This morning I was double-checking on the Google Nexus One technical specifications and noticed the charging requirements. Per Google, the Nexus One “charges at 480mA from USB, at 980mA from supplied charger.” It’s really no surprise that it’s going to take longer to charge from a computer over USB than from the wall. USB 2.0 is the currently used specification in most devices and it tops out at 500 mA for supplying power. Of course, USB 3.0 is on the way, so I did a little digging into how it handles power. I thought I knew everything there was to know about USB 3.0 but I didn’t. Now I do and I like where this is heading in terms of recharging mobile devices.
There are a few factors that come into play here, so let’s start with “power loads.” USB 2.0 is restricted to five loads, while USB 3.0 ups that to six. OK, so that’s a 20 percent increase in how many loads a USB port can supply, but there’s more to it. Each load in USB 2.0 is 100mA of current. Simple math confirms the 500mA power supply for today’s USB interfaces — five loads at 100mA equals the 500mA that USB 2.0 can supply a device.
The specification for USB 3.0, however raises the not only the number of loads, but the current per load as well — 150mA, which is 50 percent more per load. Combining the six loads of USB 3.0 and its higher 150mA current per load nets you 900 mA for power supply with the new specification. Consequently, the current can be spread among multiple loads with USB 3.0, so more devices can be charged at the same time.
That 900mA for USB 3.0 is nearly equivalent to the wall charger my Nexus One came with and could theoretically charge the same device in half the time when connected to a computer. At least, that’s how I’m interpreting this data — aside from the faster data throughput, I expect to see my compatible mobile devices get more power in less time thanks to USB 3.0. I’m going to review the USB 3.0 specification to see if I’m off base, so don’t hesitate to chime in on this topic while I’m reading.