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Discussion Starter · #1 · (Edited)
Charging laptops off leisure battery

I've got a cigarette socket charger for my laptop and was wondering a couple of things before I plug it into the 12v from my leisure battery.

I want to calculate how much energy draw it will have so I've used the following calculation, is this correct?

Input 12v - Output 19V at 3.42Amps

19V * 3.42Amps = 64.98 Watts (call it 65 Watts)

So 65 Watts / 12V = 5.4 Amps

So does this mean it's going to be drawing out 12V at 5.4Amps to be able to convert to 19V at 3.42Amps ?

Also, I understand wherever power is converted there is power loss, how much would it be in this situation?

Cheers guys and feel free to rip me a new one if I've got this completely wrong!
 

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Do actually mean USB charger or a cigarette lighter adapter for you laptop?
my laptop has a 120W power brick, if I unplug it and look at the discharge rate of the battery its about 20W just web browsing.
The max power rating would only be used if say you were gaming, screen brightness turned right up, and charging the battery.
A DC to DC converter to go from 12v to 19v will be 90% efficient at best.
If you've got a multimeter the best thing to do is measure it.
 

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Discussion Starter · #4 ·
Yea, sorry my mistake I mean a cigarette lighter adapter. Have no idea why I said USB? I guess it was late. I'm just wondering what the power draw on the battery would be so I can work out how viable it is to try and charge it off that. I've used it before off the engine battery on my old Prugeot 306 and didn't have any problems but I'm a bit more protective over my can that my 306 shed.
 
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