There was quite a list of tasks that I wanted to do before the Corolla would be back on the roads. These included:
- Adding a second charger
- Adding an emergency stop button
- Finishing the motor controller assembly
- Modifying the Cycle Analyst for higher voltage
- Revising all electrics
- Adjusting the controller software
- A lot of testing
Here's Corolla's newest main circuit diagram revealing the car's current electric drivetrain in full.
I started to tackle my task list by mounting the emergency stop button and the second charger. The emergency stop button simply disconnects the traction battery pack with two Gigavac GV200 contactors. The added second charger was identical to the first Powerfinn PAC-800 charger. Now each 24S LiFePO4 battery pack have their own charger. In the picture above also the motor controller's display can be seen located next to the Cycle Analyst.
The next task was to find a suitable place for the Gigavac GV200 contactors. I chose to mount them under the rear battery pack. Moving to a higher battery voltage required new fuses rated accordingly. My choice for the traction battery fuses were NH1 type 250A fuses rated to 440Vdc. For the smaller current high voltage fusing needs I chose 6,3x32 ceramic fuses rated to 400Vdc.
My next job was to update the motor controller assembly. The pictures above show the result. I used Meanwell MDR-series Din-rail power supplies as isolating DC-DC power supplies. The bigger one provides 12V to the Motoc SR250V500A-V2 controller, Pre-charge contactor and a 12V 20W fan. The smaller one powers the Cycle Analyst after modifying it to measure voltages up to 300Vdc (to be future proof :)
This is how the Kostov K9HV looks below just before placing the bottom covers. I think the K9HV is a good fit for the Corolla:)
The next step was to remove the 72V system electrics and build it up again to support 144V voltages. The changes were not big but I had to make changes into every enclosure that the Corolla had so it took quite a while.
No project comes without problems. This time I made a mistake by carelessly connecting the charger into the rear battery pack. While making the connection to the cell terminal I was unlucky to have the chargers connection inrush current flowing through the SBM circuit board. As a result the balancing control IC and mosfet were shorted on the SBM's most upper cell circuity. This caused a few weeks timeout as I had to figure out how to fix the fault. I was not able to source the broken unknown Chinese components used in the SBM (marking R2RP) so I decided to replace the balancing controller IC with a LMV421 circuit. My LMV421 circuit ended up having quite much higher leakage current than the original balancing control IC. To prevent serious unbalance problems due to differences between different cell circuity leakage currents I decided to match each cell's circuit leakage current by applying suitable sized shunt resistors on them. After careful testing I am convinced that the SBM is again working as expected and I mounted it back to work.
After all needed changes were done, it was time to cover up everything. This is how the Corolla looks under the hood at the moment.
Time for test drive! It's always nice to make test drives and even more so when there is more power available than before:) Some PI-controller parameter iterations later I got a result where the throttle response is instant without any oscillation. The DC-link current limit (set to 200A) seems also work accurately as can bee seen on the Cycle Analyst display showing the highest current draw and lowest battery voltage resulting in close to 27kW power! The smaller display shows some information that I wanted to be displayed from the Motoc SR250V500A-V2 controller. The upper row shows temperatures of the XMC1302 microcontroller, motor thermistor and IGBT-module's thermistor. The lower row displays current DC-link voltage and motor current.
The Corolla is now ready for its yearly inspection to be road legal again after 10 long months! The K9HV motor and SR250V500A-V2 controller have changed the car from sluggish to more like a normal car. Despite of a rather small increase in peak power (from around 21kW to 27kW) the new drivetrain provides the available power in a far broader RPM range than with the ME1003 motor and Kelly Controller. With the K9HV motor I can drive up to 93km/h using just the second gear, which I hope will make my daily driving just like it should with an EV; no more gear shifting:)
