Is it safe to use an AC laptop charger in a plugginable AC outlet rated for a lower wattage than the laptop charger?

[john01dav]

Hello

 

Soon I will be taking a long trip in a car, and I would like to use my laptop during that trip. I have an adapter that can plug into the car's "lighter" outlets and provide two standard wall outlets. This adapter is labelled with 200 watts. I am thinking of plugging in my laptop's charger into one of these standard wall outlets to ensure that it does not run out of charge. When I checked the labelling, however, the laptop charger requires anywhere from 230.1 watts to 300+ depending on whether I use the input or output amp/volt pair* and whether I use 100V or 240V as the input voltage, since the labelling says it can do either or anywhere in between. This shows a deficit in the amount of available power.

 

If I plug it in anyway, I do not expect it to charge the laptop while I am using it under heavy load. But, if I am using it under light load (ie. programming, tethered web browsing) can I expect it to charge? What if the laptop is fully off? Is it even safe to do this, or will it cause damage to some part of the laptop if it doesn't get enough "wall" power?

 

Is there some place I can get an affordable charger that is rated for much higher wattage (Ideally 400w+) in a few days?

 

EDIT: Can I use this? It says it is rated for 300 watts, which is below some measurements on my laptop charger.

 

* Watts is equal to amps times volts.

[LUUD18]

You might blow the fuze.

[mariushm]

The laptop adapter you have is designed to be able to charge the batteries AND provide the maximum power your laptop may ever use during operation .. so basically much more than what your laptop usually consumes.

 

Imagine your batteries are fully depleted and you plug the laptop adapter in the back of your laptop and you start a game. The batteries start charging drawing maybe 50-100 watts from the laptop adapter and the laptop itself will also take maybe 50-100 watts from the laptop adapter as you're gaming... for this reason, your laptop adapter must be made to be able to provide more than just those 50-100w required for you to game.

 

The batteries will suck more power the emptier they are. If your batteries are almost empty they'll take quite bit of current from the laptop adapter... the more they're charged up, the less they will take. If the batteries are close to full (let's say over 80% charge) they may even be in a sort of trickle charge mode where they only take in about 10-20 watts of energy to slowly fill up to 100% 

 

It's not an accurate thing, but you can sort of figure out how much batteries will suck in by looking at the mAh value of your batteries. Usually batteries are charged at 0.1-0.25x the value listed there. So for example if your battery is listed as 16.5v and 8200mAh then it will most likely be charged at  0.1.. 0.25 x 8200 = 0.8 .. 2A so you'll take about 19v (the laptop adapter voltage) x 2 A  x  1.2 (120%, because the laptop adapter is maybe 80% efficient) = 19v x 2 x 1.2 = ~ 30 watts to charge the batteries.

 

The laptop itself should not use a lot of power unless you're running games. While watching movies or reading some ebook or doing anything graphics heavy (video games) your laptop should use between 5 watts and maybe 25-40 watts

 

Applications like Aida64 or other diagnostic tools or even some tools the laptop came with should tell you how much power the laptop takes from the laptop adapter or from the batteries. For example, I only have an old IBM T40 here but it came with some battery status software and if I pull out the Dc in cable, I can see in the software how much energy the laptop takes at any point from the batteries. Maybe you can do some tests and figure out how much power your laptop actually uses while doing various things, you may be surprised to find out it uses less than 50 watts while doing most of the things you're used to.

 

--

 

ps what you plug in that car cigar lighter is called an inverter. It takes 10v.. 15v from the car lighter plug (which is connected to the car's battery and the alternator of the car) and creates 110v or 230v AC (depending on what you use) and can create UP TO 200 watts.  The limitation of 200 watts is for two reasons, one is the inverter is small and can get too hot if it was made to provide more than 200 watts to devices and two .. the wires going from the car battery to the car's lighter plug are too thin to be able to give the inverter more than 200 watts.

Also, the car's battery and the alternator are not really designed to push so much power through that lighter plug.

 

So anyway.. the inverter will produce up to 200 watts, depending on how much the laptop adapter actually needs.

The laptop adapter is most likely designed for universal input, meaning it will work with either US voltages let's say 90v..110v  or voltages specific to other countries like 200v..240v for Europe .. it will automatically detect the voltage and work correctly. It will be slightly more efficient if it's powered from higher voltage but in your particular case an inverter that converts 12v DC to 110v AC would be more efficient than an inverter which converts 12v from your car to 230v .. so if you're in US ideally you'd use a 110v inverter and a laptop adapter running from 110v created by the inverter.

 

The laptop adapter's power is usually specified on it's label.. common values are 65w or 95w or 120w .. it means up to that much power can be delivered to laptop and the laptop can choose to charge its batteries or use it to work or both.  That much power is produced with certain efficiency, usually above 85% .. so you multiply that number by 1.1 or 1.2 (90% or 80% efficiency) and you have about how much the laptop adapter would take from the AC socket if the laptop actually takes all that energy in.

Everything is UP TO and more often than not, your laptop doesn't take ALL that energy.

 

 

 

[john01dav]

3 hours ago, mariushm said:

The laptop adapter you have is designed to be able to charge the batteries AND provide the maximum power your laptop may ever use during operation .. so basically much more than what your laptop usually consumes.

 

Imagine your batteries are fully depleted and you plug the laptop adapter in the back of your laptop and you start a game. The batteries start charging drawing maybe 50-100 watts from the laptop adapter and the laptop itself will also take maybe 50-100 watts from the laptop adapter as you're gaming... for this reason, your laptop adapter must be made to be able to provide more than just those 50-100w required for you to game.

 

The batteries will suck more power the emptier they are. If your batteries are almost empty they'll take quite bit of current from the laptop adapter... the more they're charged up, the less they will take. If the batteries are close to full (let's say over 80% charge) they may even be in a sort of trickle charge mode where they only take in about 10-20 watts of energy to slowly fill up to 100% 

 

It's not an accurate thing, but you can sort of figure out how much batteries will suck in by looking at the mAh value of your batteries. Usually batteries are charged at 0.1-0.25x the value listed there. So for example if your battery is listed as 16.5v and 8200mAh then it will most likely be charged at  0.1.. 0.25 x 8200 = 0.8 .. 2A so you'll take about 19v (the laptop adapter voltage) x 2 A  x  1.2 (120%, because the laptop adapter is maybe 80% efficient) = 19v x 2 x 1.2 = ~ 30 watts to charge the batteries.

 

The laptop itself should not use a lot of power unless you're running games. While watching movies or reading some ebook or doing anything graphics heavy (video games) your laptop should use between 5 watts and maybe 25-40 watts

 

Applications like Aida64 or other diagnostic tools or even some tools the laptop came with should tell you how much power the laptop takes from the laptop adapter or from the batteries. For example, I only have an old IBM T40 here but it came with some battery status software and if I pull out the Dc in cable, I can see in the software how much energy the laptop takes at any point from the batteries. Maybe you can do some tests and figure out how much power your laptop actually uses while doing various things, you may be surprised to find out it uses less than 50 watts while doing most of the things you're used to.

 

--

 

ps what you plug in that car cigar lighter is called an inverter. It takes 10v.. 15v from the car lighter plug (which is connected to the car's battery and the alternator of the car) and creates 110v or 230v AC (depending on what you use) and can create UP TO 200 watts.  The limitation of 200 watts is for two reasons, one is the inverter is small and can get too hot if it was made to provide more than 200 watts to devices and two .. the wires going from the car battery to the car's lighter plug are too thin to be able to give the inverter more than 200 watts.

Also, the car's battery and the alternator are not really designed to push so much power through that lighter plug.

 

So anyway.. the inverter will produce up to 200 watts, depending on how much the laptop adapter actually needs.

The laptop adapter is most likely designed for universal input, meaning it will work with either US voltages let's say 90v..110v  or voltages specific to other countries like 200v..240v for Europe .. it will automatically detect the voltage and work correctly. It will be slightly more efficient if it's powered from higher voltage but in your particular case an inverter that converts 12v DC to 110v AC would be more efficient than an inverter which converts 12v from your car to 230v .. so if you're in US ideally you'd use a 110v inverter and a laptop adapter running from 110v created by the inverter.

 

The laptop adapter's power is usually specified on it's label.. common values are 65w or 95w or 120w .. it means up to that much power can be delivered to laptop and the laptop can choose to charge its batteries or use it to work or both.  That much power is produced with certain efficiency, usually above 85% .. so you multiply that number by 1.1 or 1.2 (90% or 80% efficiency) and you have about how much the laptop adapter would take from the AC socket if the laptop actually takes all that energy in.

Everything is UP TO and more often than not, your laptop doesn't take ALL that energy.

 

 

 

What I am taking from your post, and correct me if I am wrong, is basically that my laptop almost certainly won't pull more than 200w unless charging and under heavy load. What happens, however, if it does? It is conceivable that I may want to play a game (it has a 1070, so it is more than capable of such things), or even that the OS ramps up the CPU for some random thing while the battery happens to be low. If this happens and the power draw goes over 200w, is there any risk of damage to the car, inverter, laptop charger, or laptop? You mentioned the wires are too thin to carry more than 200 watts; will this cause the car to light on fire if my laptop uses too much power or will less power simply be sent thus causing the battery to charge more slowly? If a fuse is broken, is it easy to reset that fuse without taking it to a dealer or even opening the hood? I, nor the people the trip is with, are car people at all -- none of us have any idea how to fix such things. Even if the chance of going over is very small, I can't assess that risk without knowing the consequences of such an event.

[mariushm]

Figure out how much power your laptop actually uses first. Look on the label of your laptop adapter, it should say 65w , 95w , 120w ... whatever, the maximum power it can provide to the laptop. The laptop adapter will NOT take more than what it says there on it , + about 10%  (due to efficiency of conversion).\

 

A desktop GTX1070 with 8 GB of memory reaches in the most intensive benchmarks up to 150 watts of power consumption. IN a laptop, the cards are more optimized and they run at lower frequencies than the desktop parts, so basically the power is typically less than 120 watts for the graphics.

The rest of your laptop is unlikely to use 80 watts ... but if you want to reduce the video card's consumption a simple first step would be to enable vsync and lock the fps at 60 and you could also play from the video card's driver to lower the power limits (if you even have the option) to reduce the frequency boost.

 

The inverter most likely has some sort of fuse or protection which would turn off the inverter if the power is more than its advertised power for some period of time (for example 250w for more than 10s). In the cheapest inverters you would actually have to open them up to replace the fuse.

 

The car also has a fuse box, and pretty much everything in a car should be equipped with fuses (the car stereo, the lighter, front lights, back lights, blinking lights, roof lights, everything should have fuses. You may pop the fuse and the lighter thing would stop working until you replace the fuse.

 

The wires going to the lighter should never break down or burn, but even then they are usually in a material that's fire proof and shouldn't damage the car.

 

Also note that all this power comes from the car's battery which isn't infinite and is constantly charged back by the car's alternator... if your parents drive in some congested places and you move slow or basically don't have opportunity to use the alternator to charge up the battery, such a high power consumption could drain the battery and make the engine stop. It's hard but not impossible.

 

Still, it would be much simpler to just NOT play games while you're in the car then you wouldn't have to worry about these things.

[john01dav]

5 minutes ago, mariushm said:

Figure out how much power your laptop actually uses first. Look on the label of your laptop adapter, it should say 65w , 95w , 120w ... whatever, the maximum power it can provide to the laptop. The laptop adapter will NOT take more than what it says there on it , + about 10%  (due to efficiency of conversion).\

 

A desktop GTX1070 with 8 GB of memory reaches in the most intensive benchmarks up to 150 watts of power consumption. IN a laptop, the cards are more optimized and they run at lower frequencies than the desktop parts, so basically the power is typically less than 120 watts for the graphics.

The rest of your laptop is unlikely to use 80 watts ... but if you want to reduce the video card's consumption a simple first step would be to enable vsync and lock the fps at 60 and you could also play from the video card's driver to lower the power limits (if you even have the option) to reduce the frequency boost.

 

The inverter most likely has some sort of fuse or protection which would turn off the inverter if the power is more than its advertised power for some period of time (for example 250w for more than 10s). In the cheapest inverters you would actually have to open them up to replace the fuse.

 

The car also has a fuse box, and pretty much everything in a car should be equipped with fuses (the car stereo, the lighter, front lights, back lights, blinking lights, roof lights, everything should have fuses. You may pop the fuse and the lighter thing would stop working until you replace the fuse.

 

The wires going to the lighter should never break down or burn, but even then they are usually in a material that's fire proof and shouldn't damage the car.

 

Also note that all this power comes from the car's battery which isn't infinite and is constantly charged back by the car's alternator... if your parents drive in some congested places and you move slow or basically don't have opportunity to use the alternator to charge up the battery, such a high power consumption could drain the battery and make the engine stop. It's hard but not impossible.

 

Still, it would be much simpler to just NOT play games while you're in the car then you wouldn't have to worry about these things.

I tested with furmark and prime95 running at the same time, and got the battery drain to be ~85 watts. The battery charged at 30 watts under no load at around 80%. While I can certainly not play games, I am not comfortable running my laptop off a car without first being sure the worse case scenario won't cause issue -- and that's games -- since there is no guarantee that it won't go above a safe wattage. Your answer has a lot of "probably"s and "should"s. This shows there is a small chance of any sort of bad things happening, such as the engine stopping mid-drive or the car bursting into flames. As such, it appears that I have my answer: I can't run the laptop safely off the car. The risk of this, however small, simply isn't worth it when you are driving at 60 mph down a crowded highway and the engine stopping basically means death.

 

Thank you for your help