During the first test of the staggered start of the Gen4 at Le Castellet with the others three generations cars, the Gen 4 car refused to start.
This forced a repeat of the procedure for the cameras (see video), and upon inquiry, it emerged that the problem was a false alarm from the isometer.
The abbreviation ir155-3204-100k0-0v B 9106 8139v4 may not mean much to the layman, but if you read page 60 (Appendix 3B) (click here) the FIA supply tender for Gen4 batteries shows that it is a safety component mandated by the FIA and serves to ensure that the battery’s internal components are not leaking into the external casing.
These devices are called insulation meters and work by monitoring whether the electrical potential of the casing is approximately halfway between the potential between the positive and negative poles of the battery.
If this potential begins to shift toward one pole, it means the parasitic resistance is unbalanced toward that same pole. To measure insulation resistance, this device artificially introduces a known resistance between the pole and the casing and reads how much and how quickly the potential of the casing shifts. The greater the variation caused by the known resistance, the higher the actual resistances are, indicating that the battery has good insulation (high insulation resistance).
The ISO/DIS 6469-3.2:2010 standard requires a minimum value of 100 Ohm/Volt for all vehicles (racing or otherwise) for all systems with voltages between 60 and 1000V, and the Gen4 with its 800V battery falls squarely within this standard.
If the insulation resistance is too low, it indicates a problem with the battery or other system components. The Formula E Gen4 battery is equipped with two meters specifically to determine whether the problem lies with the battery or the rest of the system. These devices are also what give the “green light” on the car, indicating to all outside personnel that the vehicle is safe.
In electric cars, to prevent interference to highly sensitive electronics, suppression capacitors are placed between the positive and ground and between the negative and ground terminals. These capacitors absorb any electronic noise arising from high-voltage systems.
The Gen4 car is equipped with generously sized filter capacitors to ensure that all racing equipment (telemetry, attack mode sensors, pitlane sensors, tire sensors) function perfectly. The problem is that these large capacitors also filter the noise artificially introduced by the insulation meter, causing a false insulation loss alarm that could prevent the car from starting.
And this is exactly what happened at Le Castellet. Nothing particularly serious, all it took was turning the vehicle off and on again to see the Gen4 hurtling around the circuit. But details like this are the small refinements that differentiate a development car from race-ready cars.
The specifications for the isometer bender require a capacitance of less than 1 microfarad. Currently, the car has a capacitance of around 3 microfarads, so small problems or false readings are something the developers had already anticipated and considered.
In the near future, slightly smaller capacitors or even simply a different software calibration of the Isometer will make problems like the one seen at Le Castellet a distant memory.
At the following link, you can view the installation manual for the Isometer Bender ir155-3204-100k0-0v B 9106 8139v4: https://www.bender.de/fileadmin/content/Products/d/e/IR155-32xx-V004_D00115_D_XXEN.pdf
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