How much charge does your device need?

How much charge does your device need?

Mobile devices charge at different rates and require different power via different types of USB connection.

The graph opposite highlights the watt range of the common mobile devices. 


29-100W : Laptop0%
100 %
18-30W : Tablet0%
50 %
18-27W : Smartphone0%
25 %
5W : Smartwatch0%
12 %

Why do Amps matter?

Current is supplied by a power supply or charger. A product (e.g a phone or tablet) consumes current. It will try and take as much current as it needs.


If a product requires 2.1 Amps then the power supply should be able to supply 2.1 Amps or more. If the power supply can supply more than 2.1 Amps this doesn’t matter as the product will only take 2.1 Amps. If the power supply can only supply 1 Amp then either the product will fail to work/charge or charge slowly as it can’t get enough current (or power) to charge the battery. Here charging will take twice as long.

This means it is important to match voltage between the charger and device. It doesn’t matter if the power supply / charger can provide more current then the device requires.

Providing less current will prevent charging or slow it down the same as a poorly designed charger can also prevent charging or slow it down.

See the table below for more information on how mobile phone and tablets charging methods compare.

5W = 1A                     7.5W = 1.5A

10W = 2.1A                12W = 2.4A








Charging from a computer (USB 2.0). If you’re charging from a computer (USB 2.0 port), the maximum current it can provide is 0.5A. This is much slower than charging from the mains.




Charging from a computer (USB 3.0). If you’re charging from a computer (USB 3.0 port), the maximum current it can provide is 0.9A.




Most smartphones come with a 1A charger.




USB Hubs. Supports BC1.2.  




iOS devices and many tablets, including the iPad, require a 2A charger. Some smartphones can also use a 2A charger (e.g. Samsung Galaxy Note II).




Most iOS devices.

Power refers to the rate at which energy is added to the battery. It’s calculated by the formula: Power (Watts) = Current (Amps) * Voltage (Volts).

Why charging at the wrong level could damage your device.

Charging devices not at their optimum charging level has a number of issues.

Firstly, the device won’t charge correctly as designed by the manufacturer. This isn’t ideal for the long-term health of the battery. But more importantly charging will not happen as fast as it could.

Take this iPad example
Requires a charger which is capable of supplying 2.1 Amps at a voltage of no less than 4.97V at the charger connector on the cart/case (when the iPad is connected and charging).

Failure to supply this amount of current at the right voltage will extend the amount of time required to charge the iPad battery. This detrimental effect can be easily demonstrated by charging an iPad, from empty to full, with an iPhone charger. An iPhone charger can only supply the iPad with 1 Amp (referred to as ’1A’).

Choose a USB charger that delivers power with control

Cambrionix industrial USB hubs auto-detect attached devices and automatically adjust the current output to the highest level permitted by the device manufacturer and USB specifications.

If the charging device supports BC1.2 and charging downstream port (CDP), high current charging during syncing is supported. Our intelligent charging algorithm can be updated to support new devices and charging protocols, ensuring your Cambrionix USB hub keeps up with market changes.

Want to find out more?

Read the BC1.2 Charging Specification for more information. 

SB-IF Battery Charging Specification revision 1.2 (BC1.2) and the full specification can be found here  This specification was created to try to unify battery-charging attributes for USB 2.0 in the future. The idea was to minimize the number of cell-phone chargers ending up in landfills, by converging on one USB-charging specification. The European Union has been an early adopter to the notion of less waste. Specifically, they have committed using the same microUSB connectors on data-enabled cell phones, but they have yet to fully adopt the BC1.2 specification. In the BC 1.2 specification, there is a mode referred to as Charging Downstream Port (CDP) that allows for data and higher charging currents. If a voltage between 0.4V and 0.8V is sensed on D+ of a host or hub device, then D- should respond with 0.5V to 0.7V. Once CDP has been established, peripheral devices are allowed to draw up to 1.5A and simultaneously communicate data. Devices with this technology, including cell phones, should be showing up this year.

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