# In how far is the Ampere number important for USB powered devices?

Currently, I have three devices that can be charged via USB:

• Digicam: Panasonic Lumix DMC-TZ41
• Tablet: Samsung Galaxy Note 10.1 2014 Edition
• Smartphone: Nexus 4 (LG)

They have three different chargers:

The output of the three differs:

• Panasonic: 5V, 800 mA = 0.8 A
• Samsung: 5.3V, 2.0 A
• LG: 5.0V, 1.2A

Is the voltage difference important? What does the ampere difference mean?

I think (but I'm not sure about it) that it means when I load the devices with the Panasonic adapter they will load slower. The Samsung adapter can support "heavier load". But does that mean I could load all three devices with the Samsung adapter?

I have heard that the tablet recognizes when the charger is not a Samsung charger. How could it do that? Is there a chip inside the Samsung adapter that sends information while loading?

• I've just seen that the "Anker® Astro E5 15000mAh Dual USB Port Externer Akku" has a 1.0A and a 2.0A output. So I guess the ampere number is important and I should not load other devices with that. Apr 28 '14 at 20:50
• Your power supply must provide more power than your devices consume. Apr 28 '14 at 21:09
• Devices will not draw more current (amps) than they need so its okay if the power supply is capable of providing more current than the device requires. Too much voltage, on the other hand, can do damage. Apr 28 '14 at 21:34
• @PeterFitzgerald If that is the case, why does the Anker Battery have two USB ports - one with 1.0 A and one with 2.0 A? Wouldn't it then be plausible to build two 2.0 A ports? Apr 30 '14 at 9:49
• Making all ports were 2 amps would probably present some design issues. For one, the device would require a much larger power supply. Also, not many devices can utilize 2 amps. Apr 30 '14 at 11:15

With all 3 chargers, the voltage ranges of 5, 5.3 and 5 are all pretty close to each other and I would not worry too much about that. Think of electricity like this

The­ three most basic units in electricity are

• voltage (V)
• current (I)
• resistance (r)

Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.

A neat analogy to help understand these terms is a system of plumbing pipes.

The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.

There is a basic equation in electrical engineering that states how the three terms relate. It says that the current is equal to the voltage divided by the resistance. Let's see how this relation applies to the plumbing system. Let's say you have a tank of pressurized water connected to a hose that you are using to water the garden. What happens if you increase the pressure in the tank? You probably can guess that this makes more water come out of the hose. The same is true of an electrical system: Increasing the voltage will make more current flow. Let's say you increase the diameter of the hose and all of the fittings to the tank. You probably guessed that this also makes more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow. Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage multiplied by the current.

The water analogy still applies. Take a hose and point it at a waterwheel like the ones that were used to turn grinding stones in watermills. You can increase the power generated by the waterwheel in two ways. If you increase the pressure of the water coming out of the hose, it hits the waterwheel with a lot more force and the wheel turns faster, generating more power. If you increase the flow rate, the waterwheel turns faster because of the weight of the extra water hitting it.

So, with your higher amperage (current) adapters, devices will charge quicker because it allows the 5vdc to flow faster than your .8 amp charger.

Your tablet knows if it is connected to the right adapter because it can detect the volts/amps being supplied via the USB cable. If you do not supply the correct voltage/amps to the device, it is detected by the power subsystem on the device itself and then you get a warning message saying that the charger might not be compatabile with the device.

You should not use a single adapter to load multiple devices unless it is specifically meant to perform that function. An example would be a DC converter in your car that has multiple USB ports, that would be fine to use. Unless the power adapter has the ability to charge more than one device, don't do it.