Green Transportation

Moving toward a transportation system that fuels healthy people and a healthy planet.

Converting your Prius or other Hybrid into a Plug-in Electric

3/22/2012 8:34:55 PM

Tags: Enginer Kit, Electric Vehicles, 100 MPG, David Hrivnak

Move over Chevy Volt, there is an alternative, now!  Imagine improving the gas mileage of the already best in class Toyota Prius an additional 25% on in-town trips. I discovered this is possible with the installation of the 4KW Enginer plug in upgrade. This boosts the battery capacity 4 fold from the base 1.3 KWH system in the base Prius.  For the last 18,000 miles we have averaged 43 mpg with our 2005 Prius in real world driving in the hills of NE Tennessee. With the Enginer kit, we have seen our mileage jump to 55 mpg over the last 2100 miles. A friend in the Knoxville EV club claims 120 MPG but admits he drives VERY slowly.  he system, installed on Feb 5th, has given us our five best tanks to date. Our results are shown below.

 Prius MPG Graph 

Having converted my truck to a plug-in hybrid and building an all-electric Jeep with Leslie Grossman of the Knoxville Electric Vehicle association, I expected to find challenges during the installation.  To my surprise, the kit came with all necessary pieces and parts and after about 12 hours of work the system was up and running.  If I understood how the high voltage relay worked on the Prius, I would have saved about 5 hours as I panicked when the car would not start.  A revised install manual includes these extra details.

The image below shows the kit with the charger, DC to DC converter, BMS, and batteries together in a neat box that fits under the existing trunk floor of the Prius. 

 Figure 1  Enginer Kit in the box 

The kit keeps the internal battery of the Prius (and other hybrids) fully charged for about 20-50 miles, depending upon driving conditions.  Because the internal battery maintains a higher state of charge, the car slips into EV mode more often allowing the engine to stay off much of the time.  Since we rarely run in pure EV mode with all the hills, we drive about 50 miles before the Enginer kit is out of power.   After plugging in for a a few hours the system is once again ready to go.

 Enginer Prius Kit 

The kit is not for the faint of heart, as the dash needs to be pulled apart to install a switch on one side and to and make 3 connections on the other side.   Then, the right side channels and rear side panels are removed to run the wires to the dash switch, tie into vehicle power and feed the BMS.   Finally one must drill six holes through the trunk floor and frame to secure the box. 

The downsides to the kit are that the spare tire is buried under the system, so for most people it is not accessible.  We solved this issue by sticking a can of Fix-a-Flat® in the car, similar to what Tesla does.  Another downside is that you lose the handy hidden storage under the floor.  But the Prius still has about 20 cubic feet of storage:  nearly double what is available in the Volt.  When fully installed the system is invisible.   Our “trunk” looks like that of any other Prius.  The only obvious differences are the plug mounted on the rear bumper for charging and the switch on the dash to turn the system off  with the status LEDs

 Enginer Prius Kit 3 

After wrestling months getting hard to find parts and waiting for replacement parts on my other conversions, it was fun to be able to finish a project in a weekend and experience the results.  While one does not gain a full EV “grin” from such a conversion it does take us one more step toward reducing our need for  imported oil.  At a price of $2995, the Enginer system is more affordable than other conversion options s and a good way for people on the fence to gain experience and a better insight of what is involved in a full conversion.  For more details and other sustainability projects please see or for more kit details.

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5/27/2013 9:30:15 AM

If you are in Europe a similar kit can be bought from MD-Tech at   Though there are some notable performance upgrades in the power converter output and BMS function and design. Retails at €3500 for a 4kWh kit can go 40km at 38km/h.

Brenda Martin Hrivnak
4/1/2012 9:57:50 PM
Again there is a grain of truth. But even if you get your power from 100% coal based electricity the emissions from electric drive are 50% less than a gasoline car according to the EPA. I did my own analysis using data from AEP (our local provider) which is 80% coal and A Nissan Leaf has 41% less emissions than a compaable Chevy Malibu. Granted powering the car from a solar array is even better but even if you use coal based electricity we are better off. Then there is the added benefit that the power is 100% American produced and not based on imported oil.

Robert Krayer
4/1/2012 12:48:48 PM
I understand that this is supposed to be some sort of great thing for the environment. But, in order for electric cars or hybrids to be truly effective the owner needs a home generation system of some kind. Something like a solar electric, wind, water turbine to produce the electricity needed to run one of these things. This is not an option for me.

David Hrivnak
3/31/2012 8:11:23 PM
You are right most new technology is expensive. So there is not a quick payback. Just like there was not a quick payback for a $2500 bag phone in 1990 or the first generation of PC's. But fortunately there were the early adopters who paid the price for the early R&D and showed there was a market and now we get free cell phones with a basic plan. But as I look down the road I can not see how gasoline will become cheaper. So part of my reasoning is a political statement saying I want buy American made power not imported oil. Someone needs to lead the charge or we will soon be broke and still not have an alternative to gasoline.

Eric Poston
3/30/2012 7:33:59 PM
According to the engineer website, the 2KW kit is $3495. At current gas prices, that's over 900 gallons of regular unleaded; even in my 8 year old Honda Odyssey, that's almost 25000 miles - more than I drive in a year's time. In a prius at 43 mpg, that's amost 40,000 miles - two years of driving - just to break even. I'll assume that running in full-electric mode would have reduced emissions compared to gas, but that's the only advantage I can see, especially given the fact that the hybrids cost quite a bit more than the standard version with a gasoline engine.

3/28/2012 12:18:07 PM
I appreciate your real-world experience with an electric vehicle. Your figures give me more respect for the EV.( Don't quote the EPA for references, tho. They have a political agenda and are always being reprimanded in court for using false science)...Your figures on coal plants support what I said: only about 1/3rd of the energy in the coal makes it to the user's outlet...EVs certainly have a niche where they are practrical, but they are not THE solution to the transportation/energy problem ...I've cut down my driving to 5000mi/yr, with half of that by MC @50mpg. The other half involves 100-120 mile round trips for supplies. An EV wouldn't cut it there....Wood gas burner next on my DIY list; I've got plenty of my own biomass ;-)

David Hrivnak
3/28/2012 2:20:22 AM
Efficiency varies a lot especially in an ICE depending upon condtions. Cold idling in a city would be less than 10% but warm at 45 mph it is normally better than 30%. But a coal plant is normally warmed up and operates continously and is normally above 40%. Our electrical grid is actually quite good operating at better than 93% efficiency. The EPA says 1 gal of gasoline is equivalent to 33.7 KWh, enough to allow me to drive my electric 135 miles at 65 MPH. You really owe it to yourself to drop by the local Nissan dealer and test drive a Leaf or your Chevy dealer and try a Volt. I think you will be impressed. Granted they are not inexpensive but new technology is always costly at first. I have over 9000 miles of gasoline free driving in the past year. The Prius is my wife's car. Also look at this from the Dept of Energy "Electric powered automobiles, even using the most CO2 intensive coal produced electricity, produce half the emissions of gasoline powered automobiles.[25] US Dept. Of Energy" So it is not just me. Check out and drop me an e-mail if you want my certifed calculations to show a 41% reduction in CO2 between a Chevy Malibu and a Nissan Leaf.

3/28/2012 12:10:03 AM
Thanks for the reply. Your comment on the (in)efficiency of the ICE is a non sequitur: the Geo still got 50mpg even with its inherent inefficiency. [Actually, ICEs are only about 15-20% efficient.]...An EM may be 90%efficient with the energy delivered to it, but generation & transmission of the juice is very inefficient. If the elect. comes all from coal, more co2 is emmtted by an elect vehicle than by a standard vehicle....When you get 200 miles from 50kW-hr, how fast are you driving? I have no practical experience, but by calculation, driving at normal hyw speeds, cost of elec. should approach cost of gas.

David Hrivnak
3/27/2012 9:49:55 PM
There is a grain of truth to what you say but because an electic motor is over 90% efficient versus 30% for gasoline the overal cost and pollution are less. I do have a full electric car and can and have driven 200 miles on $4.25 (50 KWh) of electricity. When I use TVA's average of CO2/KWh it beats the Prius and any other gas car on both costs and emissions.

3/27/2012 8:23:49 PM
less than 30mpg. The GM Geo was getting 50mpg 20 yrs ago.

3/27/2012 8:22:34 PM
Because 60% of the electricity in Tennessee is generated from fossil fuel, and transmission of electricity is not very efficient, your 55mpg is more correctly viewed as

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