Prius Prime: detail about Charge-Mode

I think it's helpful to set realistic expectations. It would be pretty hard to get 50 miles of EV range, unless you're driving 50mph most of the way with no stops. My commute has around 7 miles at 45-55mph with traffic lights and around 8 miles at 70mph on the highway with big hills. I can get over 30 miles of range in the summer, but probably not more than 35 unless the traffic lights and planets align. In the winter I get about 20-25 miles of range on the same drive (the weather is usually sunny and 20-40 degrees F), and just over 15 miles of range if it's snowing and I need to blast the heat the whole time.

It's pretty easy to beat the EPA estimated mileage in HV mode in the Prime. I don't really keep track, but I probably average around 60. On one unusually good drive the car reported 80 mpg over a 40 mile drive on the highway, all in HV mode with the AC on. The elevation change on that drive was a net descent of 500 feet, so that helps some.

The Prime really excels at mountain driving, because it can recover so much energy going down hills. The best I've done is driving down from Mt. Evans. I started at the top (14,200 feet) with an empty battery (and averaged 30 mpg on the way up). From the top I was able to get the battery up to about 80% on the way down to I-70. Since the rest of the drive back to Denver (5,200 feet) was mostly downhill, I made it a total of about 62 miles in EV mode from the top of the mountain.

On highways it can't recover quite as much energy because the engine comes on to protect the battery, but it's still a lot more than a standard hybrid.

 

Depends on your situation and driving style. My commute is 40 miles each way without a charger at work. I can drive all the way to work in EV mode with somewhere between 20 - 40% remaining charge.

This is an area I haven't experimented with yet, but just to break even in terms of efficiency the gasoline motor would have to be at least 10% more efficient when charging than when driving.

 

You can ask how @PiPLosAngeles does it. He has >50 miles EV range on his daily commute.

 

The range will be drastically affected by temperatures, driving speed, and how often you have to make a hard stop. On one of my common routes, speeds are 50-60 mph for 17 miles with about 19 traffic lights. On some trips those lights will force as many as 3-4 hard stops by changing at the last second. That'll take at least five miles off my range in addition to what I lose from the higher speeds.

As for charge mode, there is no free lunch. Under the right conditions, you might gain a little bit.

I noticed that while we were visiting CO. It makes me miss the mountains even more than before!!

 

That's an excellent ratio. There's one particular city along my route with a really lazy or inept traffic engineer. Of 14 traffic lights along my route in that particular city, I customarily encounter 60 - 80% of them red, even though I'm traveling at 5:00 am and there is no cross traffic to trip them. This morning 11 of them were red.

 

I'm with ya! I was just counting the ones that turn at the last second so you have to slam on the brakes. That's like throwing money out the window. We typically have to stop for over 50% of lights on almost all our roads. It's just that when you see it change early enough and traffic permits, you can coast and regen and if you can do that enough, it will actually help your mpg or m/kWh on a Prime.

 

Until the guy behind you zooms around you and has to stop at the light, forcing you to have to hit the brakes instead of coasting through.

 

EVERY DAY!! SEVERAL TIMES!!!

 

Highly doubtful .... at least for me it is one of the things I really hate about the new design.... as it adds to the aggressive front end look... it wouldn't be quite as bad if the contrast of the black grill was not so strong (imho) ... and it's one of the other reasons I like the looks of the regular Prius a tad better (as well as the color options seem a bit more diverse in the regular Prius as well.)

 

One thing I like about what I am seeing in the above video with Charge-Mode is that the Engine is running constantly even when it would normally shut-off at lower speeds, which means the Engine will run and become hot enough to expel any moisture in the system. Looks like a good mode to run the Engine every week or two.

Good point about the addition of 22 miles of EV from Charge-Mode.

 

These are really good questions. The way my Prime operates it almost seems like there are three separate batteries. Because only the Pluggin' feature actually achieves a full charge. Running in HV never moves the battery over 1 or 2 bars, so they seem seperate - as if the HV battery was split with 2 sides. But apparently, the HV battery is one unit with five banks of Li-ion cells.

I agree with what other posters have said. The car knows what it's doing and how to protect itself. Just follow best-practices as closely as possible and have fun.

 

There really, really is only one physical traction battery. There are no "HV" and "EV" partitions. It is just a single pack of lithium-ion cells. It is the hybrid software that creates the illusion of an "HV battery" and "EV battery", depending on which mode it wants to project at a given time. There is still sometimes some confusion about this due to the original Prius Plugin prototype actually having two distinct battery packs, and sometimes people stumble across this in their Web searches. But by the time it came to market in 2012, the Prius Plugin had the single software-managed battery. But the illusion is real convincing.

 

@CharlesH is correct. There is only one physical traction battery. What you are seeing are voltage levels, not sections. This way CHARGE mode can only charge up to a certain voltage level (keeps the heat down). Fully charged, the battery registers 351V or so. As the battery discharges the overall voltage declines until it gets to a point where the computer must maintain the voltage level called HV mode. The inverter is what does most of the work and delivers the same amount of power whether you have a full charge or half charge.


iPad ? Pro

 

What @CharlesH and @drash said.

As the voltage drops it eventually gets low enough that the computer switches to hybrid mode. Voltage is essentially electrical pressure. Think of it, in this case, as air pressure. As the air pressure in a tank drops no part of the tank empties more (or quicker) than any other part. Same with a battery. And as electrons exit the battery, there is less "pressure" moving them through the conductors in the system just like there would be less pressure in a partially deflated air tank to blow dust off your work bench. The difference being that elecrons (or the holes between them) don't change speed like the air does; they just do less work.

To switch analogies, I sometimes like to use plumbing terms in explaining electricity to the untrained. In fact, it was in one of my early textbooks, I think. ___ Caution! There are several parallels between water flow and electrical flow, but there are also major differences. Still, the analogy can help show the most basic relationship between volts, amps, watts, and watt/hours.

Voltage = water pressure (psi) ----- Voltage drives the current like pressure drives the water.
Current (coulombs/second or amps) = water flow rate (gpm) ----- result of voltage & resistance or of pressure & pipe diameter.
Watts (volts X amps in DC circuits) = power (psi X gpm, or horsepower if you please) ------ both are measures of power.
Watt/hours (watts (or v/a) times time) = quantiy = gallons ------- measures of work

There are lots of other possible terms in this relationship, but the point is to show in a tangible way how volts, amps, watts, and watt/hours relate to each other. And again, the analogy breaks down in a hurry if you try to expand on it. It' super basic and simplified but water is easier to visualize.

And that, in a whole lot of words, is how one battery can look like two.

 

With 3 years and 80K miles on my 2017 Prime, and routinely making extensive use of all sorts of simple and advanced strategies, here is my 2 cents worth about Charge Mode. If you're not someone who pays attention to the car to figure out what it's doing and why, I'd advise using Charge Mode for only a couple of reasons, at least until you get the hang of it by executing simple strategies well, in the two best situations for using it:

One scenario to definitely use Charge Mode is if you know you're going to be in extremely good conditions for EV driving before you plug in next, but lack the remaining EV range needed to take full advantage For instance, you're approaching a city and aren't going to be plugging in there, but you are going to be sitting in traffic a lot there, and don't already have enough EV range remaining to accomplish all your city traffic missions there. Go ahead and use Charge Mode to build up EV range to avoid needing the engine to come on in the city.

A second scenario is if you're on a commute/trip/mission where you know you'll be able to use up your EV range efficiently before plugging in again, plus you'll have to (or want to) be on the highway in HV mode during your current leg of the trip and go through a warmup cycle. Let's say you can reach the highway with 100% of your EV range left if you drive to it in HV mode, or with 50% left if you drive to it in EV mode. And let's say that your route to the highway is easy 35mph driving, some parts with lots of traffic lights and stop signs, other parts of it a nice stretch of steady cruising. And let's say you don't want to drive 75mph on the highway with an absolutely cold engine. When and how should you warm up the engine? On the stretch where you don't expect to be sitting at red lights, of course! If that stretch keeps you at a nice throttle setting near the center eco line, and if the distance is enough that it's warmed up before the next stop sign, mission accomplished, you don't need Charge Mode. But if either part of that isn't true, and you're already down to well below 80% EV remaining, use Charge Mode to get the throttle setting up into the efficient range AND speed up the warmup to complete before your next traffic light. It won't turn the engine off, even in EV mode, until its warmed up: the engine won't even stop at a red light. You can use Charge Mode to help avoid that situation. And if you DO arrive at the light and it won't stop the engine in EV mode, bite the bullet and put it right back into Charge Mode. As long as the engine is running, keep it charging, both to get closer to an efficient throttle setting, and to speed the warmup to avoid having the same problem at the next light.

Once you get used to doing things like those, and get skilled at it (but hey, everyone occasionally forgets they're in EV mode and ends up staring at the dreaded dashes for remaining EV range, don't beat yourself up over that), then you have to decide whether you want to micro-manage the EV/HV/Charge mode selection in less obvious situations.

You also have to decide how hard you're going to work your battery. Despite the car protecting itself, I'd advise strongly against using Charge Mode so much that you're in EV Mode or Charge Mode all the time, or anywhere near it. Gaining a few percent of mpg isn't worth it, if you're basically always charging and discharging the battery to get 2x, 3x, or 10x as much EV Mode usage, compared to just using up EV miles once between charges and not having additional ups an downs beyond what HV mode already does. Let HV mode figure most stuff out most of the time, and use Charge Mode for preparing for obvious EV needs and optimizing warmup timing/location.

Having said that....I eventually figure out a strategy for my most common routes, after driving them many times and trying many things. I associate certain places on the route with a target amount of EV range to have left. Doing and refining this for your commute and most common trips makes sense as your next task after mastering the first two scenarios.

My most common roundtrip is 108 miles, across southern NH, with some steep 35mph and 55mph hills, and lots of 30-40mph curvy flats. In average weather, I use 1.02 to 1.05 gallons of 87 octane. In ideal weather in the middle of the night (when I don't have to accelerate hard on one nasty stretch where it is 25-30mph right after a red light and changes to 55mph climbing a big elevation gain) I use as little as 0.91 to 0.95 gallons. In hot weather where I absolutely blast the AC on LOW/60 (always outdoor air, not recirc) and keep up with fast traffic in certain places, I use 1.1 to 1.2 gallons. When I drive that route often, my EV range after charging hovers around 42 miles give or take 1. I ALWAYS have the fan on at least 3-4 bars with outside air, never recirc/max, never set the temp above 65-68 except in winter. This forces some cool air through the battery even if the battery fan isn't on. In hot weather, I set the AC at 65 with outdoor air and again at least 3-4 bars of fan for the same reason. So, I could easily get better mpg if I didn't care about preserving my battery health over the long term. Once you start using Charge Mode, pay more attention to battery health.

Battery health first! I'm in MA, a CARB state, so if the battery dies at 149K, it would be like winning the free-battery lottery. If the battery dies at 151K, it would be a very big expense. I don't mind monkeying with a Gen 2 battery myself, I rebuilt one for a friend. But this one in the Prime weighs the better part of 400 pounds, has 95 modules vs 28, and I'd really just want a whole new battery (or set of 95 new modules) swapped in. Playing mix and match would get out of hand. Battery is slightly over $10K, should drop by the time it dies, but are you feeling lucky? Clean or replace the battery inlet air filters. Keep them clear of your stuff. Spend the few extra dollars of gas per year to use fresh outdoor air that gets pushed out of the car via the battery, instead of recirc. If you're hot and the air in the cabin is hot, the battery isn't staying cool either. Don't turn off the AC to save more gas. You're saving enough gas already. It's the best car ever made, treat it well.

 

It's not a problem to let the engine warm up on the highway. The warm up cycle still protects the engine and uses mostly EV power until it's warmed up. An exception is if the battery is cold, sometimes the car bypasses the warm up cycle if you're calling for a lot of power in EV mode, and if it thinks the battery might not be able to supply that.

Do you have a source for this? I don't know where the air leaves the battery after passing through it.

I will say, the car seems to make no effort to cool the battery if the battery is below 95F. The traction battery cooler won't run, and the fans barely run while driving. Above 95 it runs the fans at a higher speed, and it's usually able to keep it within a few degrees of that in my experience. I've only seen it go over 100 on a few occasions, but it helps that we don't often get 100 degree weather here.

 

I don't worry about the engine being unprotected if it first starts up on the highway, I trust they got that right. But I do prefer having it warmed up already, so that I have full ICE power available, and it doesn't drain a lot of EV as I accelerate uphill in HV mode onto the highway ramp followed by a genuine uphill stretch. If I'd wanted to drain EV miles there, I'd be in EV mode. It's the point where I want to use HV mode, and not have it steal/borrow more EV energy than it usually does in HV mode. Also when I go down the other side of the hill I'm climbing, I want to be able to get back in EV mode without the engine staying on to finish warming up. Having the engine on when you're descending a big hill, just because it hasn't finished warming up, is a genuine mpg disaster, hahaha.

I didn't use the term hypermiling, because I save that for things like pulse and glide, which I found effective in Gen 1/2/3, but is pretty unnecessary in the Prime. If you want to drive super slow, drive super slow, but the days of only getting the best mileage by pulsing to 40mph and gliding to 20mph are over thanks to the Prime. Just pick how fast you want to get there and drive at the speeds necessary, using EV/HV/Charge modes to keep the throttle in its most efficient range as much as possible when the engine is on, and have EV handle the low-throttle end of the spectrum that you used to have to glide for to avoid the engine coming on. No such problem in the Prime.

My source for my battery airflow theory is having torn a Gen 2 apart, rebuilt the battery, removed and cleaned the battery ducting and its blower. I haven't torn my Prime apart yet, but I see a fair amount of evidence it's the same and no evidence it's different, except for more airflow area. In the Gen 2, it takes air into the battery cooling blower from multiple locations, blows it through the battery's air inlet duct and centrifugal blower, through the battery between modules, out the battery outlet duct, to a very thin and loose rubber flap which the least bit of airflow pushes open to outdoor air in a hidden location by the side storage cubby behind the rear wheel well on the passenger side. Probably they've designed it to be in a spot where aerodymamics create outdoor air suction on it, too. I'd not be surprised if the Prime exhausts it by both wheel wells or other locations too, as it has more inlet filter area.

I could be wrong, but I'm 99% convinced that on the Prime, the battery cooling air scheme is basically the same, but maybe with 2 sets of ducts and blowers? And I'm 90% convinced that with the windows closed and fresh air being blown from the HVAC vents, one path of least resistance, probably the primary path, for that air to leave the car, is via the battery Even without the HVAC fan on, you get some air flowing through just from ram air from the car's speed, sort of like having the fan on low. It's going back outside somewhere, or more wouldn't be able to come in. My main guess is that it exits through the battery. It makes sense they'd route all air out through the filters and battery ducting, free battery cooling. Just a question of whether it's enough to open the rubber flap without the battery blower on, and it seemed to me that it easily was, in the Gen 2. The Gen 2 battery blower is a white plastic centrifugal blower wheel, which allows air to easily pass through whether or not it's spinning.

 

I really like drashs' idea in post #64 - I'm going to try to remember that and see if I can practice it a few times during those conditions.

Personally, I like to put as little load on the gas engine during warmup as I can while still moving forward and still get it overwith ASAP. So, it would have to be a new situation for me before I'd use charge mode during engine warmup. I do agree and believe that charge mode is more effiecent below, lets say for sake of argument, 40 mph. I've experienced engine shutter at the beginning of warmup cycle, while driving, in both the PiP and the Prime. And I understand when others ask about it how it fells. That makes me a bit bias to engine load scenrios during the warmup cycle. On the other hand I haven't experienced engine shutter in a long time, but I also try to think of new and better ways to reduce engine load during the warmup cycle.
If the engine comes on unexpectedly, I'm not going to worry about it, not at all. Although if I'm expecting to need the gas engine I want to have as much inertia working in my favor while the engine is warming up.

I respect ofter views and I've contradictted the OP once on this issue, to my chagrin. And I think that after anyones experienced that shutter at engine on they might also agree, it was eye opening for me.

I've never had the GOM above 36 or 7, but given the right conditions I can get 10 to 15 miles more than that if I'm really really trying and I've been really really trying to get max EV range for a long enough time prior.
I'm also not the only daily driver of the car, which I'm sure makes at least some difference.

Given the cars current condition (a dragging front pad and not padding the GOM range for almost a year) the GOM is currently as 28. I got it back up to 30 a month or two ago, but the car seems to have forgotten I ever drove it.
And I don't seem to have the patience or desire to pad the GOM again just so I can see more EV miles again.
And I've also noticed I can't beat the GOM estimate much more than about 4 or 5 miles which is beyond frustrating for me when trying to pad the GOM.

 

I agree. In fact, if you're driving on level ground at 50 mph or less, it does it's own charge mode. It just doesn't charge as much at a time. It'll put itself in EV and after a couple miles, the ICE comes on & charges the battery back up. Then, back to EV. Just like pushing the charge mode button, but always keeping the engine warm.

 

Sounds like what a regular Gen4 prius does.or am I missing something obvious? It wouldn't be the first time that's happened ....