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.