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Discussion Starter #1
Trip was 2200 miles. Battery was fully charged with 26 mile pure EV range.
The EV charge was used up after 26 miles as expected. This left the HEV battery which shows up as 1/4 of the battery capacity display. On long climbs the HEV battery would deplete but on the down slope it would regenerate to 1/4. Never ever did the PURE EV battery get any regenerated energy or generated energy from the ICE.

The battery level indicator never got above 1/4.

You could conclude that the EV part of the battery is distinct from the HEV part in that the EV battery will only charge from a power cord via the Niro converter and never from any other source.

Maybe it is just one integrated battery and some software prevents the full battery capacity being available to absorb regenerated power.
 

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I haven't competed any long trips in our 2019 PHEV but I noticed the same. If you select PHEV then battery information the display you can watch the charge time decrease when going down hill but the EV never recharges. When we were purchasing our Niro I remember the salesman saying there were three separate batteries; 12v in the right rear cargo area used to start etc, the hybrid battery and another EV battery. I have it verified this though. It does make sense tough. When we test drive the PHEV Prius that's how it is set up and the EV battery is in the middle of the rear seat so it only seats 4.
 

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HEV/PHEV battery is the same physical unit. Works the same too. The BMS (battery management system or computer) keeps charge very close to the same level once the plugin charge is exhausted. A computer managing charge is far easier than segregating physical sections of batteries. There is also a buffer that does not appear on your display to stop overcharging and help compensate for battery degradation over time.

Other than the downsides of the added weight and reduced mpg (compared to the lighter HEV) on long trips where you do not plug in, there is one potential advantage. While the car is not going to waste gas to recharge your battery fully, it can take advantage of the larger capacity (again compared to the HEV) to capture more energy should you go down a long mountain pass at a slow speed). This can be significant in certain rare circumstances.

Alex on Autos is a well known YouTube car reviewer, and his daily commute involves a mountain pass. The Niro PHEV was unexpectedly efficient in his particular case as he could recapture more energy on the downhill portion than the smaller capacity Prius plug in.
 

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Once the battery charges to 1/4, it starts to use the battery pretty aggressively to reduce fuel consumption. That's the way it should be, too. What's the battery there for if it isn't using it, afterall.


For the first 3k miles on my car, I thought the same thing as you - that the car was physically incapable of of charging itself past 25%. But then I learned that I was wrong. When coming down a very steep mountain, from about 9k feet down to 5k feet, riding the "brakes" (regenerative braking) the whole way, I actually achieved a +5 miles range on the EV meter. So the car actually does charge the EV portion of the battery if given enough downhill, BUT it needs to be a pretty aggressive downhill for quite some distance, at a relatively low speed (say, below 40mph), with a lot of regenerative braking use. At highway speeds, you'll never see the meter go above 25% no matter how steep the hill, because wind resistance is slowing the car down too much and not giving the regenerative braking much work.


In everyday driving, with only moderate downhills and not a lot of regenerative braking, you'll never see the meter go above 25%.
 

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I've noticed that if I use the switch next to the gear shift to put in in HEV mode before the electric range is depleted to zero, that the electric range reported on the dashboard gauge will go up and down by a few miles either way as I drive in HEV mode. Once it goes to zero though, I've not yet seen it come back to show more than zero miles of EV range.



I agree with yticolev: my understanding is that there's only one low voltage (12 V) battery and only one high voltage (traction) battery in the PHEV (so total of two batteries). When the latter has 100% charge, the EV range is 26 miles (or 24 miles if you have the ventilation fan on). The reported electric range drops to 0 miles when the traction battery gets to approximately 20% charge (based on what I've observed so far). After that, the PHEV behaves like the Hybrid version of the Niro: after it has put a small amount of charge into the traction battery, it shuts down the ICE and uses up that small bit of surplus charge, and then turns the ICE on again when that surplus is depleted.
 

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Discussion Starter #6
Well,
It is remarkable that in 2200 miles of driving both uphill and down hill it would deplete the 1/4 battery indication to zero and would always regenerate on the down slope to 1/4 but never ever above 1/4. Now if indeed it is capable of regenerating past 1/4 charge it is a remarkable coincidence that this never happened on a 2200 mile trip. On long down hills 1/4 battery was seen but never above that even when there was a good amount of down hill to complete.
Looks like a software design error to me. If the 1/4 is being exceeded behind the scenes then that is a display error if not ( I suspect it never in HEV mode ever charges the EV section of the battery) then it is a major design error.
 

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If you zoom down hills at speed of over 40, you will not see gains in range stemming from regeneration. Basic physics, no flaw in design. Not a coincidence you didn't see it if you were driving at normal highway speeds. Downhills will add to your SOC, but mostly from the ICE running at highway speeds, not regeneration. When you top a hill and your meter is showing zero, the ICE continues to run, right?

It is a rare hill that requires regen to stop you from exceeding say 65 mph, but there are some I experience driving into San Francisco on I-80. All you have to do is be on cruise control and look at your charge meter for charge or discharge status. Try going down hills at 40 mph to test this out.
 

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Well,
It is remarkable that in 2200 miles of driving both uphill and down hill it would deplete the 1/4 battery indication to zero and would always regenerate on the down slope to 1/4 but never ever above 1/4. Now if indeed it is capable of regenerating past 1/4 charge it is a remarkable coincidence that this never happened on a 2200 mile trip. On long down hills 1/4 battery was seen but never above that even when there was a good amount of down hill to complete.
Looks like a software design error to me. If the 1/4 is being exceeded behind the scenes then that is a display error if not ( I suspect it never in HEV mode ever charges the EV section of the battery) then it is a major design error.

It's not a software flaw, it's designed that way intentionally. When the battery is depleted to close to 0%, it uses nearly 100% power from the ICE, and none from the battery, so it can build up some energy back into the battery. Once the battery charges to 25%, it starts to aggressively use the battery again, because it no longer needs to build a charge. So whqat you'll see on the battery meter is that it climbs from 0-25% fairly quickly, but then gets "stuck" at 25% because it's not working so hard to charge the battery anymore.


It isn't remarkable at all that you didn't see the meter go above 25% on your 2200 miles drive, I didn't see mine go above 25% for the first 3000 miles either, and I only have seen it twice ever now, coming down VERY tall, steep, winding mountain roads.



Your ICE's energy is more efficiently spent propelling the car than charging the battery, so the car (smartly) directs all its energy to the wheels when it decides the battery has "enough" charge.


As mentioned several times earlier, it IS possible to charge past 25% while driving, but it's rare and requires very specific circumstances. Namely, VERY long, fairly steep downhill sections (several miles) where you are going less than about 40-50mph, riding the regenerative braking the whole way and not accelerating at all. And you're not going to see the meter climb that fast - expect about 1 mile added to the meter for every 3-5 miles of riding the brakes coming down a mountain. The most charge I ever got was +5 miles, and that was after about 30-40 minutes of nonstop regenerative braking.


Above about 50mph, the car won't be using very much regenerative braking at all, because wind resistance alone will be keeping the car from gaining any momentum.


Trust me, as much as we'd all love to see that meter climb to 100% on long drives, it's more efficient for the system to be doing what it's doing.
 

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Your ICE's energy is more efficiently spent propelling the car than charging the battery, so the car (smartly) directs all its energy to the wheels when it decides the battery has "enough" charge.
This could be true and the car BMS can certainly do this, but I'm not convinced it does. What I observe in my HEV is that when ICE is running, it is also charging the battery apparently constantly. When the SOC gets above the half way mark, the traction battery starts adding torque (or it goes full EV). It would make sense to stop charging while the traction battery is adding torque but I cannot tell exactly what is happening in that mode.

If you think about the HSG motor, it is spinning via its connected belt to the engine while the ICE is running. No choice. So there is little reason for the HSG not to be providing voltage to the traction battery. Yes, it can reduce the load to zero. We know this because in the case of HEV, PHEV, or EV maxing out their battery on downhills which is rare of course, regen braking turns off and engine braking is increased (even downshifting to maintain set speed downhill). But whether it does turn the load down to zero in normal use is unknown.

One of these days I'm going to play with OBD device and add some EV specific PIDs. Then I should be able to see what is actually happening.
 

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Discussion Starter #10
There often can be a good reason for an unusual result. If the conjecture is that when faced with a battery close to 0% due to an uphill climb the down slope can have both the ICE and the regeneration both feeding the battery until it hits 25% and at that time the ICE is turned off and any regeneration is fully consumed in overcoming motion resistance needed to maintain the chosen speed; then I can accept that.

An alternate conjecture could be that the PHEV is just an HEV with extra battery capacity and the extra capacity is very often only replenished by plugin charging.

Little difference to the pure HEV software just the choice of using pure EV for 24 miles is added.
The responses have been very informative and I thank everyone for their analysis.
 

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A lot of good info in here. One thing I've noticed with a very steep down hill on my way home is if I touch the brakes at all while going down it the Charge/Economy/Power needle drops all the way down. Does this mean no charge is happening or maximum charge is happening? I'm not sure if the "scale" "reverses" on that end.
 

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A lot of good info in here. One thing I've noticed with a very steep down hill on my way home is if I touch the brakes at all while going down it the Charge/Economy/Power needle drops all the way down. Does this mean no charge is happening or maximum charge is happening? I'm not sure if the "scale" "reverses" on that end.
It means "maximum" charge is happening. Minimum (or no) charging is indicated be the needle resting on the line between the "charging" and "eco" segments of the gauge.


The faster you're going, the less brake you need to apply for maximum charging. At 80mph, for example, barely touching the brake will cause the needle to drop to "max charging", but at slower speeds it takes harder braking to hit that point. Below a certain speed (I want to say 20mph or so) it won't hit "max charging" even if you hit the brakes really hard.
 

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A lot of good info in here. One thing I've noticed with a very steep down hill on my way home is if I touch the brakes at all while going down it the Charge/Economy/Power needle drops all the way down. Does this mean no charge is happening or maximum charge is happening? I'm not sure if the "scale" "reverses" on that end.
It means "maximum" charge is happening. Minimum (or no) charging is indicated be the needle resting on the line between the "charging" and "eco" segments of the gauge.


The faster you're going, the less brake you need to apply for maximum charging. At 80mph, for example, barely touching the brake will cause the needle to drop to "max charging", but at slower speeds it takes harder braking to hit that point. Below a certain speed (I want to say 20mph or so) it won't hit "max charging" even if you hit the brakes really hard.
Great thank you for the clarification.
 

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I agree with most of what is said above, but not all of it. For one thing, I'm pretty sure that the HSG can be disconnected from charging the battery if the computer deems it appropriate. For another thing, I think that the SOC where the computer decides that the ICE should stop charging the battery (even if the ICE continues to run) is likely to be different for the PHEV than for the HEV. The HEV has a smaller battery, and so perhaps it cuts off at 50% SOC for the HEV. For the PHEV, it seems to try to maintain the SOC that it had when it went into HEV mode, regardless of whether the transition to HEV mode was automatic (because of charge depletion) or because the driver switched it to HEV mode. But this is a somewhat loose attempt, rather than a rigid requirement.


picstart - the next time you take your PHEV for a drive that will exceed the EV range, wait until you get down to about five miles of remaining EV range and then force it to switch over to HEV mode. Then keep an eye on the EV range as you go through different kinds of traffic. What I observed was that it might go down to 3 miles and up to 6 miles, but it seemed to eventually come back to five miles (if five miles was where I forced it to transition). If you're concerned about maximizing your MPG, you can always switch back to EV mode when you're more than five miles from your destination and use up those last few miles.


And yes- you're right: A lot of what you will read here is "conjecture" (based on observations and incomplete knowledge), on everyone's part, but some of it is more in the conjecture category, and some of it is more in the experience and reasonably well informed category.
 

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Automatic Cruise Control

One related issue not mentioned here is another effective way to charge the EV battery while driving is to use the cruise control. I have ACC (so I'm not sure if plain CC is exactly the same) and it uses regen heavily to maintain the precise speed setting or to decelerate for a slower car in front. So you don't have to 'ride the brakes' to get some serious regen. I only have 3000 miles on my PHEV with no mountain passes yet, but the charge meter shows significant charging from regen even on mild hills when using ACC.
 

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ACC, standard CC, manual. While standard CC is the most efficient (best at maintaining a steady speed) with an alert driver, all utilize regen exactly the same. ACC is less efficient because of just what you refer to, slowing down because of a car ahead. Sure, it uses regen to slow, but that is not as efficient as maintaining a steady speed or coasting to slow. if the car in front is constantly slowing and speeding up, your mpg is going to suck big. Full manual driving is typically less efficient than CC because most drivers don't have the skill or focus to drive at a constant speed. On the other hand, hypermilers do better than CC because they use (obnoxious to other drivers) pulse and glide techniques, or constant power (slowing up hills and recovering on the downhill). But it really takes a lot of work and can generate road rage in other drivers.
 
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