J-Go Tech Support Team - October 8, 2020

Why am I not able to use a USB-A port to charge my laptop?

T he short answer: The voltage and power that standard USB (called USB-A) ports support are not powerful enough for laptops.

To elaborate on this topic, there are a few key things to keep in mind:

  • 1. Voltage and Power
  • 2. Power Output and Limitations of USB-A Ports
  • 3. Power Required By Laptops
  • The Wrap-up

1. Voltage and Power

Most of our devices are designed to recharge using a specific voltage to prevent damage to the device. The easiest way to figure out the voltage used by your device is by simply referring to the information printed on the original charger that was included with your purchase. You will want to look for the power output of the charger, which is typically in the format, “__V/__A”.
Example: 5V/2A 

A simple comparison would be automobiles and the type of fuel they require to operate. If you have a sedan that requires regular unleaded gasoline, filling the tank with diesel fuel wouldn’t be compatible. Our devices and the voltages they require to recharge are very similar to this. If you own a device that requires a 15V current to recharge, a 5V or 20V current would not be compatible.

With this being said, we also have to pay attention to the amount of power required by our devices. While some chargers may list the power output in watts (W), other chargers may not. The good news is that it’s very simple to figure this out.
Once you have located the power output, simply multiply the voltage (V) by the amperage (A) to determine the watts (W).
Example: 5V/2A  (5 x 2) = 10W ; 20V/2.25A  (20 x 2.25) = 45W 

Example: 5V/2A is the same as (5 x 2) = 10W ; 20V/2.25A is the same as (20 x 2.25) = 45W 

2. Power Output and Limitations of USB-A Ports

USB-A is the most common type of USB port. These ports can be found on most standard chargers that are included when you purchase small portable devices, such as a phone or tablet. However, all USB-A ports are not created equally. A large majority of USB-A ports only support a 5V current, which is fine for charging small devices, but not quite powerful enough for large devices. Depending upon the device, the included charger may support up to 12W (5V/2.4A). If you have a new USB charger, you may notice that the inside of one or more of the USB-A ports have a color, which typically indicates that it supports a “fast charging” technology. Sometimes, these USB-A ports can support 5V, 9V and 12V currents, up to a total of 18W, which allows compatible devices to charge more rapidly.

It is also worthy to note that it is extremely rare for a USB-A port to support amperages exceeding 3A or 18W, whichever is the greater. Due to this, even the most powerful USB-A chargers will only support 5V/3A (15W), 9V/2A (18W) and 12V/1.5A (18W). Some USB-A cables may also limit the amperage due to the internal wires or the type of connector on the opposite end of the cable, so be sure to use a compatible cable for your device and charger.   

3. Power Required By Laptops

The voltage and power required to recharge a laptop will vary drastically amongst various computers. Sometimes, this will even vary amongst the same laptop models due to having a more powerful processor or graphics card, so it’s always best to look at your original charger that was included with the device. A large majority of laptops recharge using currents between 15V and 20V, and require power upwards of 36W. 
 

The Wrap-Up

As you can see, the voltage and power required to recharge a laptop are drastically higher than what a USB-A port can provide, which causes this compatibility issue for charging. While there may be a few small laptops that can recharge at lower voltages and/or currents, these computers are not very common and would still recharge at a much slower speed. 

We hope that this is helpful as you look for portable charging solutions for your laptop. If you have any questions or need some assistance, feel free to reach out to our team of experts! 



At J-Go Tech, we focus on developing innovation charging solutions that primarily support USB-C charging. As USB-C charging becomes a standard way of charging, we understand that there will be many opportunities for people to charge their devices faster, easier and with less equipment. With this, we are on a mission to educate consumers on the advantages on USB-C charging technology.

Have questions or need a personalized solution? Want us to cover another topic or model?
Reach out and let us know at support@jgotech.com

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