Question about battery charging while on the go

This^. The car is incredibly intelligent. Assuming level ground, no strong headwinds, and speeds of 60 mph or less, the Prime switches back and forth on it's own. It'll go for a mile or so w/o the ICE running and then charge back up for a mile or so. The car knows the optimal conditions for each mode and makes way better decisions in most cases than we do. I've tried to out-think it. I think I might have managed a tie once but can't be sure.

To get only 50 mpg, I have to drive over 70 mph. I don't think I can go even close to 25 miles in EV at that speed. I could probably go 25 miles at 60 mph in EV, but if I go that speed in HV I'd get almost 70 mpg.

That's about what mine shows when I've played with charge mode. And then you use the charge and your average mpg is back to where it would have been if you hadn't bothered with charge mode.

My advice is to not necessarily take our word for it. Try it out yourself. Experiment to your heart's content. When you come to the same conclusion as the other experienced Prime owners, you will better understand just what a well thought out system controls the Prime. Experience really is the best teacher.

 

I personally have tried Charge Mode.

It is kinda cool,, again if you really needed usable EV mode in some circumstance, it is there for you.

Best to use Charge Mode on a highway of sorts, like 45-55mph I assume for best conversion at highest mpg cruising.
I tried mine at 67mph (65 posted limit) for about 10 miles and gained enough charge to EV mode it in parking lots and such.
And can also use it to preheat/precool cabin, or if just sitting waiting etc.
Good stuff!

Def give it a try, hold that button in!
Everyone should give it a try as @jerrymildred has mentioned.

 

Here are some of the variables to add to to calculations above while getting a baseline for the cost of using Charge mode.

It's really never as efficient to use Charge Mode when comparing to the other available modes or the plug, but there are times when having Charge Mode available to use, like when Mobile, that it is beneficial.

the driver has to try using charge mode at different speeds and different amounts of time to get a handle on what speeds charge mode works best for them, if at all. (there are a lot of reason why some wouldn't ever use it).

The visuals from Hybrid Assistant, DrPrius and Torque can help demystify what's actually going on during charge mode, keeping in mind the warnings about using the apps while driving.

 

Another confounding factor is that the gasoline engine's efficiency varies with RPM and with load. Using charge mode while driving at 30 mph is going to be different than using charge mode while driving at 60 mph.

Similarly, the efficiency of using charge mode while the Prime is stationary and in "neutral" may vary depending upon idle speed. I've never tried "racing the engine" by pressing down on the accelerator pedal while in EV or CHG mode while stopped with a completely discharged battery.

I will be interesting to see the results of this research by those Prius-chatters who are so inclined to experiment. This may be one of those phenomena which are impossible in theory but possible in practice -- or vice versa.

 

While there are scenarios where CHG makes sense, like building EV charge for driving in a city at the end of a long trip, in most cases, it is more efficient to let the car use the ICE to directly move the car, rather than using the ICE to charge the battery (with some conversion losses), and then using the battery to move the car (again, with some conversion losses).

 

So - I played with this just once, on a trip I do frequently (about 66 miles each way, rolling hills) - 1 mile to get to expressway (70mph limit) and 2 miles off expressway. I get 25-26 EV miles, and one time, purely to see what I could do, I did CHG mode after I ran out of battery, and tried to time it so I could switch to EV and exhaust EV when I arrived. I was close, and while my average MPG for that trip is normally (I'm making up #'s I need to pay closer attention next time) 75mpg, I got something like 85 mpg that time. I'll have to try it a few times and get good at figuring out what mile marker to engage CHG and turn it off etc etc. I normally just do not pay attention enough to plan it out.

 

Are you saying you were getting better MPG with using CHG mode and using the EV mode later on the same trip than without CHG mode and just using up the EV range on the same 66 miles trip? That is hard to believe.

 

Yes thats what I think I'm saying, but I want to verify next trip.

But I think it makes sense if/when done right....

Again - 66 mile trip 1 way. So....

If I'm covering 25miles at the start of the trip at I'm assuming the computer computes 99mpg for those 25 miles

Then engine kicks in, I'm on the expressway, probably getting 52mpg. So if I drive the rest of the trip, that'll be 31 miles at 52mpg
That average = 69.8MPG

Again I don't remember my specifics and I def want to try it again... but my quick excel spread sheet... assuming the computer thinks EV mode is 99mpg (is that right or does it think 999mpg?)

If I cut over to CHG mode, and get 30MPG (which I think is probably way to low, but just to demonstrate). So now if I drive 26miles getting 30MPG, but then I complete the last 15miles of my drive back at 99mpg. I now average 71.8mpg for the trip. (I don't believe that 26 miles of CHG (or whatever I did) got me enough battery to complete the trip, but it was close, I may have gone BACK to hybrid mode for the last few miles of the trip as I didn't want to have any battery left when I got there or that'd defeat the purpose of using CHG mode for what I was doing).

I guess what I have to figure out now is, when going 75MPH on the expressway in CHG mode what kind of MPG I'm getting... but also do the drive as with and without CHG mode and compute the numbers for real.

Like I said, I was surprised, but I know my MPG was higher doing the trip this way at least the one time I tried it.

C

 

Yeah, try and document it. And to make a good comparison, it must be the same trip in the same direction. So, you can't compare the one with CHG on a way to the one without CHG on way back from. If you do that, then you have to make at least another same trip to take a note for the one without CHG on a way to and one with CHG on way back from. And average the two trips. Still, for regular mpg calculation, there are just way too many variables that change regular mpg. For the occasional highway drives I do, I sometimes get only 50mpg and but exactly the same route may get 70mpg without noticeable differences in the way I drive. But if you can repeatedly observe using CHG mode and using the EV mode on the same leg of the trip gives you better overall mpg than driving without CHG mode, that would be very interesting.

If the driving conditions are exactly the same, I would think the physics makes it impossible to get better mpg using CHG mode than without. But maybe since EV mode efficiency is so much better than HV mode (133mpge vs 54mpg), maybe, converting gasoline energy into battery electricity, even with some conversion loss, and using it to move the car on EV mode does give you overall better mpg. I don't do enough of those long highway drives to test this, but I am looking forward to seeing your next report.

It is 999.9mpg... but it should be infinity. You are driving a car without using any gasoline, so whatever the miles driven on EV mode divided by zero is equal to infinity ∞. BTW, for those who drive 2017 PPs, the number is 199.9mpg.

 

Had some weird experiences with proof.

You can see two instances that I achieved over 999mpg.
Both times, I was on may way to charge but ran out blocks away from the charging station like 0.1 mile
so the engine started and HV mode took me the rest of the way.
Then after charging would drive home about 0.25 miles. the 1600mpg I drove a few other places I think.

So not sure if there is a glitch or what is happening.

 

Interesting. Of course, I suspect that display is only showing on your App, not on the dash. Or are they also showing on the dash? I think the dash display has the limitation of 999.9 being the largest number it can display. The App may be able to show actual mpg higher than 999.9. It may be programmed to display 999.9 when the value is infinity ∞, but if any use of engine is mixed then the actual number may appear on the App that exceeds 999.9? I don't use Toyota App, so I can't test it, but it would be easy for you to test it. Drive on EV mode, and just right before you reach the destination, switch to HV and run on the engine very, very short time. And check on your App. The car display stays at 999.9 for a while after the engine starts. This 999.9 display on the dash lasts for a while at least a few miles for me. Then when the number actually goes below 999.9, it starts to display a smaller number on the dash. So during the time when the HV mode is showing 999.9mpg, it is actually above 999.9, but not infinity ∞.

 

The ingenuity of this group is sometimes amazing. I'm not sure what KYBlue was doing but it sound like he was running in CHG mode when going down hill -- which is when the ICE may be acting as a break anyway. Even without CHG mode, that would be re-charging the traction battery but I'm not sure of the details of how this works and whether CHG mode might somehow glean additional energy from the descent.

There has been some discussion about the behavior of the ICE when the traction battery is at full charge and the vehicle is descending a steep hill. If I recall correctly, the engine will start to provide braking if the traction battery is full. Otherwise, some of that downhill kinetic energy will be "absorbed" into the traction battery, thus helping slow the vehicle.

There are some interesting pieces to this and it may be that under an unusual combination of circumstances (state of battery charge, downhill grade, use of regenerative braking, and use of CHG instead of or in addition to B) more energy is being delivered to the battery than in typical downhill driving.

Hybrid vehicles are constantly moving excess energy into the battery and, as needed, withdrawing energy from the battery.

A note of caution: this constant ebb-and-flow is shown on the Prius instrument display and is quite interesting to watch. However, if you watch it constantly, it can also provide an unexpected test of the collision avoidance braking system. This, of course, is not recommended.

If you choose to experiment, please do so cautiously.

 

As I said, I don't do highway drives frequently enough to do the experiment myself. But the notion that using the CHG mode to convert the energy in the gasoline into electricity and using the traction battery to propel the car gives better MPG overall is very intriguing to me. With a very high electricity rate around here, if a gas price drops again to below the threshold of $2.85 at which EV vs HV cost the same, I am tempted to use more gas than electricity especially if that makes the overall mpg better.

The 66 miles of highway speed seems to be a perfect distance to do this. My daily drive of ~40 miles is too short. I occasionally do ~70 miles round trip to a city nearby, but it is on a rural road at 50mph top, nowhere close to what I consider highway speed (above 65mph). And I don't do this drive frequently enough to be able to compare with CHG vs without CHG under similar conditions.

 

So here are the results..... Yesterday and Today. 67 mile drive. 56/57 Degrees yesterday and 55 today. Very very similar conditions.

Drive yesterday I did the following:
Drove approx 23 miles of the 67 on all electric.
Let the engine kick on as usual, it normally depletes (and it did) the hybrid part of the battery, I let this top back off/engine warm up.
I then switched to CHG mode and reset my trip meter.
I watched my Waze miles to go for my trip, and the miles of charge on the dash.
Once I was 1 mile past my waze estimated distance remaining (since the guess-o-meter is normally wrong) I left charge mode.
Charge mode was on for 25miles (BTW for at least me it seems 2 miles of driving = 1 mile of charge). I got 40.2MPG during these miles.
Once battery level = distance remaining in my drive + 1 mile (roughly 12 miles) I shut CHG mode off. I arrived at my destination with .4 miles of charge left.
Total trip MPG - 85.8MPG

Today, same drive, drove all electric, let hybrid kick in and didn't mess with anything.
Total trip MPG - 82.9MPG
Hybrid portion of trip MPG = 54.1

The drive is expressway mostly, with about 1.5 miles at start of drive at back roads 45mph or so, and 3 miles at finish at 45mph or less.
I had cruise set at 74MPH both times.

It seems that CHG mode, for this drive, which is probably half flat and half small up/down hills costs you 14MPG vs hybrid. But if done right, can net you overall better MPG for your total trip.....

 

Thank you for sharing your observation/experiment. Certainly, the difference of the mgps, 85.8MPG with CHG vs. 82.9MPG without CHG is not as dramatic as you first estimated. But it seems under certain conditions, it is possible to get better overall mpg using CHG mode to replenish the traction battery and using it to drive longer EV mode. Good to know that the CHG mode is not just a gimmick, but it can be used for improving fuel efficiency.

 

Just started a new thread on using CHG mode to increase the over all efficiency (MPG).
Can using CHG Mode be more efficient? | PriusChat

 

One way to get a more precise comparison is to monitor the plugin charge from 0% EV to 80% EV and grab the kWh's that takes. Remembering that these calculations are fairly static estimates with a bit of variation like seen in the Killawatt readings from 0% to 100%
It gets trickier when matching 100% to 0% EV range to traction pack voltage. The upper end of the voltage range (lower 370's volts) at %100 drops in voltage very much quicker than the lower %EV range until around 330 volts when the gas engine switches on. Except 100% to 99% which seems to last 2 or 3 times as long or / and distance as 99% to 98% and so on. This is not written is stone so don't quote me on it, but I've seen %66 EV match the nominal voltage of the pack which is right in the middle of (highest 373v ) and ( lowest 330v ) I've measured.
clear as mud, A !