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This article has just begun and needs a lot of work yet... It could very well be renamed aslo...

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Email 1

Subject: Jim Fell/UKK conversion
From: Felix Kramer 
Date: Thu, 08 Feb 2007 06:47:42 -0800
To: Ryan Fulcher 

Jim asked for help from you getting this info up on EAA-PHEV
> Date: Mon, 05 Feb 2007 16:12:39 -0800
> From: Ron Gremban 
> Organization: California Cars Initiative
> User-Agent: Thunderbird (Windows/20061207)
> To: Jim Fell 
> CC: Felix Kramer, Tom Driscoll, Jack Wiren, Eric Simon 
> Subject: Re: Conversion
> Nice looking job, Jim!  And it's great to see a conversion in G.B.  Thanks for sending your results and photos.
> I recommend you post your pictures and results to  You will find a very interested audience and knowledgeable people to interact with.
> Many people have had mixed results with Thundersky cells, so I wish you well.  Even with half the rated 90Ah capacity, however, you should have great electric range -- and your four spare cells may come in handy.  What are your provisions for cell cooling and temperature equalization?
> I multiply 2.2kg * 56 = 123kg = 271 lb, about the same as with 20 BB Battery modules.  You are getting much better mileage without going into EV-only mode at low speeds than I get with my driving regime, even considering your larger gallons.
> Unless your conversion will be driven almost exclusively at highway speeds, I do recommend going into EV-only mode when possible (below 55kph and with many other limitations), as you will get even dramatically lower gasoline usage.  The PFC40 gives you more control over output current and voltage than with the contactor used in CalCars' DIY conversion.  I have found that 30A output to the OEM battery is a minimum to stay in EV-only mode continuously; 40A maximum is desirable.  The higher (50-100A) currents you mentioned I talk about are because of a lack of fine control with just an on-off contactor, and/or to prop up the OEM battery's voltage during maximum acceleration or hill climbing.
> If you adjust the PFC40 to switch between two maximum output voltages -- 225V and 242V -- you can use the algorithms I developed for the contactor with little change, just by translating contactor ON to the high voltage and contactor OFF to the low.  You can't go wrong, if you want to view CAN bus information and get more careful control, than to get a CAN-View device from Norman Dick (
> /ron
> Jim Fell wrote:
>> Hello Ron
>> I have just completed a 2005 Prius conversion using the PFC40 system. It is early days but the system seems to work very well and the fuel consumption has improved remarkably.
>> For some years I have messed around with ev's and had a Fiat Seicento conversion with 60 Thundersky Li-ion cells of 90ah capacity. These cells were new in January 2005 the same time as we got our first Prius. The Fiat was sold, without the pack, charger and the BMS in October 2006 and in December these were fitted into our second Prius.
>> I could only fit 56 cells into the Prius and their capacity is somewhat reduced from 90ah so I set the current drain initially to 15 amps from the pack. The fuel consumption went from 55mpg to about 80mpg immediately over the few short test runs. Lifting this current to 20 amps I did one run at 100mpg and a few others at about 90mpg. As the pack settles down I will go up to 25 or 30 amps. Typical of Thundersky cells the internal resistance of some of the cells is quite high. I never needed to go over 50 amps in the Fiat and typical currents used were 25-30 amps for speeds of 30 to 40mph.
>> I think with my conversion I am looking at assist type add on performance rather than converting the Prius to an ev for some of the time. I note that you are talking of currents of 50-100 amps, these would not be possible with my pack.
>> A few facts. The TS cells are Li-ion and weigh 2.2kgs each, the load deck is lifted about 75mm (3 inches) because of the cell height. The BMS is my own design based on a PIC 12F675 (one per cell) and gives optocoupled high volts ( for charging) and
>> optocoupled low volts ( for discharging). Charger is a PFC20 modified to remotely control current from the BMS and log time and ahours into the pack.
>> The coupling to the Prius OEM pack is with a PFC40 as delivered.
>> The cells are heated to 15 degrees Centigrade with 10 heaters below, total wattage is 150 watts
>> Connection of pack and PFC40  are with four Kilovac DC contactors.
>> Can bus data is via a simple instrument with LCD described in the Wikipedia interface section.
>> The control system is still in a state of flux as I am learning how the Prius reacts to having an extra 10kwh of energy injected into it's pack.
>> I attach a few photos. Please feel free to put them on the wiki site, they may encourage others to take the plunge.
>> Remember our gallons are a bit bigger than those in the USA
>> My experience has been that it is much easier to put an add on pack into a Prius than to convert a car from ICE to ev.
>> At the end of the day you have a useable vehicle that can go anywhere at real highway speeds without the worry of running out of charge.
>> Regards
>> Jim Fell
>> Peterborough England

Email 2

Subject: Jim Fell UK #2
From: Felix Kramer 
Date: Thu, 08 Feb 2007 06:48:42 -0800
To: Ryan Fulcher 

> Date: Thu, 08 Feb 2007 09:43:02 +0000
> From: Jim Fell 
> User-Agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)
> X-Accept-Language: en-us, en
> To: Felix Kramer 
> Subject: English Prius Plus
> Jim
> I hope you can get a description up at, and perhaps send me something that's a mix of a description of who you are, why you did it, how it differes from other conversions, how long it took, etc., that I could send out to CalCars-News. I'd also like to put you on the list at
> Regards, Felix
> Hello Felix
> Thanks for your email.
> To try to give you some more information.
> I am a retired Electrical Engineer living in Peterborough, England. Having retired in 1995 I have always been interested in electric vehicles and converted a Fiat Seicento into an EV in 1999. This had lead acid batteries and performance was not that good, 25 miles at best and 50mph. Over the next few years I changed the pack to Thundersky Lithium and had much better range although acceleration was poor. This car did quite a few miles and rallies, finishing the London to Brighton ev rally in 2005 and 2006. After the "ev season" in 2006 I stripped out the pack and BMS then sold the car. The new owner is fitting lead acids to make an urban ev for use in London.
> In December 2005 we bought a new Prius, essentially my wife's car. The plan was to see how practical it would be to add further battery power to make a plug in hybrid. After a few years of ev ownership I realised the serious limitations with current battery technology. Since I was a lad the great breakthrough in batteries was always just about to happen.
> We liked the Prius so much, 60+mpg summer, 55+ winter, I traded my trusty Saab in for a second, high mileage Prius to convert.
> My wife wouldn't let me touch her's but I did develop my CANbus instrument on it.
> I looked at Rich Rudman's DC/DC system first and thought it a bit pricey. I had used a PFC20 as my ev charger so I knew his kit work and you sort of get some support from him. What I was really waiting for was the published drawings of the resistor method.I think these came out in November 2006. In the end I went for the PFC40 having looked at several ways of getting enough cells in the car to get the voltage higher than the NiMh pack.
> The delivery from Rich was very slow, I was just about to cancel the order when it arrived.
> Installation was straight forward, I have welding and machining facilities so made a 20mm x 20mm hollow section frame clad in aluminium sheet. The TS cells need compression so I have 7 rows of 8 cells with steel end pieces, each with two 6mm screwed rods pulling the row together. See the photos.
> The stick on foil heaters are on the underside of the aluminium sheet. The heaters have a control box and sensor in the centre of the pack. This is on a timer for cheap rate electricity and consumes 133 watts. The centre cells are about 18 C and the outside cells are about 16 C.
> Wiring is very simple, two contactors (single pole NO) connect the Li pack to the PFC40 and two contactors (single pole NO) connect the PFC40 output to the NiMh pack. There are two DC fuses in the line fron the Li pack.
> The Li pack is split into 3 sections by two no load isolating switches.Just for safety when working on the car.
> The PFC40 has internal relays that switch the mode and voltage trip point. I don't use it as a charger so only need to switch two of the relays depending solely on the SOC read from CANbus. I have a PFC20
> It is early days and I'm still playing around with the configuration. It is a big fuel saver and I think it's the best way to go until battery technology really does improve. I will keep you posted how the system works in the long term.
> Feel free to use any bits of this, edit as you see fit.
> I'm not sure how to get my previous short version on the Wiki page, would you mind sending Ryan a copy an ask him if he would be so kind as to do this?
> Regards
> Jim