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Regenerative Brakes / Full Battery

12K views 23 replies 7 participants last post by  blueowl442 
#1 · (Edited)
Has anyone ever gotten the dash message that regenerative braking is disabled because the battery is full?
PHEV thing?

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#4 ·
If I go down the hill after leaving my garage, I have a 1/2 mile of pretty steep slope. I can go about half way, and then the ICE will fire to offer compression braking. I've never seen that message on my display, though.

To avoid the ICE coming on, I can "zig zag" by taking a left turn just before the ICE would start, and I use 1% of the battery to reach the next downhill street. I can then regen the rest of the way down, bringing the battery back to 99% and no ICE needed.
 
#5 ·
Today I noticed for the first time that the battery was completely full but from what I could tell there were two bars of regeneration shown on the dash while coasting. I didn't try the left paddle shifter to increase regen. braking to see if I got that message but I'll be sure to do it the next time this happens while mountain driving.
 
#6 ·
Also, I have a few general questions about regenerative braking after taking a Denver foothill drive today if anyone can help, please.

1. When using the Smart Cruise Control, does the system only use regenerative braking when slowing as you come up behind another vehicle or going downhill to maintain the programmed speed?

2. Do the brake lights come on as I would hope when regenerative braking occurs during cruise control while coming up behind a slower vehicle, etc? I would doubt that the brakes lights would come on when just maintaining speed while going downhill. Also, there's the option of braking entirely with the left paddle shifter (by holding it) and I would hope that would also engage the brake lights. Any thoughts?

3. In my previous car (a Prius), using the brake peddle engaged regenerative braking to a certain extent as well. To what degree is the Niro like this? I noticed many more bars of regeneration shown on the dash while using the left paddle shifter to engage regenerative braking than when just using the brake pedal. I guess what I'm noticing is that use of the paddles is much more effective at regeneration than using the brake pedal and in fact, maybe the brake pedal only engages the actual brake pads?

Thanks for your help, everyone!
 
#7 ·
Even with the battery showing full, there's likely a little buffer to allow for regen. I can pull out of my garage (uphill for 20 feet) fully charged then regen down a half mile hill. I get just over half way down before the ICE will fire to provide compression braking. so even the "full" battery has a hair of space at the top.

1) Smart Cruise will use regen up to the point the system is calling for more braking than the system provides, such as the radar detecting traffic ahead. It will then apply the mechanical brakes as needed. Since yours is the 2020, the SCC is capable of bringing you to a complete stop without you needing to apply the brakes. It does this with regen until the speed it too low, and then applies the brakes. My 2019 will not come to a stop, but disengages when the car slows to 5 MPH and I have to stop it myself.

2) From what I can see when it's dark outside, regen will turn the brake lights on. What I don't know is if there's a threshold of slowing percentage where the lights come on. My previous Outback also had smart cruise, and it also had a dash display that showed the lights coming on. While that car did not have regen (not a hybrid) I could see that light braking did not turn the lights on.

3) In my 2019 (no paddles), the brake pedal is the sole means of the driver actuating regen. Above 40 MPH I can peg the power meter at full regen, but as the speed drops it will only reach mid-regen on the display. You might be misunderstanding the function of the paddles, or maybe it's me. :D I thought the paddles only controlled the level of regen. When you press the paddle, yes it might be adding additional regen, or more likely just changing the regen level, which would increase the regen (and show further into regen on the dash) for a given brake pedal pressure. But I am certain that you are using regen when you first apply the brakes. The power meter moving into regen is a pretty good indicator.
 
#8 · (Edited)
3) In my 2019 (no paddles), the brake pedal is the sole means of the driver actuating regen. Above 40 MPH I can peg the power meter at full regen, but as the speed drops it will only reach mid-regen on the display. You might be misunderstanding the function of the paddles, or maybe it's me. :D I thought the paddles only controlled the level of regen. When you press the paddle, yes it might be adding additional regen, or more likely just changing the regen level, which would increase the regen (and show further into regen on the dash) for a given brake pedal pressure. But I am certain that you are using regen when you first apply the brakes. The power meter moving into regen is a pretty good indicator.
Thanks, Dan!

Yes, the paddles offer three levels of added Regenerative Braking. The left paddle increases it and the right paddle decreases it. I wasn't trying to understand how they work while I'm adding brake pad pressure, but rather how they work independently so I can tell which offers more regeneration. When using the brake pedal alone today, I didn't notice much more than a couple bars on the regeneration indicator even if I pressed harder on the peddle. I'll check this again at different speeds the next time I have a chance to see if I can get the brake pedal to offer the same level of regeneration I'm seeing by increasing it to the fullest extent (level 3) with the left paddle shifter. You can also hold the left paddle and bring the car to a complete stop, I think. There's so much to learn and I guess that will keep my mind active for a few more years! To be honest, I thought the paddle shifters would work the same as past VW's I've had when I moved the shifter into the equivalent of the Niro's "Sport" mode. In other words, I thought they would offer up and down shifting of gears in addition to manually moving the shifter lever. Well, I'm still not 100% sure of how they operate once you enter "Sport" mode, but I did use the gear shifter today to select gears on mountain roads and was pleased to see that at least that worked similarly to past VW "Tiptronic" transmissions.
 
#9 ·
I've heard that they do control the transmission when in Sport mode, but you have to activate that yourself. In my GTI, yes the paddles will switch the transmission into Tiptronic manual mode, but it will drop back into auto mode after so many seconds unless you move the lever yourself.

Some EVs with paddles also have settings within the menus that allow setting a default regen level. I have no idea if your Niro has that, but if it does you could set the default to a higher level. And yes I believe I read that you can come to a complete stoop holding the paddle. Again, doesn't apply to my '19 so can't speak to it from personal experience.
 
#10 ·
When you mentioned increasing the default to a higher regen level, I wondered which ultimately leads to more MPG....additional battery power which you get with more regen. or coasting with the lowest amount of regen? When I coast it seems that there are a couple bars of regeneration shown on the display but not more than that. I'm sure there's a balance somewhere. For example, if I'm going to be applying the brake pedal to slow the vehicle, I would be better off increasing the regen. level. But, if I'm just coasting down a mountain hill for a ways, I would think that the least regenerative level would be best to improve overall efficiency.
 
#11 ·
There's undoubtedly a balance somewhere, and it might be something that changes based on the route. That's the advantage of the paddles, allowing you to change the regen level on the fly. My '19 has no such ability, so have never really given it much thought. In mine, just coasting provides only a small amount of regen, so coasting down the mountain is probably doing a good job of extending range. I've done that a couple of times coming back over I-90 from eastern to western WA.
 
#12 ·
Coasting provides no regen. You guys are referring to "coasting" as foot off the brakes with regen not set to zero. If your model doesn't allow that setting, then coasting can only be achieved by putting transmission into neutral. If you can come to the same stop by coasting earlier than you could have by regen (which of course slows the car faster than coasting), you have gained efficiency. I do this on occasions even in my HEV (no adjustable regen) by putting my car into neutral, usually on the upside of a hill where I can time the full stop very closely without wasting energy into heat in regen or the brakes. If I had adjustable regen with a zero level, I would also use that to coast on certain highway conditions where I see traffic slowing a good distance ahead.

Some Teslas (perhaps all with software upgrades) offer zero regen as preference with a user setting. Nice option to have, which the Niro is also capable of, but most EV manufacturers don't seem to want to offer. Simple software setting, no cost.
 
#13 ·
Thanks, Yticolev. When I'm referring to "coasting" I mean with the foot off the gas and no additional regeneration level added via the paddle shifter. I do see indication that there is regeneration going on in this situation by a couple bars showing on the battery charging monitor (which is in effect regeneration, correct?). It seems to be the sort of regeneration that is coming from what I would call "very slight engine braking" and doesn't have anything to do with physical braking. My Prius definitely seemed to do the same when coasting. I haven't seen a setting yet to completely eliminate this for true coasting but I agree that I could simply shift the car into neutral for the least amount of friction.
 
#15 ·
I do see indication that there is regeneration going on in this situation by a couple bars showing on the battery charging monitor (which is in effect regeneration, correct?).
Absolutely. And yes, the Prius does the same. On the Prius you also have the B setting to increase the regen level. If you have the PHEV, you may be able to set regen level to coast, or that may be the BEV only. Good if it is an option although each owner will have a preference - most choosing a regen level similar to slowing on a standard fluid automatic car, with some choosing "one" pedal driving. Here is a possibly better explanation of efficiency choices:

ICE cars when slowing without the accelerator, slow by engine braking. This results in 100% of that energy going into heat. There is a side benefit to engine braking - reduced brake wear. I did this religiously with my prior manual transmission cars, and my pads on my last car hit 100K (but I also brake far less than most drivers, looking far ahead).

EVs with full time regen will slow by converting some of that momentum into electricity, charging the traction battery. That efficiency is about 15% recovery at best. That 15% recovery (which includes losses both in capture and then in delivery of saved charge back into momentum) is part of the reason why hybrids get better mpg than similar ICE models. That means 85% is lost to heat.

However, if you can actually coast without regen until about 6 mph (when regen stops anyway), you have conserved 100% of your momentum into distance traveled. I am of course ignoring friction and aerodynamic losses (same thing really) as those are the same with or without regen. There are limited opportunities to use coasting (zero regen level or shifting to neutral) so a limited amount of total efficiency gain, but those of us who like to play the game of maximizing efficiency will do so.
 
#14 ·
I see the same. With foot off the gas pedal, and no brake application, the power meter indicates a small amount of regen occurring. In the '19, this not not adjustable. But with the addition of the steering wheel paddles to the '20 the driver can now adjust the amount of regen during coasting. Yes, place the transmission in neutral and the power meter moves to zero, showing no power used or regenerated. With a sufficiently high enough level of regen braking, you have what many EV drivers call one pedal driving, as the brake pedal is not used except for emergency braking.
 
#16 ·
I think regen efficiency is a bit better than that. One study (Boretti, 2013) states it ranges from 16-70%, dependent on a number of factors, including the driver and their technique. And I just found this study from Stanford University:

"While induction motors (IM) have an efficiency ranging from 0.65 to 0.94 (for urban vs highway driving scenarios), permanent magnet AC motors are even more efficient, reaching 0.83 to 0.95 for the same scenarios."
"While real-world benefit may vary depending on the scenario, some simulations show that regen braking reduces external energy consumption by a little over 20% in urban driving situations."

So they are reporting EV motor efficiency from 65-95%, depending on motor type. Take out some losses as you mention for the capture and transport of the power back to the battery, and you get "a little over" 20% reduction in fuel use. But does that translate directly into the efficiency of the regen? I don't think so, as there are probably other factors that have an impact on the overall rating. I'm no engineer, so I just go with what I can observe.
 
#19 ·
"While real-world benefit may vary depending on the scenario, some simulations show that regen braking reduces external energy consumption by a little over 20% in urban driving situations."
15% or 20%, what difference does that really make? You still lose the vast majority of your momentum into heat recovering only a small fraction of that potential energy.

It has been a while since I went through researching this topic, and the quote I remember is 17% maximum under optimal conditions (I cannot even picture what optimal conditions might entail) and 15% the usual maximum recovery. Yes, motors are very efficient but you have a double loss in regen. Then there is the inverter loss and I don't know what else. I just looked at the overall efficiency, not component efficiency.
 
#17 ·
Thanks, guys! My "Liberal Arts Head" is spinning a bit with all the info. but I think I get the gist. I may try operating at 1-Level regeneration and see how it goes. But, if the battery level is full I'd probably opt for the least amount of regeneration or even coasting in neutral where it seems appropriate. I have other questions regarding Android Auto and UVO, etc. but I'll post those where in seems most appropriate. Although maybe the "General Discussion" area gets noticed more? It looks like it doesn't matter since the newest postings are what comes up when I pull up this site regardless of which section the posting occurs.
 
#18 ·
Although maybe the "General Discussion" area gets noticed more?
I'd bet most users just look at new posts section when they come to this forum. So any subforum will get the same amount of traffic as few visit specifically unless they want to start a thread in the appropriate heading so visitors to the new thread section will have more info than just the title to decide if they are going to read your post.

Thread diverge from their original topic, so regular users may open every new post anyway just to see where the discussion is going. I open each one just to remove it from the list of new posts so I don't have as many choices next time I visit.
 
#22 ·
Coincidentally, I verified this is correct today. Holding the left paddle slows the car to about 6 mph and then you can feel the regenerative "tug" end and you must apply the brake to come to a complete stop. As a side note, I'm really enjoying the "Auto Hold" feature which keeps the car stopped when you release your foot from the pedal. I have to engage it every time by pressing the button when I start the car but perhaps there's a setting for "on" to be the default although I could see where this might not be an option for safety reasons or whatever.
 
#21 ·
That is true. In (almost all) cars with full start and stop have electrically activated parking brakes for the last 6 mph (10 kph) or so. I've read of at least one car that can energize the motor in reverse to slow the last few feet. I don't remember which one, but I assume one of the 6 figure cars recently released.
 
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