Electric Porsche 944

Archive for March, 2014

18650 Li-ion range extender

by on Mar.22, 2014, under Electric Car

For daily use my pack  provides more than enough range for what I need and want the car to do.  However there are situations where it would be nice if the car had 2 or 3 times the current range.  The Tesla Roadster and Model S have the highest range in the EV industry for production cars and they use massive packs of 18650 cells.  They benefit from the economy of scale  of the laptop and power tool industry as these are the most common cells used.  In the coming years this may reverse and the laptop and power tool industries may benefit from high quality cells developed for the EV industry.

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Jehu Garcia is currently working towards an 18650 based pack for his VW Samba Bus using recycled laptop batteries.  I already have a few hundred 18650 cells on hand so I thought it just might be a worthwhile project to build a removable high capacity battery.  Although I have a few hundred cells, what I need to make this work is a few thousand cells.  If any of you guys have a stash of “dead” or unused laptop batteries and just want to get rid of them please feel free to send them my way to speed up this project.

The IT department at my day job was happy to give me the dead laptop packs since there wasn’t an established recycling process in place yet, I’m willing to bet the same exists in many companies large and small.

To put all of these cells together there are some inexpensive plastic holders available from Fasttech.com.

18650 Battery Holder

 

The initial plan is to use small  fuse wires just like Jehu, and I may use a copper clad board as the current collector, it provides stability and is easy to solder to.  The currents won’t be that high and with a massive width of copper sheet on the PCB it  actually has a fairly high current carrying capacity.

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The main purpose of this pack is not to drive the car on it’s own, but to supplement the existing pack in the car for longer range so the maximum current output doesn’t have to be as high.  I would like to build a pack with between 60 and 100Ah at ~86 cells which is a  voltage that would match quite closely the nominal and charged voltage of the LiFePO4 main pack in the car.  Assuming roughly 2Ah per cell on average from used packs I will need 30-50 cells per module and 86 of those in series, totalling 2580 to 4300 cells for the desired capacity.  This  pack would weight around 275 to 450lbs which although significant is worthwhile for 2 – 2.7x the range.

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