Blog: inverter

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!