# Running power for laptop off a car battery

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Hello Guys

I am leaving soon for South Lebanon... Yayyy! whatever...

Anyway...

I got some infos about this part of the country and the first thing I was told is that the electricity goes off there and there are days when you get the electricity and days when you do not.

So I am bringing my laptop with me and I was wondering, beside buying a UPS over there, is there a way to buy a car battery and run my laptop of it?

Like during the time when there is electricity, have the battery be recharged, and then at night or during the day, plug my laptop to the battery when the electricity goes off..

So any idea how to proceed? I am clueless when it comes to electricity, was this mod realized before? any link?

Thanks people!

Peace!

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Unless if your laptop runs on 12v you will need to buy some extras.

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You could manipulate the 12V from the car battery to match the output from your transformer using resistors. You can also put multiple 12V batteries in parallel to to double the life span. But, don't leave it connected when the laptop battery is full. The result would be bad.

What voltage does your tansformer out put?

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Hey guys

Thanks for the help! the output voltage is 19.5V

I have a DELL Inspiron 8600

Thanks

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Thanks for the help! the output voltage is 19.5V

oh... in that case you have to use two car batteries in series (To get 12V + 12V = 24V) then use some resistor maths (that I don't know) to figure out how to get 19.5V.

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ok, but since I have a transformer... it will transform to 19.5 right?Â  8)

so all I actually need is to connect the battery to an outlet and just connect my laptop powersuply to the outlet

the trick now is how do i recharge the battery?

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ok, but since I have a transformer... it will transform to 19.5 right?Â  8)

so all I actually need is to connect the battery to an outlet and just connect my laptop powersuply to the outlet

No, you can't do that, the transformer excepts (usually) 110~230V. So giving it 24V won't work. As far as recharging the car batteries is concerned, just connect them in parallel with another cars battery (that is actually in the car) and run the car for a bit :P. You might even find a way to position them so it is secure under the bonnet so you can drive around as normal and charge them at the same time.

Also, having done a bit of Googling, it seems you will have to decide in what state you wish to charge the battery. The laptop will draw different amount of current depending on it's state (screen brightness, on/off, Full CPU/Idle CPU will effect this). And to work out what resistance your circuit needs to drop the voltage you need to know the current. So your gonna need to get a multimeter and measure how much current your laptop uses befor you can build the circuit.

On a slight tangent, it would be easier to get a 12V to 110/230V inverter (converts 12V DC to 110/230V AC). But it wouldn't look nearly as cool or gehto as two car batteries with resistors :P Still needs one car battery though. Also, I suspect the way of the inverter will be much less efficient then resistors, and so your battary will go flat much faster (time for lots of them in parallel :P)

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Resistors would be a really wasteful way of doing this, and an inverter (the 12v -> full wall voltage thing) isn't much better. A 24v battery, or 2x12v car batteries will work, but you'll wanna build a small voltage regulation circuit. I don't know much about them, nor have I made one, but I know that's basically the best way to do it in terms of efficiency and run time.

If that fails, an inverter is the basic plug and play option, but it will sap your battery dry long before a voltage regulator connected directly to the laptop would.

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Alternatively, buy this: http://accessories.us.dell.com/sna/product...p;c=us&l=en. That's basically what I just described, only pre-assembled, guarenteed and supplied by Dell. Runs on ~12v (give or take a volt or two) so it only needs 1 battery, too.

Maybe build a small enclusure with a power strip and 2 battery chargers, 2 batteries and a cigarette lighter socket in it, that was you don't even have to modify the adapter. Then you'll have a multi purpose very heavy duty 12/24v power supply (maybe add a switch?) for various things, laptop, phone(s), lights, fans, a whole range of mobile devices, including *anything* that works in a car or a truck.

Could be an ideal solution for a place where the electricity goes off regularly. Perhaps add an inverter anyway to run stuff that can't be run from 12/24v?

Could add up in price to have 2 or more batteries, and an inverter, and chargers and everything else but it could be a very elegant, very functional solution to the problem.

As for your question though, the Dell part linked above and one single car battery would do the trick. Remember though that car batteries don't like being drained, and doing so may severely cripple or kill the battery. Make sure you charge it well when it's not in use, and don't completely drain the battery while you're using it.

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