Battery Charging After Depletion?

If the EV battery is truly depleted are you even in EV Mode? My guess is you're in Hybrid Vehicle Mode (HV) and I don't think regen in that mode goes to the EV portion of the traction battery. You're running pretty much just as a traditional Prius at this point. If you bring up the "Energy" graphic display it should be obvious when you're producing regen. I think regen from normal braking isn't enough to show much change in the battery's state of charge. If you have a long downhill run you could use it to see if you get 1% or more to the battery.

 

Once you deplete EV range to zero, the car goes to HV mode automatically. At that state, car will keep the traction battery at or below EV/HV threshold which is actual SoC of ~14%. If you have a very long down hill to regenerate enough battery power, it will show up on your dash again. Your couple miles of drives in HV is not enough to capture regenerative energy to bring the SoC higher than 14%.

If you do not let the EV range deplete all the way to --, then you can switch to HV in acceleration and uphill using gas and switching back to EV on coasting and downhill portion to capture regenerative energy to bring back the SoC. I have done this many times on my commute route, and I can capture ~20% SoC in EV mode during ~40miles of the drive using this technique. So, if I start my commute with 80% SoC, I can finish it with 100% SoC at the finish.

 

charge mode?

 

Top marks for @Salamander_King. A direct hit. It can get back into EV after it hits "--" but only after a llloooonnnngggg downhill run of coasting or braking. Or lots and lots of regenerative braking mixed with firm acceleration. I don't recall the exact number, but the display will suddenly jump from "--" to almost a mile or whatever percent that equates to. And as @bisco said, there is charge mode available.

What Salamander describes is what I call ratcheting. I used to do something like that in the PiP if I was driving on rural roads with stop signs. Before running completely out of EV range, I would switch to HV. At the next stop, I'd switch to EV and back to HV while stopped in order to lock in the charge that built up stopping. I could often get several miles of EV in fairly short order that way, but at the expense of burning more gas. I guess you could call it the PiP version of charge mode.

 

One big advantage of using this "ratcheting" technique is that it can replenish EV SoC above 80% all the way to 100%, unlike CHG mode. However, I am a bit puzzled that while I can do this fairly easily to gain SoC from 80% to 100%, it is extremely difficult to bring dead "--" EV range (0% SoC) back to alive and up to 20%. There is something about a 14% EV/HV threshold that locks the car in HV mode once EV range is depleted.

 

My guess is that it keeps the car from toggling back & forth too quickly. If it got just 1% or 2% EV range and the driver made the switch, it would use that up in no time flat. The ICE wouldn't necessarily start right back up immediately if it was warm, but it might.

 

If you run out of charge while driving then do bunch of regenerative braking, it won’t switch back to EV mode, even if you add significant charge back into the battery. Or at least I’ve never seen it do so. You have to actually charge again from the charge port before it will switch back to EV mode.

However, it reassesses the state of charge each time you power up. So I have seen it, powering up again after officially running out of charge, conclude that it can stay in EV mode for a mile or two.

 

Can't you put the car in CHARGE mode while driving and let the ICE refill the battery into the EV range?

 

OK, yes, or charge it from Charge Mode. You have to explicitly charge it though; regeneration won’t enable EV Mode.

 

On a long downhill, I can regain EV range even after completely depleting the EV range prior to starting the downhill. As I commented above, I can regain EV range by what @jerrymildred calls "ratcheting" between HV and EV. I can get ~20% SoC into the traction battery by doing this on my regular commuting route of ~40miles. Although I have not tried very hard, as you and others have commented, once EV range is depleted, it is very difficult to capture enough regen energy to put the car back into EV mode. I just don't know why "ratcheting" does not work well once the EV range is depleted. For one thing, once I deplete the EV range, there is no switching back and force between HV and EV. That must be the one reason it does not work well.

 

OK, that’s interesting. I have never seen EV range go up from zero by regeneration; only by explicitly charging, or again sometimes by cycling power, letting it reassess SoC.

 

The process is called "stacking" if you do it intentionally. With the Prius PHV, it was a simple matter of switching over to EV upon decelerating. You obviously need a tiny bit of EV available to do that in the first place, but that could originate from regen. Doing that in hilly areas, you could actually stack several miles. I haven't ever tried it with the Prius Prime, but the drive down from Mt. Rushmore adds a good +10 miles without having to do anything.

 

Starting in HV (EV miles = zero)?

Speaking for myself at least, I have never seen our Prime go back into EV mode (make EV available again), after EV range goes down to zero and it switches to HV mode, without charging it or cycling power, no matter how much I’ve regenerated into the battery.

 

It isn't supposed to. Once you enter HV mode from depletion, it will use up EV capacity from regen until you either manually switch back or power off. That's mostly because the engine is warmed up already. You have to explicitly tell it not to use it, by favoring the battery even more. Having that option to choose is nice.

 

You and I don't have big enough hills to do that. It pretty much takes a mountain slope to regenerate enough to punch through the EV threshold. I've only done it in the Rockies with the Prime and the Smokies with the PiP.

 

OK, you’re presumably talking about a different scenario from what I thought you were talking about.

 

I often drive up to the summit of a nearby hill (although they call it Mountain) to watch the sunrise. The road is only 3.5miles but very steep all the way to the summit about 1500 feet elevation without any stop. On my descent from the summit starting with no EV range left, I can gain almost 10 miles of EV range (about 30% SoC) without doing anything. If you have any high elevation point you can descent without stopping, you should try it.

 

We have river valley descents here in Minnesota long enough to generate some worthwhile EV, but not much to really ever talk about.