(automotive electronics) CAN bus error if current draw for lighting too low? - Page 1
Forum section: electronics / projects

author: lilJohn
author_rank: Contributor
timestamp: September 17, 2024, 02:32:38 am
content: My question is whether or not a vehicle's system will throw or generate CAN bus errors if the current draw for a system is too low such as the side blinkers or interior cabin lights.For context, I am modifying my vehicle's side blinkers because my side blinker indicator housing has yellowed. I managed to find the waterproof connector BMW (thanks to @tooki here1) uses for the side blinkers and I am wondering if I must attach these10 W 60 Ω resistors. From the picture (Figure 1), it seems it is wired in parallel with the housing's T5 socket (Figure 2) so I am guessing that it increases the power use because the efficiency of LEDs are much greater than that of incandescent bulbs. The seller guaranteed the item would be CAN bus error-free but I am wondering if that is only if I attach said resistors.I am asking this because I need to know whether or not I need to attach a waterproofing connection for the resistor. FYI, I am planning to splice the resistors with the assembly with marine shrink tubing after snipping the connectors and then use lots of PTFE tape.Note this picture was taken before I waterproofed the side blinker housing by injecting the hole with waterproof and UV-proof glue.figure_01_device_w_power_resistor.JPGFigure 1. A 10 W 60 Ω power resistor provided with the component.figure_02_resistor_harness_&_power_in_wiring.JPGFigure 2. The power resistor harness is wired in parallel with the power input (I tested it with a multimeter, the resistance between the Red and Blacks to the respective other is 0Ω).Links:1.https://www.eevblog.com/forum/projects/what-automotive-electrical-connectors-are-these/msg5640891/#msg5640891

author: uer166
author_rank: Super Contributor
timestamp: September 17, 2024, 04:06:27 am
content: FMVSS requires the blinkers to flash roughly twice as fast if a bulb fails (this includes LED lights). So you'll definitely know if it thinks it's broken, even without CAN, assuming a US market vehicle.No such requirement on interior lights though, and I would posit that there is no detection there.No idea about other countries/EU though.

author: lilJohn
author_rank: Contributor
timestamp: September 17, 2024, 04:25:37 am
content: Quote from: uer166 on September 17, 2024, 04:06:27 amInteresting, I never knew that the blinker flash was dependent on the circuit resistance. So I am guessing the power resistor is required because the circuit resistance measured would be higher without the power resistor (less current draw, if they are using a current sense resistor).Just curious: the blinker controller would probably use a current sense resistor to measure the circuit (edit) resistance, correct?

author: uer166
author_rank: Super Contributor
timestamp: September 17, 2024, 04:33:18 am
content: Quote from: lilJohn on September 17, 2024, 04:25:37 amIn the old cars the bulb was part of the blinker circuit. Nowadays with LEDs it's normally a high side driver with a current feedback, or perhaps a shunt that measures consumption current.In the cars I worked on it was either a fast blink due to a failed bulb, or a normal slow blink, nothin in between

author: lilJohn
author_rank: Contributor
timestamp: September 17, 2024, 04:35:10 am
content: Quote from: uer166 on September 17, 2024, 04:33:18 amInteresting, thank you!