Brake light indicator for regen braking

Discussion in 'Clarity' started by gedwin, Sep 8, 2021.

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  1. gedwin

    gedwin Member

    I know there are myriad threads discussing brake light activation and regenerative braking, I don’t mean to start a rehash. But, to feed my curiosity, today I wired a simple LED indicator and mounted in the lower middle of the trunk window. With a glance in the rear view mirror, I can readily but unobtrusively see whether the brake lights are activated or not.

    I didn’t see that anyone had posted similar modification, but apologies if I missed it. Posting here just as an idea generator for others of a similar mind. Again, admittedly not particularly useful or important to know, but I was curious to know when drivers behind me are seeing lights. IMG_4278.JPG IMG_4280.JPG

    Sent from my iPhone using Inside EVs
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  3. JFon101231

    JFon101231 Active Member

  4. yeah723

    yeah723 New Member

    So... do the brake lights come on when not stepping on the brake but using the hand peddle?
  5. Groves Cooke

    Groves Cooke Active Member

    Not on 2018 Touring. You can do the same thing by driving on a dark road at night. Use the paddle; there is no reflection in the traffic signs behind you.
  6. yeah723

    yeah723 New Member

    I see, thank you for the info.
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  8. gedwin

    gedwin Member

    Yes, the brake lights absolutely do come on when not stepping on the brake and using only the paddles, but only when the deceleration requires it.

    It is apparently a government-required safety feature. If the car is slowing down, at some specified threshold the brake lights must come on so as not to surprise an unsuspecting driver behind you. (Basically, our cars must signal like a traditional car would if someone were in fact using the brakes to slow at a comparable rate.)

    I cannot quote you a hard and fast rule, but if you are at a good clip (say 30 mph or above, 4 chevrons will trigger the lights and likely even 3 chevrons would). I'm playing with my new indicator light to understand a little better the conditions under which they come on. In fact, I've discovered there is a game in this: the challenge is to try to use the paddles without triggering the brake lights. Once slowed enough from 1 chevron, you can step up to 2, and then 3, and finally 4 without the brake lights ever coming on! (I did warn in my original post that this was mostly useless!)

    On another note, adaptive cruise control can also trigger the brake lights with your foot off of the pedal, again, depending on what action the car is taking and how quickly it is decelerating. But, for example, the brake lights would light if you come up on a much slower car and the Clarity decides it must slow quickly.
    Kendalf and Fastermac like this.
  9. insightman

    insightman Well-Known Member Subscriber

    Because my battery-powered MINI Cooper SE lights its brake lights when regen braking occurs, I was compelled to add a similar LED so that I could know when I was flashing my brake lights to the cars behind me. That LED has enabled me to adapt my driving style to minimize the frequency of brake-light flashing.

    I planned to do the same for our Clarity PHEV, but I never got around to it. I wanted to know if the Clarity EVER illuminates its brake lights in response to the much milder regen braking the left paddle offers compared to our MINI. I'm glad you were able to answer my question.
    Remarksman and gedwin like this.
  10. Tom H

    Tom H New Member

    Do you have instructions on how to do this? Great idea.
  11. insightman

    insightman Well-Known Member Subscriber

    My instructions for installing an interior brake LED on my MINI Cooper SE will give you a good idea of what's required. The big difference would be how you gain access to the center high-mounted brake light's wiring.

    There is a panel in the center of the underside of the Clarity's trunk lid. This panel has a slot in the right edge which appears to be where you would begin prying off that panel.

    After removing the panel, attach a 12-Volt LED in parallel with the center brake light as I did in my MINI and you're almost done. You can drill a hole in this panel and glue the LED so it's visible just in front of the rear-view window in the trunk lid.

    For a less-permanent mounting while you decide if you want to drill a hole, simply squeeze the wires from the LED between the panel and the trunk lid so the LED dangles in front of the trunk lid window.
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  13. gedwin

    gedwin Member

    Unfortunately I did not take photos as I went, but hopefully this description below can be of some help. (All pics I have are in the original post above, please reference to see positioning of the LED.)

    - LED (for 12V, I choose red for obvious reasons)
    - Resistor (I used 1 kOhm)
    - speaker wire, single conductor (I used 22 gauge)
    - wire crimps (3) or soldering iron
    - electrical tape

    LED Primer: For those who may not know, LEDs (diodes in general) are directional; if yours doesn't light, try reversing the polarity. Also, LEDs typically offer no resistance (unless a resistor is integrated), and therefore will immediately burn out without a resistor in series to limit the current. Read your package or measure its resistance with an Ohmmeter. In my case, I used a 1 kOhm resistor. Remember, you can calculate current as I = V/R, so in my case I = 12V/1000 Ohm = 12 mA. This, by the way, will be about 0.14 Watts (V x I = 12 V x 0.012 mA). For safety, an inline fuse may be advisable to protect from shorts of your wiring system. (I admit I did not use one, but I was very comfortable with the safety of my physical implementation.) So, the basic circuit is: one wire from 12V of the brake light to your resistor then to your LED, then back via your second wire to the ground wire of the tail light. I used crimp joiners for the ends for the wires where they join to the leads of the resistor or LED, and also to join the other ends of the resistor and LEDs to each other. Physically, I arranged this in a straight line so that the LED bulb was at the very end, then wrapped the whole assembly with electrical tape to secure it. (That was about an inch and half long, and the stiffness of this assembly works out well when mounting the LED in step 6 below.)

    1. Access the left brake light by removing 3 black plastic clips from the felt covering, and gently bending it out of place. (Starting near the trunk latch catch and going up the curve to the side above the brake light.)
    2. Locate the single, white plastic plug with 4 wires that plugs into the brake light. Just leave it in place. The top two wires are the brake light (our target) and bottom two are the parking lights.
    3. Strip about a quarter inch from both wires of the speaker wire pair, and gently insert one into each of the top two wire ports on the plastic plug. I recall that the top is 12V and the bottom one is ground. (Use the LED setup to test and ensure you get light when the pedal is depressed.) Again, do this from the backside with the plug still plugged into the brake light assembly on the car. The bare 22 AWG wire can slip in snug without too much trouble, and in my experience makes a reliable contact with the car's wires inside the bracket. Ensure the insulator of your wire is right up to the back of the plug so no bare wire exposed outside of the plastic connector.
    4. Tape your wire to the car's wire bundle going to the brake light for physical support to ensure your inserted wires cannot back out of the plug. Put this tape very close to the plug to ensure support. This will be a good time to test your LED set up to ensure it is lighting when the brake is depressed.
    5. I ran my wire out from the brake light behind the felt lining to the top left of the trunk and then routed to the right straight across to the middle bottom of the trunk window to the passenger compartment. The wire can be readily hidden behind the lining.
    6. I positioned the LED dead center, and just high enough to be viewed from the passenger compartment. Sit in the driver's seat and look through the rear view mirror to confirm positioning, and then tape down against the metal below the window to hold in position (tape is behind the felt liner, and just the end of the LED protrudes to the window). I think middle bottom of the trunk window is the best location, as this lines up nicely with a decal on the outer trunk window to provide a background to the LED and eliminates any back-lighting, such that the LED is easily visible day or night, but is subtle and unobtrusive.
    Remarksman, Daniel M W and insightman like this.
  14. gedwin

    gedwin Member

    Good info, thank you. My main deviations were to go to a side brake rather than the 3rd light on the trunk lid: i) easy access, ii) easy to hide the wire behind the felt liner, and iii) avoid the movement of the trunk lid. I am very happy having it mounted inside the trunk against the passenger compartment window, which avoids the need for drilling, etc. My install is quite functional, but readily reversible (i.e., removable if you decide you don't need it, and it will be like it was never there).
    insightman likes this.
  15. gedwin

    gedwin Member

    So ... I am learning with my new LED toy. It seems the rules for the Clarity lighting its own brake lights are not hard-and-fast. I have absolutely convinced myself that it depends on the main battery's state of charge. If the battery is full, the brake lights come when using the 3rd and 4th chevron (and even the 2nd under if moving fast enough). However, my learning from yesterday is that if the main battery is not full, it is difficult/impossible to make the brake lights come on with the paddles under any circumstances.

    Do we know if the paddles can in fact trigger the mechanical brakes when the main battery is full?? I know there are circumstances in which the engine is made to come on in similar scenarios, so wondering if the car may employ the friction brakes when the paddle are used with a full battery? This might explain why the brake lights come, if they are linked to the actuation of the physical brakes? An alternative explanation would be if the car decelerates more rapidly when the battery is full, requiring the brakes to light to notify the driver behind, however I cannot imagine a full battery would make the regen braking more effective, and in fact I'd guess the opposite.
  16. insightman

    insightman Well-Known Member Subscriber

    The Clarity PHEV can respond to regen braking when the battery is fully charged by starting the engine, which somehow uses up the regen power that cannot go into the battery. I have never experienced or heard of the paddles causing the application of the brakes, but I don't have an interior brake LED to check.

    Do the brake lights ever come on with paddle use when the engine doesn't come on?
    Last edited: Sep 10, 2021
  17. The LED trick is clever and well thought out.

    But might a small, properly placed mirror work? I haven’t tried it, but one designed for a bicycle helmet or small inspection mirror could be placed so that the brake light could be viewed in the corner of the rear view mirror. If too bright some tint could be applied.

    I think. I may be missing something but may play with the idea tonight.
  18. insightman

    insightman Well-Known Member Subscriber

    For a simple check, you could tape slightly crumpled aluminum foil onto the trunk so it reflects the third brake light through the trunk window.
  19. JFon101231

    JFon101231 Active Member

    In my experience it is the opposite - a full battery will slow down via regen much less (without or with the engine forced to run) than a less than half full battery (assuming the same ambient air/batt temps etc)
    gedwin likes this.
  20. gedwin

    gedwin Member

    Good ideas, and not something I thought to test before tearing into my car! However, I just tested (aluminum foil) and in shady daylight I think there is no hope of seeing the reflected light from that 3rd brake light through the outer trunk window. May work at night(?) I can say the LED approach is easily visible in broad daylight.

    Sent from my iPhone using Inside EVs
    insightman likes this.
  21. fotomoto

    fotomoto Active Member Subscriber

    My old Subaru OutBack had an animation driver’s display showing both the OutBack and the (generic) vehicle being followed. It would activated the brakes lights on the animated OutBack model. No guessing.
    gadgetrants likes this.
  22. dnb

    dnb Active Member

    Excellent, I love using ACC and was wondering when it triggers. Would be nice to know if its related to the green regen bar on the dash or what triggers it exactly. I hope that doing general in traffic driving with ACC isn't constantly flashing break lights behind me.
  23. Mowcowbell

    Mowcowbell Well-Known Member

    Guess I'm just old school. I only use the regen paddles after checking my rear view mirror to make sure no car is following me. Otherwise, I just use the brake pedal. No guesswork on whether or not my brake lights are lit. Electricity is cheap. Getting my Clarity rear ended is waay more expensive.

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