Have you wondered how USB devices are powered? Or, how about…can certain USB devices be made portable? I explore these questions.
USB runs at 5v. The max current you can draw is 500ma. Therefore the max load is 5v x 0.5A=2.5. Watts. (W=VxI) If you try and draw more than 500mA, you may overload the port which will cause it to break.
Thus, to power a device off a USB port, it needs to be under 5 volts — as that is how much a USB port gives out:
4 x AAA = Good
4 x AA = Good
Here is a chart that shows batteries and mA
| Battery Type | Capacity (mAh) | Typical Drain (mA) |
| D | 13000 | 200 |
| C | 6000 | 100 |
| AA | 2400 | 50 |
| AAA | 1000 | 10 |
| N | 650 | 10 |
| 9 Volt | 500 | 15 |
| 6 Volt Lantern | 11000 | 300 |
Now, something cool you may not know, many USB devices can be rigged to run off batteries (even rechargeable ones — even solar). For example, I have a pretty nice USB LED light.
To make it portable, I simply bought an AA battery pack housing (for 2 batteries — for a couple of bucks), and connected the two terminal wires (one black and one red) to the outer pins on the USB LED light. See pictures for pins.
Pins lead to these wires
The pins we’re concerned about
Of course, it does matter which terminal wire goes where, so to demonstrate the working USB light, I have turned the USB connector facing upwards (the way you would plug it in), and have attached the terminal wires to the outer pins. The next step will be to buy a USB female connector, and create a more permanent solution.
Completed Reading Light Project
Notes
Some things I would like to try: Build a portable charger for cell phones, a solar powered light, a portable dual USB light.