Powering laptop etc in car from inverter?

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.

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

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|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.

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)

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.

I've got a 150W one from

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.

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

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

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.

every conversion loses power, so yes.

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.

yup! Or park on a hill.

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.

thats best, but if yours doesnt, it doesnt.

NT

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.

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.

But mine's an auto...

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

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

? where did 20A come from?

Not when I went to skool

WTF?

I'll give that a tick

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.

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

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.

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 - and were it not for the fact that the wiring was really weedy I might have toasted the entire troop !

You live & learn ....

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

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

NT

Err, no

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

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