Regenerative Braking Capacity

ajdelange

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I hope humorous posts are not discouraged here because i absolutely agree that putting a little humor into these posts is a great idea. I have also found over the years that it helps people remember what it is I am trying to get across. In case you missed it "FM" is navy slang. "M" stands for "magic".

As to the math aspects of regenerative braking the Wikipedia article at https://en.wikipedia.org/wiki/Regenerative_brake might be a good place to start. Where you go from there will depend on how deep you want to dig. Full appreciation will require basic knowledge of engineering and/or physics. If you have a background in those you will be fine. If you don't it isn't likely that you will want to undertake to obtain one but lots of non technical people do become technically versed in some aspect of technology if they have an interest or need. Math isn't the only way to understand these things. I always used to immensely enjoy observing two guys I knew work together on the same problem. One was a PHD and the other an HSG (high school graduate). Both very bright guys.
 

godfodder0901

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I hope humorous posts are not discouraged here because i absolutely agree that putting a little humor into these posts is a great idea. I have also found over the years that it helps people remember what it is I am trying to get across. In case you missed it "FM" is navy slang. "M" stands for "magic".
I'm retired Navy, and we always added a "P" (pure) in front of that to make it PFM.
 

cllc

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I think you are saying that having regen is better than not having it. That's certainly true. And I think you are saying that it is especially valuable in a heavier vehicle as a heavy vehicle puts more demand on its braking system. Also true.
You Gotter Otter.
 

Jay Olson

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So does anyone know if our Rivian vehicles will have some method to allow drivers to control the amount of regenerative braking? There was some mention of settings in Teslas. In my Outlander PHEV there are paddles on each side of steering wheel that allow me to control the regenerative braking from B-0 to B-5. I have been using those paddles for a year and a half, and I absolutely love them. What will my RS1 have?
 

ajdelange

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No one here knows for sure of course but I think we can be pretty sure that there will be a control. The advantages of regenerative braking are clear but, as this thread shows, there are Luddites in the world. They don't appreciate those advantages or find regenerative braking so annoying that they don't care about losing them. For those people there should be a means to disable it. Every EV that I know of which has it has a way to turn it off or limit it. i just can't imagine that Rivian would be different.
 

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My guess is that the brake components are sized on the assumption that regeneration will handle at least some of the braking load. To repeatedly stop a 6,000-pound vehicle using only friction braking will put a lot of wear on even the largest discs and beefiest pads, which in turn will significantly increase the unsprung weight. I suspect this is the reason that Tesla allows the driver to select a lower level of regen but not to turn it off entirely.

I know some people don't like regen braking, but it is the feature I miss most when I'm driving my ICE vehicle in traffic or through parking lots. It took me all of 5 minutes to get used to it.
 

ajdelange

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I'd assume the friction braking system is designed to handle the entire braking chore i.e. it is the same braking system that they would put on the car were no regen braking available. Keep in mind that if you have to park your car outside in temperatures as high as 50 °F you will start to lose regen (I was really surprised by this when I took my foot off the accelerator the other morning and the car didn't slow down as I expected it to*). Thus, if, for example, your commute is half an hour or less and you don't have a heated garage available you may have no regen available during the winter months in the northern parts of the US and Canada.

*This leads to a "want to have" item for the Rivian's (and Telsas): A chime and screen alert "WARNING: Battery Cold: Regenerative Braking Limited" when you put the car into Drive on a cold day.
 

Hmp10

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I didn't realize that cold weather had that much impact on regenerative braking. Comes from living in south Florida, I guess.

I would assume that the battery warming circuits that kick in during cold weather do something to reduce this effect?
 

ajdelange

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I don't spend the winters up here so I don't know the details. There is the potential to damage the battery by charging it when cold (hence the limitation on regen) whereas with discharging the main effect is reduction in effective capacity which, presumably, is recovered when the battery warms as it does with driving as the motors and the inverters are on the same loop as the battery (in the X) so waste heat from them goes to the battery and after about half an hour of driving the regen limitation goes away. That's in moderately cold weather. Don't know what would happen below 0. i'm sure the question has been studied carefully with respect to how much heater energy does it take to warm the battery to the point where the extra energy recovered is greater than the energy invested. The battery heater will come on if the nav system sees that you are enroute to a Super Charger and the battery is cold.
 
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cllc

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I don't spend the winters up here so I don't know the details. There is the potential to damage the battery by charging it when cold (hence the limitation on regen) whereas with discharging the main effect is reduction in effective capacity which, presumably, is recovered when the battery warms as it does with driving as the motors and the inverters are on the same loop as the battery (in the X) so waste heat from them goes to the battery and after about half an hour of driving the regen limitation goes away. That's in moderately cold weather. Don't know what would happen below 0. i'm sure the question has been studied carefully with respect to how much heater energy does it take to warm the battery to the point where the extra energy recovered is greater than the energy invested. The battery heater will come on if the nav system sees that you are enroute to a Super Charger and the battery is cold.
I live in Wisconsin and in the winter I purposely time the charging of my car so it reaches its designated charge with in 15 minutes before I have to leave for work in the morning so I do not have to experience the regen limitation.After work as you said I do have regen limitations for 20 to 30 minutes when it is moderately cold.
 

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That is news to me...Hopefully this will be a non-issue with Rivian's BMS. Also thankful that I am in Florida. Up in Jax we still get some pretty cold temps but nothing that lasts for days on end. Thanks for the info though.
 

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That is news to me...Hopefully this will be a non-issue with Rivian's BMS. Also thankful that I am in Florida. Up in Jax we still get some pretty cold temps but nothing that lasts for days on end. Thanks for the info though.
I doubt the Rivians will be much different. It’s a question of energy - if you want to spend energy to warm the battery prior to departure then you can reduce or remove that regen limitation. Many cars allow you to set departure timers to warm or cool the cabin and battery. Is Tesla not one that does?
 

ajdelange

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Tesla does not, AFAIK, have a battery pre-warm feature except when approaching a super charger. Seems it would be easy enough to do and not use battery energy when connected to shore power. Thus, the only option I believe one has is to do what is described in #55 and rely on the waste heat from charging done just before departure. Teslas have 11.5 kW chargers that run 90% efficient so there is a little over a kW waste heat available. The battery is pretty massive so I'm a little surprised that a couple of kWh can warm it enough but I guess it can.
 
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So does anyone know if our Rivian vehicles will have some method to allow drivers to control the amount of regenerative braking?
FWIW, I came across this in another forum:

I came across this post on the Rivian Facebook Group from a guy who attended the recent even in Atlanta.
He shared a bunch of information that he learned ...

- Adjustable regenerative braking: the engineer I asked couldn’t tell me for sure, but said it is very likely as it is only a software setting.
</snip>
 

ajdelange

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I have to correct what I said in No. 58. The 3 manual says that prewarming the cabin will pre warm the battery.
 
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