So you’re thinking of converting a vehicle to electric?  A major decision to make right at the start is to choose your ‘Donor Vehicle’.  Makes it sound like it will be giving up its heart – I suppose that’s not too far off…

With our 1992 Subaru Brumby, the consideration went something like this:

  1. I wanted to do an electric conversion.
  2. We had a Brumby.
  3. The Brumby started leaking oil out of a head gasket.
  4. My wife and I had a conversation, where I may have overplayed the possible expense of the engine repair, and underplayed the possible expense of an electric conversion.

Most electric conversions start out like this – the owner is attached to their fossil vehicle, but wants to progress.  We look for justifications that the vehicle we own is the perfect candidate.  Sometimes we are even correct!  Having said all that, there are some people who do take the sensible route and actually choose their donor vehicle to suit a conversion.  Use this guide to select the perfect vehicle to buy, or to try to convince yourself that what you have is good enough.

Purpose & Style

What sort of vehicle suits your lifestyle?  A large 4×4 because you go off-road and tow things?  Or a small city hatchback?  Perhaps a ute?  Or even a boat!  How many passengers do you need to fit?
These are the sorts of decisions you make for any vehicle purchase.  However, the limits of a converted vehicle may not suit all purposes.  Converted EVs are not generally good for long trips, as large batteries are expensive.  Conversions also cannot use DC fast chargers (not normally, anyway).  So you might decide to use your conversion for shorter trips, and keep a fossil vehicle (or a production EV) for the longer trips.  If your longer trips are only a few times a year, vehicle hire might actually turn out to be the cheaper option.
4WD vehicles can be converted, with the simplest way being to use the existing 4×4 gearbox.  Electric drive is great for towing and off-roading, with plenty of torque even at low speeds.  Don’t expect long distances on the highway from most 4x4s though, as they are not typically designed with aerodynamics in mind.
Vans and utes can be good choices, they will often have capacity for the extra weight of batteries.  And for deliveries around town, with lots of stop-start driving, electric is unsurpassed in fuel efficiency and driver comfort.
Once your conversion is complete, you might like to show it off! A classic car, converted to electric, will turn heads at car shows and eco events alike.  And a conversion will be very cheap to run, so you might as well use it for your daily drive.

Age

The advantage of an older vehicle for a conversion is simplicity. 
An Engine Control Unit (ECU) is a computer that controls many aspects of the vehicle operation.  If you remove the E from the ECU, then it may decide that it can’t C, and it may take that out on U.  For earlier models the consequence of this might be as simple as a ‘check engine’ light on the dash.  But later models will not allow you to drive the car.  You may be able to remove the ECU, or fool it into thinking that there is a properly operating engine present.  But it is much simpler on a vehicle that was built before the days of the ECU.
The car you convert must maintain all of the safety features that it had when sold.  Airbags, ABS, vacuum brake assist etc.  must not be disabled.  Older vehicles are less likely to have these features, and so are simpler to convert, but are correspondingly less safe to drive.  If safety features are controlled by a central ECU then you’ll have your work cut out for you to keep them operational once you remove the engine.

Automatic or Manual?

Automatic transmissions can be used in EV conversions, but it is a simpler exercise to convert a manual.  This forum thread is long and involved, going into the fors and againsts:
In Australia, where manual gearboxes are very common, I’d recommend buying a manual.

Size

The batteries for your EV will need to go somewhere, and in general a larger vehicle will have more space.  But smaller vehicles are lighter, and therefore will require a smaller battery! Batteries can be located under the bonnet, in the boot, in place of the fuel tank, in place of one or more passenger seats, under the tray (of a ute) etc.  Batteries can be divided up into more than one location so that the weight is distributed sensibly.
Once you’ve done all the measurements and calculations, most micro vehicles end up being too small for an effective conversion.  They are made to have zero wasted space, so fitting a decent battery in them is a real challenge.  A tiny car conversion is normally one that can’t travel far on a charge.
Very large vehicles are also not often converted, as a large battery is required to give them a good range, and a large battery is expensive.  Having said that, if you have the money then a large vehicle is probably going to give you more options for placing the battery, and might therefore be easier to convert.
The vehicles most often converted are those with an unladen weight between about 900 kg (like the Brumby) and 1200 kg.

Weight

The rule of thumb with conversions is that your final vehicle will be the same weight as the original – until you add batteries.  So if you add 200 kg of battery, the vehicle will be about 200 kg heavier than stock.  To get your conversion certified you must not exceed the original GVM of the vehicle.
In Australia, NCOP 14 describes the rules regarding conversion to electric drive.  NCOP 14 states that you must also allow for the passengers in the vehicle.  It gives a figure of 81.6 kg per person.  Your completed conversion plus 81.6 kg per person must not exceed the original GVM.  For instance, for the Brumby:
Kerb weight (unladen): 920 kg
GVM: 1650 kg
Passengers: 2 x 82 kg = 164 kg
If, on conversion, it was 920 kg as per the above rule of thumb, I would be able to (legaly) add 1650 – 920 – 164 = 566 kg of batteries.
The Brumby is a ute, so it is designed for a high(ish) GVM.  Most passenger cars will not have such a high GVM, and so adding batteries will be more problematical.  One approach ofen used is to alter the seating capacity by removing the rear seat(s).  Reducing the seating by three people equates to 246 kg gained for a battery.  This also gives you a brilliant place to locate the battery, being just in front of the rear wheels.

Other Considerations

Like any vehicle purchase, make sure you look for mechanical problems and signs of rust or repairs.  Depending on your experience, you might like to have a mechanic go over the vehicle before purchase.  In this case though, the condition of the engine is not so much of a problem! You can normally sell the engine, exhaust system, radiator, fuel tank etc. once you remove them.

Summary

The drivers for vehicle conversions have changed over the past few years.  When I started on my journey converting the Brumby in 2010, conversion was the only way to drive electric.  These days, if your sole aim is to drive an electric car, the cheapest way would be to purchase a secondhand production EV such as a Nissan Leaf.  If you decide to convert now, it is most likely because you want a unique vehicle.  Either a vehicle that you are already in love with, or a body style that is not currently available in EV (such as a ute), or something that will turn heads when it unexpectedly drives by silently.  Choose carefully, if you do a good job then this vehicle could be with you for a long time to come.

Resources

EV Album is a great place to see if a vehicle has been converted before: http://www.evalbum.com/
Join up and make a post on the AEVA forum to ask questions: https://forums.aeva.asn.au/
Go to an AEVA meeting and find like-minded people: https://aeva.asn.au/
NCOP14 contains the rules to follow to convert a vehicle for on-road use in Australia: https://www.infrastructure.gov.au/vehicles/vehicle_regulation/bulletin/vsb_ncop.aspx

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