Brake light indicator for regen braking

[ENirogus]

This is a great idea, I may have to try something on my Kia

 

[Kendalf]

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.

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!)

What year Clarity do you have? It's weird, when I first got my car (2018) I was very excited to test the regenerative braking and I used the right mirror blind spot camera to detect when the brake lights came on while driving on a dark street. I was absolutely positive that I did see the brake lights come on with regen. However, several months later when there was another discussion on this in the forum (it comes up every few months) I decided I wanted to capture this on camera. But all my attempts to get the brake lights to come on with regen only while the camera was rolling failed. I used regen when coming off a freeway at high speeds as well as on local roads. But even with maximum regen in effect, the brake lights did not come on in my car, and I became convinced that I must not have seen it happen previously.

So now with your results I'm back to being confused about whether this does or does not happen. And if it does, I'm wondering if its a change they did with newer models versus the original batch (mine was purchased Jan of 2018, one of the first several thousand produced).

 

[John Lumsden]

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.

There are indeed specifications to which the cars will be constructed.

This is from https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2018/R013hr4e.pdf
UN Regulation No. 13-H

Uniform provisions concerning the approval of passenger cars with regard to braking

I suppose the rate of deceleration will vary depending how loaded the car is, which would be why there is the "may be generated" band, so it wouldn't directly correspond to a particular regen level under all conditions.

 

[insightman]

Now someone with an app will hopefully tell us if the Clarity PHEV's regen braking can achieve 0.7 meters per second squared.

 

[gedwin]

What year Clarity do you have? It's weird, when I first got my car (2018) I was very excited to test the regenerative braking and I used the right mirror blind spot camera to detect when the brake lights came on while driving on a dark street. I was absolutely positive that I did see the brake lights come on with regen. However, several months later when there was another discussion on this in the forum (it comes up every few months) I decided I wanted to capture this on camera. But all my attempts to get the brake lights to come on with regen only while the camera was rolling failed. I used regen when coming off a freeway at high speeds as well as on local roads. But even with maximum regen in effect, the brake lights did not come on in my car, and I became convinced that I must not have seen it happen previously.

So now with your results I'm back to being confused about whether this does or does not happen. And if it does, I'm wondering if its a change they did with newer models versus the original batch (mine was purchased Jan of 2018, one of the first several thousand produced).

Mine is a 2019 model year, manufactured 12/2018.

I hope you saw my followup post that even in my car, it seems to be tied in to my battery SOC. Test yours with a full battery and see what happens?

I see others have posted regarding the deceleration requirements - that is beyond me. I can just tell you if the light comes on or not!


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[gedwin]

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? ...

I had opportunity to drive yesterday starting with a full battery and wet/rusty brake discs, and I learned something that was entirely new to me but not sure if it is already known with this forum: use of the paddles can indeed trigger the friction brakes.

Evidence while the battery SOC is near 100%:
- brake lights are triggered by the paddles when the battery is at full capacity, but seem not be when a few miles have been driven off the battery. (This I had already observed, but repeated it again.) When completely full, the brake lights come on even with just 1 chevron of paddle. Later after driving a bit, only the 3rd and 4th chevrons trigger it, and eventually these go away too.
- the energy meter shows the same amount of 'green' regen with the paddle, regardless of whether 1, 2, 3 or 4 chevrons. (Later, once the battery has been used a little, the degree of the energy meter green recovery increases with increasing chevrons steps.
- most convincingly, because my brakes had sat a bit after being wet from rain, they had that thin layer of rust that makes a low grumbly/rubbing noise when initially activated. I heard this noise definitively while using only the paddles to decelerate, and stopped the noise by stepping the chevrons back down.

Again, all of this only happens when the battery is nearly full. Once a few miles are driven off and the battery can accept a charge, the brake lights no longer come on with the paddle use, the brake noise ceased, and the green energy showing regen recovery stepped incrementally with each chevron increases.

So, it seems rather than starting the engine to deal with excess energy from attempting to regen brake on a full battery, my car (2019 PHEV) instead simply uses the friction brakes in concert with a low and variable amount of regen recovery.

I had not been expecting this and found it interesting to learn. Again, this may be old news...

 

[gedwin]

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?

To answer your question and to complement my post preceding this one, at no time did the engine come on. EV mode throughout.

 

[insightman]

To answer your question and to complement my post preceding this one, at no time did the engine come on. EV mode throughout.

Thanks! To my surprise, it appears that Honda decided to provide consistent paddle braking power when the battery is fully charged, even if it requires activating the mechanical brakes.

I wonder why my Clarity sometimes (battery not fully charged) rejects the number of chevrons I select and, instead of activating the brakes, lowers the number of regen chevrons it is willing to grant?

 

[gedwin]

I wonder why my Clarity sometimes (battery not fully charged) rejects the number of chevrons I select and, instead of activating the brakes, lowers the number of regen chevrons it is willing to grant?

And for the record, my car surely does the same thing in rejecting 4 or even 3 chevrons at times. This did not happen in my testing yesterday on flat road - 4 chevrons were accepted with a full battery at that speed, but with the apparent application of friction brakes. I’ve noticed the “rejection” in the past mainly when going downhill with significant speed and a full battery. So, it may be a question of magnitude of the energy to be absorbed? I really don’t know, but is sure seems that there is some decision making going on by the car.

I have not yet tested whether the rejection/flashing chevrons condition still triggers the brake light, but I will have opportunity to test that in the future and will report back. (I suspect it will.). This begs the question why it should reject at all, and not simply apply more friction braking? (If that is indeed what is happening as it seems to be.)




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[David Towle]

Now someone with an app will hopefully tell us if the Clarity PHEV's regen braking can achieve 0.7 meters per second squared.

On full braking, family cars nowadays can generate about 0.9 g. Sports cars can typically do 1.1 g or more.
1 g = 32 ft/sec^2.
0.9 g = 29 ft/sec^2 = 8.8 m/sec^2

So the 0.7 m/sec^2 is less than 10% of full braking. I'm 100% sure the Clarity regen can do that much, probably with a maximum of at least 2.0.

 

[GaryClark]

Regeneration needs to be able to store the energy so if fully charged you'll get very little regeneration if any and if none they you are just coasting and I'd expect the brake lights to no reflect you effectively coasting. As with any vehicle it's best to verify like many have, the characteristics of the vehicle they are in to make sure they are aware of indicators and when the friction brakes are automatically applied while in adaptive cruise if so equipped.

 

[Ton K]

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.

Perhaps a slightly simpler solution... a dab of hot glue and a foot of fiber optic cable.