We are often asked whether a vehicle with an automatic transmission can also be converted to electric propulsion.
The short answer: yes
The long answer: the process is different to converting one with a manual transmission. Most of all because you cannot keep the automatic but you replace the transmission with the single speed reduction that comes with 2nd hand EV motors. The option to keep the stock transmission as featured in our guidebook is rather impractical for a number of reasons:
- An automatic gearbox needs constant hydraulic pressure, so the electric motor has to “idle” at 700 rpm or thereabout to provide for that. That leads to a loss of efficiency
- The viscous clutch further reduces efficiency (that’s why automatics also consume more petrol)
- It also does not cope well with the high low end torque and regen-ability of electric motors
- The gear shift strategy doesn’t match the electric motors efficiency curve
When Damien Maguire converted a V12 8-series BMW which must have been pretty powerful it only took the electric motor a couple of months to make mince meat of the viscous clutch.
A good replacement for rear wheel drive cars with auto gearboxes are the Lexus 450h or 300h hybrid gear boxes. The latter being smaller, cheaper and easier to operate.
They contain two motors capable of about 120 kW and the transmission conveniently slides into the transmission tunnel, leaving the entire engine bay for ancillaries and batteries. The accompanying inverter can be run with Damien Maguires ZombieVerter. Make sure to collect the entire wires harness when salvaging these drive trains as the harness is super expensive to acquire afterwards.
For front wheel drive cars there is even more variety. Nissan Leaf, Tesla SDU, Mitsubishi Outlander or even the inexpensive Toyota Prius hybrid transmission just to name a few.
The adaptation process now involves making custom drive shafts and motor mounts all around. New drive shafts are manufactured by adapting the transmission output cup to the mating part of the converted vehicle.
Another possibility is obtaining the drive shafts from the motor donor vehicle and joining it to the drive shaft of the converted vehicle. These can be welded together but then often lack strength. Therefor such a prototype can be sent to specialized companies such as Motomax who fabricate a new drive shaft using the prototype as a template.
