Blog: r4ecv

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 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 4CV Handbrake Mechanism ¦ EV Conversion

Handbrake Mechanism Renault 4CV

Let's have a look at a detail of a technical solution in the EV conversion process of the Renault 4CV. The handbrake mechanism which spreads the force of the handbrake lever to the two rear drum brakes is mounted on the bottom of the old engine, on the cover under the flywheel (same cover as the Oil pan).

Of course this supporting part needed to go with the ICE engine, so we had to find a new solution in order to attach the handbrake mechanism at the same location.

If you followed my previous posts you might know that we built a custom clutch bell housing between the new motor and the gearbox. So this would be the location where the hand brake mechanism would need to go:

The challenge now was to draw and produce the fitting mounting brackets and parts in order to mount the mechanism onto the new clutch bell housing.

I was very lucky and got everything right in the first attempt. And this is how the mechanism now sits on its new location - which is exactly at the same place as on the combustion engine:

This is an important achievement as all changes regarding brakes etc. would potentially cause a problem with homologation if the modification would be substantial. I have to say that I am really pleased with the result, as the new mechanism sits exactly at the same place as before with the same attachments. Also, it follows my approach to keep things as original as possible!

Motor Controller/Inverter Options for the Renault 4CV

So now that we have set the system Voltage to 96V and defined the AC motor power to 15kW, we can start looking at different motor controller/inverter options available.

From the commercially available inverters, the following three were the ones that made it onto the last shortlist:
Curtis 1238e-7621 96 V 650 A
DMC SuperSigma2
Sevcon Gen4 Size 6 (40-116 VDC, 550-660 A)

Other solutions such as open source projects like OpenInverter were ruled out after some initial analysis, as the Controller is an important part of the electric drivetrain and the use of a repurposed unit could easily lead to EMC/CE/Electrical Compliance failure on homologation in Switzerland. I still follow the project with great interest, but I didn't want to take any risks in this build.

From the three shortlisted Inverters, here in alphabetical order, the Curtis is the obvious suspect, as it is probably the most widely used Controller on similar applications, such as golf cars, forklift trucks etc. A lot of knowledge out there, relatively open to program, and some commercial partner network providing (paid) support in case of problems. The Curtis in this configuration comes with a price tag of about EUR 2'300.

The DMC is manufactured in Germany, very similar to the Curtis, probably even a bit more open, with the same functions. And the DMC was also tested to work with the specific motor I selected for the build. The DMC is just slightly cheaper than the Curtis with prices just shy of EUR 2'000.

The Sevcon was initially my favourite, as it had some Renault-legacy (e.g. the Twizy is equipped with a Sevcon-Controller). They are automotive-compliant and of course they would offer a similar range of functions as the other two. But there is a huge disadvantage: The Sevcon system is rather closed, very difficult to get access and to program. Since Sevcon recently got taken over by Borg-Warner, the support structure changed, too, which makes it nearly impossible to get support as a non-commercial customer. The Sevcon was therefore put into 3rd position, despite the fact that it would have been the cheapest of the three.

The DMC would probably have been my first choice, as I still can't see any disadvantages over the Curtis, but even a few small advantages.

But later on in the project I decided that for CE and EMC Compliance reasons I wanted to integrate the Controller, DC/DC Converter and HV-Junction Box into a single component with CE approval, which got supplied by the German E-Car-Tech (, so I went for the Curtis controller as E-Car-Tech are approved Curtis dealers and system integrators, so they were able to tune the Curtis to my parameters right from the beginning. I am still convinced that the Curtis was a very good choice, I am however also sure that the DMC would have been able to provide the same performance in a standalone setting.

So in the end the order in my preference list in the end turned out to be exactly the same as the alphabetical list of the Controllers above.

You will read more about the Curtis 1238e and its Interface in a later post here!

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.

First drive in the all-electric Renault 4CV

What a great moment: 30 seconds of footage from the maiden drive of my all-electric Renault 4CV. Enjoy the show folks!