EV tear downs

Always nice to see how an EV works internally. Here are some videos that show the tear down of major components of various EVs.

Especially interesting to learn from the videos is that the Renault Zoe EV inverter appears to use the windings of its motor as inductor for the rectifier/charging circuit, see the hardware schematic in figure below. This has of course great benefits for Renault; it makes the EV inverter a lot smaller and a lot cheaper.

Renault EV inverter concept

Drawback however is that during the battery charging cycles, the motor is powered with high voltages and high currents.

In a previous post I already mentioned that the Renault charger efficiency appears to be quite low. In my non-scientific tests, I observed an efficiency of roughly 80%. Using the motor windings as an inductor instead of an optimized inductor built-in in the inverter might be a root-cause for this. This hardware design also results in a serious temperature increase of the motor windings. And since the car is not driving, forced cooling must be used to keep the motor temperature below a safe level. The power needed for the cooling fan is also a possible root cause for the observed high inefficiency.

Because the motor is connected to mains power without any form of electrical isolation, electrical safety measures must be taken to protect people (or animals) from accidental but hazardous electrical shocks. Voltages can go up to 400VDC, well above safety levels. For protection, all parts need to be connected to protective earth, and this protective earth connection needs proper earthing resistance (<30 Ohm). A Renault Cameleon inverter checks this earthing resistance and prevents a charging cycle is the value is too high. Bad earthing resistance is a well known root cause for charge cycle errors.