When Battery is fully charged, where does the power from engine braking go?
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Ours doesn't slow down when the battery is full. That's why we always use hilltop charging; to have regen when we start down the hill
jack vines
jack vines
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Mine doesn't slow down either if the battery is full. Well...of course it slows somewhat since I'm not pushing the accelerator, but not nearly as much as normal regen. My guess is the electronics won't let the car go into regen mode if there's no where to "put" the electrons.
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Geez people, these are terrible answers because they're wrong. (Although I think maybe @nautilus meant to say “can” rather than “can't” because otherwise the second sentence doesn't follow from the first.)
You absolutely can use regenerative braking when the car is fully charged. The regen icon being white (rather than green) and the thin white line on the regen display show that regen is limited (but not nonexistent). For example, it may say that you can only get up to 15 kW of regen rather than the usual amount of up to 70 kW.
Depending on how you drive, limited regen may seem entirely adequate, or completely inadequate. If you generally use regen to stop the car quickly from reasonable speed, it may even feel like so little it's not there at all.
As to where it goes, it goes into the battery. When you charge to 100%, it isn't really 100%. It's more like 96%. As the battery gets more charge (e.g., heading down a hill), the regen limit will decrease. In principle, if you get enough regen it'll go to zero and then there really will be no regen at all.
You absolutely can use regenerative braking when the car is fully charged. The regen icon being white (rather than green) and the thin white line on the regen display show that regen is limited (but not nonexistent). For example, it may say that you can only get up to 15 kW of regen rather than the usual amount of up to 70 kW.
Depending on how you drive, limited regen may seem entirely adequate, or completely inadequate. If you generally use regen to stop the car quickly from reasonable speed, it may even feel like so little it's not there at all.
As to where it goes, it goes into the battery. When you charge to 100%, it isn't really 100%. It's more like 96%. As the battery gets more charge (e.g., heading down a hill), the regen limit will decrease. In principle, if you get enough regen it'll go to zero and then there really will be no regen at all.
Another explanation: the unuseable regen energy gets dissipated as heat. Don't know the exact mechanism.
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Geez, vertiformed; one might say you're picking the flyshit out of the pepper with that wrong assertion. OK, you've convinced us there's a miniscule/limited amount of regenerative braking taking place when the battery is "not-actually-full". However, it's so slight, I've never been able to sense it taking place in two years of owning our Bolt. So, say your calculation of 20% of full regen being available is correct, in my experience I didn't feel any regen; If regen was happening, it was slight as to be considered useless for actually slowing the car. That's why we switched to hilltop charging exclusively. Having a full battery felt akin to being accustomed to driving in L and suddenly only D is available; major recalibration of one's driving techniques have to be made instantly.
jack vines
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No. This is not what happens.
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Sure, complain about pedantry if you like (I'd liken it more to “picking bullshit out of pepper” though), but despite your claims about a “wrong assertion”, actually nothing I said was inaccurate. Notably, your response doesn't refute anything I said.
Right. I didn't say significantly-limited regen is great or that I like it. Like you, I don't like driving the car with regen that feels largely ineffective for actually stopping the car in a reasonable time, and, living on a hill, I use hill-top reserve almost exclusively. That said, I know there are some Bolt drivers out there and participate on forums like this one who charge to full every day and don't think limited regen is a big deal.
Whether regen is useful for stopping the car when charged to 100% is something people can debate (and you and I are on the same side), but driving downhill, maintaining speed (rather than slowing) the car does pull regen. Staying at constant speed downhill without touching the brake is useful and still possible when charged to 100%. If we had no regen at all, as you like to claim, this wouldn't be possible.
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This is pretty much semantics. Glad we agree there isn't much regen retardation happening on a full charge and that L is our default mode.
Again, glad we agree hilltop charging is the default mode which allows L operation as the default mode. By having headroom in the battery, we usually gain two miles in range by the bottom of the hill.
jack vines
This slight regen you say is occurring might theoretically hold a constant speed on slightly sloped downhills, but I've never tried it on one with that little slope. Leaving home fully charged, I have a choice of two downhill routes, one is a moderate downhill and one is very steep. When fully charged and in L, our Bolt runs away on either; feels like it's in D. The regen retardation is nowhere near sufficient to hold a constant speed.
Again, glad we agree hilltop charging is the default mode which allows L operation as the default mode. By having headroom in the battery, we usually gain two miles in range by the bottom of the hill.
jack vines
I think probably a set of resistors is used to absorb the unuseable energy. When battery is "full" or the regen energy exceeds the little grey line (regen restricted) on the energy readout.
So what do you think happens ?
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There is no such set of resistors. You're free to imagine things it'd be cool if the car had (resistor bank, ejector seat, propeller for river crossings) but imagining things in your head does not make them real.
When regen is limited, regen is limited. Limited regen means it provides less stopping force (i.e., it can provide up-to a certain amount of deceleration and no more). Not zero, as @Packard V8 wanted to believe, and not unchanged as you'd like to believe.
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I'm trying very hard to get across I agree with you. While there may technically be regen showing on a meter, you said,"If you generally use regen to stop the car quickly from reasonable speed, it may even feel like so little it's not there at all." So one more time; I agree with you it feels like it's not there at all.
jack vines
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In theory, the excess regen energy could be routed to the cabin heater, which as I understand it, is a large resistive element (toaster). That would mimic the dynamic braking that diesel-electric locomotives have had for decades. Handy for a downhill run in the winter, not so much in the summer.
Here's a video showing the dynamic brake resistors glowing red-hot on a Union Pacific loco.
Of course this could be done. But it is not. The regen is reduced to a tickle, which goes into the battery. The Bolt battery at maximum would be 4.2 volts per cell...403.2 volts. At the end of a "full" charge, it not at maximum.
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First, as @GJETSON observed, this isn't what happens.
Second, hardly what you'd want in the summer.
Third, the heater is probably around 6 kW. Even if it's 9 kW, that's nothing compared to the 25 kW it's easy to produce with reasonably modest regenerative braking or the Bolt's 70 kW maximum. You might as well be suggesting we feed it into the heated seats.
If we're going to come up with fantasy nonsense that wouldn't actually work in our Bolts, let's come up with more grandiose fantasies… Perhaps the power could be routed to the window washers, which could be adjusted to fire the water forwards at enormous psi, providing additional stopping force. Perhaps it could be routed to the headlights, creating forward radiation pressure, thus slowing the car down (infinitesimally, but hey). Perhaps we could route the power into the speakers, deafening the driver but providing heavy bass beats for a multi-block radius. Perhaps it could be routed into the wireless charging pocket to create Nikola-Tesla-style wireless charging all phones within a 1-mile radius of the car. Or perhaps it could be sent to the electric windows, raising and lowering them with enormous speed.
I would love to know how to grab my setup, and put it in a file on my desktop, for the day my phone breaks. That is only one page of four...lots of fooling around to get what I wanted.
All you need to do is watch your 96 cell voltages. You will be able to spot the strongest and weakest cells in your pack, and put their displays on either side of the average cell display.
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First, this a great Torque Pro shot. It shows that the raw SoC is 96% when the Bolt is charged to “100%” displayed.
But, FWIW, I'm not sure that the cell max for the Bolt actually is 4.2 V. Given that the Bolt uses NMC 622 cells, I think it may be 4.4 volts (see this presentation and this paper). Someone needs to do the experiment of charging to “full”, and then driving down a hill grabbing regen until the car will take no more, and then seeing what the battery voltage is. This will tell us the in-practice max as far as the BMS is concerned (as opposed to the theoretical max from academic papers).
My understanding of the Bolt's regenerative braking system is in full agreement with Vertiformed. So to summarize:
The vehicle will apply as much regen as it feels safe for the battery in L mode when you lift the foot off the pedal. When the regen is in the limited mode (white line appearing in the gauge), it does definitely feel like there's no regen happening at all at certain times because there's much less deceleration force being applied. This does not mean that no regen is happening at all, though. The gauge definitely dips below the center line. But if you're only getting like 5 to 10kW's worth of regen, it may feel like driving in D mode at best.
All the relatively low amount of regeneration will make it to the battery. Bolt does not have any device for dissipating or make use of the recovered power elsewhere. Even at "full" charge, the actual SoC sits somewhere between 95 and 97%. This provides headroom to make a tiny bit of charging.
Just FYI, my OBD-II reader showed that the SoC hit 95.29% just as soon as the displayed charge hit 100% during a charging session. Leaving the charger plugged in, the SoC would continue to rise slowly, until the vehicle terminated the session at either: 96.08% / 96.47% / 96.86%. Battery voltage is at either 4.16V or 4.17V when this happens.
The vehicle will apply as much regen as it feels safe for the battery in L mode when you lift the foot off the pedal. When the regen is in the limited mode (white line appearing in the gauge), it does definitely feel like there's no regen happening at all at certain times because there's much less deceleration force being applied. This does not mean that no regen is happening at all, though. The gauge definitely dips below the center line. But if you're only getting like 5 to 10kW's worth of regen, it may feel like driving in D mode at best.
All the relatively low amount of regeneration will make it to the battery. Bolt does not have any device for dissipating or make use of the recovered power elsewhere. Even at "full" charge, the actual SoC sits somewhere between 95 and 97%. This provides headroom to make a tiny bit of charging.
Just FYI, my OBD-II reader showed that the SoC hit 95.29% just as soon as the displayed charge hit 100% during a charging session. Leaving the charger plugged in, the SoC would continue to rise slowly, until the vehicle terminated the session at either: 96.08% / 96.47% / 96.86%. Battery voltage is at either 4.16V or 4.17V when this happens.
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