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Paper Tape
Posts: 2
Registered: ‎01-15-2017
Location: CN
Views: 348
Message 1 of 2

Can I connect my laptop that runs on 18.5V directly to a 12V battery?

I have days of electricity outages here and I need to use my laptop. The thing is, it runs off 18.5 V 3.5 A (AC adapter output), so it is expecting 18.5 V, what will happen if I connect it to a 12 V? I know for sure some laptops will work! I tried some crappy old laptop and it ran even though the adapter its AC adapter outputs 18 V, but I did not want to try this on my laptop as I don't know what might happen.

The laptop's internal battery is dead and I have actually removed it, so should not the voltage be enough to run the laptop since now there is no battery to charge! And since the internal battery outputs 10.8V, should not the laptop be able to run on that low voltage from the power source as well?

But again I was afraid if I provide too low voltage the laptop will try to withdraw more current, and that might heat it up and fry it! But then I thought I can add a fuse to prevent the current from exceeding certain limit (say 7 A?)

And if we assume it does not work! Then I can add 2 batteries which will give me 24 V, but now I'm thinking 24 (actually almost 28V when the batteries are fully charged) might be too much for the laptop and now high voltage could really hurt!

A solution to that could be to add a linear voltage regulator, but that wastes too much energy (or does it not?), which is why I'm not using DC-AC power inverter in the first place, after all I'm trying to make this setup as efficient as possible (because as I said we have days of outages), so how do I reduce voltage without having to waste much energy?

Assuming the batteries are fully charged, thus outputting "almost" 28 V the regulator then will have to drop the volt down by 8 volts! Will this waste too much power? and by too much power here I mean like 50 watts! because the laptop runs with that much so if it will waste 50 watts or so, then it will be actually wasting the same as the actual load does! and that is a lot.

And an important question here, will I have problems with the regulator heating up? or that little difference isn't going to cause much heat?

To sum the questions up:

Can I connect my laptop that runs on "18.5 V" directly to a 12 V battery OR 24 V (2 batteries)? If I have 2 batteries outputting 24 V how do I reduce the voltage without wasting energy?


Bit Torrent
Posts: 2,379
Registered: ‎03-08-2012
Location: CA
Views: 285
Message 2 of 2

Re: Can I connect my laptop that runs on 18.5V directly to a 12V battery?


Your choices are: - get a DC to AC inverter to run off 12VDC
- Get a UPS but you have limited run time bases on its capacity & rating

A quality inverter of Modified Sine wave would be the best solution.
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