08-14-2014, 06:24 PM | #1 |
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i3 and regen braking
Read somewhere that the i3 doesn't charge the battery when you brake, only when you let go of the gas pedal and coast.
Is this true? If so what's the logic behind this? I own a prius so I'm used to hybrids/EV's using the energy from the brake to charge the battery. I'd be damned if this isn't how it works in the i3.
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08-14-2014, 11:01 PM | #2 |
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If you haven't driven an i3, go check one out. Under normal driving conditions, you do not need to use the brakes at all - as you let off on the pedal, it decreased your acceleration and once you cross the 'neutral' point, progressively increases the regen up to the point where, under normal circumstances, you don't need to use the brakes at all. If you do need to stop quicker, you're wasting energy that could have been put back into the batteries. If you want to coast, you have to keep the pedal pushed a bit to center the power direction gauge in the middle - indicating that power is neither going in or out. Keep in mind that the car has to be rolling to turn the motor/generator, so stopping quicker by using the brakes limits that. ON the Prius, using the brakes tells the computer that you do not need the power to keep going, and it switches it to regen mode...on an i3, you aren't managing an engine, and only the electric motor, so as soon as you stop trying to go, it knows and can start to switch to regeneration...no brake logic required.
The car also keeps track of whether you're turning the steering wheel into a corner, and decreases the regen to keep you from creating handling problems. Really, it's pretty seamless, and not dependent on using the brakes at all. |
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08-21-2014, 04:29 PM | #3 |
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Meaning the car does charge battery when you brake, but can't regen all the kinetic energy meaning some is wasted?
This makes more sense.
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08-21-2014, 09:04 PM | #4 |
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Any actual brake use is depriving the battery from some of the charge it could recoup since you will not turn the generator as long as if you let it provide all of the retardation.
I guess I'll have to look carefully at the power direction indicator when I have the occasion to actually use the brakes...I do not remember it going to zero, but it stays in the regen area while the brakes are being applied (I could be wrong!). |
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08-21-2014, 10:33 PM | #5 | |
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If anything, one of the frequent dings against the i3 is that its regenerative braking is too aggressive. It certainly is WAY more aggressive than in the new Mercedes B class electric drive. To me, this is a good thing for the BMW. I spent close to three months investigating (info searching and test driving) EV's before finally buying the i3. I even test drove the Mercedes B electric (as well as the Tesla S and a mix of plug in hybrids) before choosing the i3. One of the deciding factors for me was how close driving the i3 gets to a truly one-pedal experience. I get great pleasure out of watching (on the screen in front of the steering wheel) the battery recharge as I take my foot of the accelerator. And as I do that, where in an ICE I would need to be braking in order to slow down, in the i3 the car is slowing itself down. Hope this helps you. Let me know if you need more info. |
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08-22-2014, 11:44 AM | #6 | |
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To put it simply, i3 gets a better charge from letting go of the gas than braking. When you actually use the brakes, you're wasting a bit of kinetic energy, but that said, it seems like actually using the brakes only happens on occasion. Thanks all. Interesting topic.
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08-22-2014, 06:06 PM | #8 |
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You can coast...but, instead of letting off on the pedal all the way, you must keep it partly pressed so that the indication is centered at zero - i.e., between using and regeneration power. If you're using the cruise control, it's very good at doing that any time there's the slightest downhill. Or, if you want to be illegal, you could shift into neutral.
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08-23-2014, 06:52 AM | #9 | |
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08-28-2014, 04:30 PM | #11 | |
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If you lift off, the i3 will regenerate IF and TO the extent that conditions permit (steering input, speed). If you brake, it will still regenerate as above, BUT you will also ADDITIONALLY turn excess kinetic energy into heat (in the pads and discs). Hope this helps |
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09-28-2014, 06:52 PM | #12 |
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If you read the fine print in most places, moving down the road with the transmission in neutral is not legal. The idea behind that is while in neutral, you don't have any engine braking or depending on the transmission, it may not like going back into gear. ON the i3, they leave the motor engaged, but if you shut off the power to it, it is quite close to being in neutral with the ability to use regen to slow you down depending on how you position your foot.
Now, there were some cars (like some old SAABs) with 2-cycle engines whose transmission automatically went into coast mode when not loaded, but the transmission itself was still in gear. 2-cycle engines don't have much compression braking and with the throttle closed, no oil getting to the cylinders), so it was good for mileage, but bad for the brakes (which is one reason why it's not a great idea). |
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09-28-2014, 08:05 PM | #13 |
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Yes, coming from a Prius Plug In, I did a lot of coasting, and little braking. My biggest surprise, and my favorite i3 feature, other than 100% EV, is the one pedal driving. Seems so natural. My only complaint, highway driving using cruise control. When I exit off a interstate, I have to simultaneously disengage the cruise control, and accelerate getting into the "neutral zone" to coast. With experience, i'll get better. I'm really impressed with my 13.
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10-07-2014, 08:55 PM | #14 |
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I'm curious (and maybe it has been covered already), does the brake light come on as you lift off of the accelerator? The vehicle is braking... so does the light come on?
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10-07-2014, 09:23 PM | #15 |
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Yes it does. When the deceleration reaches a certain point. For me if I'm very slowly decelerating, the light doesn't come on, but if I pull my foot completely off the accelerator, then they do come on.
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10-09-2014, 07:43 AM | #16 | |
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10-09-2014, 12:31 PM | #17 |
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That doesn't mean that they don't still exist on the books! For many years into the modern car era, Rochester, NY had a law on the books where the vehicle had to be preceded by a person carrying a lantern to warn people the vehicle was approaching...obviously, things were slower then! Neutral on a single speed transmission car like the i3 doesn't present the potential problems of maybe not getting the manual transmission back into gear, or probably other things (engine braking and maybe overpowering the brakes on a long decent come to mind when coasting - especially on older cars with drum brakes), but that still doesn't mean it's a good idea. I don't know what the i3 would do if you were rolling forward and you inadvertently put it into reverse, but it may or may not be pretty - it would be one hell of a power spike!
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10-17-2014, 11:54 PM | #18 |
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You would've liked the ActiveE. The regen brakes were much stronger on it. In fact, one of my first complaints upon getting my i3 was that its regen brakes were about a third as strong as my old ActiveE.
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10-18-2014, 03:47 PM | #19 |
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Personally, I'd like to see a user adjustment to this in the I-drive menus...I think that after the last s/w update, it is slightly less aggressive than it was initially.
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02-10-2015, 05:45 PM | #20 |
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02-10-2015, 08:09 PM | #21 |
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You are trying to save quarter pennies when braking why bother.
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02-10-2015, 09:12 PM | #22 |
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No, they're trying to save electricity on an all electric vehicle with a finite supply on board.
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