Battery Charging After Depletion?

If I am in HV mode and descend a significant hill, I remain in HV mode, but the charge level can go up enough to allow me to enter EV mode by pressing the HV/EV button. Recall that the HV logic is to return to the charge level when you entered HV mode (either by pressing the HV/EV button, or running out of charge and being forced to HV mode). If you accumulate more by regeneration, it will be "burned off" by running the car on battery until the charge decreases to that HV set value, and then it will maintain that level with the ICE. It is confusing, but one has to distinguish between your HV/EV mode setting, and the instantaneous operating state. The car can be using the battery with the ICE off (EV state) even if you are in HV mode.

 

I don’t think I’ve ever succeeded in switching to EV after descending a big hill in HV. However, I can’t rule out the possibility that I just haven’t had big enough a hill.

In that case, as you descended the hill, did it start racking up EV miles?

I have not seen it rack up EV miles after switching to HV due to “depleting” (to the EV/HV threshold), even after regenerating what would typically account for a few miles of EV range. That, because of exactly what you described; in HV Mode, it uses regenerated battery capacity to keep the engine off.

 

I have no idea of whether it was logging more EV miles. All I know is that the charge level went up until it was high enough to allow me to switch to EV mode by pressing the HV/EV button. The charge level can be expressed as either %charge or Guess-o-meter EV miles. How EV vs HV miles are logged has always been inscrutable. This was also the case with the previous incarnation, the 2012 Plug-In Prius. Do you log EV miles when running in EV while in HV mode? You got me.

 

It appears that enough of us have managed to get it back into EV after depletion by going down big mountains to demonstrate that it is possible with a big enough drop in elevation. And, afaik, no on has EVER done it on flat ground, although I think it's possible if you go about it with very serious and fuel wasting methods.

As for miles logged EV vs HV, the PiP and Prime do the opposite. My PiP only counted miles as EV if I had put it in EV mode. And it showed miles in each mode as well as percent, iirc. I checked several times to verify it. The Prime doesn't care what buttons you press. If the ICE is off, those are EV miles, but it only shows percentage; you have to do the math. I've demonstrated that innumerable times by looking at the EV percentage of the trip since start on an HV mode drive. On country roads, it's usually around 33% even though I made the whole drive without putting it in EV. Just hit the trip meter button till it comes around to the "since start" numbers with the car & a flag. Put the car in HV and drive. Bring up the MID screen that shows the EV percentage. That's the percentage for the trip meter currently in use. Notice that you will gain EV percentage when the car turns off the ICE.

 

The depleted EV range "--" (i.e. automatic HV mode) can return to EV mode with about 1 or 2% SoC on normal fairly flat roads. I have seen that happen on my PIRME many times. In those instances, the car will automatically goes back to EV mode unlike @CharlesH described. No need to hit EV/HV button. This usually happens when I am driving my car on EV mode with already warmed up engine. As soon as, EV range depletes, the car switches to HV mode automatically and starts the engine. On this HV mode, if I can drive with the engine only and not use the traction battery power and coast to capture regenerative energy, the SoC usually goes back to 1 to 2% and car is back in EV mode without switching. Of course, 1-2% of EV range is used up very quickly and it goes back to "--" and back to HV. The key here is that the engine has to be warmed up already at the time of EV depletion. If the engine is cold when EV range depletes at "--" EV range, then when the car switches to HV mode, the engine has to go through the warm-up cycle. This warm-up cost too much traction battery power into HV SoC range down to ~11%, causing a small regenerative energy not enough to replenish the EV/HV threshold of ~14% SoC. I wish I can video this, but I don't have an equipment to do this like John.

I commented on the EV ratio on my normal commuting drives in this thread. Summer Hybrid Mode MPG | PriusChat
With my usual commuting drives at average speed of 28mph, I usually see around 60% EV ratio without using any EV mode. Compered to this, with mostly highway drive at average speed of 55mph had only 28% EV ratio without EV mode. What amazing is that on both driving conditions the car marks 66-68mpg on dash. This speaks of the efficiency of gas engine alone HV mode operation by Prius PRIME.

 

That makes sense. I just didn't remember anyone pulling it off. It's not a common situation for me. In fact, it's extremely rare.

 

Yes, if you are doing just EV mode drives when you reach the "--", then it won't get back out of HV mode by regenerative energy alone. My daily commute is ~36.8 miles. If I try to drive this distance on EV mode only, then most of the times I run out of EV range a few miles before I reach my driveway. The car in HV mode is just going through the warm-up cycle when I pull in. In this case I do not see revived EV mode. Then I started mix my drive with EV and HV to conserve the use of traction battery energy. For this, I try to keep the engine warm by switching to HV periodically during my commute so that engine goes through the warm-up cycle only once. With this style of driving, if I am driving in EV mode at the very end of traction battery SoC, when it depletes to "--", I can use engine to take over the HV mode immediately after EV range depletion. Coasting after that switch often results in regenerative energy 1 to 2% SoC back in the EV mode.

 

My PiP would sometimes run out of juice and start the ICE as I pulled into the driveway at home. One of the biggest reasons for the switch to the Prime along with comfort.

 

OK, my 2 weeks self-quarantine was over yesterday. Finally, I had a chance to take my PRIME for a ride. I did set up a phone to video the dash while I drove ~50 miles today. I had 60% SoC left in the traction battery, so I knew I would run out of the EV range before getting back home. I started the video when the SoC was 1% left and run all the way home, about 18 miles drive. The route I drove has some up and down, but no extremely long hills. Shortly after the start of the video (0:59 timestamp), the SoC became "--" and EV range depleted to "--.-". The car changed to HV mode and I intentionally drove it without engaging EV drive under depleted SoC for the next ~5 min to capture regenerative energy. After ~5 min (6:45 timestamp), 3% SoC and 1.0mile EV range appeared on the dash. The car stayed in HV mode at this time, so I switched to EV mode manually, then, used HV with the engine on accelerating and uphill and switched to EV on coasting and downhill to capture as much regenerative energy as I can. I finished the drive with 14% SoC using this "ratcheting" technique.

Unfortunately, I do not have a YouTube account to upload the video. Even if I have one, 20+min of the video is too big to upload and too boring to watch anyway. So, here are the snippets of video capture showing reviving depleted EV range using the only regenerative brake (i.e. no CHARGE MODE). One thing I noticed today, although in the past experience when I revived EV range after depleting to "--", I thought the car switched to EV mode automatically to EV mode after capturing enough SoC, today's drive proved that what @CharlesH described was correct. After gaining some EV range, the car stayed in HV mode. I had to switch to EV mode by manually pushing the EV/HV button.

The condition of the drive.
At start: SoC 60%
EV range: 24.1 miles
Drove ~30 miles with EV and HV switching to keep the engine warm.

At about 18 miles before reaching home, the SoC was down to 1% left. The pics are captured from the video taken at the timestamp shown right after this point.

TIME SoC EVrange Mode
0:55 1% 0.1mile EV
0:59 -- --.- HV
6:44 -- --.- HV
6:45 3% 1.0mile HV
6:54 3% 0.9mile EV
7:01 3% 1.1mile HV
12:53 8% 2.6mile EV
19:53 14% 4.9mile EV

 

OK, today I drove up to the mountain summit I go often to watch the sunrise. It is called Mountain, but it really is a small bump only 1500 feet climb. The road is 3.5 miles up to the summit from the bottom. For my first climb, I started with 60% SoC in the traction battery, when I got up to the summit, the SoC was down to 18%, but was not depleted. So, I used 42% SoC on my ascent. On my descent, I gained 23% SoC, so at the bottom, my SoC was 31%.

What I wanted to test was after EV range SoC depletes and the car goes into HV mode automatically, in the HV mode, if I descent a long enough hill...

1. Will it regain SoC by regen only that shows up on the dash? I already knew this answer, but some people have never seen it so I wanted to demonstrate it.
2. After SoC is regained, will it stay at HV mode or will it go back to EV mode? This was something I really wanted to test for there has been a notion that it stays in HV and requires manual switching.
3. What happens to the gained SoC? Can it be used for later EV mode drive? Does it require the toggling of switch EV/HV to lock-in?

For the second ascent up to the summit, I started with 31% SoC which I knew will deplete the EV range before reaching the summit. I did this drive without stopping and without manually switching EV/HV. Here is the composite of the video grab in sequence.



Conclusions:

1. After depleting the EV range and going into HV mode, Prime will regain SoC by regen only.
2. When SoC is regained to EV range of 1 mile, the SoC will re-appear on the dash. The car initially stays in the HV mode, but if the regen continues to gain more SoC, at 6% SoC, the car will automatically switch it back to EV mode. No manual switching was necessary.
   
3. The gained SoC at the end of descent is all usable for EV mode drive. Again no toggling was necessary. If I wanted to save this regained SoC for later EV mode drive, all I had to do was switch to HV mode to "save" the SoC.

 

Thanks for the test and info. Just a typo: EV is mentioned instead of HV on the 3% SoC line.

 

Whoops. OK, I fixed it.

 

Great job documenting and explaining, @Salamander_King. Can I add just one detail to your conclusion for the sake of thoroughness?

We should also take note that when you save the SoC, that's the SoC you're saving, not any additional charge you might gain if you continue to regenerate down the hill. So, if it's at 20% and you switch to HV, it'll keep the 20% even though you might get well over 20% or more if you continue to descend. To save that new, higher SoC, you'll need to put it back in EV for a moment and then bring it back to HV. Just two quick presses of the EV/HV button.


But again, really good stuff. The pictures both prove and illustrate what's been discussed.

 

Yap, that is correct and that's exactly what I did yesterday after reaching the bottom of the hill. As you can see from the last screengrab, at 3:07, I had replenished previously depleted SoC on the trip back to 19%. After reaching the bottom of the hill, I switched to HV mode to lock-in the SoC, but I continued to "stack" the EV SoC by "ratcheting" EV/HV switch on my way home for ~17miles.

I had 44% SoC in the traction battery when I pulled my car to my driveway with the expense of gasoline in HV mode. All of the gains were from HV mode not from CHG mode. My mpg at the end was down to 77.8mpg, but my daily eco log EV efficiency was 99.9miles/kWh.

 

It's 105F outside, labor day and I have a spare few hours. I'm also trying to burn off stale fuel now. I'm going to head up to Saratoga Gap right now and see how much I can regen coming down and then lock it in place. I've ridden my bike up there 1000+ times, about 2500' of climbing in 6.2 miles. It is a nice road with no steep bumps and pretty consistent grade up and down. I need to use the toggle trick to lock in the SOC.

 

I just returned and regenerated 31% from zero coming down with gentle braking and the level seemed to be lumpy. It read zero for quite some time and then jumped up to 7%. Stayed there and jumped to 11%, etc. It was not a smooth increase in SOC.

Interestingly, during the return on the flats back home I was also able to "ratchet" the SOC by switching from HV to EV and back. I'm currently sitting at 36%.

 

Charge mode seems to take about an hour to charge from 0% SOC to 80% SOC where it stops charging.
That's almost twice as fast as 240 volt charging at the plug.

There are some good reasons to use charge mode, I'm certain, I just not sure we've nailed them all down yet.

Last week I had to run HV for 100 miles. The first 50 was in charge mode, since I didn't have any EV range.
The car got to 80% SOC in the first 50 miles.
I switched to HV for the second 50 miles.
SOC fluctuated between 80 and 85% SOC most of the way.
SOC peaked at 90% SOC at about 40 miles of the return trip.
I ended up with about 87% SOC at my destination.

Not sure what all that means in the overall scheme of things related to Prime, but there it is.
One more description of what happened to me last week.

 

One amazing thing to me is the MPG around town in HV mode when the SOC is high (75% or higher). I seem to be able to get over 75 MPG effortlessly. Before with my 2014 Prius I would struggle while hypermiling to get 55 MPG with E15 $h!tty California gas. I don't know how realistic these MPG numbers are with my 2020 Prime but they are amazing MPG numbers if true.