Question about battery charging while on the go

'you can't ever charge above the threshold' is a contradiction. just because you charge above the threshold, then use that up in ev and go back to hybrid mode doesn't mean you didn't charge above the threshold.
in practice, unless you live in a mountainous area, you won't find it charging back above the threshold very often. it takes a lot of regeneration.
most of your ev will come from plugging in, unless you want to use force charge for some reason.

 

Living outside NYC I am often in this exact position. I charge up the battery, drive into NYC in EV/HV mode, and then when I get to NYC I switch back to EV or EV/Auto to use the battery.

When I am ready to come home I switch back to EV/HV until I get home so I can have some battery tootering around my home town.

SM-P610 ?

 

There is also Charge Mode. When the battery goes below the threshold ie: your %20 estimate above, you can go into charge mode by pressing and holding the EV/HV button for 5 seconds. The EV mode green indicator next to the speedo will switch to Charge Mode.
Than the gas engine will charge the battery to it's upper threshold of %80. That typically takes about 45 minutes from the bottom threshold, ie: your %20 above. Than when battery reaches the upper threshold of %80 the car switches back to - HV (I think) I haven't used Charge Mode in a while so I've forgotten when mode it switches back into. You have to watch the gauges to switch to whatever mode you want to be in if the car automatically switches into a mode you don't want to be in, and it's possible to switch into the mode you want to be in , which it's not always possible, especially near the thresholds.

The best way to learn about how the car works is to find what you like to use and practice at using it.

 

The method is the right one. But to clarify terminology, there is no such thing as "EV/HV" mode. The EV/HV button toggles between EV and HV modes. It's one or the other.

Just hit the EV/HV button to put it in HV mode as soon as you start it. The indicated percentage of charge may go down and back up a few percent as you drive since the car uses the battery in hybrid mode just like any other Prius. If you have big hills that you'll be going up and down on the way to the city, you may want to use enough charge before the hills (maybe 10%) to absorb the regeneration going down them, but they'd need to be pretty long downgrades before the Prime would have to use engine braking, even if the SOC was 100%.

Of course. It's kind of a gas waster. It's cheaper to let the car decide when to charge or use the battery, but you can do that. At city speeds, the Prime will drive for quite a long distance in HV mode with the engine off. Then it will charge the battery back up and then go back to engine off all by itself. It's incredibly efficient.

 

Back in 2013 (seems so long ago.....), I discovered this ability in my C-max Energi. I like to call it “EV banking”. I think it’s a better term for what the operator is trying to achieve. I have no hills so I employ EV banking during high-speed braking to a stop.

On my typical 90 mile out of town round trip, I can pick up 5-6 EV miles. It’s only 4 urban miles from the interstate to my house so I use those “free” miles on this final leg which also gives the ICE time to cool down before I pull into the garage (NICE!). Remembering to switch back/forth between EV and HV modes is the tricky part.

 

When the electricity rate was higher than gas price (not too long ago when gas was below $2/gal), I was using the gas engine on HV mode on all the uphill and accrecelation and switching to EV mode on all the downhill and coast/deceleration to use regen to stock up on the battery charge. I went on not charging my battery for months but always had some charge left in the battery for EV mode when needed.

 

It's a good question. However, I believe that CHG mode will only bring the battery to 80% before automatically returning the Prime to EV or HV mode.

 

As stated above by @Old Bear, CHG mode can not bring the traction battery full. Only up to 80%. But, I don't remember anyone actually measuring the amount of gas needed to bring 0% to 80%. Most of the time, CHG mode is operated while driving, so it negatively affects (lowers) MPG. But the MPG numbers displayed (or calculated) do not tell the exact amount of gasoline used for charging the traction battery since it includes the actual driving part which can be affected by many factors.

It is easy to measure this by using CHG mode whiled parked. Use CHG mode to bring the EV depleted battery to 80% while parked, and check the amount of gas used by the full tank method. Humm, I don't see CHG mode being cheaper than using the wall charge especially now gas price is higher, but I am very curious to find out this. I may try doing this experiment myself.

 

I suspect that variations in where the pump clicks off from one fill-up to the next, would make this pretty inaccurate. You'd probably need to average a bunch of tests. But aside from having a test rig to feed fuel from an external measured container instead of the gas tank, it's probably the best way to attempt it.

I'm content to know that with the price of my electricity even before solar power and the price of my gas, wall charge is WAY cheaper electricity than charge mode.

 

Yes, I see your point. After doing the math, it may not be so practical to try this experiment.

Knowing 80% charge of the traction battery is only ~5kWh of electricity, using EPA's formula, in which 33.7kWh of electricity is equivalent to one gallon of gasoline, I can estimate the single 0-80% CHG mode will use ~0.15 gal of gas (5kWh÷33.7kWh/gal). With some loss in the conversion, the actual amount is probably higher than 0.15gal. You are quite correct that I would need at least half a tank worth of gas used for the CHG mode to get a more accurate average number. That would be over 30 CHG mode (0-80%) charges and each charge has to be depleted without using gas on HV mode in between the CHG cycle. Hard to pull off as I do regular driving of longer than 25miles.

 

@john1701a did a video long ago on a 2017 Prime

Roughly 40mpg on dash for 0-80% in charge mode

CHG MODE

 

The full charge on the battery is less than the full capacity of the battery which is 8.8kWh. The actual full charge from the wall is somewhere around 5.8-6.8kWh and the actual usable charge in the battery is about 5.4-6.0-kWh. The precise number of this "usable" capacity has not been disclosed by Toyota, and various owners of PP have attempted to estimate it with some variations. But it is most likely to lay somewhere in that range. So 80% charge is likely to be 4.4-4.8kWh.

Your electric rate is similar to mine. I pay $0.21/kWh. At this rate, when the gas price is below $2.85/gal, it is cheaper to drive using gasoline on HV mode. If the CHG mode conversion is lossless, then your assumption is correct that at your electricity rate and assuming $3/gal gas price, CHG mode gas will cost roughly the same cost as using wall charge. But be reminded that using CHG mode to charge the traction battery will not save you any money. It is cheaper to drive purely on HV than using CHG mode at any instance. Purely for an economical term, PHEV or BEV makes no sense in our high electricity rate area, but if your grid electricity is cleaner like mine, 100% renewable, then using less gas more electricity makes some contribution albeit minuscule in combatting the global climate change problem.