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