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How are the trailer brake lights engaged when letting off accelerator pedal?

TN2NFL80

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I’ve never owned a EV vehicle so I’m not familiar with the capabilities with regard to towing a trailer. I imagine it’s a software mode but wanted to ask the forum how are the trailer brake lights engaged if all (or mostly) one is using to slow the vehicle is to let off the accelerator pedal? Is the software programmed to engage the trailer brakes/lights when one releases the accelerator?
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I’ve never owned a EV vehicle so I’m not familiar with the capabilities with regard to towing a trailer. I imagine it’s a software mode but wanted to ask the forum how are the trailer brake lights engaged if all (or mostly) one is using to slow the vehicle is to let off the accelerator pedal? Is the software programmed to engage the trailer brakes/lights when one releases the accelerator?
The trailer brake lights are wired to the vehicle brake lights. As discussed in other threads, when you let off the pedal the regenerative breaking engages the vehicles brake lights which would in turn engage the trailer brake lights.
 

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its a round pin so should be able to do trailer brakes as well as the lights. I would assume they would match the trucks tail lights on weather they come on at regen or not.
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TN2NFL80

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its a round pin so should be able to do trailer brakes as well as the lights. I would assume they would match the trucks tail lights on weather they come on at regen or not.
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I haven't seen any info on how it's actually going to work with the Rivian's Regen system. If Regen is strong enough to slow the vehicle and a loaded trailer without using the trailer brakes, you might not want it to act that way if you are on something other than clean dry pavement. But using the trailer friction brakes will mean reducing your range, since you aren't recuperating as much energy from stopping.

From a physical standpoint, they have said there is an integrated trailer brake controller and the Rivian has the standard 7-pin connector that's needed to control trailer brakes.
 

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There's a vehicle standard out there from DOT or someone that I think calls out something to the effect that if the regen is slowing you a certain amount (I want to say 0.3G, but that sounds a little too high), the vehicle must light up the brake lights. This is generally how EVs work. There's a SW threshold for where regen is being used enough to trigger the brake lights, regardless of brake pedal use.
 

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There's a vehicle standard out there from DOT or someone that I think calls out something to the effect that if the regen is slowing you a certain amount (I want to say 0.3G, but that sounds a little too high), the vehicle must light up the brake lights. This is generally how EVs work. There's a SW threshold for where regen is being used enough to trigger the brake lights, regardless of brake pedal use.
To add a data point, in my Bolt EV in L mode (which is max Regen) the brake lights will come on shortly after the accelerator is fully released, even in situations where the vehicle is not actually slowing down because of Regen limitations and you aren't using the brake pedal. If the brake lights on the car come on, the trailer lights will as well.

It doesn't have to be fully released for the lights to come on in situations where you are actually slowing down from regen.
 

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There's a vehicle standard out there from DOT or someone that I think calls out something to the effect that if the regen is slowing you a certain amount (I want to say 0.3G, but that sounds a little too high), the vehicle must light up the brake lights. This is generally how EVs work. There's a SW threshold for where regen is being used enough to trigger the brake lights, regardless of brake pedal use.
I drove stickshifts for years and we engine braked. Never touched the brakes until under 20mph. They never lit up. This must be an EV thing.

As long as the lights aren't tied to the trailer brakes, I don't care though. Traditionally they are, but the computer might be smart enough to not do this.
 

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There's a vehicle standard out there from DOT or someone that I think calls out something to the effect that if the regen is slowing you a certain amount (I want to say 0.3G, but that sounds a little too high), the vehicle must light up the brake lights. This is generally how EVs work. There's a SW threshold for where regen is being used enough to trigger the brake lights, regardless of brake pedal use.
I too think that DOT regs require the brake lights to illuminate whenever the vehicle decelerates by more than a threshold amount. Clearly the motor controllers must know rotor speed precisely in order to do their thing and the vehicle may have independent accelerometer(s) as well so certainly the software knows the vehicle state and can turn on the brake lights (and thus send a signal to a connected trailer's lights as well) whenever the vehicle slows whether the brakes are pressed or regen is on or both.
 

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I drove stickshifts for years and we engine braked. Never touched the brakes until under 20mph. They never lit up. This must be an EV thing.

As long as the lights aren't tied to the trailer brakes, I don't care though. Traditionally they are, but the computer might be smart enough to not do this.
That's because manual transmission engine braking is such an old thing, it's from well before anyone even thought of adding "logic" to turn on the brake lights when you do so - the brake lights engaged based on a switch attached to the brake pedal, that's it. Many modern cars with "throttle/brake by wire" systems (which includes all EVs and many non-EVs now) the computer has to decide when to turn on the brake lights. So why not turn it on when you're decelerating hard even if you're not stepping on the brake pedal?

As for trailer brake lights coming on - my old diesel pickup's third party trailer brake controller will turn on the trailer brake lights if I use the trailer brake control, even if I'm not stepping on the truck's brake pedal. I would expect the Rivian's integrated trailer brake controller to do the same.
 

pc500

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That's because manual transmission engine braking is such an old thing, it's from well before anyone even thought of adding "logic" to turn on the brake lights when you do so - the brake lights engaged based on a switch attached to the brake pedal, that's it. Many modern cars with "throttle/brake by wire" systems (which includes all EVs and many non-EVs now) the computer has to decide when to turn on the brake lights. So why not turn it on when you're decelerating hard even if you're not stepping on the brake pedal?

As for trailer brake lights coming on - my old diesel pickup's third party trailer brake controller will turn on the trailer brake lights if I use the trailer brake control, even if I'm not stepping on the truck's brake pedal. I would expect the Rivian's integrated trailer brake controller to do the same.

Yep that's not the issue though. What I want to ensure is that the trailer brakes are not actuated, when merely the brake lights come on. The trailer brakes should only be actuated when you actually press the pedal.

There's a fine difference I'm okay with the light coming on but not with the brakes themselves activating.

Why is this important because in most pickup trucks today the trailer brake controller actually just taps into the brake light for a signal on when you're actually braking. So if you falsely illuminate the brake light even on a pickup truck that's gas today your trailer brakes will start dragging the whole package when you don't want it.
 

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Yep that's not the issue though. What I want to ensure is that the trailer brakes are not actuated, when merely the brake lights come on. The trailer brakes should only be actuated when you actually press the pedal.
I don't actually think that's quite right.

I understand the EV + regen mindset of "don't use the friction brakes unless you have to because I want to get that sweet energy back"

But if the tow vehicle is slowing down *drastically* and the trailer isn't applying brakes at all then the truck/trailer system can quickly go awry.

Why is this important because in most pickup trucks today the trailer brake controller actually just taps into the brake light for a signal on when you're actually braking. So if you falsely illuminate the brake light even on a pickup truck that's gas today your trailer brakes will start dragging the whole package when you don't want it.
The trailer brake wire out of a controller to the trailer harness has a variable voltage signal, from 0v-12v.

0v = "No brakes"
6v = "Some brakes"
12v = "MAXMIUM BRAKES"
... all on a continuum.

There's two types of trailer brake controllers: Time-delayed, and proportional.

Time-delayed generally tap into the brake-light signal and they have an algorithm that ramps up the trailer brake signal depending on how long the brake lights have been on. They have some other smarts and tricks for guessing when to give more or less, but they're driven solely off of the "on/off" nature of the brake light signal.

Proportional controllers are driven based on how much braking force the tow vehicle is undergoing to make sure the trailer matches up.

My money is on the R1T controller being proportional.

THAT SAID, I would actually be surprised if it didn't apply trailer brakes under moderate regen - The type of deceleration that an ICE vehicle could only accomplish with the brake pedal pressed.
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