Does anyone know the efficiency of the hybrid battery charge mode? I assume I lose ICE range as power is diverted to the battery. Do I lose more ICE miles than I gain EV miles?

Between my infrequent driving due to covid, and the electric battery covering basically all my daily driving, I haven't put gas in my car yet. I'm around 650 on my odometer. I've got 325 miles of ICE range left. And I have a 350 mile drive to North Carolina coming up. Add on 40ish EV miles and maaaaybe I can get to my destination and cross 1,000 miles before filling up for the first time?

Getting 40 ev miles to start, and charging another 30ish ev miles while on the highway would give me a nice cushion. But I assume I'd lose more than 30 miles in gas range doing that?

Charge mode of course takes a hit on MPGs, but unfortunately I'm not exactly sure how big of a hit. A guy on YT did an unscientific test with his R4P sitting running in charge mode in his driveway, and found it took approx 1.7 gallons to have charge mode fill the traction battery from empty to ~80%, and based on EV miles gained from that charge (38), approximated ~22 MPG. I just took a road trip (600+ total miles) and used charge mode a couple times since I didn't plug in at all. When I wasn't in charge mode, I was in HV mode on the highways, then would switch to EV mode when I knew speeds would consistently be under 50 mph. It takes a fair amount of driving in charge mode to go from empty to full (I'd estimate 60-90 mins of driving), and it doesn't actually take it to full, but around 80%. I hear the engine change tone (if that makes sense - similar to how a standalone portable generator motor changes as load increases/decreases) during charge mode, and it makes me wonder if it isn't varying the amount of charging its doing, considering regen braking and other conditions, so it seems the hit to MPGs may not be constant. I'm sure it has to do the dance of moving the vehicle down the road under various conditions and charging the battery, determining what power goes where, and when. I love the flexibility of this vehicle, there are different ways to go about the whole gas/electric game, and it takes careful planning to maximize the electric. On the other hand, you don't have to plan at all, and just drive it, knowing you can fall back on the ICE at any time (so long as there's gas in the tank).

 

Does anyone know the efficiency of the hybrid battery charge mode? I assume I lose ICE range as power is diverted to the battery. Do I lose more ICE miles than I gain EV miles?

I think it's a wash when driving. That is, the extra gas you use putting 10 miles into the traction battery is the same as you would use driving those same 10 miles in HV mode. I've tested this more than once.

 

You are paying the power transfer cost (friction, resistance, overhead, ...) twice. ICE to battery, and battery to wheels. You are always going to lose total miles using ICE to fill the traction battery.
Owner’s manual Page 78;
“When in the hybrid battery (trac- tion battery) charge mode, the hybrid battery can be charged while driving. However, the gaso- line engine runs to charge the battery and fuel consumption becomes higher compared with driving in HV mode.”
I have not seen any science based estimates for MPG hit for forced charging.

I follow this advice in the owner’s manual (some good, some from lawyers) page 92;
“Primarily using EV mode and AUTO EV/HV mode when driv- ing in cities and using HV mode when driving on highways (or freeways) can help conserve fuel and electricity. (P.78)”
I like HV for highway driving because;
1) I like the full hybrid system 302HP (ICE + EV miles to boost).
2) It is using most efficient systems for highway speeds.
3) I like the growl of the ICE.

 

I was in ICE mode running low on gasoline (I was trying to burn off 6 month old fuel) and decided to try charging the battery while driving on the interstate as a backup.

Trip average miles per gallon dropped from 37 to 32 mpg after 30 min of driving in charge mode. I added 13 miles of range to the battery in that 35 miles using ICE or about 1 EV to 3 miles in ICE charge.

I was surprised how fast I added 13 miles of EV range while driving 70 mph in ICE charge mode but economy dropped in 30 minutes 5 miles per gallon or about 15%.


It was not the most pleasant mode of driving. The engine runs at a higher rpm in charge mode and you loose acceleration but if you are running low on gas and don’t want to stop to gas up that is an option to fill the battery as a backup.

Russ

 

Russ, I liked your MPG observations w and w/out charge mode. My post was written in response to rsl360. I consider your experiments reproducible and scientific.

We are brave/stupid about the small amount of gas we have put into the wife’s Prius Prime. I put stabil in with each approximately 3 gallon fill-up. I just don’t fill-up often enough, or she does not use ICE enough. I’m am even more brave/stupid when I had my Prius v and ScanGaugeII showing me more raw fuel level readings. I ran it down to 0.3 gallons (too close I know) twice. One of those was a little scary, driving around looking for gas station in unknown rural area.

My ScanGaugeII reads the fuel level in my R4Prime so I have seen the generous reserve at the bottom of the tank and a 0.8 gallon air pocket at the top. I can’t get above 13.7 gallons (OBD value) on my fill-ups. Fuel gauge always shows above full tick-mark.

I have read that running a high pressure fuel system (like we have) dry is especially hard on that fuel system. So I will try very hard not to run out of gas in my R4Prime. I’m not so worried about overheating fuel pumps. I don’t think it happens anymore. I think Toyota has fuel pump overheating covered.

Stay warm Russ.

 

Thanks Chazz

Looking forward to Spring. I Love to work in the yard Enjoy gardening and freeze drying what we grow.
Take Care,

Russ

 

M

 

Thanks! Exactly what I was looking for.

Seems like charge mode isn't very useful

 

Dsc123

Yes you are correct, not a benefit to use ICE EV charge if you are trying to save money.

I only used charge mode once because I wanted to add a few miles on the battery in case my tank ran dry before I reached home but in real life I cannot see using it to charge the battery vs plugging into our L2 in the garage at .09 cents per kWh. (.09x14.6kwh= $1.31 full usable charge)

The charge mode really does zap the acceleration and it does Rev higher while in that mode which if cruising down the freeway does get a little annoying.

I see no benefit unless you are approaching a city that may have EV driving benefits like EV designated lanes so charging up may benefit but a 3 miles gas to 1 mile EV charge would require you start charging about 2 hours before entering an EV friendly city assuming you are driving around 60 mph.

You will also need to plan on about a 15% drop in fuel economy while driving in ICE charge mode for the time you are charging the battery.


Note: You can only get an 80% charge using ICE charge mode.

Russ

 

I'll bet charge mode comes in handy (like in Texas recently) during extended power outages at home (assuming you don't already have a portable or whole house generator)...

 

Jmartin

Great point. I did not think about the generator aspect assuming your have an inverter.

I have a 3850 duel fuel (gas/propane) generator and 8 bbq grill bottles (5 gallon) and enough 12 gauge extension cord to operate our two fridges two freezers fans to the two natural gas fireplaces we have. (Furnace uses too much juice for our generator if I am also operating the appliances.)

I figure if I run the generator 8 hours in a 24 hour period of time the 40 gallons of propane will get me about 10 days

After that we will need to have a neighborhood bbq.

Seriously, my heart goes out to the families suffering in Texas. We all grow a custom to electricity and when you are without it for half a day we feel like life is unfair. Can not imagine weeks without it.
Russ

 

This has been an interesting topic, but to put it all into perspective I think we should ask Professor Stan Wagon the mathematician to explain it. It may take days to read his post, but that's ok. Yep, Chazz8, just drive it. Even better, merge this thread with New Owner Query thread.

 

Hah! This is a physics question, not math. I myself have wondered why I would ever use the Charge mode. I see that people here have their reasons, but I cannot imagine using it myself.

 

Exactly, that's what I've trying to say. (in this and other postings)