Laptop failing to charge from car cig lighter

I posted a few weeks back asking about reliability and safety of using

12V car cigarette-lighter adapters for mobile phones, laptops etc (and IIRC generated a major sh*tstorm as a result...!) Anyway here's a followup to the query...

I decided to acquire a car adapter for my new notebook PC (an Asus EEE PC900) to enable it to be used to double as a DVD player for the kids on long journeys. Had no option but to buy an unbranded 3rd-party adapter since ASUS hasn't produced one yet, although rumour has it that one may be in the pipeline).

Yesterday I tried out the car adapter for the first time, but unfortunately it didn't work properly. Although the adapter's LED indicator lit up continuously, and there was definitely no loose connections, the PC's notification window popped up to say 'AC charger connected', only to be replaced 5 secs later by another window saying 'changing to battery power' (or words to that effect). It then cycled continuously between battery and charging mode every few seconds.

My impression is that the machine is trying to charge, but as soon as it does so the current provided by the car falls below some threshold, and the computer cuts it off and reverts to battery mode, whereupon the current is able to increase again, allowing the computer to switch into charging mode again, etc etc. Sound about right?

What is "responsible" for the problem - is it the adapter, the computer, or the car? Is it in anyway surmountable? The laptop needs "+12V, 3A, 36W" according to the label on its base. Surely not too much to expect from a cigarette lighter? Wondering if a 240V inverter would be better (I have one at home :-( )

I'm currently connecting on wifi from a tent in the middle of France, with no electrical tools, instruments etc, but would *really* welcome a solution before setting off on the journey home next weekend - though somehow I don't think that's going to happen ;-( ) Another 8 hours-worth of I-spy, number-plate bingo etc ahead....

David

Reply to
Lobster
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You dont say if the car was running or off when you tried it. Car batts can go well below 12v when not being charged, plus there are V drops in the wiring and connectors. You might find its fine with the engine running.

If it was running when you tried it, you've probably got a poor connection. If not, and the laptop doesnt like what its getting, theres really nowt more you can do in the middle of a field.

NT

Reply to
meow2222

Most lighter sockest are fused at 10 or 15A A so you are well within tha= t limit.

It might be but I have one charger that refuses to work off my invertor =

everything else is happy on it though.

Agreed. What is the adapter? Does it regulate and filter the cars voltag= e down to 12v. The raw car supply can be incredibly noisy and up to 14 or =

15v with the engine running. What is the rating of the adapter? It has t= o be more than 12v 3A.
Reply to
Dave Liquorice

Its also possible that the laptop might be objecting to too high a voltage when its designed for regulated 12v. I dont run laptops on car supplies, so I cant say from experience that will happen, but it could be that. So if the car was running before, try it ignition off.

NT

Reply to
meow2222

Only if they're knackered.

Reply to
Conor

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Lobster saying something like:

Are you trying it with the car engine off? If so, see what happens with the engine running and bringing up the battery voltage a bit.

Reply to
Grimly Curmudgeon

Yes

Is this adaptor one of the variable voltage ones, with voltages higher than

12v available? If so, there should be an output power stated on it somewhere, it might be under rated for your laptop, so it...

1 trips out

2 resets 3 goto 1

It's worth a try - make sure the continuous output (A or W) rating is higher than the input rating of the laptop's power supply though, or you will be in the same situation!

Toby...

Reply to
Toby

How are you sure there's no loose connections? When I tried running one of these EEEPCs from a 12V car adaptor, I found that the +ve centre pin in the EEEPC was a non-standard size, and made only intermittent contact with a standard plug. From memory, the standard pin sizes are 2.1mm and 2.5mm, and the EEEPC was neither of those.

That would work.

John

Reply to
John Henderson

Turn the notebook off and try charging it. A running laptop requires a lot of power, 2 to 3 amps is typical. Your car/adapter/wiring probably cannot supply this current and the current required to charge the battery without dropping the voltage to a level that the notebook refuses to use. Maybe a notebook is 1 to 2 amps, but anyway, turn it off.

Gareth.

Gareth.

Reply to
Gareth Magennis

If the car or wiring is unable to provide 5amps, I'd be rather worried. Especially as the wiring is nominally for a cigarette lighter.

If the notebook charger is unable to provide the current it is unfit for purpose. Which I suppose is quite possible, since it obviously isn't working -- whatever the reason. I think it's most likely to be the adaptor, possibly just a badly fitting plug as another poster mentioned.

Reply to
David Taylor

Yes

The cable (certainly in my car) feeding the 12v socket is so thin that when the cigar(ette) lighter is in use (I don't use it normally, just a test) that the volts across the socket drops to 9 if the engine isn't running (10.something if running). This means I can't use the inverter to feed anything more than a neon lamp with the engine stopped without the inverter squeeling out a low battery alarm,and shutting down.

With a universal mobile PC psu I can use the PC.

I intend to re-wire the car socket directly (but via a fuse) with much thicker cable. The cable used must be flexible suitable for automotive applications, don't use mains cable, I nearly lost a car many years ago with using 7/029 which failed due to vibration and shorted the battery making a mess of the wiring harness in the process. I now use proper cable, suitably fused.

Reply to
<me9

Yes but the point is that a cigarette lighter doesn't care what voltage drop occurs, it just wants lots of current, while a laptop might be concerned about this shortfall and decide not to use it, particularly if the laptop is in use.

Reply to
Gareth Magennis

Sure, I'm not saying it's impossible -- just that I'd be rather worried. Since the battery is presumably charging well enough to continue to start the car, a significant voltage drop in the car wiring would imply something is getting very hot and potentially about to burst into flames.

Reply to
David Taylor

Cigarette lighter sockets often do that though.

Reply to
Duncan Wood
[...]

I'm sorry, but there is no way that a marginally sized cable would drop that amount of voltage if used within the 10A constraints of the socket rating! You either have another fault, or an under-reading meter. (Or just possibly an old Italian car :-)).

If you were using 7/.029 when it was available, it was pre-1972! Most cars at that time had lots of their electrics unprotected by any sort of fuse.

The correct cable to use for car wiring is (unsurprisingly) automotive rated cable to BS6862.

Most car makers would specify 1mm2 (14/0.3mm) for a cigarette lighter socket. This has a rating of 8.75A. A better choice would be 1.5mm2 (21/0.3mm) with a rating of 12A. There would be no gain in going any higher than this due to the inability if a plug/socket system designed for a very low duty cycle at perhaps 5A, being unable to cope with a continuous load greater than this.

If one was prepred to carry out rewiring in order to improve the limitations of the installed connector, perhaps a better solution would be to also use a more suitable plug/socket?

Chris

Reply to
Chris Whelan

The Eee is quite a high current device, and needs something which can pump out 2.5A continuously. I suspect that your charger is overheating or otherwise cutting out every five seconds or so. Reports say that a lot of el cheapo Eee chargers don't work well - which one do you have?

Ian

Reply to
Ian

14/0.3mm has a resistance of around 18 ohms/kilometer
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so a drop of 3.6V (12.6 -> 9) with 10A would require 0.36 ohms, which is 20m. Just about possible in a stretch limo, I suppose!

Ian

Reply to
Ian

Surely this is just a passive device, 12 volts in, 12volts out. It is just wire. My laptop supply is regulated, I suspect most of them are. Even an unregulated supply usually kicks out at least, usually a bit more, its rated voltage. I also suspect this is what is required here - a few amps at not less than 12 volts. You are not going to get that with a car battery in a stationary car with its wiring harness etc etc. The laptop will spit its dummy out and demand the whole 12 volts.

Gareth.

Reply to
Gareth Magennis

I hope not. You can get spikes and allsorts on car supplies. I would expect a DC-DC convertor. I wouldn't buy one unless it was a DC-DC convertor.

Reply to
dennis

A fully charged car battery should produce around 12.7 volts even after standing overnight. When 75% discharged, it should still be around 12.4 volts.

This should be enough to compensate for any wiring voltage drop at the suggested current of 2.5A

Chris

Reply to
Chris Whelan

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