# accelerometer for regen brake lights



## rwaudio (May 22, 2008)

Since you mention the regen current, that's probably how I would do it. One of the panel current meters with relays built in would do it and make it adjustable, if you already have a shunt, or have a meter you are good to go. (If it's your main meter you would need to confirm the relays can be tripped with a negative current) or switch the measurement direction.

http://www.lightobject.com/Programmable-4-Digit-Red-LED-ACDC-AmpCurrent-meter-with-dual-control-Good-for-HHO-System-P415.aspx

Tweaking the filter settings would give you a bit of hysteresis and noise filtering.

A JLD404 could do the same thing if you program one of the relays to work off the current measurement.

What AC system do you have that doesn't already have provisions for brake lights?


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## tomofreno (Mar 3, 2009)

I have a Curtis 1238-7501controller. It has a brake input which is similar to the throttle input, i.e. it can operate with a potentiometer or 0 to 5V input. People use a pot operated off the brake pedal (cruisin posted on that approach here somewhere) or a pressure transducer in the brake line (the approach HPEVS uses) with this controller, but I prefer to operate regen off throttle as in the Tesla S and BMW i3.

I tried for a couple years to get Brian at HPEVS to add some VCL code to control a controller D.O. for the brake lights off of the regen current parameter in the code without success. There are issues such as:

1) If you use a transmission as I do then the rate of decrease of motor rpm for a given vehicle deceleration rate depends on which gear you are in since motor rpm = g*wheel rpm, g is the overall gear ratio so using pulses from the motor encoder doesn't work. Using pulses from the speedometer bypasses this one.

2) The brake lights can flash on when you shift gears if you are triggering regen simply by negative current or by deceleration rate. Adding a delay of 1/3 second or so would seem to address this one.

You have to decide what threshold deceleration triggers the lights – high enough that the lights don’t come on if you slow moderately going around a bend or for other low decelerations. You don’t want them to come on with any value of negative current or they will be flashing on and off too frequently, so current has to be negative for some minimum time and above some minimum magnitude. 

Both my TBS gauge/shunt and the Curtis Spyglass can display battery current (Curtis estimates it, no shunt), but I don’t have easy access to those signals. Using regen current would work better for the above reasons. I would need to test if adding the JLD to the shunt would affect the TBS readings. If there is an alarm that can be used to trigger on some threshold current, then yes, with some filtering to add a delay it might work well. I thought adding a few lines of VCL code in the controller would be the easiest, but I don't have access. It seems all that is required is to trigger an available D.O. when the regen current parameter is above some threshold for some minimum amount of time.


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## arklan (Dec 10, 2012)

might seem like a dumb idea but why dont u just change the brake light switch in the brake pedal over to the accelerator pedal, so when u lift ur foot off the brake lights come on.
if having the brake lights come on for a few seconds between gear shifts bothers u, just put that delay tomo was talking about


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## rwaudio (May 22, 2008)

Most regen systems are variable and brake lights would be desirable long before the regen level of removing your foot from the throttle completely.


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## Roy Von Rogers (Mar 21, 2009)

Why not put a switch on the accelerator so when your completely off the pedal the brake light is on, even when sitting at a light it doesn't hurt to have the brake light on, all automatics ice vehicles do it by default.

I think you all overthinking this.


Roy


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## QuietCar (Jan 3, 2013)

A simple trailer pulling brake accelerometer could do that and is adjustable for sensitivity too. (You know, the one you use to signal trailer brakes. Only use it for brake lights.........

ANY deceleration above a set point = a brake light signal.

QC


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## tomofreno (Mar 3, 2009)

Roy Von Rogers said:


> Why not put a switch on the accelerator so when your completely off the pedal the brake light is on, even when sitting at a light it doesn't hurt to have the brake light on, all automatics ice vehicles do it by default.
> 
> I think you all overthinking this.
> 
> ...


 See post #5 just above yours.


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## tomofreno (Mar 3, 2009)

You mean like the fourth one down here:

http://www.curtmfg.com/Category/200/Brake%20Controls

- or the more expensive ones below it? $190 is much more than I paid for all the components and the board to make what I have and it is much smaller than the above control so it easily mounted under the dash. That one might be made to work by someone who didn't want to make a circuit. I still like triggering off regen current better, just don't see a way to do it easily with my set up.

I've driven with it more now and it is working well enough that I don't have much motivation to look into anything else.


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## dcb (Dec 5, 2009)

why are electric cars re-gen off accelerator, that seems so, ICE like. Besides you will look like you are riding your brakes up every steep hill with an accelerometer :/

brake lights belong on the brake pedal (as does regen). coast at throttle off and you will go farther per watt. Brake when it is time to brake, two different functions.


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## tomofreno (Mar 3, 2009)

dcb said:


> why are electric cars re-gen off accelerator, that seems so, ICE like.


 Uh, my ice cars have all had a separate brake pedal for braking. If I release the accelerator I get some slowing in an ice vehicle, but not nearly as much as you can get with regen. But it helps hold my speed going downhill, which is another thing I use regen for, like engine braking.



> Besides you will look like you are riding your brakes up every steep hill with an accelerometer :/


 The opposite, downhill, which wouldn't be all that bad, but it doesn't do that on grades I've driven on.



> brake lights belong on the brake pedal (as does regen). coast at throttle off and you will go farther per watt. Brake when it is time to brake, two different functions.


 Too simplistic. You can't coast when the car in front of you is going slower than you can coast, nor can you slowly coast to a light holding up traffic. When it is time to brake, brake regeneratively and recapture some energy rather than burning it off with friction. You can coast simply by easing up on the throttle to give zero current. I've been driving this way for 5 years and enjoy it. You drive the way you want.


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