Revelations From a Visible Brake Light

Discussion in 'MINI Cooper SE' started by insightman, Sep 19, 2020.

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  1. insightman

    insightman Well-Known Member Subscriber

    I was frustrated by not knowing when my MINI Cooper SE was autonomously illuminating its brake lights in response to regenerative braking. Rather than tape a piece of aluminum foil to the hatch to reflect the high-mounted, center brake light into the hatch window, I wired an LED in parallel with the center brake light and mounted it where I could see it in the rear-view mirror. I have put an illustrated step-by-step description of my modification online.


    After my visible brake light was operational, I was disappointed to discover how little regenerative braking is required to illuminate the brake lights. Regardless of whether I choose High-Energy Recovery or Low-Energy Recovery regenerative braking, I found the brake lights flash on and off frequently as I drive. I am using the indicator LED to train myself to know instinctively when I'm displaying brake lights to the car behind me.

    Some tail-gating drivers see my MINI Cooper SE's display of brake lights as an aggressive driver-instigated signal to back off. Other drivers probably assume I'm carelessly driving with my left foot on the brake pedal. My goal is to prevent the brake lights from flashing on
    and off in short, random-seeming bursts.

    The most surprising and disturbing behavior I noted was that the brake lights go dark after the regenerative braking brings the MINI Cooper SE to a complete stop. So if you want to be sure the driver of the car coming up behind you realizes you are stopped, remember to use the brake pedal to illuminate the brake lights.

    I wish the MINI engineers could have developed an artificial intelligence that would illuminate the brake lights more appropriately. Evidently, MINI's lawyers deemed even the level of deceleration typically provided by engine-braking in a gas-powered MINI to be dangerous without illuminating the brake lights of this electric vehicle. Where were those lawyers when it was decided a stopped MINI Cooper SE would not always illuminate its brake lights?

    BTW, I have 48 of these LEDs left over because I had to buy 50 on Anyone who wants a couple can PM me and I'll send them free of charge.
    wessy, Jbrando, Urbanengineer and 7 others like this.
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  3. Miniev1

    Miniev1 New Member

  4. Miniev1

    Miniev1 New Member

    Annoying though it is, it's probably helpful when one is on the learning curve with regen braking.
    Huge help to know that it goes off too.
    I still tend to put my foot on the brake pedal at stop signs etc.
    Force of habit.
  5. Puppethead

    Puppethead Well-Known Member

    Thanks for answering that question! I was planning to rig something up this weekend to see when the brake lights went off and now I don't have to.

    This explains some of the reaction I get from drivers behind me, but I consider them to be tailgaters. Personally I don't care how often the brakes light up or what others think of my driving; EVs are a different kind of vehicle. It would be interesting to compare the regenerative braking lights to other EV makes, though.

    I consider it a fail if I have to touch the brake pedal, and pretty much only step on it when I'm on a downhill since the regenerative braking won't hold the car still.
    NewGreen likes this.
  6. Rich M.

    Rich M. New Member

    I understand the logic behind the brake lights turning off at a stop. Can anyone explain why the manufacturers opt for this?
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  8. insightman

    insightman Well-Known Member Subscriber

    Yes, I, too, would like to know how other EVs handle the brake lights during regen braking. The Honda e displays an image of the car on the dash and its brake lights correspond to those of the real car, but I haven't read how sensitive the brake lights are in relation to regen braking.
  9. KeninFL

    KeninFL Member

    Thanks for all this info, Insightman. Your directions w/pics is first-rate. I was going to take you up on your offer for a LED but it blinking on all the time in my rearview would drive me nuts.
    It's disappointing to know MINI set up the brake lights to flash on so easily. I don't like being behind (ice) drivers who ride their brakes. Their brake lights always flashing is like crying wolf and after awhile you just ignore them coming on -- which is the opposite of what brake lights are for!
    Let's hope soon MINI will issue a service bulletin so that it can be adjusted to be less sensitive.
    polyphonic and insightman like this.
  10. insightman

    insightman Well-Known Member Subscriber

    Remember, lawyers.
    MichaelC likes this.
  11. Puppethead

    Puppethead Well-Known Member

    Off the top of my head, what would be ideal is if regenerative braking lights were another color like yellow (caution), and red reserved for the brake pedal (full-on braking). Or maybe red lights if the deceleration was a certain threshold (second derivative, I believe -- change of velocity over time). There's already an algorithm for when ABS kicks in, so this should be reasonable to accomplish.

    You'd think engineers would have sorted this out after having electric vehicles on the road for over a decade.
    NewGreen, insightman and MichaelC like this.
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  13. CuriousGeorge

    CuriousGeorge Active Member

    The behavior of the SE sounds very much like that of other EVs, e.g,. the Bolt. Indeed, if you think about it would be a bit challenging to have it act otherwise - the brake lights are probably triggered by an accelerometer, and turn on and off as the rate of slowing crosses a threshold. You could make them less sensitive, but then you risk them not coming on when they should. (The threshold might even be set by law...I can't recall.)

    As for them going off once you come to a stop, that's no different than an ICE vehicle with a manual transmission (remember those?).
    joshf2k and ScottIJ like this.
  14. Rich M.

    Rich M. New Member

    Sorry, I meant to say:

    I don’t understand the logic behind the brake lights turning off at a stop. Can anyone explain whythe manufacturers opt for this?
  15. insightman

    insightman Well-Known Member Subscriber

    This MINI Cooper SE is my first car in more than 40 years that didn't have a manual transmission, so my memory is fresh that I could not use engine braking to bring those previous cars to a complete stop. Knowing that the brake lights come on with regen braking would lead one to believe they would stay on after regen braking brings the car to a complete stop. It must have been a conscious decision to have the brake lights turn off after regen braking brings the SE to a stop, but I cannot figure out the rationale.
    wessy likes this.
  16. CuriousGeorge

    CuriousGeorge Active Member

    I imagine that it's not "logic", but just simpler engineering. To have them remain on would require monitoring speed as well as rate of deceleration, versus just relying on an accelerometer.
  17. CuriousGeorge

    CuriousGeorge Active Member

    I wouldn't necessarily expect that behavior.
  18. insightman

    insightman Well-Known Member Subscriber

    I believe the car would be safer if the brake lights were on when the car is stopped. I can't come up with any reasons to turn them off when the car is stopped. The computer that turns on the brake lights during regen braking knows when the car is stopped, so it could keep the brake lights on then to reduce the chance of a rear-end collision. What would the lawyers say?
    wessy likes this.
  19. Puppethead

    Puppethead Well-Known Member

    The only reason an ICE car's brakes are on when one is stopped is because the brake pedal is pressed. Without the brake an ICE car creeps forward, unless shifted into neutral. My 2015 Hardtop had a mode to shut off the engine when braked to a stop, and would start up again when taking the pressure off the brake.

    It seems the SE basically works the same way at a stop, needing the brake pressed to engage the brake lights. The friction from regenerative braking increases the times when you don't need to stand on the brake pedal, but it's similar to an ICE car on a level surface. I don't see why the brake lights would be on if the brake pedal isn't pressed, ICE cars don't and the regenerative braking isn't stopping the already-stopped vehicle.
    joshf2k and F14Scott like this.
  20. insightman

    insightman Well-Known Member Subscriber

    "ICE does it this way" talk doesn't address the issue of safety. Is MINI more worried about wearing out the brake LEDs than having a clueless car pile into those dormant brake LEDs when the SE is stopped on foggy day or in a driving rainstorm? Is there any reason to have the brake lights turn off when the car is stopped other than that's the way it's been done forever?
    wessy likes this.
  21. F14Scott

    F14Scott Well-Known Member

    I'll play devil's advocate with a couple of scenarios.

    A person is backed up to a window to test whether the brake pedal is activating the stop lights. If the car automatically applies the lights at a stop, there would be no way to know if the brake pedal switch is operative.

    Sometimes, at night, I use the glow of the brake light to help me determine if my pedal is applying braking force (usually while backing up). If it's on all the time, I would lift off the brake pedal but not be able to tell that the car was now free to roll, or, worse, I'd think the car is being held when it is actually free to roll.

    I think the stop lights should be triggered only when a) the brake pedal is depressed, or b) when the car decelerates at a rate greater than the max engine braking decel power of an ICE F56. This would provide consistency across the platforms.
  22. MichaelC

    MichaelC Well-Known Member

    I was previously in the camp that the brake lights should remain on after coming to a complete stop via regeneration. But I think that should only be true if the car can remain at a complete stop without using the brakes. As I have read/seen in some video reviews, it will only remain still on fairly level ground--it will creep/roll with enough of an incline. My guess is they expect the driver to use the brake pedal to remain stopped, even if that stop was achieved via regenerative braking.
    joshf2k likes this.
  23. CuriousGeorge

    CuriousGeorge Active Member

    So I looked it up. While the US apparently doesn't have any specific rules, international law prohibits illuminating the brake lights ("stop lamps") when the rate of deceleration is <0.7 m/s^2: Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:

    Vehicle decelerations Signal generation
    ≤ 0.7 m/s² The signal shall not be generated
    > 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
    > 1.3 m/s² The signal shall be generated


    The question then devolves to what extent Mini wished/wishes to make market-specific modifications to their software.

    (BTW, I just read elsewhere that the Hyundai Kona has been changed to keep the brake lights illuminated even after the vehicle is brought to a stop using regenerative braking...presumably only in the US, of course.)
    Last edited: Sep 21, 2020
    wessy and MichaelC like this.

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