AMITIAE - Thursday 5 September 2013

Cassandra: Rumored Apple 17 Watt Charger - Maybe not a Mystery After All (Updated)

apple and chopsticks


By Graham K. Rogers

Apple rumours have expanded greatly this week as the news about the Apple Event scheduled for 10 September spread. This soon became "events" with the addition of China; and then expanded to include Berlin and Tokyo, causing much excitement. What the next iPhone will be, is still open to speculation, despite what has appeared online. As well as the (sometimes misleading) stories, AppleInsider put out a rumour about a new charger being developed by Apple for a mystery device.

Late Wednesday night, after reading about the rumour that Apple was to produce a 17 Watt charger for some, as yet-unknown device - like Neil Hughes who wrote the AppleInsider article - I sat down with the products (and chargers) I had, to try and figure out what the mystery item could be.

With the current lineup of devices that Apple has, there is nothing that would appear to fit the bill: Macs need much more, iOS devices less power. The Airport Extreme Router is close at 25 Watts, but the power supply is now integral, so this would not seem a likely candidate: why un-design something that looks fine as it is?

Still wondering about what the charger might indicate for a new area, I went into my office. Luckily, I work at a department of Electrical Engineering, so was able to pick the brains of one of my colleagues. To make it easier - English teachers and Engineers do not always think along the same lines - I produced some diagrams to go with my thoughts.

Situation One: Normal

The devices each have different power supplies. These are iPhone (5W), iPad (12W), MacBook Air (45W) and MacBook Pro (85W). If the right adapter is connected to its device, then all is good.


Situation Two: Low Power

If we use the iPhone adapter for the iPad, or the MacBook Air supply for the MacBook Pro, there is no problem, other than one of time: it takes longer to charge the device. This is especially noticeable with the iPad which takes a long time to charge even with the right adapter, but (mercifully) takes quite a long time to discharge.


Situation Three: Higher Power

When the iPad adapter is used to charge the iPhone (or the MacBook Pro power supply with the MacBook Air), the charging may be a little faster. With one or two uses (occasional) there may be no real danger as long as the voltage output from the power supply is the same. The iPhone takes 5 Volts as does the iPad mini. However, there is a risk that, over time, components like resistors or capacitors may deteriorate. Phut!


Situation Four: Hypothetical

This is where the conversation became rather interesting and there was a moment when the penny dropped. I brought in the idea of the Airport Extreme Router. The new one I have at home takes 25 Watts. The old one was in the office and the information on the base showed that it uses 12V at 1.8 Amps. Immediately my colleague said that this is 22.5 Watts. This makes sense as the latest router now uses the 802.11ac IEEE wifi standard which understandably would use more power. [Note: it is actually 21.6 Watts. My colleague told me, "about 22" and I tried to work it out in my head. Maths is not my strong point.]

Power Power

Older iPad and Airport Extreme Power Adapters

We could now group the devices: iOS devices taking lower power, with computers drawing more; and in the middle the routers at over 20 Watts. It was only then that I mentioned the rumoured 17 Watt power adapter. What could that be for?

My colleague thought for a moment and implied that I was barking up the wrong tree. It might be a device, of course, but you would also need more power, he told me, if the battery was to have a larger capacity. Increasing this - measured in terms of amp/hours - would require a higher power for charging.

It is well known that Apple has brought in a number of innovations for battery technology and seems to be deeply concerned in bang for the buck: making the device thinner, while at the same time increasing the hours that a charge will last for. One of the more interesting videos from Apple was produced for the introduction of the MacBook Pro 17" at MacWorld 2009 in which Bob Mansfield explains some of the technical and industrial processes that Apple had introduced for the new battery types. These were later used in all the devices.

While a 17 Watt power supply may suggest a new device, it could be that Apple has improved on the current technology and is managing to squeeze more out of the batteries that will be installed in devices that appear next year: perhaps as significant a development in itself as a new device.


My thanks to Dr. Phumin Kirawanich, head of the Department of Electrical Engineering, Faculty of Engineering, Mahidol University, for technical comments and insight.

Graham K. Rogers teaches at the Faculty of Engineering, Mahidol University in Thailand where he is also Assistant Dean. He wrote in the Bangkok Post, Database supplement on IT subjects. For the last seven years of Database he wrote a column on Apple and Macs.



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