Formula Student -- Brake System Plausibility Device
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LTC6994.json
README.md

README.md

BSPD

Formula Student -- Brake System Plausibility Device

Brake System Plausibility Device

Formula Student
Ruleset: FS-Rules_2018_V1.1
This BSPD passed scrutineering at Formula Student UK 2018
Please let us know if you used this design for your car or if you have used it and made useful improvements to it
Also if you have any questions please let us know --> SDU-Vikings

BSPD PCB Render

Schematic and PCB

The project is made in KiCad. Get it here --> KiCad 5.0
The schematic layout and PCB layout is found in the KiCad/ subfolder.

Components

The design is made for a battery supply of between 11 V and 15 V.
The current consumption is measured at between 63,0 and 90,3 mA with a 12,7 V supply.

For current measurement LEM HAS 100-S is used. The Hall Effect Sensor needs +-15 V supply hence the TEN 8-1223.
For brake presssure measurement EPT3100 is used.
The relay for the safety chain is TE-OJ-SS-112LMH2.

Debugging LED's

The design includes SMD-sized LED's for easier debugging. D3 and D4 can be removed altogether and D6 replaced by an ordinary P/N-diode.

Delay-block

LTC6994 is as delay-block. The delay-block is configured for a delay of 500 ms. See LTC6994 One Shot to configure delay and use LTC6994.json for the setup.

Latch and latch-reset

The signal from the delay-block is received by a latch CD4043B that will latch on to the signal requiring power cycling of the low voltage system to reset it again.
However the latch will latch on to a high signal when the low voltage system is turned on initially. The 555-circuit is used for generating a pulse, that will reset the latch. The pulse has a delay of approximately 500 ms at turn on.

Input signals and voltage dividers

Current

HAS_100-S has a output voltage range of -12V to +12V with a voltage signal of 4 V for every 100 A in the wire.
With a nominal battery voltage of 510,6 V the current to the motors at 9,8 A is below 5 kW as required by EV7.5.5 in the rules.

510,6 \,\mathrm{V} \cdot 9,7 \,\mathrm{A} \approx 4.953 \,\mathrm{W} 

At this current in the HV-wires the voltage output from the hall effect sensor is 0,388 V.
The voltage divider between R6 and R11+R12||R13 gives a voltage treshold of 0,380, which corresponds to a current of 9,5 A in the wires.

\frac{2600}{100000 + 2600} \cdot 15\, \mathrm{V} \approx 0,380\, \mathrm{V}

Change the value of R6, R11, R12 and R13 to adjust the voltage treshold of the comparator.

Brake

Change the value of R27 and R33 to adjust the voltage treshold of the comparator for the brake pressure sensor.

Current Measurement

The design includes operational amplifiers whose purpose is to convert the voltage range of the hall effect sensor signal from (-12V/+12V) to (0V/10V) for interfacing with a controller.
It is not required for the intended functionality of the BSPD and can be removed.

U10B is a summation operational amplifier. The gain on the current sensor output is -5/24. This is summed to a voltage of -2,5 V converting the voltage range to (-5 V/0V). U10A has a gain of -2 converting the voltage range to the desired (0V/10V). U11A is a buffer.

Labels in the schematic

DCDC+ +15 V
DCDC- -15 V
BSPD_TEST - Signal from controller to simulate 5 kW drawn from the battery pack
BSPD_STATUS - Signal to controller to show BSPD status. High when there is a BSPD fault
SC_IN - Safety chain in
SC_OUT - Safety chain out
Latch_Reset - From 555-timer-circuit. Used to pulse reset the latch
Current_Sensor - Voltage signal from LEM HAS 100-S
Brake_Sensor - Voltage signal from EPT3100
Analog_GND - Supplied GND to EPT3100. This is shorted to GND at the controller
Analog_5V - 5 V supplied to EPT3100