PLUG OK license plate
Do-It-Yourself Conversions: By Popular Demand
Oct 25, 2005 (From the CalCars-News archive)
This posting originally appeared at CalCars-News, our newsletter of breaking CalCars and plug-in hybrid news. View the original posting here.
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In response to many peoples' request for a group-sponsored effort to help individuals with advanced technical skills work on their own conversions of hybrid cars to plug-in hybrids, the national Electric Auto Association has agreed to sponsor a group to facilitate these projects.

Because we believe the more people who are involved in developing and promoting PHEVs, the better are the chances that the major auto companies will also do so, CalCars welcomes this effort. But we are NOT its sponsor. Those involved in our first PRIUS+ conversion have agreed to help as appropriate.

I'm reproducing below, first the EAA announcement, then the comments and cautions by Ron Gremban, CalCars' Technology Lead,­group/­priusplus/­message/­523 From: "Jerry Pohorsky" Pohorsky@... Date: Tue Oct 25, 2005 12:29 am Subject: [priusplus] EAA board approves PHEV SIG

The EAA (Electric Auto Association) approved the formation of a Special Interest Group (SIG) for Plug-In Hybrid Electric Vehicles (PHEV) at their October 15th 2005 Board of directors meeting. The intent is to make the information needed to convert a Hybrid Electric Vehicle such as the 2004 or 2005 Toyota Prius into a PHEV (with substantial EV-only range) available to our members and others. Some of the information is based on a working prototype PHEV Prius that has demonstrated the proof of concept. Several hybrid related email groups already exist, however the information related to this EAA-PHEV project will be stored at the following website thanks to the efforts of EAA member Ryan Fulcher who is affiliated with the Seattle WA chapter.­wiki/­EAA-PHEV

At this website is an email list archive and instructions for subscribing to the EAA-PHEV email list .

There are also links to relevant information and photos of work that has been done by some of the more advanced Prius experimenters and developers of hardware and software tools that enable PHEV technology.

Additional information about batteries, chargers and related items will be added as time permits and progress is made. Once the information about the Prius has reached a certain level of maturity, other hybrids (such as the Ford Escape) that are capable of EV only operation may be added depending on member submissions. Eventually there may be step by step plans although this information may take quite a while to develop and refine. Initially much of the information will be contained within the text of various email messages and through links to other websites.

Those who join the group are reminded to observe standard email etiquette and be respectful of each other. The information is provided as a public service and the EAA assumes no liability for its use. Anyone modifying a Prius or other vehicle does so at their own risk and may void their manufacturer's warranty.


Jerry Pohorsky
EAA Silicon Valley Chapter President
and EAA board member
Pohorsky at comcast dot net­group/­priusplus/­message/­504 From: Ron Gremban rgremban@... Date: Mon, 03 Oct 2005 00:16:07 -0700 Subject: Re: [priusplus] Step-by-step instructions

Especially since the Associated Press article came out and gasoline prices have surged, we have seen a groundswell of requests like yours, including hundreds by phone and email to myself.

Our first response has been to refer everyone to EDrive Systems (, who will be coming out with a professional PRIUS+ conversion, using a Valence Technologies Li-ion phosphate battery pack, with a target price of $10-12,000 in 2006.

However, many, many experimenters still want to do their own conversion, so the Experimental Automobile Association ( is starting a special interest group for people interested in converting hybrid vehicles -- and especially the 2004+ Prius -- into pluggable hybrids. Unlike CalCars, whose mission is to get automobile manufacturers to produce ecologically superior vehicles, the EAA is an experimenter organization that knows how to educate and support electric propulsion systemerimenters in both conversion techniques and safety procedures for high voltage, high power electrical systems. They hope to come up with one or more reference conversions, a set of instructions, and possibly even a kit.

We expect that limited consumer availability and pricing of appropriate batteries will be the largest hurtle for such carefully pre-designed do-it-yourself conversions. The choices will probably be lead-acid, as in CalCars' prototype PRIUS+, with the following limitations:

  • short PHEV range (10 miles EV-only or 20 miles of doubled gasoline mileage) despite 200 lb added vehicle weight
  • the battery MUST be recharged within hours after each use to prevent sulfation, thus making charging required rather than optional
  • low battery cost (<$1000) but short lifetime, around 1.5 years of daily use
  • city mileage decreased 10% in HEV mode, due to increased weight without an increase in battery efficiency -- or a custom NiMH or Li-ion pack with the following different limitations:
    • high cost, $7000-15,000, and limited availability
    • frequent pack redesign required by rapid evolution of the battery marketplace
    • possibly complex and expensive charge control and charge balancing electronics
    • the possible need for very careful cooling techniques to avoid high temperatures and temperature differentials
    • with Li-ion, the potential for thermal runaway and fire, requiring special safety engineering techniques
    • unknown and possibly limited lifetime (e.g. 6 years) despite the high cost

    When the EAA is ready to open this project up to group participation, they and we will announce the project and its contact info, both here and on the calcars-news list.

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