usb - Can I use a charger with more output amperage than the device needs?

  • Jorge Fuentes González

    I've just bought a portable battery, but the portable battery don't comes with an adapter for the house current; it only comes with a USB cable so I can charge it with my laptop. My mobile phone came with a charger, and I want to know if is safe to use that charger with the battery without problems, even though the output has a higher amperage. These are the specifications:

    Battery input: 5V, 1A
    Charger output: 5V, 2A

    Will the output only give the quantity that the input is requesting, or will the input overheat because it cannot handle all the current it receives?

  • Answers
  • tapped-out

    TL;DR: yes, it is absolutely safe to charge a device with a charger that has more current capacity than needed.

    Ohm's law tells us the relation between current, voltage, and resistance:

        I    =     V      /     R  
    (current =  voltage  / resistance)

    Since the voltage is held constant (5V), the only factor that determines current draw is the load (another term for resistance) the device places on the charger. Thus, the device will only draw as much current as it needs and no more.

    Speaking from personal experience, I've had no problems charging my phone (which only draws 700 mA) with my Kindle charger (850 mA) or my iPad charger (2.1 A).

  • Matthew Williams

    Expanding on tapped-out's answer. These chargers work the same way the internal power of a desktop computer would work.

    When you buy, for example, a gaming computer you will notice PSU (power supply unit) options exist which run way above and beyond the requirements of anything you could ever likely get inside the case. Obviously if the PSU controlled how much power was taken in by a component you would fry most systems fairly quickly. Clearly it is done by the components which require power.

    It is useful to use higher PSUs when, for example, you might decide to upgrade your components at a later date. If your new pieces require more power than their counterparts they will simply take more in.

    I don't think anything I run these days has the right power supply. My television runs from a laptop charger...

  • Related Question

    adapter - Can you charge any device with Mini-B USB receptacle from any charger with Mini-B USB plug?
  • Jim

    I've got several devices with a mini-B USB receptacle - including my mobile phone/PDA and some headsets. Each came with its own AC adapter. I'm wondering if I can charge any of these devices from any charger with a mini-B USB plug - (1) AC adapter (2) car charger (3) computer USB port with A-to-mini-B cable.

    With wall warts I know you've got to match voltage, polarity, DC plug, and the charger must supply enough amps to power the device. But if the charger has a mini-B USB plug, does that take car of the voltage (+5V) and polarity?

  • Related Answers
  • Broam

    Yes it does, in terms of polarity and voltage, but not current. Some chargers short pin 5 (iirc) in order to tell the device that "hey we're breaking the USB standard here and you can draw more current."

    Motorola phones will happily send 750 mA down the line, Blackberries 800 mA (that may be reversed). Usually extra current is just extra capacity and you're fine--it won't hurt a device. Under-current, however, will most likely fail to charge. Poorly designed devices may malfunction.

    The USB 2.0 standard is for a device to draw 100 mA--and then ask for more current; most devices don't follow that part of the standard. (I have a device that does...and it has a mode that says "draw 500mA no matter what")

    USB 3.0 will increase the currents allowed to 900 mA, and allow 150mA inital draw.

  • RiddlerDev

    I have had a problem with our GPS. It and my blackberry have a mini-usb connection, yet the GPS does not work on that charger. I would have said no for sure before I saw this with my own eyes, as I would think the very nature of USB would require the same size to work the same way.

  • Ivo Flipse

    I think if it's the mini USB plug it's a standard connector and can be used on any device.

    So far my HTC Hero hasn't had any trouble with the wires I got for other devices.

  • AnonJr

    Check the Voltage/amperage:

    • If they match then there shouldn't be any reason why it wouldn't.
    • If they don't match, I wouldn't bet my equipment on it.