Is that dangerous :

  • for the computer (without the battery)
  • for the cells

If possible, explain why.

Edit : Here are some more assumptions : Without the battery included, there is no risk of overheating the cell, or over charging them. But there is still some dc to dc conversion taking place on the motherboard. I assume this dc to dc stage to be quite tolerant. What kind of trouble can I run into when using 20V instead of 19V ? Overheating ?

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    Voltage means less than the current rating of the power supply. Your power supply should always be able to safely supply more current than the device will draw. What are the current values for the original walwart vs. the new one? – Richard Hoskins Dec 7 '09 at 15:12
  • I added a "why" to the original question, as I think it would be useful to have answers explaining why it is dangerous, to have other answers than "just don't do it". – Gnoupi Dec 7 '09 at 15:25
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    Gnoupi, want me to post a list of each and every component on the mainboard that may get toasted due to higher voltage, illustrated with images of fried mainboards and laptops gone up in smoke? sure thing, go and "satisfy your curiousity" elsewhere! :) – Molly7244 Dec 7 '09 at 17:56
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    @Molly, not this kind of curiosity for images of "how it is when it goes wrong". But it is more useful to know why something is dangerous, when we can be led to think that laptops are able to adapt themselves to different power. The reason for the "why", is to call for an answer from someone who would have knowledge is electronics, to explain why exactly, not simply to say "yes it's dangerous don't do that". – Gnoupi Dec 7 '09 at 20:05
  • The amount of wrong information in the answers here is mind-boggling. I'm voting to close since the question has attracted low-quality, opinion-based answers, and this thread is not a reliable source of information. – fixer1234 Jan 24 '17 at 4:35

15 Answers 15


It's always inadvisable to use the wrong voltage power supply. However, most power supplies are so cheap that they may vary a couple volts from design spec. Most electronics have some tolerance built in. Batteries themselves are even more tolerant (but special charging circuits, if they exist, may not be).

I can't recommend doing it since the risk of damage is high enough to make it a bad idea. However, the other posts that seem to suggest that using the wrong power supply will immediately cause the LHC to overpower and create an earth destroying black hole, are a bit extreme. :-) You might get away with it. You might cause a fire. You might not notice any problems at first, but have one of those early unexpected failures shortly down the road...

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    Brian, you forgot to mention the shift of the magnetic poles! (my favorite doomsday scenario :) – Molly7244 Dec 7 '09 at 17:26
  • Too little amperage is worse then too great of voltage. – Jeff F. Jan 12 '11 at 18:00
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    @Jeff Eh, not really. As amperage supply drops below the demand, you end up with a heat problem and usually a failure to operate (but rarely a fire). Over voltage you eventually end up with blown up parts (and the rare fire). Under current is usually more recoverable/less permanently damaging. :-) – Brian Knoblauch Jan 12 '11 at 18:05
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    @Jeff That's a horribly broken analogy. Try again please. :-) – Brian Knoblauch Jan 12 '11 at 18:28
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    @Brian Meh, you're probably right, it's been a long time since I took those classes. And this is DC not AC. Anyhow the formula is like V=IR? So lower amperage at a fixed voltage would mean higher resistance. But if I is fixed at a low level and R is obviously fixed then V would actually be lower hmmm. So thinking about it I should be incorrect with my former statement, I think I just heard that somewhere and picked it up. Thanks for making me think about what I say :) – Jeff F. Jan 12 '11 at 19:02

ATX specification (which describes power supply units for desktop computers) says that:

Generally, supply voltages must be within ±5% of their nominal values at all times. The little-used negative supply voltages, however, have a ±10% tolerance.

It applies to power delivered directly to sensitive microelectronics: mainboard and CPU, memory, graphics card, drives.

But in case of laptops, I belive, microelectronics are not fed directly from AC/DC adapter, because still various components need different voltages - it's not a desktop, but it still has CPU, memory and drives.

20V is 5,26% more than 19V. I wouldn't worry about damaging laptop or batteries. I'd just measure if it really produces 20V (or at least it's within 10% from 19V).


I have the definitive answer: IT DEPENDS.

It depends, not on the text "19V" or "20V" written on the power supply, but on the actual voltage and current profile as provided by that power supply... which can vary wildly from the writing on the outside.

Comparing the proposed replacement supply voltage and idle, medium current and full current versus the original (requires still having the original) is the only way to find out for sure. Another caveat is what happens in a short situation. If one power supply has OCP (over current protection) and the other happily provides more current, that can be an issue too.

Technicians and Engineers regularly replace power supplies on equipment, it is one of the most common mods that gets old equipment working again, especially where strange old proprietary battery packs were involved. Often performance can be improved by providing more consistant voltage over a broader range of current draw. These mods are well within the hobbyist's capability, provided they are able to spend the time, do the tests, and set up a test load (12V automotive light bulbs work well) and use a multimeter.


yes, it IS dangerous and may very well destroy the notebook.

higher voltage can cause serious damage to your mainboard, damage that is not covered by any warranty.

also the batteries can overheat, potentially causing burns, an explosion or a fire.

  • Even if I remove the battery, and just use the power supply ? – user4444 Dec 7 '09 at 13:26
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    even then, i would NOT do it. – Molly7244 Dec 7 '09 at 13:31
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    sorry to say but power supplys are DYNAMIC. If the device draws less powere then the charger's output the charger will produce what the device needs. thats why you can buy a universal charger that works with several models and different tips...think about it... – mike Dec 7 '09 at 15:45
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    sorry to say, mike, but this is rubbish, you are confusing watt with volt. if you use a power supply with a higher voltage than your equipment is designed for, then chances are that you're going to toast it. and what good would a "universal charger" do? a charger is not a power supply unit. A power supply is a constant VOLTAGE supply (and NOT dynamic). A charger is a constant CURRENT supply (dynamically adjusted). – Molly7244 Dec 7 '09 at 16:10
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    universal notebook powersupply usually come with a knob to select the desired voltage. – user4444 Dec 7 '09 at 16:26

"if you use a 20v charger on a 19v rated thing, you will be "forcing" an extra 0.235A (V=IZ, Z is the appliance's impedance) into the device in addition to the 4.47A."

This does not make sense. I don't think impedance has a place in this?

Laptops have sophisticated DC-DC converters, and are fine with a little overvoltage.

Even my cheap 12V LED bulbs (halogen retrofits) have a little buck (step-down) converter build in, making sure the 3 led-chips in each bulb gets the right voltage and amperage. I tested this on a variable power supply, driving an LED bulb from 0 to 17 volts (I stopped going higher). At about 9V it started lighting and increased up to 11,3V, from where it actually got a little dimmer as current control kicked in. The light kept the same level all the way up to 17V, however the amps dropped as voltage increased. This is because the power draw (wattage) stayed virtually the same.

The same thing happens in a laptop's internal power converter.

Hope it makes sense :)


Disclaimeer: ... in my experience - your mileage may vary ...

The cells will be fine. One volt won't do much difference if the other parameters are the same.

I don't know about running the laptop directly from the brick - never done so.

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    Cells can handle overcharging, the damage occurs only after some time, or they can overheat when fully charged. – user4444 Dec 7 '09 at 13:29
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    I did say your mileage may vary. So everything he's doing is at his own risk. My old laptop used to run with a similar (but not quite same) block for quite some time ... nothing happened (I think it still works; anyway, I bought a new laptop in the meantime, so ...). In any case, it worked on an almost 24/7 regime, and there was no overheating nor damage occuring (I rarely turn my machine off). – Rook Dec 7 '09 at 14:14
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    But people in here tend to be somewhat conservative, so I gather the final answer will be "never do it". Still, sometimes, one doesn't have the luxury of always having original replace parts. – Rook Dec 7 '09 at 14:18
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    @Molly - I didn't see nothing in the question that would suggest the laptop being under warranty, or even mentioning echnical support. So I don't see how they play the part in here. I just stated my exp. under the circumstances. And besides, I don't think that even the most liberal tec. support takes arguments like "the nice folks at SU" under consideration when dealing with warranty issues ... – Rook Dec 7 '09 at 18:02
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    I also believe the OP got the answer to his original question, so it may be time to let it go, and allow the other questions to "climb up the hill" ... – Rook Dec 7 '09 at 18:03


1V doesn't sound much, neither does 0.5V, but I had my external HDD fried because I used a 9v instead of 8.5v (or was it 9.5V instead of 9V?)

"Microelectronics", if you will, can't handle 1V more. It's not the same as putting in 240V to a 230V bulb. That'll shorten it's lifespan, but because a bulb is so simplistic, it'll hold much longer.

A laptop on the other hand is full of small electronic components who run at a much lower voltage. Giving them 1V more may and will cause them to say "Noez, I'm dead, kktxbai! U gief to much powah!", if you catch my drift. They can't handle such a huge surplus of power/voltage. They operate in millivolt, even microvolt area.

Long story short: DO NOT DO IT, if you want your laptop running.

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    Yes but usually electronic board have a power supply stage with dc-dc regulator, that handles this kind of conversion. Laptops are used to variable voltage input, since they work from battery. – user4444 Dec 7 '09 at 14:05
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    @shodanex: I agree fully with your point. We are talking about a laptop here, which is indeed able to work with different power ranges. The "external HDD case" is not relevant in this case, as it wasn't at all designed to work in other power conditions. In laptop case, if there is a power problem, it will be handled in a specific area, it will most likely not propagate to the "sensitive microelectronics". – Gnoupi Dec 7 '09 at 15:19
  • as i commented elswhere, i have a HDD enclosure here, the owner used a 9.5v PSU instead of the original 9v and it fried the curcuit board of the hard disk. now he'll have to pay big €€€ to get his data back. – Molly7244 Dec 7 '09 at 17:22

Take a look at the AVERAGE specs of laptop charger:

  • Input voltage...100 to 240Vac ±10%, full range
  • Input frequency...47 to 63Hz
  • Current...2.5A max. at 115Vac, 1.2A max. at 230Vac, full load
  • Inrush current....40A max. at 110Vac, 80A max. at 220Vac, cold start
  • Hold up time.......16mS min. with DC output at full load and 115/230Vac input
  • Turn on time....90% typically voltage in less than 3 seconds
  • Input fuse ....Slow blow T3.15A/250V fuse to line input
  • Line regulation dc voltage within tolerance when ac varies within the range specified
  • Dynamic load regulation....±5% excursion for 50-100% or 100-50% load change of dc at any frequency up to 1KHz (Duty 50%)
  • Ripple and noise .....200mV
  • Over voltage protection ..... 135% max, of nominal voltage
  • Voltage isolation dc ground isolated from ac neutral and ac live.

Now you can see all of the symbols on any laptop charger and by these specs you can see that they have a MAX. This MAX means that is the MOST it will produce and that ALSO means that it will regulate the power to the devices needs UP TO the MAX. so your computer will be just FINE. Also i keep my battery OUT of my laptop and run on a UPS so as not to damage the battery (i keep my laptop plugged in 24/7).

  • How come out of all these specs, none of them are output voltage, which is what the poster is specifically asking about? – davr Dec 7 '09 at 17:16
  • davr, don't worry about such minor details as the output voltage! :) – Molly7244 Dec 7 '09 at 17:24
  • why can't you do any research molly?? – mike Dec 8 '09 at 5:48
  • you can look at what i post ... but you won't go and read up on it...that kills me...at least i went out and researched about laptop chargers and chargers in general. thank god for that tech class in college. – mike Dec 8 '09 at 5:50

While it is correct that there are tolerances built into machines and power supplies, note that these tolerances exist on both ends. As others here have said, it is not safe to exceed voltage thresholds. Also, note that connector polarities are not standard, so just because an adapter has the right voltage and the right connector, it does not mean that the polarity is correct, check the polarity as well. Doing any of this will cause overheating, immediately melting chips and likely causing a fire.

However, what I have not seen mentioned here is that it is not as dangerous to connect an under-voltage or under-current power supply temporarily. This is essentially a brown-out. Brown-outs are not good for your computer, but unless lengthy or frequent, they're much less likely to cause permanent damage.


I have an Acer netbook that uses a 19 volt charger and I run it all the time on 24v dc. I watched the current in as I increased the voltage in and noticed that the current went down as the voltage was increased. This means that a switching power supply is changing that voltage to a different voltage inside. Keep in mind that the battery the powers a laptop is considerably lower than 19 volts. So voltage conversion is taking place within the device. The 19 or 20 volts is not being used directly on the motherboard directly. The reason I do this is so I can use the same charger to charge an external battery that I carry with me. This battery is made up of 6 x 2 18650 lithium ion cells. So it needs 24 volts to come near full charge. I have been doing this for over a year without any problems. This may not be true for all units but it works for me with my Acer. Ed


I used a lower voltage power supply for a laptop for a while (emergency solution) and the battery life seems to have drastically have shortened after that. In general you should stick to exactly the power supply needed, preferrably the one your laptop supplier provided.

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    With a lower voltage power, it is highly possible that it was taking on the battery all the time, or at least for high usage. In such case, you would have been like the first laptops: charging and discharging the battery at the same time. This would explain the fact your battery life dropped drastically. – Gnoupi Dec 7 '09 at 15:28

No, it won't kill the PC. I run mine with battery in and I use it for ages.

There is a crowbar circuit on the battery to stop it overloading, and the laptop's power input is fused, so if it was excessive I'd know by now. Even with the battery pack installed the unit never overheats.

It's a myth as my Acer laptop stays at 55 degrees with standard 19v and 20 volt adapters


It's best to use charger of same specification and model. 20v can be used for 19v as long as the current rating of 20v is the same or higher but only temporarily. Best to charge the battery and the then unplug and run the laptop, notebook etc on their batteries themselves to ensure the correct input to the circuitory. Runng 20v for 19v directly is not advisable. Hope that answers the questions.


19v supply sounds like a Dell. You can probably pick up a cheap replacement on Ebay or Craigslist. They are very plentiful in the marketplace.

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    Not answering the question, though. – Gnoupi Dec 7 '09 at 15:22
  • and 19V is used with quite a lot of notebook nowadays. – user4444 Dec 7 '09 at 15:46

usually the voltage is very important when it comes to chargers. an appliance will only draw the current it needs at the specified voltage. you usually have rating such as 19v 4.47A this means at 19v the safe max. current that can be supplied is 4.47A. so if you use a 20v charger on a 19v rated thing, you will be "forcing" an extra 0.235A (V=IZ, Z is the appliance's impedance) into the device in addition to the 4.47A. this raises the current to about 4.7A above the rated max. depending on other factor this might be with acceptable limits or not. if not high current causes heating as the device only uses the amperage thats required, have more amperage than required is safe as it only uses whats required.

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