General amount of Current drawn from wall outlet for Laptop charger

Thread Starter

jlawley1969

Joined Feb 22, 2021
18
I am working on an inverter circuit that will generate 110VAC 60hz but I do not know what to make the current rating. It will be used to charge laptops so I need to know what is the max you guys have seen for the input of a laptop charger. From the various charger circuits I have been able to get a hold of they usually Convert to DC then drop the voltage and increase the current.

So basically I am wondering if 110VAC 60hz 3Amps is overkill?
 

BobaMosfet

Joined Jul 1, 2009
1,780
Look for laptop adapters on Google and check their ratings. I don't think 3A is overkill. Might even be under. I've seen laptop power-supplies outputting 10.3A. I think if you think in terms of wattage, it' will help you. Example: 400W @ 12V is 33.3A. Motherboards usually have 12, 5, and 3.3V rails.
 

Ian0

Joined Aug 7, 2020
2,289
Most laptops seem to be somewhere around 20V at 2 or 3 Amps, on a DC power plug of varying sizes. Why do you need to generate 120V AC when most laptops take 18-24V DC?
 

Ylli

Joined Nov 13, 2015
1,052
Adapter wattage / line voltage = current draw. So if you are using a 180W adapter, then it will draw 180/120 = 1.5 amps. Add about 10% as a safety/efficiency factor and you get about 1.65 amps for that 180W adapter.

But it certainly would be more efficient to generate the same output as an adapter, rather than generating 120 VAC and plugging in an adapter. You would most likley need 19 - 20 VDC.
 

Papabravo

Joined Feb 24, 2006
16,188
I don't think there is a single number that you can rely on. Any number you pick will probably be wrong for some class of devices or for multiple devices connected to the same inverter output. I assume you have a compelling reason to do this.
 

Thread Starter

jlawley1969

Joined Feb 22, 2021
18
Okay thanks guys I agree it would be a lot more efficient to plug convert to just 20VDC. but I am making this as a consumer outlet for use in airplanes so people might be using other things than laptops (I cant really think of what) so I have to make it versatile.

But what boba and Ylli say kind of contradict each other. Or maybe it is just that how chargers are rated differ between manufacturers? Like as in is the wattage rating a measure of the input or the output of a laptop charger?
 

Ylli

Joined Nov 13, 2015
1,052
Like as in is the wattage rating a measure of the input or the output of a laptop charger?
Normally the wattage rating would apply to the output side of the power supply (charger). Switching supplies are normally 80-90% efficient, so input wattage should not be more than 10-20% higher than output wattage.
 
I am working on an inverter circuit that will generate 110VAC 60hz but I do not know what to make the current rating. It will be used to charge laptops so I need to know what is the max you guys have seen for the input of a laptop charger. From the various charger circuits I have been able to get a hold of they usually Convert to DC then drop the voltage and increase the current.

So basically I am wondering if 110VAC 60hz 3Amps is overkill?
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I'm going to assume your intentions are to create 120Vac from an Airplane's DC source. Nearly all airlines limit you to 15V @5A (75W) per power port. See Below from: Guide to Laptop Power Ports on Planes | SeatMaestro

Types of In-Flight Power Ports
Now that you have an idea of the availability of in-flight power ports, let’s talk about the kinds of ports you’ll find.
  • AC Power – AC Power is the standard wall power charger that came with your laptop, iPhone, or iPad.
The AC power on an airplane is usually 110V AC, and it features a receptacle that’s semi-universal and accepts the following plugs: US non-polarized 2-blade plug (both blades are same size), US polarized 2-blade plug (one blade is bigger than other), US non-polarized 2-blade plug with ground (3-prong), European standard 2-cylindrical prong plug (2 round prongs).

  • DC Power (Cigarette Power) – This is the type of power port that you’ll find in most cars. On airplanes, this plug typically has 15V DC power at up to 75 watts per outlet. If you want to plug in your laptop, you’ll need an adapter (sometimes called an air/ auto adapter).
  • EmPower DC Power – EmPower is a widely-installed in-seat power system on many aircraft. More than 40 airlines, in fact, use this type of power outlet.
EmPower provides 15V DC power at up to 75 watts per outlet. You’ll need a power outlet that is compatible with EmPower to use this port (if you have a Cigarette DC adapter, you can just buy a small adapter that will let you hook it up to EmPower).

If you’re wondering whether the available power will be enough to charge your laptop or device, consider the following:

  • Most power systems on airplanes are limited to 75 watts of power per seat, which means a new 17’’ laptop might not get enough juice to stay charged. Some laptops just use the power to operate, and not to charge. Others won’t work at all if they don’t get enough of a charge.
  • Airlines like Continental specifically state that they do not want passengers using outlets to charge their devices. Apparently, working or playing around on a laptop on their planes is okay, but they don’t fancy themselves as a free source of charging power.
 
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