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How to know if a USB c charger can charge my laptop (20v)

So my laptop charges via USB c (3.2 gen2)

 

It says on the bottom of the laptop for USB c charging, 20v, 5amps, dc.

 

Now as far as I understand, most USB c chargers are 5v right? Like my phone charger says 5v on it.

 

So how exactly does this work. Do I have to look for a specific 20v charger? Then I can't also use that 20v charger with my, or phone can I?

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If the charger is usb pd compatible it will charge the laptop in some way.

 

A 5v phone charger will usually just trickle charge the laptop when its in sleep/off

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There's various charging standards ex qualcomm's quick charge,  usb power delivery standard etc 

 

quick charge : https://en.wikipedia.org/wiki/Quick_Charge

usb power delivery : https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery

 

The charger typically starts at 5v and the laptop has to communicate with the charger through the data wires and both have to agree to a higher voltage and current. If they agree, the charger then bumps up the voltage and current. 

 

The cable itself also starts to matter when it comes to higher wattages .. ex a regular usb type-c cable may be fine for 30w or so (ex 12v 3A) but you may need a special cable for 100w (ex 20v 5A)

 

edit: most likely you'll need a charger that support usb power delivery and can output 20v (among other voltages). 

There are phone chargers which can not do that - for example my Xiaomi charger can only do 5v/9v/12v up to around 18 watts.

 

Your laptop may refuse to charge if it can not negotiate 20v because it would make charging circuits simpler (only doing conversion from higher voltage to lower voltage to charge battery, instead of having to boost up a lower voltage to the battery's higher voltage).

For example, if your laptop battery has 4 cells in series, then the maximum voltage the batteries need would be 4 x 4.2v = 16.8v, so 20v would make sense, and 12v or 15v would be too little. 

 

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