Dear Colleagues,

You all know about fiddly power cables and the proliferation of different power supplies and plugs with the myriad number of different electronic gadgets in our busy lives. A veritable nightmare. The USB (Universal Serial Bus) has definitely simplified my life by simplifying my connections here. Today most phones, cameras, 3G modems and other devices (including my wife’s Kindle) can charge from a simple USB cable plugged into a computer (or adaptor).

The only challenge is that the USB connection can’t deliver too much power. Approximately 2.5watts at present (500mA-5V, 900mA with USB 3.0, to be exact). Despite this drawback, some ingenious designers have used the USB port to power fridges and fans and other exotic products. But certainly power is an issue for most devices.

Interestingly, Power over Ethernet (PoE), also provides a similar option although up to 57Vdc (rather than 5Vdc for USB). It is difficult to distribute USB power at 5 volts throughout a building due to the voltage drop on cables (but easier for PoE at 57volts).

The Next Big Change - Power
From 2014, USB will be able to provide power to larger electronic devices up to 100 watts. This is called the USB PD (Power Delivery) standard.

This will certainly revolutionise the office and home. As it is a widely applied standard with massive manufacturer support. Thus direct current power (dc) will be used to power a growing number of devices. You can see that the alternating current approach will be less obvious in the future. This fits in well with solar panels which produce dc power and are a growing feature of our home and work landscape.

The Interesting History
Mr Ajay Bhatt of Intel (the ubiquitous chipmaker) invented the USB connection to cut out the hassle of plugging a variety of different devices into a computer (e.g. keyboard, mouse and speakers). It was certainly not designed to power devices. Although, it is definitely the default device for charging a wide range of electronic gadgets (at low power).

Forget About Fantasies
There are now suggestions that flowing from the rapid growth of USB connections that dc power will be used more widely outside the office and home. Highly unlikely. The existing power grid is standardized on high voltage ac low amperage cables and is the only feasible way of transmitting large amounts of power over long distances using transformers. High voltage dc transmission systems are certainly used (and the equipment to lower their voltages is around); but are still relatively rare and expensive. Will this change? I doubt it; but as we know technology is never quite predictable.

What are the Take Away Ideas?
USB is a fantastic standard – widely used and widening its impact.

Providing significant dc power from USB devices will make a huge impact on the home and office.

One minor glitch
One thing that does irritate me (admittedly, ever so slightly in the grand scheme of things) is that the USB plug fits into the socket only one way (apparently the original design was to make the plug as cheap as possible). Ajay Bhatt is now working on making the USB plug ‘flippable’. That would be a brilliant innovation.

USB is certainly getting to this point with Arthur C. Clarke’s comment: Any sufficiently advanced technology is indistinguishable from magic.

Yours in engineering learning,


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