Why do computer chargers need those big adapters? Why can’t you just connect the devices to the power outlet with a cable?
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Because you need a power adapter to store and convert the power. If this was inside the computer your computer would be even bigger and heavier. It converts AC to DC voltage. It’s also very hot and we don’t want more heat generated inside the device.
The power coming out of the outlet is alternating current (AC). The power your computer uses is direct current (DC). Your laptop’s power brick is converting AC to DC. It is also stepping down the voltage from 120V is something more suitable for charging your laptop’s battery. Typically 12V to 20V.
You could, but then that big adapter needs be built in to the laptop, adding to its size, weight, and heat.
(really ELI5)
The power coming from the outlet is like a fire hydrant. Ever seen a gushing fire hydrant? That’s a lot of power! But the computers or phones can’t take that amount of power, kind of like you couldn’t drink straight from a fire hydrant: you’d be thrown in the air!
So chargers are adapters, that can take just a little bit of power at a time in a way that the computers can actually use without frying from overload.
Also, the power from the wall is “AC” (Alternating Current). It’s wiggling back and forth, kinda like a bike chain where you’re just wiggling the pedals, not turning them completely. This is a useful way to transfer power because it’s easy to change it to higher voltages (like strength of chain pull), which is useful for long-distance power. But computers need DC (Direct Current), like pulling the chain constantly in one direction. DC is easier for electronics to work with, and batteries in phones or computers can only work with DC. The adapters do that necessary transformation.
Alternating current changes the direction of the flow of electricity many times a second, along with the voltage. Direct current stays at the same voltage and doesn’t change direction. High voltage AC is easier to transport over long distance power lines, but the way computers work is by setting specific voltages inside their components, which other components can detect. They differentiate between detecting a specific voltage or at a near 0 voltage and set their output voltage based on what they detect (the 1s and 0s people talk about come from here). This distinction needs direct current to work.
The power brick, as others have said, converts AC to DC and to the specific voltage the device needs. Desktop computers have the same setup, except their power brick is inside the case and instead of a single output cable that powers the computer, it has multiple. A laptop powers everything through the motherboard, a desktop powers some of its more power hungry components directly
The better answer is ,,, you could make a laptop without a charger, but it would be worse because you have to include all that power circuitry inside the laptop.
That circuitry is heavy so your laptop would be heavier on one side and would most likely make the laptop thicker, because some components in this circuitry are bigger and are hard to make smaller, if we’re talking about laptops that consume a lot of power.
For laptops that consume very little power, like 10-30w at most under regular use, there may be a time when the equivalent of a 40-60w phone charger could be squeezed inside so that you wouldn’t need a separate charger. But at that point, it may still be easier to just carry the charger along with a small mouse in the same bag you normally use to carry the laptop. It’s not a big deal now…. won’t be a big deal in the near future as chargers shrink even further.
High voltage is dangerous, risk of electric shock, death and all that, so that’s why the conversion from high voltage (110-230v AC) to a lower DC voltage is done in the separate power brick / power supply, because the package can be easily sealed in the plastic case (ultrasonically welded and no water can come inside and cause problems.
Another reason is also that you’re removing a source of heat from the laptop case and moving it away from the laptop … conversion from AC to DC is not 100% efficient, there are losses, heat is produced.
The conversion is also “noisy” in the sense that the power supply produces some electrical noise which can be picked up in wires as if those wires are antennas, and in the components around the power supply.. So if the power supply is inside the laptop, they may have to put extra care to shield more sensitive parts of the laptop from this power supply noise, the wires going to the screen may need to have extra shielding … all this could add to the weight of the laptop.
In addition to the other answers, one of the reasons the power brick is so big is not because of the lower voltage, but actually because of the current drawn at the lower voltage a laptop needs.
There’s a [‘triangle’](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/dccircuits-dcp24.gif) used in physics calculations, which is:
Power (Watts)
over
Voltage * Current (Amps)
This is a quick way to convert between any of them – [power divided by voltage will give you current, divided by current will give you voltage etc.](https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/dccircuits-dcp25.gif) And it also helps to illustrate one thing about electricity – all three values are directly related to each other. If power is constant, reducing one of the other values means the other has to increase. (NB. the symbol for current is I, not A). Wattage (Power) is the measure of how much ‘work’ electricity can do, so you can adjust the other two values up and down but still get the same amount of power.
Every laptop has a different power rating, but they tend to average around 40-60 Watts for a cheap do-everything computer. At mains voltage, 60 Watts is nothing – at 120V, it’s half an amp, and at 240V, it’s one quarter of an amp (see how the triangle works? Double the voltage, halve the current). However, laptops on average use 19-20V. So 60 Watts at low voltage needs a current draw of 3 amps.
The thing with current is that it causes a heating effect. Higher current produces more heat. Chargers for small things like torches/flashlights are often very small because the device only wants a few hundred milliamps, meaning it doesn’t produce a lot of heat when charging. Even if the charger is producing a very low voltage, meaning there’s a big difference between the input and output, if the output current is very low, the charger can be very small – for some reason I remember how small the charger for my Game Boy was, partially because it was see-through and I could see the small cluster of electronics inside the casing, and it was surprisingly neat. From a 240V input to a 3V output, it only output 300mA, so it was small enough to fit in the palm of my hand.
Laptops needing many amps, however, need to be very careful with how they design the power supplies. If you cram the components too close together, they can easily overheat. So the power packs are larger to allow the components to be spaced apart enough to stay cool.
You’ll find that the amount of current a laptop needs directly affects how big its charger is – my work laptop maxes out at 90W, but my big gaming laptop needs a huge 255W at full load. The power brick for the latter is twice the size even though they both work at 19.5V. This is, again, to ensure that the brick doesn’t overheat when it’s pulling its maximum.
It’s also why laptops work at relatively high voltages for something battery powered – if the voltage goes lower, the current goes higher to do the same amount of work, so it would generate more heat. Running your average laptop at 5V, or 3V, would cause it to waste so much power as heat that it wouldn’t run on battery for long. 20V has become a comfortable value – high enough to limit the current from overheating things, but also low enough to be safe if something goes wrong. You can be seriously injured by mains voltage, but on the whole, 20V is safe for humans and you won’t get a nasty zap from it. There’s a lot of electrical safety components in the power brick to make sure that mains voltage never comes out of the low-voltage end if something breaks, which also takes up space in the charger, but every laptop charger has them. The difference in size is mostly for the amount of power they need to output.
A long time ago some laptops did have the transformer inside the case, but they soon decided to move it to the cable to reduce thickness and weight, and make it easier to use the laptop in every country regardless of the shape and voltage of AC power supply prevalent.
Aside from OP’s question, I’d like to ask why does the box of the charger (The one that converts AC to DC) is larger than a cellphone?
Computers have always used power supplies, which convert the high voltage, dangerous AC current from the mains into low voltage, high current DC. computer components run at 5V, newer components at 3.3V or possibly even lower. That is because the components need (DC) current to operate, but the power usage is current multiplied with the voltage, so the higher the voltage the higher the power loss in the form of heating.
So what they did for laptops is to simply move the bulky power supply to outside of the computer, in the shape of an adapter (he bulky block).
Actually the computer might still contain a step down converter, making an even lower, fixed, voltage (possibly at a higher current, if using a switching stabilizer) from the already low DC voltage.
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