 8A from battery.
Say 10A, due to inefficiencies.
A 70Ah battery will supply 10A for slightly less than 7h.

In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the
inverter.
If it's measured at 12V, you don't.

HI Dave

On Sun, 14 May 2006 13:29:36 +0100, "Dave Plowman (News)"
wrote:

In article ,
aussie bongo wrote:
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.

A reasonable sized car battery will be around 70 amp/hour at the 20 amp
rate. 20 amps at 12 volts is 120 watts, so it would be reasonable to
expect something like 3 hours use at 100 watts 240 volts.

But isn't there something about car batteries being designed for
delivering lots of current for a very short period of time ..?

You might get this sort of duration from a 'leisure' battery - as
they're designed for lower current over a longer period.

Years ago, when I was young and foolish, I tried providing lights for
several tents in our scout troop - using a car battery and car
sidelights.

Load would have been in the region of 60watts or so - lasted about 15
minutes before the battery died.

Just as well really - it was before I knew about fuses g - and were
it not for the fact that the wiring was really weedy I might have
toasted the entire troop !

You live & learn g....


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

True....

Don't know how efficient modern inverters are - I guess it's be fairly
easy to find out with the aid of a multimeter and a mains light
bulb....

Regards
Adrian

======return email munged=================
take out the papers and the trash to reply

Dave Plowman (News) wrote:
In article .com,
wrote:
Be careful that there is enough charge available to start the car.

yup! Or park on a hill.

But mine's an auto...

I tried starting one I once had with the crank handle, coudnt get it to
turn tho, nor could anyone else. Most disappointed.

NT

"Ian Stirling" wrote in message
...
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the
inverter.

Err, no

you have to add in the INefficiency, ie if 80% efficient then add in 20%

If it's measured at 12V, you don't.

????? The extra current due to the inefficiency of the conversion has to be
supplied from 12V!!!!

wrote:

Dave Plowman (News) wrote:
In article .com,
wrote:
Be careful that there is enough charge available to start the car.

yup! Or park on a hill.

But mine's an auto...

I tried starting one I once had with the crank handle, coudnt get it to
turn tho, nor could anyone else. Most disappointed.

NT

I managed to start a Morris Minor Traveller with a crank handle when I was
about 7! Bloody hard going though, and the kickback was deeply unpleasant.

Proper engines - those were the days...

Yesterday, my Daewoo Lanos ECM computer decided to throw a fit and, although
the car had done 4 journeys that day, it locked the malfunction light on
and refused to inject fuel (based on sniffing the exhaust whilst SWMBO was
cranking it - ooerr Missus). Lots of fuel and pump OK...

Piddled around with it for 3 hours, reseating connectors. Gave up in
disgust. Read most of the workshop manual I got off some bloke on CD, which
is missing some finer points for my '98 model... Pushed it into the garage
today, with the aim of testing the sensors etc to see if any had gone open
circuit, gave it one last crank and the old toad started first time.

Been fine today. Think I'll have to get Vauxhall to do an ECM diag on it,
see if it's logged anything. Unfortunately it's got an GM/ALDL diag port -
if it were the more modern OBD-II, which later Lanos's have, I might have
got a copy of ScanTool - would be fun to see what's going on...

******* over-complicated electronics...

Tim

"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 did with a dell lt, not again, i didnt like the feel of the laptop power
module(230 to 18) it got very very hot compaired to warm on full fat mains
power.

Lobster presented the following explanation :
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

A switch mode PSU (which is basically what an inverter is) has an
efficiency of between 70 and 90%. Powering a laptops own PSU from one
means that you would have two steps in voltage conversion, each with
losses. A better way would be a purpose designed inverter which
directly replaces the laptop PSU with one which takes in 12v and
outputs whatever the laptops needs. Maplin do such an item with various
output voltage settings, various plugs and at 3amps.


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...

Agreed, but it is the 12v socket commonly fitted to most cars.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

In article ,
Slurp wrote:
A reasonable sized car battery will be around 70 amp/hour at the 20 amp
rate.

? where did 20A come from?


20 amps at 12 volts is 120 watts,

Not when I went to skool


so it would be reasonable to
expect something like 3 hours use at 100 watts 240 volts.

WTF?

Remind me not to post while on the phone. ;-)

I meant the 20 hour rate, which would be around 3.5 amps discharge.
A 150 watt invertor takes approx 12.5 amps, and the higher discharge rate
means the battery won't deliver quite its full capacity.

But 3 hours from a 70 amp/hour battery driving a 150 watt invertor at max
isn't a million miles out. ;-) Although theory says nearer 6.

Sorry for the rubbish post.

--
*I'm not being rude. You're just insignificant

Dave Plowman London SW
To e-mail, change noise into sound.

presented the following explanation :
Be careful that there is enough charge available to start the car.

yup! Or park on a hill.

Or carry a battery charger so you can plug that into the inverter to
charge the battery back up :-)

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Slurp" wrote in message
...

"Ian Stirling" wrote in message
...
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops
use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the
inverter.

Err, no

you have to add in the INefficiency, ie if 80% efficient then add in 20%

If it's measured at 12V, you don't.

????? The extra current due to the inefficiency of the conversion has to
be supplied from 12V!!!!

That's just what Ian said.


--
Malc

"When I say 'Run like ufck and commit assault on a police officer
several times,' run like ufck and commit assault on a police
officer several times."
- Channon
Transmetropolitan

On Sun, 14 May 2006 11:48:36 +0100, Dave Fawthrop
wrote:

On Sun, 14 May 2006 10:23:38 GMT, Lobster

wrote:

|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

Yes! assume your invertor is 80% efficient.

|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...

Be careful that there is enough charge available to start the car.

There are two sorts of invertor Modified sine wave output as below

|---|
--| |--| |--
|--|

These are quite cheap but electronics do not like sharp edges anywhere
near
them. You should *check* that they will work *your* laptop. I was
warned
off using one of these with a TV Set Top Box by Bill Wright on
uk.tech.digital-tv

Others are pure(ish) sine wave which cost 3 times as much and should be
OK.

For myself I would buy a laptop which will run off 12V, which I did with
the STB.

Laptop PSUs (unless youve got one from the 80s) are quite happy with any
of the inverters. However the direct converters from Maplin are cheaper &
more effecient.

Ian Stirling wrote:
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the

He did. Which bit of "assuming 100% conversion efficiency" don't you
understand? It might not be a valid assumption but the method is
perfectly clear.

MBQ

Lobster wrote:
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

A lot of laptops need more than 12V so you would still need a DC-DC
converter to run from the cigar lighter. It then depends on the
relative efficiencies of the inverter and the DC-DC converter.

By "on the road" do you actually mean driving? If parked then just be
careful your battery can withstand being discharged repeatedly.

MBQ

In uk.d-i-y wrote:

Ian Stirling wrote:
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency = 10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the

He did. Which bit of "assuming 100% conversion efficiency" don't you
understand? It might not be a valid assumption but the method is
perfectly clear.

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.

"Ian Stirling" wrote in message
...
In uk.d-i-y wrote:

Ian Stirling wrote:
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops
use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency =
10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the

He did. Which bit of "assuming 100% conversion efficiency" don't you
understand? It might not be a valid assumption but the method is
perfectly clear.

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.

"Ian Stirling" wrote in message
...
In uk.d-i-y wrote:

Ian Stirling wrote:
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops
use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency =
10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of the

He did. Which bit of "assuming 100% conversion efficiency" don't you
understand? It might not be a valid assumption but the method is
perfectly clear.

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

"aussie bongo" wrote in message
...

"Ian Stirling" wrote in message
...
In uk.d-i-y wrote:

Ian Stirling wrote:
In uk.rec.cars.maintenance Slurp wrote:

"aussie bongo" wrote in message
...
snip myu comment
but is that 40w &15w at 240v or the normally 18v that most laptops
use??
this makes a big differance


40W is 40W whether its at 1nV or 306MV
P(WATTS) = VOLTS x AMPS

40W from an 12V battery = 3.3A
40W from 240V rms supply = 0.167A rms
Average car battery = 35Ah, assuming 100% conversion efficiency =
10hrs

Err, no.
If it's measured at 240V, you've then got to addin the efficiency of
the

He did. Which bit of "assuming 100% conversion efficiency" don't you
understand? It might not be a valid assumption but the method is
perfectly clear.

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)

In article . com,
wrote:
By "on the road" do you actually mean driving? If parked then just be
careful your battery can withstand being discharged repeatedly.

What do you reckon the capacity of the laptop's internal battery is?

--
*Very funny Scotty, now beam down my clothes.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
aussie bongo wrote:
the current drawn at 40w on 18v is around 2.222222222222-amps // but
40w at 240v is about 6-amps


watts
amps = -----
volts

So 40w at 18 volts is as you say 2.2. But watts are sort of an absolute
measurement of power, so increase the voltage and the current goes down,
so 40 at 240 volts is 0.17 amps.

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.

--
*I used to have an open mind but my brains kept falling out *

Dave Plowman London SW
To e-mail, change noise into sound.

In uk.d-i-y "Dave Plowman (News)" wrote:
In article ,
aussie bongo wrote:
the current drawn at 40w on 18v is around 2.222222222222-amps // but
40w at 240v is about 6-amps
snip
So 40w at 18 volts is as you say 2.2. But watts are sort of an absolute
measurement of power, so increase the voltage and the current goes down,
so 40 at 240 volts is 0.17 amps.

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

In article .com,
wrote:
Dave Plowman (News) wrote:
In article . com,
wrote:
By "on the road" do you actually mean driving? If parked then just be
careful your battery can withstand being discharged repeatedly.

What do you reckon the capacity of the laptop's internal battery is?

Why is that relevant?

Because it's likely to be be tiny compared to the car battery.

The OP wants to power the laptop from a car battery. In the past I seem
to have buggered a car battery by allowing it to discharge to much
(courtesy light left on for a few hours).

Most courtesy lights don't draw much current - or those that do often
switch themselves off after a time.

Maybe it was on it's last legs
anyway.

Sounds rather like it.

--
*Errors have been made. Others will be blamed.

Dave Plowman London SW
To e-mail, change noise into sound.

In uk.rec.cars.maintenance "Dave Plowman (News)" wrote:
In article .com,
wrote:
Dave Plowman (News) wrote:
In article . com,
wrote:
By "on the road" do you actually mean driving? If parked then just be
careful your battery can withstand being discharged repeatedly.

What do you reckon the capacity of the laptop's internal battery is?

Why is that relevant?

Because it's likely to be be tiny compared to the car battery.

Smaller, but not tiny.
Many laptop batteries are 10% of the capacity energy-wise of the car
battery.
7Ah@12V or so (9 Li-ion cells, for example).

In article ,
Ian Stirling wrote:
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.

--
*Any connection between your reality and mine is purely coincidental

Dave Plowman London SW
To e-mail, change noise into sound.

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.