Will 12v dc battery be able to charge 19v laptop input? - Page 1
Forum section: electronics / beginners

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: January 09, 2025, 07:45:19 am
content: I already have a laptop but it is a low power one geared more as a tablet/laptop so I guess smaller power consumption. That one charges in the range between 7-12v. As per previous posts I made about it though I think the port is busted as it is extremely difficult to get it to charge having to wiggle it round usually for 15 minutes or more to hit the 'sweet spot', Not the barrel as the volts are consistent on the voltmeter. Anyway that is another issue already discussed.I have another laptop which is older and of the more traditional type and on the mains adapter it states 19v. Will the 12v battery (which usually sits around the 13v region) be sufficient to charge it or would I have to get a buckboost to give it a consistent 19v?I plan to do like I did with the first one and connect the wires direct to the fuse block. In that case I had to get a step down/regulator so it would stay at a consistent 12 as 13 was too high. After a lot of research it turned out to be overvoltage protection which would prevent it from charging even though the light showed it was on charge but would not charge until I got the regulator.So would plan a similar setup here to rig it direct to fuse block. None of that convoluted dc-ac-dc inverter nonsense.

author: amyk
author_rank: Super Contributor
timestamp: January 09, 2025, 09:06:53 am
content: No.Those which use ~12V input are usually with a 2S battery pack (8.4V fully charged), while those which use ~20V input use either a 3S or 4S pack (12.6 - 16.8 charged).

author: Aldo22
author_rank: Super Contributor
timestamp: January 09, 2025, 09:31:40 am
content: Maybe something like this? (Just an idea, I haven't tested it).https://www.aliexpress.com/item/1005008250983714.html

author: PGPG
author_rank: Frequent Contributor
timestamp: January 09, 2025, 01:07:20 pm
content: 2 years ago I have bought 3 cigarette lighter socket laptop supplies having 19V at output. Offer was very cheap as seller had lot of them and they had not popular plug, I think.Except them I have got some cables with plugs according to laptops we use.Till now I have changed cable in 2 of them (one is used for HP and one for DELL). Third is waiting.

author: CaptDon
author_rank: Super Contributor
timestamp: January 09, 2025, 01:18:47 pm
content: If the voltage of the battery pack is higher than your 12 volt battery then no and the short answer is also probably no since the charge circuit will require some additional overhead. Example, in a 3S pack the fully charged voltage could be 12.0 or slightly higher and the charging circuit would need probably 1.5 to 2 volts of overhead meaning and input of 13.5 to 14 volts. Add another 4 volts to that number if it is a 4S pack. Most laptops do not use a buck/boost charging circuit, they rely on a current and voltage controlled buck circuit.

author: Infraviolet
author_rank: Super Contributor
timestamp: January 09, 2025, 08:03:48 pm
content: What about replacing the problematic charger input port on the lower voltage laptop? That seems the obvious answer, if you can't find the right sort of port to replace it with which is compatible with it's own charger than consider a standard DC barrel jack for it, and powering it in future from a lower voltage wall wart with a normal DC barrel jack. Be very careful to ensure both are wired as centre positive, some supplies are occasionally centre-negative with disastrous results if plugged in to something expecting centre-positive.For the 19V one you're better just getting a new charger brick, traditional older ones with a DC barrel jack (and no third condutor in the jack) are compatible with any decent quality well regulated 19V power brick (mains AC to 19V DC output, brick or wall wart). You won't be able to build a 12V to 19V step up converter more quickly, easily and cheaply than you can simply buy a 19V power brick.Anything where you're attaching custom made power supplies to something important and priecy like a laptop, you want to make sure you've got very good voltage tolerance protection on there. A good quality power brick or wall wart will already have this, and if a datasheet is available will likely state the details of how overvoltage or undervoltage it's output can get before cutting itself off. If anyone does start discussing that, I'd be interested to hear about techniques for making an "absolutely can never output more than X volts or less than Y volts" circuit protector.

author: amyk
author_rank: Super Contributor
timestamp: January 10, 2025, 01:03:32 am
content: Note that "19V" is a nominal value, as the limiting factor is usually 25V capacitors on the input. Some laptops say they take a "20V" supply, which is within 5% of 19V and will work equally well.Quote from: Infraviolet on January 09, 2025, 08:03:48 pmZener diode and fuse.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 01:36:08 am
content: Quote from: amyk on January 10, 2025, 01:03:32 amHmm; no crowbar? for the worst-case scenario?

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: January 11, 2025, 09:28:23 am
content: I have been powering laptops from 12V for several years, firstly with a Toshiba, then an Asus and now a Dell. There are plenty of “car” laptop adapters that will work with the 2 wire Asus laptops, you are stuck if wanting to charge a Dell as the socket uses 3 connections to communicate between the charger and the laptop… you can power one, but not charge it. Dell do not sell 12V adapters that are compatible with my Vostro, neither does anyone else that I know of.Is there a problem using an ordinary mains adapter?SJ

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: February 28, 2025, 10:42:41 am
content: Quote from: Solder_Junkie on January 11, 2025, 09:28:23 amThe problem is that I don't have AC power in the vehicle...pretty large obstacle there.Not intending to do dc-ac-dc conversion. That just seems silly and wasteful/inefficient.