# Regenerative braking and Brake lights



## njloof (Nov 21, 2011)

My DMOC445 has outputs for brake lights; from the docs it looks like they kick in when deceleration rate crosses a threshold, regardless of the inputs.


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## Karter2 (Nov 17, 2011)

cts_casemod said:


> Measuring the regenerative current back from the motor is also not a good indicator, since I could be traveling at a constant speed, downhill, hence regenerating, but not necessarily braking.


 without regen ..(in an ICE ) ..when rolling down a hill ,..to keep under the speed limit,.. i use the brakes ,and hence the brake light are on at constant speed.
....situation normal , why be concerned ??


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## 914Mike (May 12, 2013)

http://www.unece.org/fileadmin/DAM/t...gs/R13hr2e.pdf

The relevant paragraph that refers to regen brakes and the stop lights is 5.2.22.4 which lists deceleration limits for regen. Below 0.7M/s/s (Meters per second per second, or per second squared) the requirement is for no stop lights. Between 0.7M/s/s and 1.3M/s/s stop lights are optional, "The signal may be generated". Above 1.3M/s/s stop lights are required, "the signal shall be generated", i.e. stop lights should be lit. 

So you need a way to measure the deceleration to see if the brake lights need to come on. Tesla does this now, brake lights only come on with the pedal or regen above 1.3M/s/s, IIRC.


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## cts_casemod (Aug 23, 2012)

Karter2 said:


> without regen ..(in an ICE ) ..when rolling down a hill ,..to keep under the speed limit,.. i use the brakes ,and hence the brake light are on at constant speed.
> ....situation normal , why be concerned ??


Well... I dont. I change to a lower gear and let the engine do most of the work to avoid overheating of the brakes. Also the ECU cuts the fuel.

Lets supose you are applying the brakes gently to keep the car at a given speed and suddenly you apply full brakes because something gets in your way. The driver behind you will take some time to realise that causing a dangerous situation. Effectivelly its the same as not having brake lights because the driver behind will have to "guess" that you suddenly lost speed.

On my point of view this is an issue cars with auto gearboxes/transmissions have: people use the brakes to mantain speed down hill, so it is wrong for the brake lights to come on, because they are not indicating any danger, rather they are making people behind brake and cause the drivers/traffic behind to slow down without reason

If I could do that, yes I could, but I travel with a child on the back seat most of the time, so anything that can avoid a rear colision is welcome.


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## cts_casemod (Aug 23, 2012)

914Mike said:


> http://www.unece.org/fileadmin/DAM/t...gs/R13hr2e.pdf
> 
> The relevant paragraph that refers to regen brakes and the stop lights is 5.2.22.4 which lists deceleration limits for regen. Below 0.7M/s/s (Meters per second per second, or per second squared) the requirement is for no stop lights. Between 0.7M/s/s and 1.3M/s/s stop lights are optional, "The signal may be generated". Above 1.3M/s/s stop lights are required, "the signal shall be generated", i.e. stop lights should be lit.
> 
> So you need a way to measure the deceleration to see if the brake lights need to come on. Tesla does this now, brake lights only come on with the pedal or regen above 1.3M/s/s, IIRC.


Yeah, I know that, the porpose of this topic is to do some research on what systems people are using, other than factory/controller fitted since I am developing everything on my convertion. If I cant find anything then Ill built my own, but chances are someone already built this before {or maybe not... }


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## njloof (Nov 21, 2011)

Can we assume you have a manual transmission, or are you directly coupled? If the latter, you could correlate motor deceleration to vehicle deceleration.


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## cts_casemod (Aug 23, 2012)

njloof said:


> Can we assume you have a manual transmission, or are you directly coupled? If the latter, you could correlate motor deceleration to vehicle deceleration.


Manual, but I have acess to the gearbox speed sensor, my controller uses that to operate in closed loop.
It would be aceptable to have some device that would read the sensor, the other option is an acelerometer.


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## skooler (Mar 26, 2011)

Could you not control regen from the brake pedal vice the accelerator?

There is usually some travel in the brake pedal before the brakes are actually doing anything (i.e. pads hit disc). using a pressure transducer would be a tried and tested method.

The brake lights could be on at any point in the travel but this should be easy to tweak. In cars I've seen is either a switch on the pedal or a pressure switch on the servo/reservoir.

Hope this helps,

Mike


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## Roy Von Rogers (Mar 21, 2009)

I know this may not be exactly what your looking for but would at least give you some safety when decelerating.

Put a switch on your accelerator pedal, so when its all they way up it actuates the brake signal, you can tie it directly across to your brake switch, so either actuates the brake lights.

Connect the hot to ignition on.

Roy


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## 914Mike (May 12, 2013)

Roy Von Rogers said:


> I know this may not be exactly what your looking for but would at least give you some safety when decelerating.
> 
> Put a switch on your accelerator pedal, so when its all they way up it actuates the brake signal, you can tie it directly across to your brake switch, so either actuates the brake lights.
> 
> ...


So the brake lights would be on at all times other than cruising?
That would be very annoying to someone behind you and would increase the likelihood of someone ignoring your brake lights due to "sensory overload". There's a reason they are referred to as "brake lights", the purpose is to warn driver's behind you that you are slowing down quickly. Lifting the go pedal and slowing at a minimum rate does not warrant lighting the brake lights, in fact it would be a liability to manufacture for sale such a system. Unnecessary brake lights are thought to contribute to traffic jams as well. 

Shouldn't be too hard to find/build a switch that turns on when it decelerates, think ball-in-cage or mercury switch. Calibrating it to the precise legal limit might be a bit more difficult.


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## Ziggythewiz (May 16, 2010)

Someday I want to see all cars have 4 color accerleration indicators. Green lights if you're speeding up, blue if cruising, yellow if coasting, and red for braking.


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## cts_casemod (Aug 23, 2012)

skooler said:


> Could you not control regen from the brake pedal vice the accelerator?
> There is usually some travel in the brake pedal before the brakes are actually doing anything (i.e. pads hit disc). using a pressure transducer would be a tried and tested method.
> The brake lights could be on at any point in the travel but this should be easy to tweak. In cars I've seen is either a switch on the pedal or a pressure switch on the servo/reservoir.
> Hope this helps,
> Mike


I get your idea but thats not really what I am looking for.



Roy Von Rogers said:


> I know this may not be exactly what your looking for but would at least give you some safety when decelerating.
> 
> Put a switch on your accelerator pedal, so when its all they way up it actuates the brake signal, you can tie it directly across to your brake switch, so either actuates the brake lights.
> Connect the hot to ignition on.
> Roy


I already do that. But its pretty much useless. Releasing the acelerator on my car is the same as step hard on the brake (100% Deceleration).
Thats why I never take the foot to the brake. I am already "braking" way before I have time to reach the other pedal
Also the lights stay on whith the car stopped even if I am not applying the brakes, which is a nonsense I want to get rid of.



914Mike said:


> So the brake lights would be on at all times other than cruising?
> That would be very annoying to someone behind you and would increase the likelihood of someone ignoring your brake lights due to "sensory overload". There's a reason they are referred to as "brake lights", the purpose is to warn driver's behind you that you are slowing down quickly. Lifting the go pedal and slowing at a minimum rate does not warrant lighting the brake lights, in fact it would be a liability to manufacture for sale such a system. Unnecessary brake lights are thought to contribute to traffic jams as well.
> Shouldn't be too hard to find/build a switch that turns on when it decelerates, think ball-in-cage or mercury switch. Calibrating it to the precise legal limit might be a bit more difficult.


Haha, No his idea is to use a switch to power the lights when the trottle is not pressed and the ignition is on. But still, not the ideal sugestion
Hes's right, if I take my foot of the acelerator 80% chance you would crash into my car. Takes 2.5 seconds to go from 35mph to zero.
To Cruize I have to keep the acelerator at 50% travel, below that sets negative torque (I control the ammount of de-aceleration as I would with the brake).



Ziggythewiz said:


> Someday I want to see all cars have 4 color accerleration indicators. Green lights if you're speeding up, blue if cruising, yellow if coasting, and red for braking.


I might do that on the future. 
One feature I want to implement is to disable all power to the motor if the requested torque is less than 15% This, allong with a dynamic voltage control depending on the output torque, and not rpm, should further increase the efficiency of the AC motor.
So yes, it would be nice to have some lights telling the driver what was going on


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## ga2500ev (Apr 20, 2008)

> Originally Posted by Ziggythewiz : Someday I want to see all cars have 4 color accerleration indicators. Green lights if you're speeding up, blue if cruising, yellow if coasting, and red for braking.





> cts_casemod: I might do that on the future.
> 
> So yes, it would be nice to have some lights telling the driver what was going on.


I'm not sure if you understood Ziggy's point. He was talking about rear lights to signal to the driver behind you what is going on.

This cannot be done on today's vehicles. It is against regulations to have lighting other than the standard lights that are on the rear of the vehicle. Precisely to eliminate confusion.

At the end of the day you will need an accelerometer to detect deceleration to activate the brake lights. 

ga2500ev


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## cts_casemod (Aug 23, 2012)

ga2500ev said:


> I'm not sure if you understood Ziggy's point. He was talking about rear lights to signal to the driver behind you what is going on.
> 
> This cannot be done on today's vehicles. It is against regulations to have lighting other than the standard lights that are on the rear of the vehicle. Precisely to eliminate confusion.
> 
> ...


Thanks, I thought he meant on the cluster 

There are some mods like on the newer BMW's that iluminate half the cluster for normal deceleration and full cluster to indicate an emergency stop. And other methods like flashing ligts. Honestly have no idea why in todays age something like that is not mandatory.

Agree. If no one comes with a solution thats what I am going to use. Just looking to see if I can save some time. Too many projects at same time


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## JRoque (Mar 9, 2010)

Hi all.


Ziggythewiz said:


> Someday I want to see all cars have 4 color accerleration indicators. Green lights if you're speeding up, blue if cruising, yellow if coasting, and red for braking.


I've seen buses that have something similar. The yellow lights come on when they take the foot off the gas pedal. But having too many lights, IMHO, would cause information overload. You really want to be alerted only when there's a significant change and the different hues, reflections and lightning conditions could create confusion. I'm opposed to daytime running lights for similar reasons.

I think rate of deceleration is a good parameter to determine when to have the brake lights come on. But I also think that, ideally, regen should only be active when the brake pedal is pressed.

JR


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## TooQik (May 4, 2013)

cts casemod said:


> There are some mods like on the newer BMW's that iluminate half the cluster for normal deceleration and full cluster to indicate an emergency stop.


Maybe look into how the BMW's sense the deceleration and see if you can obtain the sensor(s) and adapt it to your purpose.

Another thought is to look into race car telemetry kits/sensors that include g force measurement. This looks promising http://www.race-capture.com/


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## shock (Jul 16, 2011)

JRoque said:


> I think rate of deceleration is a good parameter to determine when to have the brake lights come on. But I also think that, ideally, regen should only be active when the brake pedal is pressed.
> 
> JR


Great thread here. Thanks!

I have a Model S. The brake lights come on using a decelerometer. When I lift my foot from the petal the car immediately goes into regen mode (yes, this is configurable by the driver). It can actually be rather aggressive and brings the car to a stop much more quickly than you would expect. With practice, I almost never touch the brake until that last 5 mph to not tap the car stopped in front of me. This works well, because if I'm in a steep downhill and in regen mode, there are no brake lights because I'm not slowing quickly even with full regen on. It seems to be a perfect balance to notify drivers behind me to be aware when I slow quickly, but not to come on every time regen kicks in.

My DIY car (Porsche 944) has the same challenges listed in this thread. Somehow I have to simulate the Model S for consistency in driving for everyone in the family. If anyone has ideas for decelerometer that integrates into the various controllers we all use please share!

Cheers!
Shock


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## cts_casemod (Aug 23, 2012)

JRoque said:


> Hi all.
> 
> I think rate of deceleration is a good parameter to determine when to have the brake lights come on. But I also think that, ideally, regen should only be active when the brake pedal is pressed.
> 
> JR


Thats the good thing about converting. I drive my way, not the way the manufacturer decided I should drive. My controller can be set between 0 and 200% regeneration, obviously what suits one may not suit another and so on. Personally I find the vehicle overal much more responsive using the throttle only (or at least with less effort).

I drive inside the city, people stop abruptly all the time, pedestrians that dont look before crossing, cars with both brake lights blown (ony the center one working), etc. Half a second saved by changing pedals is a good safety margin. Also I also feel the car more solid, since the speed I want is the speed I get pretty much instantly.


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## tomofreno (Mar 3, 2009)

ga2500ev said:


> ...At the end of the day you will need an accelerometer to detect deceleration to activate the brake lights.
> 
> ga2500ev


 I've played with this a bit. A simple accelerometer can be made from a lever with a magnet on it, with sufficient inertia about an axis of rotation, and a unipolar hall effect device with some hysteresis. A spring determines the threshold force (lever mass*deceleration) to move the lever and turn on the hall device which might then be used to control an ssr to operate the brake lights (threshold depends on the mass of the lever, spring constant and attachment point to the lever, and c of m of the lever). 

The 1.3g threshold mentioned above seems much too high, at least for this mechanism. I measured general slowing for a curve or another vehicle at < 0.2g and most of my stops are < 0.3g. The threshold is also effected of course by incline, so the lights will turn on at lower deceleration going downhill, higher going uphill. You need a more sophisticated device to avoid this. This simple device gives some crude control of brake lights, but likely not as much as desired. The lever/spring does provide good immunity to false triggering due to bumps, as the spring is a poor transformer of vertical to horizontal motion. If a manufactured device, such as the BMW one mentioned, can be found in a junkyard it would likely give more satisfactory operation. Would like to know if you find something.


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## Siwastaja (Aug 1, 2012)

cts_casemod said:


> Thats the good thing about converting. I drive my way, not the way the manufacturer decided I should drive. My controller can be set between 0 and 200% regeneration


You may have taken this already into consideration, but just remember that you need to limit the amount you regen in bad weather. There is a reason why all four tires have brakes and why the brake forces are checked in the vehicle inspection...

Thinking about last winter, our RWD Mitsubishi pickup (not converted yet) was a bit of a challenge to drive safely; even the motor braking from the original diesel engine was enough to put the car into drift on icy roads - even with proper (spiked) winter tires.

So have a regen limiter with three settings: full (e.g. 100%), rain (e.g. 20%), ice (off).

This is why a 4-motor conversion would be so nice; the mechanical brakes would be _really_ only for keeping the car stationary or for electrical failure.

Maybe this is only important in an RWD, but just saying...


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## Duncan (Dec 8, 2008)

Siwastaja said:


> This is why a 4-motor conversion would be so nice; the mechanical brakes would be _really_ only for keeping the car stationary or for electrical failure.


Nope won't work
Re-Gen is limited by the motor size
There are NO cars on the road where the "Braking Power" (from the brake system) is not significantly greater than the drive power

Example
My Subaru Legacy can brake at 0.5G at 120mph
1600kg x 0.5G = 8,000N x 55m/sec = 440Kw = 586Hp

The mechanical brakes will still be needed for when you REALLY want to stop


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## TooQik (May 4, 2013)

Maybe try one of these also: http://www.motec.com.au/sensors/forcemotion/

Actually, just found this link which seems to do exactly what you need, brake light brightness based on deceleration : http://www.freescale.com/files/microcontrollers/doc/app_note/AN3380.pdf


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## cts_casemod (Aug 23, 2012)

Siwastaja said:


> You may have taken this already into consideration, but just remember that you need to limit the amount you regen in bad weather. There is a reason why all four tires have brakes and why the brake forces are checked in the vehicle inspection...
> 
> Thinking about last winter, our RWD Mitsubishi pickup (not converted yet) was a bit of a challenge to drive safely; even the motor braking from the original diesel engine was enough to put the car into drift on icy roads - even with proper (spiked) winter tires.
> 
> ...


Hi,

I have up to 200% regeneration, but I never use that. It is innefficient as in most energy being lost as heat on the electrical system, overloads the batteries etc. I have set the controller to stop the car in about 3-4 seconds at 30MPH and yes I did loose traction a few times when I went into roads with loose debris/sand on the past, but the system now is *dynamic*, meaning I controll how much negative torque I require.

If I press the brake hard the ABS kicks in. No exception, so the front wheels are mainly drivem by the motor, but I have rear mechancal brakes to aid.

As with winter, I set the controller on a similar way as V/Hz. *TIMERS* 
Using timers, even if I command full acceleration (negative or positive) the car will limit how fast you can change speed. So if the wheel is blocked the motor will immediatelly force that wheel to spin. This is much better for traction. Of course it makes you drive a bit slower, but why would any serious driver would be driving fast with ICE/Snow in the road?





Duncan said:


> Nope won't work
> Re-Gen is limited by the motor size
> There are NO cars on the road where the "Braking Power" (from the brake system) is not significantly greater than the drive power
> 
> ...


 

I Think he meant avoiding using the service brake brake under normal situations. I mostly do. I am not making emergency stops all the time and I dont drive agressivelly, so it fits the bill 95% of the time. The remainder takes the rust off the disks  Isnt electric all about economy!?

So effectively for my car size, the only reason the mechanical brakes are just slightly more powerfull that the electric brake is, obviously because the rear brake still does about 30% work, however if I had a 4WD then my electric motor could easialy have 200% of the braking power I had for acceleration, which is close to what manufactires choose for their vehicles (a 1l polo does not have the same brakes as a 2l GTI), more it could make a better use of the rear axle, since it would not be allowed to slip under icy conditions where even ABS is not very efective


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## ken will (Dec 19, 2009)

cts_casemod said:


> but why would any serious driver would be driving fast with ICE/Snow in the road?


That is the most fun time to drive fast! When you are on the edge of losing control. 
When you are close to dying it reminds you of how precious life really is.


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## GizmoEV (Nov 28, 2009)

With many speedometers using a pulse signal for speedometer wouldn't it be relatively easy to just monitor the speedometer pulse and turn on the brake lights when the pulse rate drops by more than a given rate?


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