I am looking at getting a 3 port USB wall charger, to save having so many individual ones plugged in. A lot that I've seen offer Qualcomm FastCharge, and other similar things, which are around 2.4A, or higher.

The chargers that I currently have (which are cheap ones) are alll 1A or less (with the exception of my Lenovo tablet charger, which is 2A). I'm slightly concerned that using such a charger will overload my devices (eg phone), and cause damage to the battery. I have a fairly large powerpack, I think 10Ah, and it says that it should be charged with a 1A current.

Am I right to be concerned?

A very related question is "Choosing power supply, how to get the voltage and current ratings?". It's not a duplicate question, but the answers there provide an answer for this question. The answers to this question given confirm that the answers to the linked question do indeed apply here.


closed as off-topic by winny, JRE, Scott Seidman, R Drast, laptop2d Jun 28 '18 at 17:49

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    \$\begingroup\$ Possible duplicate of Choosing power supply, how to get the voltage and current ratings? \$\endgroup\$ – JRE Jun 27 '18 at 10:51
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    \$\begingroup\$ This isn't phrased as a duplicate, but the answers to the linked question provide the correct answer. Anything posted here would only duplicate the existing answers. \$\endgroup\$ – JRE Jun 27 '18 at 10:53

Maple already answered this, but I want to say it differently:

The current is determined by the device, not by the charger.

All USB chargers output a constant voltage, and all USB-powered devices are designed to take only as much current as they need from the constant voltage source, but...

...There is a limit to how much current any given charger can provide. Your 1A charger is only capable of providing one Ampere. The USB charging protocol allows a charger to tell the device how much current the charger is able to provide, and the device can then decide what to do about it.

A device that needs more than 1A will simply refuse to take power from a 1A charger.

Some devices (e.g., most things that use USB power to charge a battery) will adjust the amount of current that they take to match whatever the charger is able to provide. So, for example a "power bank" device or a tablet computer might charge its battery quickly when connected to a 2.4A charger or, more slowly when connected to a 1A charger.

Some (especially older) devices will never take more than 1A (maybe not even 1A) no matter how much current the charger is able to provide.

Same goes for the really old 0.5A chargers.


The charging circuit in your phone/tablet will limit the current to safe level for the battery in it.

If your wall adapter can supply more it only means it would be less strained to deliver required power.

  • \$\begingroup\$ Ok, so when my powerbank says to only charge it with a charger rated 1A, it's basically talking non-sense: if I charge it with a charger rated 100A, it will still only draw 1A? \$\endgroup\$ – Sam T Jun 27 '18 at 12:20
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    \$\begingroup\$ They probably mean at least 1amp. A lot of older chargers can only supply 0.5amps as that was what the original USB spec require \$\endgroup\$ – John Burton Jun 27 '18 at 12:58

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