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• Testing
• CAN Display

CAN SOC Display testing

Test procedure

• Connect 12 V to the SOC display
  • Ground to pin 1
  • 12 V to pin 4
• Make sure that SOC display is not controlled by the BMS controller, in one of these 4 ways:
  • The BMS controller is off, or
  • The BMS controller has Elithion hardware messages turned off, or
  • The BMS controller is set for a CAN rate of something other than 500 kHz, or
  • The CAN bus is disconnected somewhere between the BMS controller and the SOC display
• Check that all LEDs (5 colored LEDs, 10 green LED bar) light up
  • If not, follow the troubleshooting procedure below
• Connect also the CAN wires
  • CANL on pin 2
  • CANH on pin 3
• Make sure the BMS controller is set for a CAN rate of 500 kHz, and that the Elithion hardware messages are turned on
• Turn on the BMS controller
• Check that, within a few seconds, the SOC display has some LEDs on and some off
  • If not, follow the troubleshooting procedure below

Principle of operation

Refer to this schematic diagram.

Supply

• 12 V supply comes in from the 4-pin connector, drawing between 3.5 mA (all LEDs off) and 30 mA (all on)
• It powers U3-3
• U3 generates a voltage reference on pin 8, which is adjusted to 5.5 V by the ratio of the values of the resistor on pin 10
• That reference drives the base of voltage follower Q3, whose emitter provides a buffered 5 V supply to power the remainder of the ICs
• The 5 V supply drives the base of voltage follower Q2, whose emitter provides a buffered 4.3 V supply to power the LEDs; this transistor gets very hot

CAN buffer

• The CANH and CANL lines are terminated by R1, a leaded resistor, which can be clipped off if no termination is required
• The CAN lines are connected to CAN buffer U1, that converts the CAN signal to a receive (RSD) and a transmit (TXD) line
• Those lines are connected to U2, CAN expander

CAN expander

• CAN expander U2 uses Y1 as a 20 MHz clock
• It communicates to the CAN bus through U1
• It drives the 5 colored LEDs directly
• It generates a 50 kHz PWM wich is low-pass filtered (by R3 and C1) to work as a D/A converter, to create a 0 to 5 V control the SOC level bar graph (0 V = no lEDs = 0 % SOC; 5 V = 10 LEDs = 100 % SOC)
• It is programmed to turn on all LEDs at power-up: pins 1, 2, 4, 4 and 6 driven low, pin 3 at 100 % duty cycle
• At power-up it sends out a single message at ID 3FFh
• It receives messages at 680h from the BMS controller, to determine the status of its outputs

LED bar driver

• LED bar driver U3 drives the 10 LEDs in the SOC LED bar directly
• The number of lit LEDs is proportional to the voltage on its pin 5, with respect to the voltage on its pin 6 (which is tied to the 5 V supply); therefore, as the PWM duty cycle from the CAN expander ranges from 0 to 100 %, and the voltage on C1 ranges from 0 to 5 V, the number of LEDs ranges from 0 to 10.

Troubleshooting

All LEDs off at power-up

• Check the voltage of the 5.5 V, 5 V and 4.3 V supplies
  • If not within 10 % of the nominal voltage, the problem could be Q2, Q3 or U3
• Else, check U2, Y1, C4, C5

All LEDs remain on

• Check the CAN bus, to make sure that the SOC display is indeed receiving the correct messages

• Check U1 (it can be blown if you apply high voltage to the CAN lines)