Contactor unit Overview
Here is a overview of the contactor unit and a brief description on what they are all doing.
Safety Disconnect
This is a removable disconnect that will isolate the battery pack from all of the output connectors. The pack will still be live when this is removed so normal EV care to be taken when working on the pack, but this is essential when anyone is performing mechanical maintenance on the vehicle.
400A serviceable Fuse
At no point should more than 400A be coursing through the veins of the car, however if there was a short somewhere the 400A fuse is there to protect the car and passengers. You could in theory use this as a safety disconnect however why scrimp and save at this point.
400A CCS Fuse
Although there is a 400A fuse protecting the pack, there is also a 200A fuse for the charging, this is in case there was any fault on the charging unit (External to the car) something that will trip before the 400A fuse as damage could have already been done by that point. The 400A fuse is so high to cope with the peak current he motor can demand. However the charging current is more stable and wont have to cope with any sudden peaks.
Pre-charge Contactor
If you were to open the contractors to the pack the instant load could potentially be damaging. The pre-charge contactor gives a path to the pre-charge resistor so it can slowly provide power to the HV system rather a huge inrush current.
Pre-charge Resistor
The pre-charge resistor is used to prevent the inrush current when the HV contactors are open.
Pack Negative Contactor
Contactor to connect the negative side of the pack to the output connectors.
Pack Positive Contactor
Contactor to connect the positive side of the pack to the output connectors. This will open a few seconds after the pre-charge resistor has been active.
Controller connector
HV connection from the pack to the motor controller. Here I could have saved money and potentially made it more visually appealing by fitting glands and bolting the motor controller wires directly to the bus bars, however, kit cars are all about people tinkering I wanted the HV battery pack to be able to be completely fitted and removed without any need to open the potentially lethal battery box.
CCS connector
HV connection from the CCS charging port to the battery pack, note these are downstream of the other 2 pack contactors so the pack contactors act as a secondary safety cutting power off to everything.
Positive CCS
Contactor to connect the positive cable of the CCS charger to the pack, the main pack contactors still need active to allow charging. In theory you could have the case where the motor could be powered while the vehicle is on charge, definitely not ideal so this will be controlled in the software, also just good practice so you don't drive off while connected and rip the charging cables out.
Negative CCS
Contactor to connect the negative cable of the CCS charger to the pack, the main pack contactors still need active to allow charging. In theory you could have the case where the motor could be powered while the vehicle is on charge, definitely not ideal so this will be controlled in the software, also just good practice so you don't drive off while connected and rip the charging cables out.
Auxiliary Outlet 1 & 2
Fist will be the HVAC system, there will be a 400V motor for the air conditioning and also a 400V PTC heater for the heating.
For the second output there will be a water heater that is used to heat the battery pack, although I don't exactly see myself using this car that much in sub zero temperatures throughout this project I'm making it as functional as an OEM car. So I need to install a mechanism to heat the batteries in cooler temperatures to prevent damage to the pack when charging / discharging.
Contactor programming
The contactor programming will be something like the following.
In the PDM I will have a status variable called "Pack Energised", or something to that effect, once the sequence is complete the pack will be energised and the drive mode can be set to Drive or Neutral.
IF DRIVE MODE = Neutral {
Pre-charge contactor = ON
Negative pack contactor = ON
Wait 3 Seconds
Positive Pack connector = ON
Pre-charge contactor = OFF
Pack = Energised
else alarm (Drive mode needs to be in Neutral)
The drive mode will be from a 3 position rotary switch, however the switch its self doesn't actually set the drive mode, it requests the drive mode and then from the PDM I can either set it to the requested mode or alarm. (I'm loving the flexibility this PDM give me, I have a feeling I'll be geeking out a fair few times on the possibilities this allows)
Variable "Drive mode" = Neutral
IF Drive mode switch = "Drive" & Pack Energised = "True" {
Set "Drive mode" to "Drive"
}
Else IF Drive mode switch = "Drive" & Pack Energised = "False" {
Alarm ("Pack needs to be energised before selecting Drive")
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