A Special iPad Air
I received some really great feedback about my article last week describing how little ol’ open-source me managed to successfully migrate myself over to an iPad Air. I think the thing that people like myself forget is that if you have the skills, you can make just about any technology work for you and meet your needs. If that’s the case, why not go with a solid platform on really nice hardware?
One thing I didn’t really mention in my previous article was how much the iPad’s battery life influenced my decision. It was almost as important in my decision as iOS 7. So far, I’ve been very impressed. For such a large-screened device, and a powerful processor driving so many pixels, it’s very impressive that it easily lasts a full day with moderate use. With lighter use, I could see going a solid two days, or maybe even three, but that would be pushing it.
In short, there are so many good things to be said about the iPad, and how well it can work for different people and different situations. There’s one thing about my iPad in particular though that makes it special. No, I don’t mean that mine is space grey and others are silver. I don’t even mean that mine is cellular and others are wifi only. The thing that makes my iPad so special is that since getting it in mid June, I’ve never plugged it into a wall electrical socket.
What?! Ok, so the iPad’s battery is good, but clearly, it’s not more than two months good, especially with how much I use it. So what’s going on here? Some readers may remember a while back I wrote an article on a miniature 50 watt solar power station I was building at the time. Well, since then, that system has become more refined, more stable, and has been put to regular use. In fact, I basically use it every single night to run my primary floor lamp. Once I got the iPad though, I knew exactly how I wanted to challenge myself. Could I run my iPad exclusively using power from my system?
Well, it’s been two months and my iPad doesn’t even know the meaning of grid power (ok, Siri might, but that’s another story). The best part? It hasn’t even really been that difficult. Occasionally I have to consider how much I’m using my iPad if I’ve had a few bad sun days, but mostly, I do have enough power. Granted, my system is overpowered for something like an iPad alone, but keeping the iPad topped off hasn’t stopped me from using my floor light each night, or any of the other things I use the power station for.
At first, the power station’s only output was 120 VAC from a 300-watt pure sine inverter. In my initial designs, I had always planned for one or two 12V automotive sockets, but when I first got the iPad, I still hadn’t added even one. So for about a month, I had to charge the iPad using the standard power block by plugging it into the inverter. This worked well, and I still do it sometimes, but it’s not too efficient. The inverter consumes about 5 watts just by being on. Although Apple’s power blocks are pretty efficient, it’s just silly to go from 12 VDC to 120 VAC back down to 5 VDC for USB. When I charge the iPad that way, I end up drawing somewhere between 15 and 18 watts from the battery.
The inverter is much less efficient at converting 12 VDC to 120 VAC when the power draw (around 12 watts for Apple’s power block) relative to capacity (300 watts in my case) is low. A few weeks ago, I installed a single 12V automotive socket, and bought a 2.1 Amp iPad-compatible car charger. Now when I charge the iPad using the 12V socket, it draws a much smaller amount of power from the battery. In my tests, charging from the 12V socket only draws about 6 watts from the battery, making for a 66% reduction in power consumed! Car chargers use something called DC-DC switched-mode conversion to drop the voltage and while they can be electrically noisy (from high frequency switching and inductor harmonics), they are typically very efficient. Of course this all means I can continue to keep my iPad running without using wall grid power for even longer.
This was (and continues to be) a really fun challenge, but I definitely wouldn’t recommend it to everyone. The power station was a project I’d been planning for years, and was totally independent of getting an iPad. When I saw the two things together though, I saw an opportunity to merge my interests. Further improvements may include an auxiliary Li-Po power pack so I can bring some of my solar power with me on trips. I’m also planning on doubling down my efforts in my thermoelectric power generator designs to see if I can charge the iPad that way.
I will definitely say that doing something like this is basically guaranteed to not save you money, but that’s not why I’m doing it. It’s been a huge learning experience so far, and talking about why my iPad in particular is special is a great conversation starter.