# inverter for laptop



## elbino

I'm looking to buy a small inverter, either 150w or 300w that will plug into the cig lighter rather than hard wiring just to run the adapter for a Dell laptop which requires 65w. Do I need a pure sine wave inverter or will a bog standard modified sine wave suffice without knackering the computer ? I only ask as there is a big difference in prices


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## teensvan

Hi.

We have for the past 2 years run our laptop of a 350 watt hard wired bog standard invertor when not on hookup. All OK so far.

steve & ann. ------- teensvan.


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## Snelly

You will get away with modified sine wave, but of course it is always best to use pure sine.


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## DABurleigh

I recall some laptop PSUs have been fussy in the past, but you will almost certainly not have a problem with a 20 quid [email protected] fanless inverter.

Dave


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## 107925

I couldn't agree more with Dave; my laptop into a Maplin 150w inverter, plugged into my portable battery starter, goes on for hours. 

Shaun


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## chrisjrv

Maplin sell a charger which plugs in the cigar lighter and the other end straight into the laptop. It has adjustable output to suit different laptops, I bought the dearer one which was about £20 and it works fine. I can leave the mains charger at home.


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## sallytrafic

Just be aware that if your laptop draws say 120W thats 10A coming from your vehicle battery.

a the wiring might not take it.
b the battery will get a hammering.


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## geraldandannie

We use a 150W inverter off Ebay. Not only does it recharge my laptop, it has the added benefit of being able to charge mobile phones, my rechargeable razor, iPod and anything else we cart around with us.

Gerald


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## dilly

I dont use an inverter i bought a lead that plugs into the back of the laptop and the other end goes into the cig/accessory socket ,sorted.

Ian.


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## 107990

Anyone know if Apple macs are big power consumers ?. I currently use a Sony TR series on my travels and when off hook up but rather fancy trying a mac next. I use a kensington power adapter that i bought from PC world, excellent piece of kit.


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## geraldandannie

DollarYen said:


> Anyone know if Apple macs are big power consumers ?


I don't think so. One of the reasons I bought my iBook was for its low power consumption. Of course, it all depends on which Mac you're using (I presume one of the laptops), and what you're doing with it.

:: Here :: it says the 15" MacBook Pro will get 5 hrs from its 60Whr battery, which gives you a power consumption of 12W. the 17"-er consumes something like 15W.

The :: MacBook Air :: only consumes 7.4W.

These are, of course, Apple's figures, and may show little resemblance to real life figures.

Gerald


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## 105062

I would not use an inverter as they use far too much current as inverters do, if your laptop takes 3 amps the inverter will take 60 amps and flatten your battery in about an hour plus heat up the wiring a fair bit!

I use one of these adapters designed to run a laptop from a cig socket and only take 3-4 amps.

http://www.ebuyer.com/product/123812
cheers
Paul


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## Smilo

Perhaps you'll understand that having read this far I now don't know what to think! I already have a 150W invertor which my tame computer expert has said would be OK. The adapter at ebuyer (above) would appear unsuitable perhaps for my new laptop (is notebook another word for laptop?) underneath which it says *3.9A* and *DC 19V*. Is it unsuitable?


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## 98742

Dell present some unque challenges for 3rd party power adapters. First of all the tips they on their cables are unique to Dell. Trust don't supply them so you can't use the Trust adapter with a Dell. We do have some, but not all, Dell tips.
If that isn't bad enough some Dells (Certainly Inspiron and Latitudes) also have a "handshake" between the power adapter and the laptop. If the laptop doesn't receive the correct handshake it simply won't use the power adapter!
For a Dell I'd recommend a 150watt inverter and I sell 12v adapters!

Regards
Doug


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## sallytrafic

Tribute_650 said:


> I would not use an inverter as they use far too much current as inverters do, if your laptop takes 3 amps the inverter will take 60 amps and flatten your battery in about an hour plus heat up the wiring a fair bit!
> 
> I use one of these adapters designed to run a laptop from a cig socket and only take 3-4 amps.
> 
> http://www.ebuyer.com/product/123812
> cheers
> Paul


Apart from the fact that 3A at 230V equals about 700W and 700W at 12V nominal is about 60A this post makes little sense

a. no laptop draws 700W 
b. no inverter even a 700W one draws *that much* more power than it delivers.
c. inverter efficiency is usually at its best somewhere between 50 and 80% of full load so if your laptop draws say 50W at 230V a 150W inverter will draw say 60W at 12V (ie 5A) a 75W inverter may only draw 53W at 12V (about 4.5A). A 700W inverter will have a fan and will be inefficient at only 50W delivery but even there will only draw a max of I guess around 100W.

hope this has helped.


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## 107925

I shall echo what Doug said above. The proper 12v adaptor for my Dell Inspiron costs £75. There are loads of generic adaptors with a range of tips, which might well suite a range of laptops (yes, they're the same as notebooks, to answer the question), but they won't work with Dell - there may also be other types of laptop which will struggle with cheapy 12v adaptors.

It was because I was faced with paying £75 that I preferred to pay £23 from Maplin for the invertor, which has a multitude of uses. I can also confirm that using the laptop with the invertor with my portable battery, is rather good, as I can get over five hours out of the laptop (and that excludes the time from its usual battery). Others will use either their vehicle or leisure battery, which is no different in principle to a portable battery. You just have to keep an eye on how much charge you're using, and that will only come with experience.

Shaun


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## sallytrafic

There is also a safety issue with 3rd party electrical equipment some not made by the OEM has been shown to be very unsafe. South Today ran a piece on it last night stuff from eBay didn't pass safety inspections. I'm just about to post a thread about it.


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## elbino

Got me confused too.Dell Laptop power adapter is 19.5v and 3.34a which I calculated as 65watts. Problem with universal chargers is that very few deliver 19.5v as an option and I was advised not to use one that gave only 19v or 20v....Maplins actually advise not to use their universal where 0.5v was required. So by my reckoning this should draw 5amps and would only be needed for maybe half an hour every few days. And Thats supposing we were'nt on hook-up and had recharged the laptop batteries.
Which brings me back to the original question .. pure sine wave or modified ? Since the power is going to an adapter rather than direct into the computer it sounds as though a modified will do....which is what most contributors to this thread have said.


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## 107990

Perhaps you'll understand that having read this far I now don't know what to think! I already have a 150W invertor which my tame computer expert has said would be OK. The adapter at ebuyer (above) would appear unsuitable perhaps for my new laptop (is notebook another word for laptop?) underneath which it says 3.9A and DC 19V. Is it unsuitable?

Unless you have some sort of weird and wonderful machine it would be fine. I have used one of those myself and it was excellent. I only bought something else as my son borrowed it !. Laptops and notebooks are by and large the same, it's just marketing speak.


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## geraldandannie

Smilo said:


> I already have a 150W invertor which my tame computer expert has said would be OK.


Here's another saying it's OK. It's by far the best option (in my opinion, of course), because you can use it for other things, as I explained in my other post. If the only bit of rechargeable kit you have is your laptop (and from my post before, I forgot my digital camera which needs recharging), then maybe a DC-DC adapter is a good idea.

Yes, theoretically, the efficiency is lower with a 240V inverter but, to be honest, it makes a gnat's wotsit of difference to me. I am a heavy user of a laptop when I'm away (not just for MHF-ing, but for maintaining several weblogs too), and I run the laptop off the battery until it tells me it's nearly out of juice, and then I charge it up again, whilst I do something else (like get some fresh air, or do some shopping, or have a leisurely breakfast, or read the paper).

Whatever figures people quote, this is what I've done with my laptop, and it's been a very good, cost-effective solution for me, and I would recommend it every time in answer to this sort of question.

Items which might need recharging when we're away:
* Laptop
* Mobile phones
* Digital camera(s)
* iPod
* Razor
* Batteries for portable radio / iPod speakers

Gerald


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## 105062

sallytrafic said:


> Tribute_650 said:
> 
> 
> 
> I would not use an inverter as they use far too much current as inverters do, if your laptop takes 3 amps the inverter will take 60 amps and flatten your battery in about an hour plus heat up the wiring a fair bit!
> 
> I use one of these adapters designed to run a laptop from a cig socket and only take 3-4 amps.
> 
> http://www.ebuyer.com/product/123812
> cheers
> Paul
> 
> 
> 
> Apart from the fact that 3A at 230V equals about 700W and 700W at 12V nominal is about 60A this post makes little sense
> 
> a. no laptop draws 700W
> b. no inverter even a 700W one draws *that much* more power than it delivers.
> c. inverter efficiency is usually at its best somewhere between 50 and 80% of full load so if your laptop draws say 50W at 230V a 150W inverter will draw say 60W at 12V (ie 5A) a 75W inverter may only draw 53W at 12V (about 4.5A). A 700W inverter will have a fan and will be inefficient at only 50W delivery but even there will only draw a max of I guess around 100W.
> 
> hope this has helped.
Click to expand...

sorry salytraffc but you are wrong (again) you better read up on your inverters and laptops, simple inverter info :
http://www.power-inverters.co.uk/inverters.php

My laptop states 240v 2.5amps on the power unit = 600w and its brand new so there are sure to be more inefficient versions around which will draw my generalisation of 3 amps :roll: !!.

therefore using the info from the above link to calculate the inverter power. 
600/10 = 60 amps

unfortunately there is no magical world where you get out for nowt, if you step up the voltage by 20 then you have to step up the current by a similar amount DOH!

elbino the adapter I have in that link will do 19v ( see specification)
eg
Switchable 15/16/18/19/20 Volt (3.5 A) and 22/24 Volt (2.9 A) DC output

cheers
650


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## 108526

I've got one of these
http://cgi.ebay.co.uk/Universal-12V...ryZ48632QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
works a treat


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## geraldandannie

Tribute_650 said:


> My laptop states 240v 2.5amps on the power unit = 600w and its brand new so there are sure to be more inefficient versions around which will draw my generalisation of 3 amps :roll: !!.


Tt just goes to show how dangerous numbers can be.

I have a brand new Tosh laptop infront of me.

The power _rating_ of the PSU block states 100-240~1.5A *input*, 15V 4A *output*. By your method of calculation, 240V X 1.5A = 360W input, 15V X 4A = 60W output, effeiciency - 60/360 = 14% 8O

So no, your laptop isn't taking 3 times as much power as a desktop PC. Most laptops have batteries of between 3Ahr and 6Ahr. This laptop here has a capacity of 4.4Ahr @ 14.4V, giving a power of 63Whr, meaning if I took it's AC input power as my guide, the battery would last 10 minutes (against the rated time of 2 hours).

Something not right somewhere. :roll:

Gerald


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## 105062

geraldandannie said:


> Tribute_650 said:
> 
> 
> 
> My laptop states 240v 2.5amps on the power unit = 600w and its brand new so there are sure to be more inefficient versions around which will draw my generalisation of 3 amps :roll: !!.
> 
> 
> 
> Tt just goes to show how dangerous numbers can be.
> 
> I have a brand new Tosh laptop infront of me.
> 
> The power _rating_ of the PSU block states 100-240~1.5A *input*, 15V 4A *output*. By your method of calculation, 240V X 1.5A = 360W input, 15V X 4A = 60W output, effeiciency - 60/360 = 14% 8O
> 
> So no, your laptop isn't taking 3 times as much power as a desktop PC. Most laptops have batteries of between 3Ahr and 6Ahr. This laptop here has a capacity of 4.4Ahr @ 14.4V, giving a power of 63Whr, meaning if I took it's AC input power as my guide, the battery would last 10 minutes (against the rated time of 2 hours).
> 
> Something not right somewhere. :roll:
> 
> Gerald
Click to expand...

Hi Gerald,
Yes thats because you are plugging in your power unit to the inverter not the lap top 15v dc socket so it is nothing to do with the efficiency of the power unit or the 15v power requirements of the laptop!. For safety you can not ignore the power rating of the power unit. The adapter I mentioned plugs into the laptop and as you point out has a lower power requirement. So it is a better setup than an inverter because you are not going through this process

12v step up x20 to 240v then step down / by 16 ...now thats inefficient.

Inverters are good for emergencies and for appliances that only take 240v but they will zap your battery by about x20 the appliance stated current ! I have one onboard which will take 3000w but only use in dire emergencies like the wife needs to use a hair drier :roll:
cheers
Paul


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## sallytrafic

Tribute_650 said:


> sallytrafic said:
> 
> 
> 
> 
> 
> Tribute_650 said:
> 
> 
> 
> I would not use an inverter as they use far too much current as inverters do, if your laptop takes 3 amps the inverter will take 60 amps and flatten your battery in about an hour plus heat up the wiring a fair bit!
> 
> I use one of these adapters designed to run a laptop from a cig socket and only take 3-4 amps.
> 
> http://www.ebuyer.com/product/123812
> cheers
> Paul
> 
> 
> 
> Apart from the fact that 3A at 230V equals about 700W and 700W at 12V nominal is about 60A this post makes little sense
> 
> a. no laptop draws 700W
> b. no inverter even a 700W one draws *that much* more power than it delivers.
> c. inverter efficiency is usually at its best somewhere between 50 and 80% of full load so if your laptop draws say 50W at 230V a 150W inverter will draw say 60W at 12V (ie 5A) a 75W inverter may only draw 53W at 12V (about 4.5A). A 700W inverter will have a fan and will be inefficient at only 50W delivery but even there will only draw a max of I guess around 100W.
> 
> hope this has helped.
> 
> Click to expand...
> 
> sorry salytraffc but you are wrong (again) you better read up on your inverters and laptops, simple inverter info :
> http://www.power-inverters.co.uk/inverters.php
> 
> My laptop states 240v 2.5amps on the power unit = 600w and its brand new so there are sure to be more inefficient versions around which will draw my generalisation of 3 amps :roll: !!.
> 
> therefore using the info from the above link to calculate the inverter power.
> 600/10 = 60 amps
> 
> unfortunately there is no magical world where you get out for nowt, if you step up the voltage by 20 then you have to step up the current by a similar amount DOH!
> 
> elbino the adapter I have in that link will do 19v ( see specification)
> eg
> Switchable 15/16/18/19/20 Volt (3.5 A) and 22/24 Volt (2.9 A) DC output
> 
> cheers
> 650
Click to expand...

I have to tell you Tribute_650 not only can't you spell my user name you are no electrician. First what is probably a simple typo:



Tribute_650 said:


> if you step up the voltage by 20 then you have to step up the current by a similar amount DOH!


DOH indeed the current reduces by the same factor.

Then you are making a beginners mistake



Tribute_650 said:


> My laptop states 240v 2.5amps on the power unit = 600w and its brand new so there are sure to be more inefficient versions around which will draw my generalisation of 3 amps :roll: !!.


Just because your power supply is rated at 240V 2.5A does not mean that your laptop consumes anything like that

Have you thought what 250W of heat on your lap would feel like? No, although your power supply is rated like that the current is no doubt the peak possible from the power supply and from time to time your machine on start up or fan start up might take a little more than average but I assure you not 600W. Never multiply the current and voltage of a power supply and assume that the device it is feeding draws that much.

My desktop, measured not rated, draws between 70-85W during all of its running.


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## sallytrafic

Tribute_650 said:


> Hi Gerald,
> Yes thats because you are plugging in your power unit to the inverter not the lap top 15v dc socket so it is nothing to do with the efficiency of the power unit or the 15v power requirements of the laptop!. For safety you can not ignore the power rating of the power unit. The adapter I mentioned plugs into the laptop and as you point out has a lower power requirement. So it is a better setup than an inverter because you are not going through this process


You are wrong here as well let Gerald plug this supply into his home mains no inverter in sight.

If Gerald's switched mode power supply was drawing 360W and only giving out 60W then 300W would be dissipating in a small block of black plastic, instant meltdown.


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## geraldandannie

Hi Paul



Tribute_650 said:


> For safety you can not ignore the power rating of the power unit.


Well, that's not quite true. As Frank says, the power supply could say anything on it, but it doesn't mean you will consume that amount. These little power blocks are used across a range of devices, and are made by the million. Much better to actually look at the laptop (as I did this morning) and see what the laptop is rated at (i.e. maximum *usage*)

Just because a fuse is rated at 10Amps, it doesn't mean you will always be drawing 10Amps through it.



Tribute_650 said:


> 12v step up x20 to 240v then step down / by 16 ...now thats inefficient.


Yes, but the marginal reduction in inefficiency is more than made up for by the quantity of devices I can / need to use on it. Whether it takes me 10 minutes of engine running to recharge the cab battery or 12 minutes (equivalent to a 20% variation in efficiency between the 2 methods of recharging my laptop) doesn't make that much difference to me.



Tribute_650 said:


> but they will zap your battery by about x20 the appliance stated current !


No. It will take from the cab battery about 20 times the *actual, running current*, not the rated current. My laptop uses a 45W PSU. Assuming it's running at full blast (unlikely), it will be taking a couple of Amps at 20V, which _might_ be up to 4 Amps at 12V from the cab battery. If I charge for 1 hour, I will use 4Ahr from the 85Ahr or so the battery has. Not really a problem for me.



Tribute_650 said:


> I have one onboard which will take 3000w but only use in dire emergencies like the wife needs to use a hair drier :roll:


Ah, well fortunately, I don't have a need for that much 240V. If I did, I think I'd stay in a hotel. No offence :wink:

Gerald


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## sallytrafic

geraldandannie said:


> Hi Paul
> 
> 
> 
> Tribute_650 said:
> 
> 
> 
> For safety you can not ignore the power rating of the power unit.
> 
> 
> 
> Well, that's not quite true. As Frank says, the power supply could say anything on it, but it doesn't mean you will consume that amount. These little power blocks are used across a range of devices, and are made by the million. Much better to actually look at the laptop (as I did this morning) and see what the laptop is rated at (i.e. maximum *usage*)
> 
> Just because a fuse is rated at 10Amps, it doesn't mean you will always be drawing 10Amps through it.
> 
> 
> 
> Tribute_650 said:
> 
> 
> 
> 12v step up x20 to 240v then step down / by 16 ...now thats inefficient.
> 
> Click to expand...
> 
> Yes, but the marginal reduction in inefficiency is more than made up for by the quantity of devices I can / need to use on it. Whether it takes me 10 minutes of engine running to recharge the cab battery or 12 minutes (equivalent to a 20% variation in efficiency between the 2 methods of recharging my laptop) doesn't make that much difference to me.
> 
> 
> 
> Tribute_650 said:
> 
> 
> 
> but they will zap your battery by about x20 the appliance stated current !
> 
> Click to expand...
> 
> No. It will take from the cab battery about 20 times the *actual, running current*, not the rated current. My laptop uses a 45W PSU. Assuming it's running at full blast (unlikely), it will be taking a couple of Amps at 20V, which _might_ be up to 4 Amps at 12V from the cab battery. If I charge for 1 hour, I will use 4Ahr from the 85Ahr or so the battery has. Not really a problem for me.
Click to expand...




Tribute_650 said:


> I have one onboard which will take 3000w but only use in dire emergencies like the wife needs to use a hair drier :roll:


Ah, well fortunately, I don't have a need for that much 240V. If I did, I think I'd stay in a hotel.

Gerald[/quote]

Sock it to him Gerald  Sallytrafic wrong again forsooth I think not


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## sallytrafic

.....and if any further proof was needed of what gerald and I are saying see attached. Its a switched mode power supply rated at 100-240V 1.2A input 12V dc 3A output. In the photograph its powering an external hard disk and the photo was taken shortly after switch on. You can see from the meter monitoring the input power that it is reading 10W and the maximum when writing was 21W 

No where near the 36W (output) or 240W (input) derived from the rating plate.

so out to the van and plug it into a 75W inverter which of course if only powering 10W as I have said will be very inefficient. As it happens it shows that the device hard disk is drawing 11W at the moment I took the photo. I had a meter on the current input and that is shown also as 1.57A call it 1.6A so I measured the voltage 12.3V so the input wattage was 19.7W.

Therefore at a measured load of 11W a 75W inverter is running at 15% of its rated capacity and turns in an efficiency of 63%. I seem to recall saying that in this very thread. 

So QED I think Gerald


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## johng1974

> plug it into a 75W inverter which of course if only powering 10W as I have said will be very inefficient.


 8O

I didn't know this.. so if you buy an inverter way over the power you need to draw, it is badddd.... ( I wrongly assumed the inverter would only take what was needed from it)

thanks
John


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## sallytrafic

johng1974 said:


> plug it into a 75W inverter which of course if only powering 10W as I have said will be very inefficient.
> 
> 
> 
> 8O
> 
> I didn't know this.. so if you buy an inverter way over the power you need to draw, it is badddd.... ( I wrongly assumed the inverter would only take what was needed from it)
> 
> thanks
> John
Click to expand...

Yes somewhere between about 50 and 80% is normally the sweet spot where the efficiency can be in the high 90s. The larger ones have fans, in some poorly designed ones they are on all the time even if you take no power. So power out equals zero, power in just a bit result efficiency 0%


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## geraldandannie

johng1974 said:


> I didn't know this.. so if you buy an inverter way over the power you need to draw, it is badddd.... ( I wrongly assumed the inverter would only take what was needed from it)


More or less. An inverter is designed for maximum efficiency at its rated current / power. The best you could expect would be around 95% from a well-designed PSU. Anything less than its rated power, the inverter efficiency drops.

Having said that, think of what you need to do with it. A 150W inverter should perform reasonably well, and cover a wide range of uses in the motorhome. And they're price competitive! :wink:

Gerald


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## johng1974

I may be lucky  I have a 300W inverter

but if wildcamping would like to power pc, ps2, 19" LCD, skybox and sony amp.. all told that's about 200-250W (I posted the actual figures somewhere on this site but can't find them now.. I was using a power meter like Franks)
John


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## Boff

Hi,

maybe I can clear up part of the confusion. Sometimes it helps being physicist and techie at the same time :wink: :

*First of all the conclusion: Dell laptops, like practically all others, will run fine from a bog-standard 150w inverter.* I have done this with 4 different Dells so far. There was only one generation of Fujitsu-Siemens laptops some years ago which had difficulties on a non-sine inverter.

Now, to prove my point, some words about watts, volts and amperes:
Right now I have my Dell AC power supply in front of me. It says there, besides a lot of Chinese:

90W-AC ADAPTER
INPUT: AC 100-240V~ 1.5A 
OUTPUT: DC 19.5V 4.62A
EFFICIENCY LEVEL: III

Now, like all modern computer power supplys, this is a switching power supply which automatically adapts to the input voltage. Therefore the wide range of input voltages. As power=voltage*current (or "Watts=Volts*Ampere"), the input current is inverse proportional to the input voltage, to maintain a constant power output. So the maximum current of 1.5A will only flow if it is run at the minimum input voltage, which is 100V. And even then only for a very short time, namely when you plug it in and the built-in capacitors charge up. Which corresponds to a maximum input power of 150W. Any inverter that is rated for 150W continuous output can handle up to about 300W for a short time, so no problem here.

About efficiency: "EFFICIENCY LEVEL III" refers to the "External Power Supply International Efficiency Marking Protocol", and for a power supply of this range this means the efficiency under load must be at least 84%. So if the laptop draws full power (in my case 90W), then the input power must not exceed 107W. Which means that at 230V (240V is a thing of the past) a current of not more than .47A is drawn from the inverter.

Now modern inverters have efficiencies of 90-95%, so on the 12V side the inverter connected to my laptop would draw a current of between 9.4A and 9.9A.

Connected to elbino's laptop supply (65W at output, so 77W or less at inverter) the inverter would draw between 6.8A and 7.2A on the 12V side.

This all assumes that the laptop runs under full power, which in only does if the backlight is switched to maximum, all BIOS power saver options turned off, CPU, hard disk, CD/DVD drive and graphics chip 100% busy, and the battery being recharged at the same time. Under normal circumstances the power demand will almost always be lower than that.

In the end that means: If you have a fully-charged 100Ah leisure battery, you can run elbino's laptop for almost 14 hours before completely depleting the battery, and 7 hours before reaching the 50% charge level which is considered safe.

Dedicated 12-volts laptop power supplies hardly ever exceed 80% efficiency (at least I haven't seen one that did), so the combination of the standard mains power supply and a good inverter is at least as efficient.

Best Regards,
Gerhard


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## DABurleigh

Just catching up on MHF after work and all I can say about this thread is I have a mental image of my Honda genny going nearly flat out solely so I can do emails.......

Usually a favourite saying of mine is "a little knowledge goes a long way", but sometimes Clint Eastwood's "a man's gotta know his limitations" is more appropriate.

Dave


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## sallytrafic

DABurleigh said:


> Just catching up on MHF after work and all I can say about this thread is I have a mental image of my Honda genny going nearly flat out solely so I can do emails.......
> 
> Usually a favourite saying of mine is "a little knowledge goes a long way", but sometimes Clint Eastwood's "a man's gotta know his limitations" is more appropriate.
> 
> Dave


Or no need for extra heating in my van I just leave the lappy on


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## muffinn

What about using the 150w inverter with a 80watt slow cooker - is that going to work?


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## DABurleigh

Yes.

Now what are you going to use your last post on, I wonder?

Dave


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## Autoquest

Interesting thread, which by sheer coincidence I was about to start! 

I plugged by monster laptop into a 150w inverter a few days ago and was surprised to see my van voltmeter going totally nuts wild swings back and forth, the inverter cycling through what appeared to be a minimum and then a maximum power surge and the notebook itself cycling through a charged/no charge state along with the screen dimming in and out - Not good 8O 

I have clearly got my sums wrong... My PSU states 100-240 V / 2.0 Amp in and 20 V and approx 6.0 Amp out. I think I will be going for one of those 12V Maplins units instead. 

I think I remember reading somewhere that if you intend to use your laptop in the van then it's best to remove the battery first (not that I did) apparently more than 50% of the power demand is purely to recharge it.


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## ianhibs

Blimey Tribute. You've certainly stirred up the natives.

Elbino. I've got a Dell laptop too and it's a nightmare getting a 3rd party 12v charger. Yes, it will run fine from a small inverter but not below 100W. However, although I've got an inverter I still intend buying from HERE (they seem to be the only ones I can find who know about Dells). The reason is to avoid long leads across the floor as I sit at the table with my computer in front of me and I have a 12V socket positioned in the right place.

Ian


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## sallytrafic

ianhibs said:


> Blimey Tribute. You've certainly stirred up the natives.
> 
> ...clipped
> Ian


By and large people are entitled to their opinions but when people post stuff on a technical matter that is wrong, and is easy to prove wrong, then I think it behoves those that really know the subject to post a rebuttal. Especially given the strength of Tribute_650's assertions. Otherwise beginners might go away with the wrong info and may buy the wrong device.

So sorry if the 'natives' are revolting but Gerald Gerhard Dave and I do know quite a bit about the subject.

Autoquest posts a good description of what happens when an inverter is unable to cope with the peak load but it may not be the load _per se_ that is the problem. If the 12V supply isn't sufficiently stiff (long leads poor connections) when the start up load comes on the 12V may dip below what the inverter can compensate for with identical symptoms.


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## Autoquest

I need 20V and upto 6 Amps supply and I think I would rather ditch the inverter. Can anyone recommend these things?

http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=44736&doy=1m4#spec


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## 107990

I've just bought one of these on ebay for my new MacBook. I had a Kensington one for my old Toshiba pc which worked perfectly. I paid PC World about £45 for the one for the Toshiba but this one came to about £13 with p&p. If it works as well as the old one i will be well pleased.

http://cgi.ebay.co.uk/ws/eBayISAPI....m=120235548504&ssPageName=STRK:MEWN:IT&ih=002


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## Autoquest

Thanks for the link - I think I will need a bit more juice for mine


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## Boff

Autoquest said:


> I need 20V and upto 6 Amps supply and I think I would rather ditch the inverter.


Ditching the inverter might not solve your problem! Because in your case it is most probably not the inverter that causes the trouble, but the 12-volt wiring of your van:

Your "monster laptop" seems to take quite a bit of power from the inverter, but still within specs. The inverter responds to this by drawing a high current on the 12v side. Because of this high current, and a too high resistance somewhere in the wiring, the input voltage at the inverter drops.

Modern inverters can compensate such a voltage drop on the input side (within certain limits), but they do this by drawing an even higher current. This makes the voltage drop even further, until the inverter's built-in voltage monitor cuts out. Immediately the input voltage rises again, and the cycle starts again.

Inverters up to 150 watts are, like dedicated laptop car power supplies, usually connected via a cigarette-lighter type plug. And the minimum requirement for a cig-lighter socket is to deliver a current of just 8 amps! So before ditching the inverter, and replacing it by another power supply that might run into exactly the same problem, first the wiring behind the socket should be checked. Or the inverter should be connected directly to the battery.

Best Regards,
Gerhard


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## Autoquest

I suspect you are right Boff and I shall heed your advice. My 12V socket is wired and rated for 10 Amps max but I did notice that the wire I had supplied betwixt the van's two pin socket and my female cigarette lighter socket was a tadge warm 8O 8O I shall beef that up first and try again with the inverter (but having removed the lappy battery first)


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## CliveMott

*laptop power supplies*

Many Laptop manufacturers also provide (at cost) an alternative 12 volt power supply cord. Use this if you can. Also available are aftermarket versions of the same thing. These work but should they go wrong your Laptop warranty will be out the window!
Like many I just run my Laptop off the modified sine wave inverter I have plumbed into my sockets using the supplied mains PSU supply module and cord.
Nearly all Laptop (and flat screen TV) power supply units use high frequency switch mode techniques to transform the power format available into the power format required. Basicly the first thing that happens is that the incomming "mains" is rectified by diodes then smoothed by a capacitor. The mains waveshape therefore being of little consequence. Then this raw DC voltage is chopped up at high frequency and transformed down using a ferrite cored transformer. Then its rectified and smoothed once again but at the lower voltage required by the Laptop. The clever bit is that the waveform and mark - space ratio of the high frequency "chopper" is controlled so as to regulate a constant voltage at the output for a wide range on incomming mains voltages. Many Laptop power supply units span from 90 to 260 volts AC input.
The amps figure on the side of the PSU unit will be the maximum amps which might be seen when the laptop is working flat out and the mains voltage is at minimum voltage.

For much of the time however the power consumption of the laptop will be much lower. If it were as great as quoted in some of the above posts it would soon catch on fire.
Say 2 - 3 amps from the 12 volt supply average to run a laptop is realistic.

Hope that helps
C.


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## sallytrafic

Going on from what Clive says there is a fault mode you don't see very often now but used to arise when a poorly designed quasi sine wave inverter was followed by an insufficiently smoothed and controlled switchmode power supply. The fault was that the switching instead of running at high speed could get synchronised to the input steps on the sine wave with the result that it could be trying to extract power from the input waveform when there was zero current to be extracted this used to play hell with the stability of the output circuit. 

The last one I encountered like this was when trying to demonstrate a 12V LED Buoy lantern to a group of visitors on a light vessel moored alongside. The demo rig was designed to run off the mains and included a switchmode psu of unknown vintage. It worked perfectly on shore on mains. As the lightvessel was 24V and no mains power leads had been run ashore it was easier to take a feed from the 230V produced on the vessel from an inverter used for maintenance tasks, but it just sat there in 'sulk' mode producing the odd blip of power.


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## teckie

Hi everyone... think I'll add my own Laptop experience to this thread...As we all know the supplied laptop battery gives us approx 2 hours of use ! and having always taken my laptop with me for the past 6 years I have used a PSU purchased for the laptop and a few Inverters 150/300/600/w and found all seemed to flatten a 110amp battery in no time so I purchased a little Honda EX350 Gennie from a friend and it's a great little thing and has solved all my problems. I can even use a battery charger to top up the leisure battery while using the laptop.

Teckie


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## alunj

my 2p
acer notebook , works best with a maplin 12v->whatever dc adaptor
macbook pro, doesnt work at all with a stepped square 150w inverter. Works with a 300w pure sine but hammers the battery on the van, currently awaiting a magsafe (the funny magnetic power connector on the air and pro) to ordinary dc connector so i can use the maplin unit.


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## sallytrafic

I see tribute_650 is no longer a subscriber pity as he never came back to edit or 'prove' his assertions on this thread.


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## EuropeanCampers

All very confusing this.

My fathe ris running his latop from a small 75w inverter and he says it works fine. Is he running a risk doing this with only a 75w inverter?

Thanks


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## DABurleigh

No.

It is only confusing because people state with absolute certainty stuff which is utter bol.....

Dave


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## teckie

Hi there... I used a 300w Inverter for my laptop and found it drained the battery pretty quick.. then I bought a Stabilised 12v PSU multi voltage for laptops from a local computer shop (£15) it works great and the battery lasts a hell of a lot longer considering I have a 17" screen.

Teckie


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## RichardnGill

I have just read through this thread with intrest as we use to use a 150W Maplins invetor to power the TV (15" LCD) Sky Box and to charge the laptop when required. It did this no problem and at the time I reaserched and got a 150W as I thought it would be more efficent that using a 300W which it probally was. 

We then had a problem with the 85Ah battery going flat after 1 day when using the invetor, but this was probaly due to having 2 kids with us and the TV never being off.

Just recently I have ditched the invetor and got a 12V TV and 12V Pace Sky box, which seems to be giving a far better battery life. But we now have the problem of charging the Laptop. I was planning to get a 75W invertor for this but now I am thinking of going down the DC>DC route. 

How much diffrance would using a 75W Invertor over DC>DC make in power consumption. As I will still need an invertor to charge Phones and I pods, but could do this using the Laptop USB via DC>DC.

Richard...


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## teckie

Hi Richard... since buying the 12v PSU for my laptop and by just plugging it into a cigar lighter socket connected to my leisure battery whenever I need to use it I have found that I can go all weekend mostly Thursday to Sunday without any need to charge the laptop battery.

Teckie


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## Boff

Hi Richard,

the "sweet spot" for any inverter, so the point at which it runs with best efficiency, is at about 50% of the rated _permanent_ load. So for an average laptop consuming approx. 70-75 watts, a 150 watts inverter would be best. Charging a mobile phone or something like that from this inverter would however be rather inefficient.

DC-DC power supplies are, effectively, nothing else than specialized inverters with built-in PSU. And in many cases they are rather inefficient. However, with one of them you avoid the additional losses in the mains PSU.

However, while good (reads: expensive) inverters can have efficiencies up to (and over) 95%, while other, cheap inverters that come out of some far-east sweatshop might be not more than 80% efficient at best. And the same goes for DC-DC PSUs.

The advantage of the inverter solution is that with just one inverter you can charge (almost) all your devices with their ordinary mains PSUs. Depending on the quality you might pay for this advantage by reduced battery life. Including all devices you might want to buy in future.

Best Regards,
Gerhard


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## johnandcharlie

Since installing my solar panel and new 110 amp battery I've been running my laptop with a Maplins DC-DC converter. There's no point wasting power charging the laptop battery, so I've removed it, and it's normally drawing around 1.9-2.0 amps. I must have been using it for 8 or 9 hours yesterday, and it wasn't a particularly sunny day, but I had no problem with power. Everything I regularly use in the van now runs off 12 volts, so I rarely need to use the inverter.


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## jm2209

*So confused!!!!*

Hi all,

Just read through this topic and am very confused by the whole MH power issue!

We're moving into ours next month for a 3 month trip round Europe, we need to charge 2 digital camera batteries, a mobile phone, use the vans radio and charge/run 2 laptops for an absoloute minimum of 5 hours a day, probably more like 10 with watching a film in the evening etc...

We have a leisure battery (not sure what size) and an invertor (i think its a plug box under the drivers seat).

Ideally we'd like to be able to wild camp a 4/5 days a week to keep costs down, sometimes not moving for 48 hours. We don't mind sitting in McDonalds or Starbucks to charge the power of the laptops and use their wifi if needed.

Basically, whats the best solution for us? Should we get the dc adapter things, solar panel, bigger leisure battery or something else?

As you can probably tell our knowledge of this stuff is virtually nil so any help is greatly appreciated!


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## peribro

As a start point you need to try to estimate what your power consumption is likely to be by working out what else will be drawing power from the leisure battery (lights, pump, TV) and also what the consumption of the laptops is. They can vary greatly. You need to establish the size of the leisure battery and your inverter. You should be aware that if it is not a pure sine wave inverter it may not work on all your appliances, so you should test it first on your appliances. 

I doubt though whether one leisure battery will be sufficient so as a starter you should be thinking about a second. You also need to give thought to how they will be recharged - will it be through a long drive every 48 hours? A solar panel can be very good indeed and you should go far the largest that you can accommodate. Assuming you have the time before you go away, then I would suggest a trial run for a couple of days to see how your power consumption pans out.


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## Christine600

A very interesting thread! 

My MH come with a rather large it seems 1200W inverter. Which most of the time will be used to charge a mobile phone or two and sometimes a laptop. 

Perhaps the most cost efficient would be to get a smaller 150W inverter to use on those occasions?


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## Ken38

My laptop running off a 150W plug in invertor pulled 3 Amps from the battery.

If I look at the ratings on the PSU and laptop they are far higher. So you need to measure the actual current not go by ratings.

The invertor is definitely not pure sine wave but the PSU seems to cope.

I choose this as the cheapest and most flexible option as I can charge any mains charged equipment whilst driving. I can also run off the battery if I need to when not on hookup.


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## JHC

*Wild Camping & Power Requirements*

Hi jm2209

If you haven't already sorted out how to meet your power requirements and also haven't already headed-off on your 3 months European tour I am happy to share with you what I did last year to meet our Wild Camping power needs - living away from the mains almost completely whilst touring.

I'll await your response before offering any detail.

James


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## Jenm

Hi JHC

I'm John's wife Jenny and we'd love to hear any advice you can give us 

Not heading off till May so have a bit of time to sort everything out!


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## JHC

*Wild Camping & Power Requirements*

Hello Jenny

If you prefer I am happy to send you information on the power system that I opted for prior to going on a 2 week Wild Camping tour of Ireland last year. We wanted to be able to use our Sky+ Box as well as our LCD TV, DVD Player and be able to use halogen lights without fear of running out of power. We also wished to charge up our mobile phones, digital camera battery and use my laptop from time to time. I had a Dome Satellite TV system fitted at the same time. We have longer term plans for spending long periods touring Europe and maybe Turkey - so power was a limiting factor that needed to be solved.

It is fair to say that as we tour as much in the winter as in the summer we wished to cater for the long evenings off-mains Wild Camping when the power demand is at its highest with lights and entertainment.

So, after a lot of research we opted to have a bank of 2 x 110Ah leisure Lead Acid Batteries installed in a spare external cupboard and had these wired to a fused distribution board in an internal cupboard from where a feed was wired directly to the Dome Satellite system and another to a new 12v Cigar Socket mounted near to the existing 12v Socket at the TV location. I decided that I wanted to have the entertainment system (TV, Sat, DVD) all running off this new bank of batteries - so leaving the on-board 2 x 90Ah leisure batteries to provide for lighting, water pump and central heating fan.

Then to charge the new bank of batteries (the entertainment supply) I had a Sterling BB1250 Charger installed which delivered up to 50Amps from the vehicle's alternator (it gets around the problem of the alternator going into trickle charge when the vehicle starter battery is fully charged). If I feel that the entertainment battery bank needs topping-up when we had been stationery for a longish time all I need to do is start the vehicle engine and leave it running for a short while. Obviously, as soon as we moved-off to another location the batteries would be charged by the Sterling unit.

I could have had the system integrated into the existing leisure battery system but I wanted to avoid possible complications especially with the Auto-trail warranty by not interfering with their on-board leisure charging and battery system. I also feared that the on-board charger appears to be limited to delivering a very low rate of charge and appears not to provide sufficient for our Wild Camping lifestyle (I guess it assumes mostly Caravan Site usage with mains hook-up - which is contrary to our's). Also, the annoying fact that all motorhomes produced after 2006 seem to have a cut-out relay which isolates (cuts-off) the habitation electrics when you start the engine means that you cannot top-up those batteries whilst using them to power our entertainment and of course the lighting. We found this a nuisance prior to having the extra power and battery system as well as our Dome Sat system installed.

If you wish to have more detail including costings I am happy to provide those directly to you via e-mail and/or phone. I find it helpful to be able to explain things in a two-way conversation that by writing up all I have done - as your needs might be different to ours. Hence, a telephone call would be far better than this forum or e-mail. To start with my email address is: [email protected] for us to exchange phone numbers.

James


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