VCM requirements

This page collects the main requirements for the DIY VCM. Even though it will likely never be formally tested, it is a useful thing to have a grasp of before finalizing the design — and good documentation for future reference. The overall reasoning behind the safety choices is in the Safety architecture post.

Environmental

The VCM will be mounted inside the driver compartment, but it still needs to be fairly rugged. Since the car will be driven in Sweden, low temperatures are more likely than really high ones — though it may end up a nice-weather-car.

Ingress protection

The VCM shall have IP67 ingress protection.

Temperature

The VCM shall be designed for an operating temperature of −40 to +60 °C.

Condensation

The enclosure shall be fitted with a GoreTex breather membrane to prevent internal condensation.

Electrical

Supply voltage

The VCM shall be designed for a nominal voltage of 12 VDC but be fully operational between 8 to 18 VDC.

Supplies

The VCM shall have three different supply rails with the following current consumption.

Constant

Operational: 100 mA
Sleep: 0.1 mA

Ignition

Operational: 10 A
Sleep: disconnected

Crank

Momentarily: < 10 mA (digital input only)

High side driver

The high side driver shall be able to supply 3 A continuously, and 10 A during inrush events. It shall be supplied from the ignition input.

Low side drivers

The low side drivers shall be able to sink 1 A continuously, and 5 A during inrush events. They shall be grounded to two separate pins on the connectors.

Mechanical

Most mechanical properties are set by the ModICE enclosure.

Enclosure

The VCM shall use the Cinch ModICE ME-MX enclosure with breather vent.

Part number: 581-01-30-075

Connectors

The VCM shall use the Cinch ModICE header with two 12-pin Molex MX150 connectors.

Part number: 581-01-24-011

Matching wire harness connectors:

Keying A (black): Molex MX120 33472-1201
Keying B (light gray): Molex MX120 33472-1202

Pin terminals:

14–16 AWG (1.5–2.5 mm²): 33012-2001
18–20 AWG (0.5–0.75 mm²): 33012-2002
22 AWG (0.34 mm²): 33012-2003

Mounting

The VCM shall be mounted using 2 × M6 screws with washers. The distance between the mounting holes is 101.6 mm (4″).

I/O

The connectors have the following pinout:

VCM pinout.

Pin	Keying A (black)	Keying B (light gray)
1	GND	LSD GND
2	CAN1 Low	CAN2 Low
3	CAN1 High	CAN2 High
4	TBD	Waterpump PWM Out
5	Charger connected	Waterpump PWM In
6	TBD	Ignition
7	Accelerator GND	LSD GND
8	Accelerator IN1	Lower contactor
9	Accelerator IN2	Upper contactor
10	Accelerator +5V	Precharge
11	Brake IN	High side drive
12	B+	Ignition

Functional states

The VCM has the following functional states:

stateDiagram-v2
    Sleep --> Precharge: Ignition on
    Precharge --> Ready: Precharge done
    Ready --> Drive: Crank
    Drive --> Ready: Ignition off
    Ready --> Sleep: 15 min
    Ready --> Charging: Charger connected
    Charging --> Ready: Charger disconnected
    Drive --> Fault: Safety critical fault
    Charging --> Fault: Safety critical fault

Sleep

The main DC/DC inside the VCM is switched off and all electronic circuitry is unpowered. The only way to wake the VCM from sleep is to supply 12 V to the ignition pin.

Precharge

The precharge contactor is activated to slowly (within seconds) charge the inverter capacitor bank through a power resistor. Once the inverter capacitor voltage has reached 90 % of the full battery voltage, the VCM moves into the ready state.

Ready

Precharge is done and the main contactors are closed. Can also be entered by turning off the ignition while in drive. After 15 min of idling, the VCM enters sleep.

Drive

If the key is turned to the crank position while in ready, the VCM moves into drive mode and starts monitoring the accelerator pedals, providing a corresponding torque request to the inverter.

Charging

If the charging cable is connected in ready mode, the VCM moves into charging mode — preventing the car from driving and allowing the PDM to charge the HV battery if the cable is connected to 240 VAC.