# Laptop charging - lowest Amps method



## nicholsong (May 26, 2009)

I am currently charging my laptop with a Maplins N59AC, which converts cigar/DIN socket 12v to 19v.

When I am charging and using the laptop ( I know some say don't do it! ) it draws 5.5 amps, which is a lot when wild-camping, especially when waiting for GPRS downloads.

Would I get lower draw with a more sophisticated 12-19v charger?

Or would the Inverter method draw less?

(despite the inefficiencies of both methods)

Geoff


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## nicholsong (May 26, 2009)

Just trying to revive my OP above

It had 100+ views but not one reply

Maybe the Brightest and Best MHFers were on holiday.

Any help gratefully received

Geoff


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## peribro (Sep 6, 2009)

Why do you think your Maplin charger is inefficient? Is it heating up quite significantly - at least more than any other charger? If not and also assuming that it's not being noisy or giving off light, then I imagine that whatever energy goes into it is being used to charge the laptop. I wouldn't have thought an inverter would be any more efficient (possibly operating at 80% to 85% efficiency) but without knowing how efficient your Maplin device is, it is difficult to know.


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## C7KEN (May 27, 2005)

I have a 17" Dell and use a proper 12v to 19v charger from the cig lighter. The Dell mains charger is rated at 4.62 amp (just using it now so looked at it) When using the 12v charger I do notice it is taking plenty out of the batteries. But I try to run off the laptops battery and charge the battery back up when moving so making sure it is no big problem. Bert the Dutch man who sells and fits solar panels etc down here thinks an invertor is a better way but that is how i used to do it before I bought the proper charger which I am very pleased with as its so convenient and neat.


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## nicholsong (May 26, 2009)

Thanks to peribro and C7KEN

No the charger is not getting hot. When I referred to inefficencies it was only because stepping up from 12v to 19v is not ideal, nor is an inverter because one is firstly stepping up from 12v to 230v and then using a domestic laptop charger to step back down to 19v,

C7KEN, please, when you have time could you check what discharge your ammeter is showing, obviously with all other systems off, when the charger is

a) just charging the laptop battery

b) charging the laptop when it is running

It is possible that mine drawing 5.5A is normal, but my battery (old laptop) does not last more than 45 mins.

I do charge the laptop while on the move.

Is it possible to buy an additional battery which will plug into a USB port? - now I am really showing my ignorance!

Thanks for your help guys.

Geoff


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## geraldandannie (Jun 4, 2006)

Hi Geoff

Sorry I missed the original post.

I would imagine that the dc-dc converter you're using is probably better than the 12V dc - 240V ac - 19V dc method you're thinking of. Only one set of conversions must be more efficient, assuming identical quality of design.

I know my Mac shuts down the power it takes when the laptop is fully charged. Maybe you could charge it whilst you're making and having a meal or something?

However, I suspect the only solution is to get a lower power laptop, or invest in more leisure battery power, or both.

We use an inverter with the standard charger to charge laptop(s) when we're out, and have not had a problem with flat batteries, despite wild camping at rallies and shows for up to 6 days. We have a 120W solar panel.

Gerald


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## stuffed2 (May 9, 2005)

You might be better off with a new higher capacity battery for the laptop. You can also get a power pack which is in effect another battery. If your existing battery is failing it might be drawing a higher current .


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## DiscoDave (Aug 25, 2008)

your 12v to 19v charger will be the most efficient of the options, however you may be able to get a more efficient version of your charger it all depends on the components used etc etc.

My money would go on a solar panel, I have an 85W panel (it came with a previous van and stayed when the van went) and that is more than capable of replenishing the power used by my laptop, lighting and heating, what i'm getting to is than with the solar I don't have to worry about it, to the point that i don't bother with hook up unless it's included in the price of the pitch.


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## gaspode (May 9, 2005)

I did a test some time ago of a Maplin 12v to 20v converter against a 150w inverter and the laptop power supply using a Fujitsu laptop with AMD processor and 15.4" screen. Can't remember the exact figures but I do remember that the Maplin converter was significantly more efficient (as I would expect).

Don't forget that a large laptop is quite a power hungry beast and will consume a fair current at 12v. A better option is to buy a small netbook. Also my Eeee PC runs at 12v so no voltage conversion necessary thus cutting out the need for a voltage conversion with subsequent losses.


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## nicholsong (May 26, 2009)

Thank you all for contributions.

I have been a little slow in responding because I was getting drop-outs on my Voda dongle in the Peak District and knew I would soon be back on house broadband.

All replies were useful - just the best of MHF tech advice.

Thanks to Gerald and Keith for confirming that direct 12V-19V is best.

For many reasons I will upgrade my charging with new and bigger batteries, solar, sterling B2B, upgraded cable and relays etc. 

As to suggestions about a smaller consumption netbook etc., I will investigate, but I like the idea of a 12V machine.

Gratefully, Geoff


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## pippin (Nov 15, 2007)

Don't overlook the fact that a 12V machine might not like the 13.8V or higher that comes out of your sockets when the leisure batteries are being charged.

My personal view is that the 12V to 19V converter is the most efficient method.

It chops up the 12V DC into high frequency AC, feeds it into a step-up transformer, rectifies it back to DC and then regulates to the required output voltage of (say) 19V.

It is done at high frequency because that allows the use of much smaller and lighter components.

The design will be pretty much standard with little difference in efficiency between various makes.

I would suggest using your laptop on its battery and then recharge when travelling or on EHU.


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## nicholsong (May 26, 2009)

Thanks Pippin

More useful info

From all this I am gradually defining the system I need, but it has to relate to being without EHU and not driving to re-charge.

Geoff


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## gaspode (May 9, 2005)

pippin said:


> Don't overlook the fact that a 12V machine might not like the 13.8V or higher that comes out of your sockets when the leisure batteries are being charged.


Hi pippin

Yes, I'd agree with that statement. In fact the 12v lead that I use to run/charge the EeePC on the road has a small regulator built into the 12v plug to eliminate the danger of excess voltage. I would imagine that all the 12v leads sold specifically for use with these netbooks should contain a regulator of some description.

PS: As an afterthought - it goes without saying that these small netbooks can run for an extended time on their internal battery as a result of the low current consumption. Mine has a 10" screen and a solid state hard drive which saves considerably on consumption yet it's still practical for most purposes whilst traveling. I can get 5hrs continuous use from a single battery charge without too much trouble.


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## ActiveCampers (Jun 17, 2005)

Another "solution" may be to change the laptop. 
I changed from Dell to an Asus UL30 laptop which is lighter and has a better screen, but also a ultra-low voltage CPU and thus the standard battery lasts 10 hours (maybe 7-8 in real use with screen bright).

Battery is lower capacity than the one on the Dell laptop which lasted maybe 1.5-2 hours.

OK - same charger effcienies/inefficiencies apply, but you get more life out of laptop per charge.

Technically its slightly slower, but for normal use it is absolulteyly perfect. Fairly cheap too.

Details here http://www.doyourdream.co.uk/2010/07/new-laptop-ideal-for-taking-in-van/ but it appears no longer available. But it may be worth looking for similar models.


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