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evric 12-14-2015 06:02 PM

2008 Gen 2 Prius Plug-in Conversion
My project to convert my 2008 Prius to make it Plug-in is now complete.
I used the 10KW kit from Plug-in Supply without the charger, batteries and BMS. The latter I purchased from within in Australia to save freight costs.
I used 76 Winston 40Ah prismatic cells in a custom steel frame.
The way I did this conversion left most of the trunk space available for strollers and car seats etc for my wife to cart the grand kids around.
At the moment we are getting around 2.4 Litres per 100Km (98MPG(US) or 118MPG IMP)) and very happy with this long term average over 1000's of km.
By charging each night we are now getting around 2000km to a tank of petrol.
In fact the other day I filled up when the petrol gauge was down to 3 bars... after filling I found that it only took 35 Litres so there was 10 Litres left which would have allowed us to go at least another 400km !

Please see the Blog on my website:

I'll put some photos up here soon...


Vman455 12-14-2015 10:57 PM

Wow! Very nicely done; I like that battery layout.

evric 12-18-2015 07:20 AM

This photo shows the layout of the 76 cells in the back of the Prius...

evric 12-18-2015 07:24 AM

This is a closup of how the cells are held down.

The threaded rod are welded to the base of the battery frame and the top nut/washer (silver soldered) combination (eventually covered with felt) supports the clear poly-carbonate cover.
In the final production, instead of the nut and split washer combination, I used Nyloc nuts (a special nut with a nylon insert crimped in), these offer great resistance against vibrating loose
Checkout the blog for more photos:

oldtamiyaphile 12-19-2015 09:37 AM

I bought my Prius with the intent of doing a plug in conversion, but it only costs five cents/ km in petrol (best case EV's quote 3c/km), so based on your 50/50 petrol/electric usage, the monetary saving is in the order of one cent/ km.

If the conversion cost was a modest $3,000, the pay back would take 300,000km.

Sad but true :(

evric 12-19-2015 04:39 PM

Hi Oldtami...
Thank you for your comments. Where did you get the 50/50 petrol/electric usage figure from? (hopefully not from my website)
That figure would be correct for the standard Prius. My conversion now would be more like 25/75 petrol/electric.
I worked out that even with a total conversion cost of around $7,000 (including 76 LiFePO4 cells) the payback would be around 270,000Km.
In the meantime I am enjoying a very quiet driving experience for most of the time... and less trips to the smelly old petrol station.

oldtamiyaphile 12-19-2015 08:03 PM


Originally Posted by evric (Post 502715)
Thank you for your comments. Where did you get the 50/50 petrol/electric usage figure from? (hopefully not from my website)
That figure would be correct for the standard Prius. My conversion now would be more like 25/75 petrol/electric.

The stock Prius might use it's electric motors 50% of the time, but 100% of that energy came from petrol. Compared to my car (and most other G2 models), you've halved your petrol consumption, so it's safe to assume that half of your car's energy now comes from the grid.

If electricity is free, then your fuel costs have come down to 2.5c/ km. In which case the payback would be around 270,000km. But electricity has a cost too (even if you have solar panels - you probably do- and produce excess power you'll get money back from the electricity supplier).

I've calculated around 4c/km (as have others) is the cost to fuel a Nissan Leaf. So if you run 50% on EV at 4c/km and 50% on petrol at 5c/km. You're only saving 0.5c/km.

That's a 1.4million km payback :eek:

3c/km for EV power is the best case scenario if you live where electricity is cheap or have a super efficient EV.

The only way I can see myself doing the plug in conversion now is if I did something like a 2kWh conversion, enough for ~10km of range, that would be enough for 100% EV usage on 95% of my Prius trips. So I probably use around one tank of petrol a year, but still, I'd only be saving 1c/km.

I realize that money saving isn't really the point of a project like this, but it still has to be considered. Just as a comparison I'm contemplating swapping the 4.0l I6 in my Jeep for a 6.2l LS3. People who've done this swap have reported a 2l/100km improvement in economy (going from my current 12 down to 9.5l/100km). That's a 2.7c/km saving but still 370,000km until payback...

evric 12-19-2015 08:28 PM

I don't really want to keep this fruitless discussion continuing, but I would just like to say that the long term average of 2.5 Litres / 100km consists of driving which consists of much hill work and high speed driving(by my wife, most of the time). Both of these types of driving are not suited to using the Prius in 100% electric mode. I can drive it 100% electric (and I do) around the metro area (on the flat and only up to 60km/hr) for distance of around 75km... and loving it.
Over and out.

Baltothewolf 12-20-2015 04:24 AM

Very well done. I wish something like this was available for the insight, I can imagine 200+mpg averages would be doable. Depending on the commute distance of course.

Daox 12-20-2015 08:20 AM

Great looking conversion! Thanks for sharing. I like how the pack doesn't intrude into the normal usable space.

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