I love commodity parts and I like cars, so this one caught my interest. The Tesla Roadster (http://www.teslamotors.com/) battery pack is made up of many cells exactly the same as the IBM T60P that I’m typing this on. Laptop battery configurations differ dramatically, but most contain multiple 18650 form-factor batteries http://www.molienergy.bc.ca/specs/ICR18650G.pdf). The 18650 designator comes from the cell dimensions of 18mm in diameter and 65.0mm in length—a bit larger than an AA battery. Billions are sold each year.

How can an automobile with a nearly 250-mile range use the same power source as a laptop computer with four hours battery life?  Use lots of them. The Tesla uses 6,800 cells in their pack where each cell is roughly 2,000 mAh.  These cells are combined into in a 375V battery capable of delivering 53 kW/h of energy or roughly 200kw of power.    

This battery pack has a fairly high power density as does gasoline or anything else capable of storing enough power to accelerate a car from 0 to 60 MPH in under 4 seconds. High power density gets work done but, if released quickly, can be very destructive so numerous safety devices are employed.  These include an assortment of environmental sensors for conditions such acceleration, smoke, heat, humidity, current, and moisture that actively disconnect the battery pack when anomalies are detected.  In addition to these active safety devices, an array of passive safety measure are in place as well.

For more details on the Tesla battery pack design: http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf.

Lead-acid batteries, the common choice for data center backup power, are less dense and much more maintenance intensive than Li-ion. Large arrays of 18650’s might be more cost effective.  This backup power technology might even be a better choice for distributed uninterruptable power supplies (UPS).  In this configuration, rather than a large central UPS, a small UPS is installed near the servers (typically one per rack).  Li-ion cells don’t emit hydrogen gas as lead acid cells do when charged and are more tolerant to the higher temperatures found near the servers.

                                                --jrh

Update: I'm now with Amazon Web Services: http://perspectives.mvdirona.com/2008/12/14/JamesHamiltonJoinsAmazoncom.aspx.

I’m an architect on the Microsoft Windows Live Platform team and maintain an internal blog called Perspectives.  My postings focus on high scale services, data center operations, very large database, flash memory, service design principles, power efficiency and power management.

I made that blog internal because it opens up interesting content that can’t be posted externally. I discuss internal products that haven’t yet released, data that will never be released, and take positions without regard to how they would be perceived outside the company. I realized after maintaining the internal blog for a bit more than a year that about 25% of the content is public and could be posted externally. That’s the genesis of this blog.  I’ll post less frequently here, since only some of the content can be released externally. But what can be released externally will be posted here.

My external Microsoft web site is http://research.microsoft.com/~jamesrh.

At home, most of my interests revolving around boating and boat related travel and photography.  Jennifer and I write for regional and national boating magazines and the home web site is http://www.mvdirona.com.  We also maintain a blog is http://blog.mvdirona.com.   

Welcome to Perspectives.

                           --jrh