Blog: motor

Choosing the Motor for the Renault 4CV ¦ Electric Conversion

Let's talk about the motor options for the Renault 4CV.

I had four (and a half) parameters to consider:

1) power around 15 HP (+/- 10%, although there is some play with peak power and nominal power)
2) Voltage of 96V
3) CE conformity mark and documentation
4) air cooling
...and suitable dimensions to use the existing motor mounts (these were not super strict as I could have fabricated necessary mountings if needed)

The first idea was to use a LETRIKA/ISKRA motor of the type AMV7118, which can be found in the Renault Twizy. This motor however uses a different system voltage than I was planning.

I then got to know Erich from bdrive.ch who successfully converted a classic Mini into full electric drive and passed the homologations in Switzerland. He used a motor of the Italian manufacturer Fimea Engineering which comes with a full CE documentation and passed the Swiss testing procedures. The dimensions were super ideal, too, and it is an aircooled unit. And as I am living close to the Italian border anyway, that decided it for me!

This thing is perfect, and I am still convinced that it was the best choice for the Renault 4CV. The only little downside is its weight, which is over 60 Kg, but that's the price of air-cooling I suppose.

If you have a quick glance at the technical specs, you will see that this motor fits perfectly to the original power output of the Renault 4CV engine. A bit more torque, which could also be limited through the controller settings. The problem with too much torque is that the original gearbox could be damaged, and the driveshafts could snap. This is a common problem with the Renault 4CV, the tuned or Gordini-prepared versions of the car were changing the driveshsafts for those of the Renault Dauphine, as these were more stable. And we're still talking sluggish petrol engines here, not electric torque from 0 rpm!

The guys at Fimea were super supportive when placing the order which gave me further confidence. About a month later I went down to Milan to pick up my new motor!

Here's the motor in my workshop, ready to be installed into the car:

As the motor is pretty heavy (about 66 kg), I used a forklift to lift the motor into the vehicle. On the far side you can see the adapter plate towards the gearbox.

And here you can see the whole drivetrain installed for the first time in the car. Note how perfectly the motor sits on the original motor mounts (the crossmember below the motor is actually the original part that used to support the petrol engine!)

Still super happy with my choice, I can recommend Fimea Engineering to anyone!

Renault Zoe R240 motor for the Renault Fuego?

Let's have a quick and exclusive look at the Renault Zoe R240 motor. This - in theory - would be a perfect candidate for the conversion of the Renault Fuego. Sharing a bit of history with the Renault family, with similar power and dimensions (length) like the original Fuego engine, it would have been a pretty good match.

Unfortunately, I have tried to look a bit closer into this motor, but I couldn't get any further.

With three lines and a neutral, it looks like the motor is Y-wired whereas most usual 3 phase motors are delta-wired. I think this is due to the fact that Renault used the motor as a part of the Chamaeleon charging system which allowed charging up to 43 kW (!!) on the Continental model and 22 kW on this R240 Renault inhouse unit without water cooling using the stator windings as part of the charging circuit - presumably as a transformer for charging from an AC source. This might be the reason for the unusual stator winding (with a neutral). Remember that all other EV's (including premium cars like Tesla) only offer charging up to 11kW as they are working with a separate, dedicated charger.

The problem for me with this motor now is that due to its powered rotor and wye-wired stator the only practical way to drive this motor currently is the OEM inverter-controller. It wouldn't respond to any other standard industrial or automotive inverter. Unfortunately, the OEM Renault inverter unit is still a black box at the moment, so we have no practical way to gain control access directly to the motor as we speak. I have one of these R240 motors in storage at the moment, so in case somebody will eventually find a solution to drive these motors, I can still look into this option. If anybody out there would have more information, please get in touch with me!

Battery, Inverter and Motor System Voltage

A few thoughts on the motor and battery choice - and related system voltage.

When I started the conversion, my original plan was to stay as close as possible to the drivetrain of the Renault Twizy, which I had the opportunity to study in-depth beforehand. Here's a picture of my "research vehicle" to show you how the drivetrain looks like:

So my original plan was to work with a LETRIKA/ISKRA motor of the type AMV7118 coupled to a SEVCON Controller GEN4 4845 (450A). The Letrika motor would have delivered about 13kW which would have been pretty close to the nominal requirement (15kW ) of my build (I had to stay within +/- 10% nominal power for homologation). The battery system of the Twizy is at 60V voltage.

Problem with this configuration was that:
- It wasn't clear if the Letrika motor would have a CE approval for automotive use when used on its own without incorporation into the rest of the Twizy system.
- The Sevcon-controllers are very proprietary and hard to program, some functions are locked.
- The battery voltage of 60V is a bit odd to achieve with some standard battery modules.

So at the same time two other things happened: I got to know a motor manufacturer (FIMEA) in Milan, Italy, who produced a fully CE-compliant automotive motor with 96V/15kW AND my original concept included the use of 4 tesla modules in series for a total of... 96V too! So that was the starting point of the 96V system concept.

I couldn't use the Tesla modules for various reasons in the end, but the 96V system voltage (and the motor) stayed, and I am quite happy about it for a small car like the 4CV. The only downside of the 96V system is that it will never be able to use DC charging as both the Chademo and CCS protocol are requiring voltages of well above 200V, for CCS preferably even over 300V. But the 4CV is not a car for long distance drives anyway, and 96V is still a rather safe voltage to work on. Higher voltage than on a Twizy also means less strain on the HV-system, even when driving steeper mountain roads, which is important in my region, too.