I've been asked a lot over the past few weeks to explain all about my Plug in Prius, who is affectionately named Velma. 
Velma - the Plug in Prius, charges at a Bristol charge point.
My previous plug-in car was a 1998 City El EV. The El was sold in August 2008. I miss her, but I couldn't justify having two cars (at least, not at that time). I was sad to sell her but had no real option to keep her. (I really wanted an EV, since after nearly two years of driving on pure electric I was completely converted!) The options available to me were very limited and I knew I didn't have the time or garage space for a full-blown conversion. Instead I set about finding a cheap Toyota Prius. My partner Kate already had one which we'd purchased new in 2007 and the fantastic ride and excellent fuel economy sold it to me.
I'd tried to buy various EVs new, but no-one in London would sell me an EV 120 miles away. At least, no-one who would service the car and offer warranties AND had a car I could afford... I had already known that I really wanted either a Tesla, or a Rav4EV. The first was out of my price range and the later, although I'd been totally smitten by a drive in one in 2007, was too difficult to import to the UK from either the USA or Japan.
With my choices really limited (and under a pressure to find a suitable vehicle in a two week vacation period) I settled for a Prius. At least, until a 100+mile, motorway capable EV came my way... Part of my bargain with Kate was that I was allowed to eventually convert Velma to a PHEV. I'd followed the CalCars project with interest ever since Kate had got her Prius, so we knew it was possible. I'd also ridden in the commercially converted AmberJac Prius and had seen fellow DIY converter Jim Fell's Prius. Jim, like me, has an interest in EVs and had converted his own EV several years ago. As I'd already upgraded the batteries in my City El with a very complex Battery Management System (BMS) and charger system - I had less worry about doing the PHEV conversion. Listening to Jim talk about his conversion made me want one even more. The problem though was cost. In the US, there's quite a few options now available to anyone wanting a PHEV Prius. Ranging from simple DIY kits costing upwards of $5,000 US right up to expensive 'company installed' units such as the Hymotion Prius, there are many ways to get a Prius with a plug. We could afford some of the cheaper options there - but in the UK there were only two options.
Pay Amberjac a huge sum of money to convert Velma into a PHEV (currently. £17,250)
Or...
Do a D.I.Y. Conversion and suffer the consequences if it went wrong.
Since I didn't have £12,000 I really had to find a way of getting that PHEV by doing my own conversion. Parts from the states were an option. Several suppliers of PHEV kits were willing to ship the battery box, electronic circuits and wiring looms from the US to the UK. I would then have had to find appropriate batteries and a charger here. The cost was still a little expensive and the kits were mainly based upon heavy lead-acid batteries which at most, would last three years in the back of my car. Not only that, but the lead acid kits added so much weight to the back of the Prius that you'd be faced with a low-riding rear or a swap out of the rear shocks. A company in CA do sell uprated shocks - Luscious Garage. Owned and run by a woman, I have a soft spot for them. But of course, this added cost added money to a build that I really wanted on the cheap. (Normally 'on the cheap' means 'Inferior quality'. Of course, I make no bones about my solution being better than the commercially available ones out there because, quite frankly, it isn't. Hymotion's Lithium Ion solution is elegant and sophisticated. It also does more miles in EV mode than my car will. Mine just cost less and as a consequence I'm happy to live with a reduced range compared to some of Velma's big brothers and sisters.)
With lithium out of my price range for this conversion and lead being too heavy I decided to look into using the original battery chemistry the Prius shipped with, NiMH (Nickel Metal Hydride). As luck would have it, a chap by the name of Norm who runs a company in Canada called Hybrid Interfaces has been there and done that.
Using a set of battery packs from scrapped Prius he was able to build an additional three Prius battery packs into the back of his Prius to allow for four times the original battery capacity. In order to allow you to use that extra capacity, Norm developed the BMS+, an ingenious device which sits between the original Prius battery and the car's CAN Bus communication system. Combined with Norm's excellent CanView device, which allows you to see what's going on inside your Prius' CAN Bus system, you're half way to a good PHEV. You don't strictly need CanView to enable a PHEV Prius conversion using this route, but it sure helps to know what's going on if you want to check everything is healthy!
(It should be noted that as of early March 2009, Norm is only able to make another ten or so V3+ Can Views. These are the ones which are compatible with 2004-2006 Prius. Norm will continue to sell CanView V4+ for owners of 2006-2009 Prius, but these require an external monitor due to changes in the way the Multi-Function Display (MFD) in the Prius has been modified. If you have a high resolution MFD, you'll need a V4+ CanView.)
With the CanView installed some months ago I was getting close to my PHEV dream. I'd even managed to salvage some Prius batteries from scrapyards. It's important to find batteries which are not damaged and which come from the same model Prius as the one you're converting. You really shouldn't use 1997-2003 Prius batteries in a 2004-onwards conversion. Converting a pre-2004 car is not dealt with here and is believed to be extremely difficult. To my knowledge, no-one has done that yet, and the CanView and BMS+ would be incompatible anyway. Try google! For my batteries I'd found a 2006 Prius which had been subjected to a front-end flood from Cornwall, and a 2008 Prius which had been in a garage which had caught fire in Norwich. Luckily both cars had intact batteries which happily displayed open circuit, no-load voltages of 214+ Volts.
A happy Nikki with a Prius battery pack for her project
I was one happy girl! With batteries, electronics and a vision all I had to do was find a charger. NiMH batteries are a bit tough to charge; They continue to accept a charge even when they've reached full. This energy can't be stored and is turned into heat instead -Not good when you have a whole pack of them in the back of your car! To prevent fire in the original Prius, Toyota only charge the batteries to 80% of their total capacity, since it's this last 20% of charge which can lead to overheating (or thermal runaway as it is better known).
I'd been advised by Norm and other PHEV pioneers that a final charged voltage of 238V would be the safe limit that I could charge my pack to. I would need a charger which would cut power immediately when reaching 238V and not allow any kind of float charge as used with Lead Acid batteries.
That's easier said than done when most commercially available chargers are designed to be used with Lead Acid batteries. At least, that's the case when you're dealing with a pack which operates at 238V. A few years ago, companies who made and supplied electric vehicle chargers would not have entertained the idea of making a charger for NiMH batteries which could have been purchased off the shelf. Sure, NiMH chargers existed, but were generally very expensive and out of my price range. Or they were part of a factory-built EV, such as the RAV4EV. But recently charger manufacturers have started to reaslise that customers do want to use more advanced battery technologies in their vehicles.
My luck was in. I turned to Zivan, who make the NG range of chargers. Initially I hit a brick wall - the sales team did not know of an appropriate charger curve which could be used on NiMH batteries and said to try elsewhere. Giving up, I contacted Brusa, whose very expensive charger range came with computer software to manually adjust any parameter of the charging process on-the-fly. Brusa's head office told me that I should deal directly with the UK agent. Unfortunately the UK agent for Brusa was AmberJac - the same people who charge £12,000 for a plug in Prius and, quite possibly, the reason why there aren't more PHEV Prius in the UK.
I wrote many emails to AmberJac and heard nothing. Even a few telephone calls with messages for the sales team to call me went un-returned. I guess they didn't want me making a cheaper PHEV conversion... That was it! I was stuck in a rut and had no-way of getting past my Charger dilema. Fortunately though, one of the sales team at Zivan had passed my original enquiry email onto one of the engineers who, as it happened, had just returned from a trip to Zivan's head office in Italy, where the company had been working hard on developing new charge algorithms for more advanced battery chemistry. NiMH was one of them!
I was asked if I'd like to order a charger and after a few weeks of correspondence back and forth between Zivan UK agents Electrofit-Zappi and various PHEV pioneers I was able to order a specially adjusted Zivan NG3 charger, with an SX charge curve, cut-off voltage of 238V and a maximum charge current of 4A. Success! The Zivan NG3 arrived just before Christmas 2008 and was huge. I couldn't believe the size of it, but with some planning I started to think about how things would work in my Velma. I'd been involved in a car-crash a few weeks before the charger arrived and for most of December was without my Prius - she was being fixed up by a local repair shop and I was attending physiotherapy for whiplash injuries following our being the filling in a German car sandwich. 2009 soon followed Christmas and I was back at work. As Velma is my main and only way of getting around for work I knew I couldn't take her off the road for two weeks to do the conversion. No, this had to be a piece-by-piece effort.
You can't hack a Prius in snow! Hampered by snow and freezing temperatures I was unable to do anything to my project for nearly a month but at the end of February I finally was blessed with enough free time and good weather during the early spring break that I was able to install the high power cables and modify Velma's loom. Using a spare wiring loom from a scrap Prius I was able to integrate Norm's BMS+ into Velma's wiring system without cutting any original wires and, with a bit of cunning, used one of the scrap battery covers to modify the original battery enough to allow me to pass out the 6AWG cables I'd need to attach the additional batteries.
These two battery packs add extra beef to the conversion.
With both additional batteries modified to include a 50A 600V Anderson connector to allow me to quickly and safely connect and disconnect the additional packs, I was able to trim the additional packs to help them fit in the trunk. Sadly though, even with all their excess weight trimmed, they just wouldn't fit. I had to figure out a way of mounting the batteries safely and followed the principals set out by Norm in his excellent description of how he mounted his batteries, so I'll not repeat it here.
For a few months I drove with the batteries securely lashed to the trunk floor with copious luggage ties - just to make sure the batteries worked correctly. It was all very Heath Robinson and rattled a lot - Not at all what you want. I'm pretty certain too that it wasn't all that safe. I ended up having to keep all my luggage on the back seat too, which was highly impractical. I needed to figure out a permanent mounting solution.need to quickly remove the batteries!
Planning some time where both the weather was good (I don't have a garage big enough for me to work on the car in) and when I had three days when I didn't need to use the Prius was quite hard. After a few months of getting by with my temporary 'testing' solution, I was able to spare some time in the half-term spring break in the school system around the May bank holiday.
Initially I'd planned to fabricate a sheet aluminum box which would hold all two batteries in a repackaged environment - using just the under-boot (trunk) area. The batteries would hinge upwards and also would allow for access to the spare wheel. It soon became apparent, however, that the box would be both too heavy to lift with two batteries inside and would also have no room left for cooling or ventilation.
Shortened Battery pack
Instead, I decided to split the two batteries up into three physical packs - with the third pack being electrically split between the two packs.
All of the packs were repackaged using aluminum angle, which was drilled to make new battery mounting brackets.The top two packs (the ones I planned to have on display) used the original compression ends and shortened studding - while the bottom one used wooden compression ends. As this would be hidden from view in the spare wheel well I didn't mind so much.
It was then a matter of figuring out how to mount the batteries. I wanted a conversion option which didn't require any drilling and, should I decide to sell the car, be completely reversible. That meant no welded bits and certainly no unsightly holes. By this point I'd decided that minor cosmetic alterations, such as drilling and cutting the original lower trunk liner, would be acceptable as they're quite easy to buy second hand from scrapped cars.
Bottom 'pack' bolted to the car's spare wheel mount
Using an old section of square box section and an appropriate M8 bolt, I was able to bolt the bottom pack to the floor of the car using the hole designed to take the spare wheel nut.
With the bottom batteries securely bolted in place (and forced ventilation provided using the built-in drain plugs on the car) 
Battery packs are bolted to the original moulded sub-trunk areaI was easily able to modify the original moulded ABS under boot (trunk) liner to take the two remaining physical packs.
In the photo opposite the blue and yellow insulation helps me keep track of which battery pack is electrically connected to which pack. It also prevents any nasty short circuits!
It is now mid June and I've been driving the plug in conversion now for nearly three months and everything has performed impeccably. Unlike many PHEV owners I have to drive long distances as part of my day job and over the past three months I have covered nearly 2,800 miles. This includes some long-distance trips down to London and back - a total of over 200 miles per trip. My particular PHEV conversion works best around town, when I can drive in all electric mode at up to 32 mph for 10 miles without turning the engine on. For longer distance trips my pack can improve my car's fuel economy from 50 mpg to over 90 mpg for the first 20 to 30 miles. Once my trip goes beyond this figure the car goes back to operating like a standard Prius, although all three packs can be used to capture more energy from regenerative braking than a non-modified Prius can.
You can watch a little video (below) of me talking about my converted car and sharing why I like it so much. It's not a pure electric vehicle and yes, I wish it were - but for now it's a good intermediate measure for someone who wants a low emissions vehicle with a long range.
After the success of my own conversion I've been encouraged by several people to start converting other people's cars. Given that the batteries I used were second hand and fine for my own conversion (I have no preconcieved ideas about the longevity of the pack and can tackle any problems if they occur) it is going to be hard for me to repeat that exact conversion on other people's cars.
However, I'm currently working with several people to bring a UK Plug in Prius conversion company to the South-West of England, selling installation kits and performing installations for the whole of the UK. At the moment we're looking for interested parties to participate in the initial first wave of installations. Cost-wise we're anticipating a fully-fitted installation of a lead-based plug in Prius conversion kit to weigh in at somewhere around the £4,500 inc. VAT mark - giving between 10 and 15 miles of EV only operation and retaining the use of the spare wheel well, and a much more palatable and affordable solution than the £17,250 Amberjac option! We are also investigating other installation options too, between £5,000 and £7000 in price.
If you're interested please drop me a line [nikki at aminorjourney dot com].