Technology

For a couple years now I've been seriously considering building a portable solar power system for my laptop (a 17" Apple Powerbook G4, 1.67GHz). The two motivations behind such a project are to achieve a real understanding of photovoltaic technology and the power consumed by my computer. I use the qualifier "considering" because I've yet to find a source for all the necessary components. Let me explain.

Most consumer solar power systems consist of one or more solar panels, a charge controller, and one or more batteries. The solar panel(s) supply power to the charge controller, which regulates the storage of that energy in the form of a battery charge. The battery energy can then be used when direct sunlight isn't available to the solar panel(s). Connecticut Solar sells just such a package (60 watt, 16 amp) for $795, and it's specifically marketed for laptops and consumer electronics applications. The "rub" is that you're unnecessarily complicating the issue with such packages. You shouldn't need a charge controller and battery when your laptop already has those components. Another downside is that these systems only supply enough power to run the laptop - not charge its internal battery.

What I would like to build is a portable solar power system for my laptop that eliminates all of the duplicate components. This should require only one or more solar panels and a DC to DC converter. The challenge has been to source a DC to DC converter that can take power from a set of solar panels and produce ~2.65 amps at 24 volts DC (the exact output rating of my AC-DC laptop power supply). Any ideas?

You might suffer from an addiction to latte art or roller coasters, but I have an addiction to a certain category of gadgets. My particular "fix" comes in the form of gadgets that perform an automated data acquisition task. (Geek Alert!) An example is the real time temperature monitor I recently installed at our data center. The latest "kick", however, is Garmin's new Forerunner 305. Having previously owned two of Timex's Ironman speed + distance systems (one with, and one without heart rate monitoring) and several other handheld GPS units, I can authoritatively state that Garmin has finally succeeded in an odyssey strewn with antecedent carcasses.

"Such strong words," you say? I'll let you in on a couple dirty little secrets about most portable GPS units. After spending between $300 and $500 on each, you'll learn to your chagrin that they only work in the middle of a desert on a clear day for the ten minutes that their double "A" batteries hold out. That's right. They're so pathetic that trees and clouds will reduce them to nothing but a battery consumption apparatus (which, ironically, they are exceedingly good at). Did I mention high-tension power lines? How about outside tall city buildings?

Don't get me wrong. GPS has held enormous potential. It's just that those of you, like me, who have purchased model after model need to start being honest about their shortcomings. Or, like me, you need to toss the lot of them and buy the Garmin Forerunner 305. (No, I'm not being paid my Garmin.) It's compact, easy to use, and reliable. I'm searching for something I don't like about it.

Let me explain.

The Forerunner 305 is an oversized wristwatch combined with a traditional heart rate monitor chest strap and, optional, cadence sensor (for cycling). I've been using it for running, cycling and hiking. In those activities, I most often have the unit's display set to indicate event duration, distance, pace or speed, and heart rate. Unlike pedometers or bike computers, GPS provides truly accurate speed and distance measurements. (Elevation calculation is a bonus that pedometers don't even pretend to deliver.) The advantages, however, aren't limited to the course or trail. A provided computer interface enables transfer of the acquired data to a web-based training log and analysis service (subscription required: www.motionbased.com). That's where the trifecta of GPS, data acquisition and Web Services reach a mesmerizing crescendo.

Take, for example, the following log of the past three running events at Greenlake. They were all fairly slow and short runs, but you can begin to image how such a log would aid in training over the season.

Motion Based logs all of the data acquired by the Forerunner, and combines it with weather data, a graphing system, and a handful of mapping systems. For instance, I can see that this morning's Greenlake run weather was noted as "scattered clouds at 1000 feet" (from the Boeing Field weather station). The average, low and high temperatures, relative humidity and wind speed were also recorded. Sitting like a maraschino cherry on the top of all this delicious data acquisition dessert is the Google Earth feature. (Your jaw will drop when you first see a Google Earth tour of an event recorded with the Forerunner.)

The image to your left is just a still photo of the Google Earth tour. If you want to experience the real thing, here are a couple Google Earth files from my training log: Greenlake (running), Lake Washington (cycling), and Rattlesnake Ledge (hiking). [You'll have to right-click on the links and save the files to your computer. You will also need to download the Google Earth software from http://earth.google.com.]

I'm not even scratching the surfice of Motion Based's data analysis features with this blog post. You can combine the data in several different ways to produce line, distribution and pie charts. Here's a simple one showing heart rate and elevation of this afternoon's hike to Rattlesnake Ledge.

The Garmin Forerunner 305 receives my strongest endorsement.

When planning on being abroad for more than a week, and traveling with electronics that require direct power or battery recharge, you'll have to address the issue of power adapters. Since most consumer electronics have auto-switching power supplies (i.e., support for 100-240 volts and 50-60 hertz), the biggest concern is the type of plug required for power outlets in the country or countries you will be visiting. I'm trying to eliminate any unnecessary equipment, so things like the iPod power adapter stays at home -- it can charge while connected to my Powerbook. As for the Powerbook's power supply, Apple sells a World Travel Adapter Kit with all of the plugs you might need. I expect to only need one type of adapter, which will be the only one I take on the trip.

You should always make sure and check whether the power supply supports auto-switching. Plugging a 110 volt power supply into a 220 volt source will destroy the power supply. Trust me on this. I once blew up a $2,000 laser printer by plugging it into a 220 volt outlet on a Norwegen-built ship that I worked on.

It's a good rule of thumb to assume that any non-portable consumer electronics lack auto-switching power supplies. In such cases, you'll need a step-down transformer, rated at the approprate wattage.

The nifty temperature sensor (mentioned in a previous post) showed up on Thursday, and was installed at our data center today. This is when the geek in me really shows. Here's a device that combines an embedded server (probably Linux-based, although I haven't checked for certain) and a data acquisition component (in this case, one or more temperature sensors). The result is a compact, rack mountable device that will display real time temperatures for multiple locations. It will also log the temperatures at a variable time interval, which defaults to every 5 minutes.

I've rack mounted the device in the top of the cabinet, and run the second sensor to the bottom (a distance of approximately 72 inches). The important thing to know is that the cooled air flows through the raised floor; therefore, the differential between the two temperature sensors will represent how much heat is added by the equipment in the cabinet (i.e., servers, disk arrays, switches and firewalls). So what are my expecations?

First, the cool air supplied through the raised floor should not fluctuate much. Fluctuation in the temperature of the supplied cool air would indicate a failed cooling unit or thermostat.

Second, there's a possibility that a measurable differenital in temperture could coincide with the daily network traffic patterns. Now that would be interesting. Also, there could be a spike in temperature during the scheduled backup procedures when the multi-terrabyte nearline array is running at full clip.

The small sample taken following installation today indicates an average differential of 22^o F. That puts the temperature in the top of the cabinet at 82^o F. (Does anyone other than me think 82^o F is a bit too high?) I realize that the upper tolerance for the equipment is 104^o F, and that I'm measuring the exhaust temperature (not the temperature of the air flowing through the equipment), but additional equipment planned for the cabinet will push the temperature even higher.

As with most new information, there are new questions to consider. Additional temperature sensors might need to placed in the cabinet to test for air circulation patterns. The cool air should be flowing from the front to the back, in addition to flowing from the bottom to the top. If this isn't happening, the equipment could be starved for cooled air.

I'll post graphs once I have a large enough sample size to work with.

Gavin has been working on an AJAX project in his "spare time". The project melds both his interest in roller coasters and the desire to demonstrate what's possible when you harness various Web technologies in new and creative ways. The resulting invention (coast2coaster) is quite amazing. You should definitely pick a park and switch to the satellite view. Doing so will allow you to zoom in and, in many cases, actually see the roller coaster. That's way too cool for words.

He's got a more detail explanation of the project on his blog. Sighhhhh. I guess this means that I'm going to have to publish something cool too.

How'd you spend your weekend? I had to spend most of mine in our data center. We've been busy adding new servers and decommissioning old ones. The really good news is that we're about halfway finished with this particular project. I'm just waiting on a couple new "intelligent"
power distribution units (PDUs) and a nifty temperature sensor. The intelligent PDUs will provide real-time monitoring of power consuption (i.e., AMPs) via an embedded Web server and SNMP polling. The temperature sensor will provide real-time monitoring of the temperature for two location in the cabinets (i.e., the base an the top). Since the cooled air flows from the raised floor up through the cabinets, motivated by a high-volume fan in the top, our main interest is in the differential between the two temperatures. The temperature data will also be presented via an embedded Web server and SNMP polling. I can hardly wait.