Self-Charging in the Prime

Whew! There's a lot of good information in here and a bit of conjecture as well.
I will just have to drive the Prime and hope the learning curve is not as steep as all the complexities mentioned seem to suggest.

 

The only thing I can say is, for best mileage, drive the way the car wants not the way you want. I've been hypermiling for over 10 years and this is still a learning experience for me. I'm still learning new things all the time. Oh yeah, keep on reading here.

 

Correct. This includes 25 EV miles reported by the system.

 

According to Fuelly you have filled-up your tank today (9.66 gal) and your last tank produced only 57.5 mpg. Have you already abandoned this method of 'oscillating charge mode'?

 

No, continue to test. This is "EV" until out of battery power and then "HV" without using charge mode.

 

Looking forward to a full tank of oscillating charge.

 

Interesting. I wonder why Toyota would offer this mode. In what circumstance will it be useful? Going down a long hill?

I don't think recharging the battery from the engine is more efficient than just using the engine to drive, because of more energy conversions.

 

Could be handy when you enter a place where you want to drive on electric power. So you can charge when you are on the highway.

 

There are several discussions of that in this forum, one of which is *in this thread*!

 

New Prime owner here. Our 2010 Gen3 (we're now a 2-Prius [Prii?] household) waits until about 25% and then charges the battery to about 75%. If I'm understanding these posts, HV mode on a Prime (ignoring regen breaking and not using B mode) cycles between 23% and about 28%, and you need to go to Charge mode to get it up to 80%, right?

 

HV mode holds charge wherever it was when you activated HV mode, give or take one or two percent. Charge mode will charge it up, as will a long descent.

 

Interesting to know that!

We do a lot of driving between KC and Denver. Basically 15 miles of in-town EV-friendly driving at either end of 600 miles of HV-only (75 mph across Kansas and eastern Colorado, mostly flat).

So... a question for you Prime veterans: On a KC-to-Denver trip, would it make more sense to (a) leave KC in EV/auto mode, let it run down to ~25% and drop into HV mode on its own after a few miles, and then switch to Charge mode a few miles out of Denver so I can finish out the trip in EV; or (b) switch to HV a little earlier with the battery at ~65%, hold that charge all the way into Denver, and then switch back to EV?

Comes down to the efficiency of intermittent charging in HV mode to hold a good charge vs. a bit more EV at the near end and full-on recharge for a few miles at the far end.


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I've driven that route dozens of times. I personally prefer to use EV to get to the highway, then HV. For safety, I like to charge up to 80% so if anything happens, I have 20 or so miles of EV range to get someplace.

Once, I filled up in KC, drove all around KC for four days, mostly on HV, then drove across Kansas to Goodland (!) before finally filling up. Quite the range.

 

I played with charge mode on a long trip. Waste of gas due to the laws of physics. My practice is to use EV at low speeds and switch to HV when I hit the interstate or when the EV SOC gets down around 25% so I'll have some for future low speed operations. If you use charge mode, you burn gas charging the battery, but you also burn gas to cover the heat losses involved in conversion and the charging itself. That all generates heat that you pay for at the pump.

I would only use charge mode if I accidentally used up all the EV range and wanted to have some available for the next time I started up in case I was only just moving the car. That would be so the engine wouldn't start up due to no EV availability. In HV mode at low speeds, the Prime will run mostly in EV all by itself anyway once the engine is warm.

 

There are ways to use charge mode to beat HV mode. I've done it, and averaged over 70MPG (I've managed up to 78mpg on a round-trip this way). The idea is to switch to charge mode when the engine is operating but at low power - long and slow, slight downhill, etc. That operates the engine in a far more efficient power range and you get to use the energy later efficiently.

 

I've wondered about that. But there are very few situations like that where I live. The few times I've tried it have been too brief to be very informative. To me, it seems to have a lot of potential since the car does pretty much that same thing itself at low speeds, switching between ICE & battery for a mile or two at a time. Unfortunately, our biggest hills are highway overpasses. So, I just let the car do its thing for as long as it wants to.

 

You live in Florida. I have a meteorological tower at the site where I work that's taller than the state of Florida (440 feet vs 345 feet).

I live in Colorado. My drive to work (11 miles) involves ascending 700 feet net. I ascend 600 feet to get to the flying field where I fly R/C. I get to test this any time I'm not in EV mode. Now, in fairness, I'm always in EV mode between home and work and between home and the R/C field. But I've been across the Rockies in my Prime several times, and I've been out of town in Colorado around a hundred times, some of which involved altitude changes of over 6000 feet. I've had lots of opportunities to test this. It totally works.

 

We lived in the Denver area 30-40 years ago (Broomfield, Wheat Ridge, Thornton) and still have friends there. Last time we were there, we came by way of Mesa Verde, Grand Mesa, and the Eisenhower Tunnel (actually, the Johnson Tunnel ). The Prime was INCREDIBLE in the mountains. I still miss the mountains but even more so now with this car.

 

You are bit off but general idea is correct. The actual SOC for HV mode range (after running out of EV range) is more like 8%-14%. When I run out of EV range, the SOC is always around 11%.

As others have chimed in, using EV in city low speed and HV for highway is a good practice, but for over 600 miles of trips, IMOH it really does not matter where/when you use EV, your overall efficiency is mainly determined by the way you drive on HV.