How To Do A PHEV Conversion Right


David Stands Beside The Most "Conversion" Model - The Toyota Prius

David Stands Beside The Most “Conversion” Model – The Toyota Prius

Years ago, before the Leaf and Volt were available, I was involved in several conversion of hybrids into PHEV. I even made this video about it back in 2010 (yep that’s me in the video). Most of the information here is obsolete now, but you can get a better idea of what I’m going to be talking about.

I noticed the PHEV conversion scene pretty much dried up within a year or two of the Leaf, Volt, and PiP coming onto the market. I was sort of surprised by that because I figured, if anything, this would encourage more conversions of regular hybrids as a cheaper alternative. But it didn’t. In retrospect, I think I know why. And I think I know how the problem could be solved.

Why the PHEV conversion market dried up.

  • Clean Install Of An Aftermarket Plug-In System

    Clean Install Of An Aftermarket Plug-In System

    For starters, the kits were hard to install for people who were not familiar with working on cars. Many mistakes were made causing the systems not to work right, or possibly damaging the car or the PHEV system.

  • The cost was very high compared to the return on investment. It was hard to justify on a financial basis because they systems didn’t work well enough to give the user an all-electric driving experience, thus it only reduced their gas bill minimally.
  • The systems had a reputation for being unreliable, constantly breaking and needing repair. This was my own experience as well, some systems not working more than a few days or weeks at a time without breaking.
  • Poor integration with the car’s computer systems. The car was not really aware of the PHEV kit and many solutions involved tricking the car’s computer. As such there was no instrumentation telling the driver about his battery status, or how many more miles he could go. Also the computers would sometimes throw codes, causing warnings on the dash and sometimes causing the car to stop working. This really kills the “driving experience” of driving a PHEV or EV.
  • The charging ports were usually rigged into the bumper, an uncomfortable place to plug in, and often leading to drivers forgetting the cord was still plugged in when they drove off. Without any mechanism to prevent the car from moving, damage could be incurred. Also the 120V charging plugs were not compatible with public J1772 stations.

Faced with all of these challenges, the prospect of buying a manufacturer built EV or PHEV suddenly seemed a lot more appealing, despite the higher price tag. However, I’ve thought a lot about it and I think it would be possible to resurrect the PHEV conversion business but it would require a lot of up-front capital for development. Here’s what would need to happen:

How do do it right!

  • A Sturdy Plug-In Receptacle Located In The Proper Place Goes Along Way

    A Sturdy J1772 Plug-In Receptacle Located In The Proper Place Is A Plus

    Most importantly, somebody would need to reverse-engineer the Prius (or whatever car you are using) hybrid computer. Then, reprogram parts of it and create a new firmware that could be uploaded into the hybrid computer. This would have several HUGE advantages, which I’ll get to shortly.

  • Instead of trying to just sustain the charge the existing NiMh battery pack, it needs to be removed. It could then be sold on the used market to recoup some of the expense. Then replace the entire battery pack with a Lithium battery pack. With the new computer firmware, the hybrid computer will happily accept this new battery and use the available power accordingly. This will also eliminate the need for any sort of expensive (and failure-prone) DC-DC converter, as well as the associated heat buildup.
  • Engineer a nice looking J1772 port and charge door that can be installed into the side fender of the car, much like a factory PHEV would have. The hybrid computer’s new firmware would also check to see if anything is plugged in before allowing the car into drive.
  • With the new firmware, the driver should be able to put the car into EV mode and have it stay there until the battery runs out or the user cancels EV mode. Also the NAV screen should be able to show the user the current state of charge on the battery, driving range, etc. The NAV computer may be separate from the hybrid computer and thus need its own firmware change.
  • As for how to market it – There should be no attempt to sell the system or even give a price for it. The customer should be unaware of the cost of the system. Instead, the company should buy up tons of used Prii on the used market and completely refurbish them at the same time adding this system and selling off the used NiMh battery packs. They could even repaint them or add their logo to the car somewhere. Then sell the cars at a price that should easily undercut every brand-new PHEV on the market. They should also be able to claim some government money for aftermarket PHEV conversion.
Aftermarket Plug-In Dash Controls

Aftermarket Plug-In Dash Controls

So, with this setup a customer would be able to order a car online or buy one locally that is already converted. It should have a price tag of under $20,000 and yet have the look and feel of a factory PHEV with around 20-30 miles of all-electric range. They can charge at public stations, drive on pure EV power as far as the battery will let them, and hopefully the system would be as reliable as anything from the factory. They should get the full PHEV experience and be able to drive their daily commutes every day on EV power with exceptions of really cold days when the heat is needed.

Having customers buy the car as a complete unit also has another HUGE advantage for sales. For many low-income customers, they might be able to get a loan for a car. But they might not be able to buy a car and fork over many thousands of dollars in cash for a separate PHEV system. But if it is all together, they should be able to get a loan for the whole car much easier.

Like Their Production Cousins A Heads-Up Dashboard Readout Giving All The Pertinent Stats Is A Must In Any Good Conversion

Like Their Production Cousins A Heads-Up Dashboard Readout Giving All The Pertinent Stats Is A Must In Any Good Conversion

This concept should not be any more expensive per-vehicle than the previous generation of PHEV kits because it eliminates many of the expensive components by just replacing the NiMh battery pack. The up-front cost would be the expense of reverse-engineering the computer systems for a new firmware. And by taking the price-tag of the system out of the equation, it would make it harder for customers to attempt to mathematically justify the cost since they would not be able to see the direct cost. The reliability should be much better having all of the conversions done in-house instead of at a variety of shops all over the country.

I still think the 2nd generation (2004-2009) Toyota Prius is probably the best target for such a system for several reasons:

  • The design of the car’s cargo area and spare-tire area has lots of hidden room for batteries and a charger..
  • The availability of used 2nd gen Prii on the market.
  • Their known reliability, especially of the electrical parts of the drive train.
  • Affordable prices of the 2nd gen on the used market.
2nd Gen Toyota Prius Couple With An Engineer Kit (20 mile range) Netted David About 100 MPGs on a 40 Mile Trip

2nd Gen Toyota Prius Couple With An Engineer Kit (20 mile range) Netted David About 100 MPGs on a 40 Mile Trip

The only real pitfall might be the top-end EV speed of the 2nd generation’s transaxle. It might be limited to 52 mph due to the risk of over-spinning the smaller motor-generator. (this was fixed in the 3rd gen Prius by adding extra gearing) Still, 52 mph is fine for anyone who commutes in city traffic. When driving on the highway, they’d just have to deal with the fact the ICE would be running and consuming a small amount of gas. Still, any Hybrid-Synergy-Drive based vehicle would be a candidate. Sorry, Honda IMA systems would be out of the question.

So I doubt I’ll ever see this happen. Any company willing to do this would have to make a large investment, and thus a large risk. There’s no guarantee of success. But I would still love to see it happen because it seems such a pity that there are all of these used hybrids all over the road that have the potential to be so much more, but probably never will be.

I often wonder if it weren’t for the patent encumbrances of the NiMh batteries at the time Toyota was designing the Prius, how would the car have been different? At the time, NiMh battery patents were owned by Chevron (thanks to GM for selling it to them) and Chevron stipulated that any use of the battery in a car would not be allowed to be charged externally, and that the car could only run on gasoline. Had this not been the case, I suspect the original Prius would have probably been a PHEV from day one.

Category: GeneralToyota


14 responses to "How To Do A PHEV Conversion Right"
  1. Anderlan says:

    Well, at least the full EV conversion scene is still vibrant. It’s a good thing, because it’s still a big part of the progression of EV drivetrain technology.

  2. Ocean Railroader says:

    I tried looking at a EV Conversion but we are very car illiterate and now with the flood of new electric car choices on the market it is cheaper to buy a new electric car then buy a old one and convert it.

    1. David Murray says:

      Indeed it is if you want an EV that can go 80+ miles and have nice acceleration. New is the way to go. It is cheaper to convert an old car to EV if you are willing to make some sacrifices on range and performance, or dare I say reliability.

      1. Ocean Railroader says:

        It might be more economical to convert a existing gas car to electric if you live in Australia do to the cost to import a new EV is so sky high.

        But personally the fact that a new EV has a grantee on it from a dealer or from a car company that is why I like the idea of buying new so much.

      2. BraveLilToaster says:

        I looked at EV conversion before the Leaf came out, and being very car literate and fairly mechanically inclined to boot, I was totally willing to try, except:

        1. Money. Or telling the bank “you want to do *what*?”
        2. I lived in a townhouse in the city. Which, from a “need a car” point of view, all but negated most of the reason for car ownership at all. It also meant that I didn’t have the garage to do the work.
        3. Converting modern cars is problematic. At least, if you want to keep such nifty features as “traction control” and “ABS”, because when the mass of the car changes dramatically, so do the calculations they use to make the magic work. Most converters work around this problem by removing these features entirely, but that just makes for another reason to buy new these days.
        4. The reliability of these conversions is a huge question mark, and depends greatly on your knowledge of converting and the skill (and time) you have to do the job right.
        5. Time. I have little kids, so… yeah.

        Thankfully, all we had to do was wait a couple of years for someone to build the electric hatchback that exactly fit our needs. That, and we moved to the suburbs because Grandpa. Which is a different and long story.

  3. James says:

    You had me nailed at negative reason ONE. Yet negative reason two was also
    nearly equal to reason one for not converting my stock Prius. You forgot negative
    reason 3 which would be approximately equal rationale for not tearing up a good
    stock Prius for PHEV conversion, and that is the voiding of the factory warranty.

    Not many but the most fanatical activists, or experimental engineers or somebody
    who thinks the end result could somehow profit fleet buyers….Would literally be
    insane enough to buy a $24,000+ car and begin tearing it up, ruining it’s value.

    When I bought my Prius, I had already been online and reading books about
    Li Ion conversion kits and fantasizing that if I somehow could scrape together
    9 or 10 thousand dollars, it would seem logical to justify a $35,000 Prius with
    no factory warranty. I am an artistic, creative dreamer-type at heart, but even I
    couldn’t fantasize THAT MUCH until coming back down to reality.

    I read Plug In America, and saw the early California conversions that made it
    to Washington D.C. to “prove” to Congress that PHEVs were viable. It all looked
    so good on paper until your negative reasons 2, 3 and 4 started to raise their
    very ugly heads. When videos started popping up on YouTube of Prius PHEV
    conversions on long trips that were showing maybe 10-15 mpg advantage
    over a long trip, I really started to wish OEMs would follow through on some
    of their PR press and really build a factory unit. I mean, COME ON MAN!, …
    All that tearing up, and I’d have to hire someone with expertise or rely on an
    electric car guru from a local EV group to help me because I am no electrician,
    nor computer genius, nor mechanic. The whole thing was so PIE-IN-THE-SKY!

    Your article is interesting fodder, but definitely, again – written by an engineer and
    enthusiast, because nobody in their right mind with any business sense would
    read past the second paragraph. The what-ifs are extensive, and the profit margins
    from this sort of folly would be paper thin to non-existent.

    But thanks anyway for a very interesting read, because it reinforces why major
    manufacturers with the resources and capital to make these things work
    and warranty-able. The costs for retrofits is sky-high, and the legalities and
    on, and on…would just make this silly. I waited for the PiP for years, driving
    my stock one, and eventually caught wind that those dreamy, nonsensical
    EREV ads in consumer magazines really might take shape in a Volt. At
    that time with all it’s ups and downs, the Volt finally came into reality with some
    sort of sense behind it, and of course – extremely expensive and seating 4.

    All in, I ended my 25 year ban on buying American or GM, and bought a Volt.
    Today, they can be purchased for much less than I spent. I should have
    waited a year or so. That said, I am very happy with the car, it’s overbuilt,
    exceeds expectations and makes the lousey Plug In Prius look like an afterthought
    by Toyota.

    1. James says:

      Sorry, no edit feature here – I should re-write the first sentence to paragraph 6
      saying instead, ” But thanks anyway for a very interesting read, because it
      reinforces why it takes major manufacturers with the necessary resources and
      capital to make these kinds of cars ( PHEVS and BEVs ) viable and warranty-able.”

  4. James says:

    David, I have to pinch myself sometimes, and remind myself how far we’ve
    come in a very short amount of time in history. When the Hymotion and other
    conversions were new news, and started many fantasizing about what
    would happen if we could go lithium and add a plug – it was only seven
    or eight years ago. There were four or five years ( including the infamous
    Compaq laptop battery incident which Toyota used as rationale to dump any
    ideas of using lithium packs ) wherein cars such as Volt, Ford’s Energis or
    PiP seemed like vaporware and never to see the light of day.

    Now with LEAF, Tesla and possibly BMW’s i3, we see a possible revolution
    in the making. Cars like your Prius PHEV conversion aren’t very long in
    the tooth, but they pale in comparison to what’s been placed on the market
    today. Reminding me of those hard days when those Prius conversions
    were just about all that was out there besides a $100,000 2 seat playtoy
    from Tesla helps keep things in perspective. It’s an exciting time to be
    sure to be a plug-in enthusiast! While waiting for Model E or GM to get it’s
    head out of it’s collective beancounter a** and making EREVs that make
    sense ( not ELR ), or a Volt gen II ( not looking so good ) sometimes feels
    like watching paint dry – it’s articles like yours that put it all in perspective
    and give us hope that EVs and PHEVs are here to stay!

  5. Cavaron says:

    I would support any such enterprise, but I highly doubt success. Let’s say they need 18 to 24 month to develop and test such a conversion system AND build up converting capabilities (like a very small factory or a larger workshop). What will be the price of an used 2010-2012 Volt or PiP by then? Compare it to an 2004-2009 refurbished and converted Prius. How much cheaper would it have to be, to be attractive? But maybe it could work with a good lease-deal or as a Taxi for privateer drivers. Could also be interesting for second hand car markets with cheap labour like India, South America, Afrika…

  6. Mark H says:

    I thoroughly enjoyed that, thanks for sharing David. And I enjoyed comments from James. You David actually did what James and I were reading about a decade ago. I was pretty busy during those years with my engineering firm.

    The real kiss of death for retrofits lives in your personal example. You made the conversions then moved on to buy both a Volt and a LEAF. I think we all would still love to know how many retrofits are out there.

    Maybe in another decade the HEVs millions will see breakthroughs that make it more practical to make the conversion.

  7. ModernMarvelFan says:

    Conversion no longer makes sense.

    Your #2 point on why the market dries up pretty much sums it up…

    There are about 3 types of buyers for “hybrids” such as Prius:

    1. Want to save gas and mainly save $$$
    2. Want to save the planet by being green or appear green.
    3. Just want a cheap and reliable transportation.

    The type 1 are upgrading to Volt and LEAF which are cheaper to operate unless they have long range miles need per day. Even the Prius Plugin after discount and federal incentives is about a mid level Prius cost anyway. Plus, in CA, most of the PIP buyers will get the Green Carpool stickers (most them bought the car for that reason anyway).

    The type 2 are upgrading to BEVs such as LEAF or Tesla b/c that is the latest “green” thing.

    The type 3 would care less about what kind of powertrain it is and they just want to drive their existing car as long as possible.

    Conversion market is “dead”.

    Like someone else said, it will only make sense to do a full BEV conversion right now.

  8. kdawg says:

    Do converted vehicles get HOV stickers? If not, that is a huge negative against them vs. buying a manufacturer’s PHEV.

  9. Open-Mind says:

    Wow … doing that to an expensive hybrid would take *guts*.

    For those who like to tinker, it seems the lowest risk path would be to get an old cheap non-running manual pickup, then replace its ICE parts with EV parts from a company like this:

    Such an old truck would be mechanically simple and have a solid frame to weld/bolt things to.

  10. GeorgeS says:

    Hey David. That’s my Prius (and a million others). I too looked long and hard at the Enginer kit but ended up discarding the idea. Hats off to you for having the guts to try it yourself. We still have our ’08 Prius. My wife loves it and is a bit like Charlie H when it comes to my Volt. I have to admit. The Prius is a fine little work horse of a vehicle…..not sure what we will do when it needs replacing as neither one of us like the Gen 3’s. I don’t think I’d buy the piP but a Prius with a pure BEV as a second car is really a perfect combination and that is what I may do next when my Volt lease runs out…….that is assuming GM doesn’t do squat on gen 3 Volt which looks more and more like a reality.

    Thx for taking the time to write the article.