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

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bengkui
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Joined: Fri Nov 24, 2017 3:03 am
Location: Shenzhen, China

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

#1 Post by bengkui » Fri Nov 24, 2017 3:30 am

I went to my grandmother's home where is a beautiful country, but recent days there has wind all day :( , so 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?
Thanks all guys who taking time to read my question.

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

#2 Post by axur-delmeria » Fri Nov 24, 2017 4:51 am

No and no.

For Thinkpads, the acceptable voltage range is generally between 0.5 volts lower and 1.5 volts higher than the specified input voltage.

You need something like this: http://www.bixnet.com/dd120xc.html
Planned Purchase: T480s i5-8350 FHD Touch
Impulse Buy: Thinkpad not named for safety reasons :lol:
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thinkpadcollection
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Location: kingston, ontario, Canada

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

#3 Post by thinkpadcollection » Fri Nov 24, 2017 4:54 am

Does not hurt to try. The adapter voltage is higher in order to able to charge the battery properly via battery's internal microcontroller. When not on adapter power, the computer runs off the 10.8V battery voltage via same circuits as adapter's, first few electronic components are there just in case to cut off power adapter and also second purpose to prevent battery backfeeding into power adapter with mains unplugged.

Besides, you'll love to have internal battery replaced and buy automotive's power adapter. Automotive's battery runs anywhere from 9V (starting) to 15V at fully charged while car running off alterator to juice your notebook properly without having to build anything. In other word your 12V system works exactly like what it does because they are lead acid technology.

Cheers, thinkpadcollection

bengkui
Posts: 2
Joined: Fri Nov 24, 2017 3:03 am
Location: Shenzhen, China

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

#4 Post by bengkui » Fri Nov 24, 2017 8:26 pm

axur-delmeria wrote:
Fri Nov 24, 2017 4:51 am
No and no.

For Thinkpads, the acceptable voltage range is generally between 0.5 volts lower and 1.5 volts higher than the specified input voltage.

You need something like this: http://www.bixnet.com/dd120xc.html
Thank you.

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