Hybrid Zap Xebra Project Wednesday, Apr 8 2009 

Back in 9th grade my shop teacher explained something that has always stood out in my mind.  He told a suspicious class of “Ford-vs-Chevy” types that despite what car companies would tell you, you could make a car go 60 miles per hour with no more than 5 horsepower.

He went on to explain how, with the proper gearing (a transmission with many speeds) this was not only possible, but large trucks use just this sort of arrangement to haul amazingly heavy loads.

When I first read about series hybrid vehicles, this lecture came back to me.  Instead of using a complex gearbox, the series hybrid accomplishes the same results by running its internal combustion engine at a constant speed regardless of vehicle road speed.  When the vehicle is using very little power (cruising, decelerating, etc.) the surplus is stored in a small (relative to battery-only electric vehicles) battery pack; when additional power is required, the SEV’s motor can draw on this reserve to provide additional acceleration.

I first came across these vehicles while reading a book about electric vehicles around 1988 (published in 1981).  There was a small section on hybrid vehicles but the focus of the book was battery-electric vehicles (bev) and the idea of hauling around an internal combustion engine just seemed to defeat the purpose and spoil the elegant simplicity of the electric drivetrain.  Anyway, better batteries were just around the corner, right?

In 1999 Honda introduced the Insight hybrid to America.  This was a parallel hybrid; perhaps this is a good time to compare the two approaches.

While the definition of the terms are sometimes stretched, the key difference is that in a series hybrid, the wheels of the vehicle are driven by an  electric motor exclusively; in a parallel hybrid, both the electric and internal combustion engine can drive the wheels via any of several arrangements.  There are of course variations, but this is the key difference between the two.  The series hybrid is really an electric car, it just happens to use a generator in addition to a battery pack.

With the Insight, Honda proved that a hybrid car could provide value (in the form of increased fuel mileage), be reliable and be manufactured using mass-production techniques.  This opened the door for other hybrid vehicles to American markets and within ten years established the hybrid drivetrain as a common alternative in the same way you may have selected the four or six cylinder engine over the v-eight for fuel economy in cars of the previous decades.

However the mass-produced series hybrid (one that drives the wheels exclusively using electric power) remains elusive.  I find this surprising because, of the two arrangements, the series hybrid appears to be the simpler of the two with fewer potential engineering, maintenance and service challenges.

In 1979, Mother Earth News published an article about Dave Arthur’s home-built series hybrid and even produced plans for building your own.  While the article over-simplifies the system, and undoubtedly leaves out the engineering and operating challenges the car faced, the fact that it worked at all is impressive given the state of electric motor, battery and in particular, speed/charge controller technology at the time.

This has been a loosely-organized, rambling and somewhat stream-of-consciousness post so far, but the point is to give you some context for an upcoming project.

My friend Preston owns a Zap Xebra electric vehicle and recently approached me about adding a hybrid function to increase the vehicles range.  As it’s already an electric-drive vehicle, a series hybrid is the logical approach.  Aside from the implementation advantages of sticking with the electric drive arrangement, I believe the series hybrid is a superior approach to hybrid vehicle design and I plan to use this project to determine the validity of this claim.

Preston has expressed an interest in implementing this system using off-the-shelf parts as much as possible, to make reproducing the design easier for others.  I generally agree with this approach however due to the somewhat unique application, we may have to weigh the efficiency and cost-effectiveness of using existing components.

I’m currently in the process of researching all of the key components that will make up this system and collecting documentation.  As the project evolves, I’ll post updates, findings and results of experiments whenever possible.  If you have any questions, comments or ideas that you’d like to share, feel free to comment on these posts and I will respond as best I can.


This post is mainly for my dad Tuesday, Dec 2 2008 

Over the weekend I mentioned a few cool things on the internet that he might be interested in.  First is Ponoko, where you can submit your CAD drawings and receive parts to build your design:


Next up is White Zombie, currently my favorite electric car:

White Zombie

White Zombie


Finally ToolMonger, apparently the web’s first tool blog, but I found out about it only a few months ago:


Toolmonger has a podcast as well, which I started listening to this week.  It’s pretty good (although the segway music and the dialog could be mixed closer to the same level).  My father-in-law would probably dig these guys too.