To Drain the Traction Battery or To Not Drain the Traction Battery? That is the question.

That's true. I believe the important consideration is the efficiency of the ICE when producing and storing energy. When driving at low speeds (say below 35 mph) the ICE efficiency is low so the gas needed to charge the battery is higher than would be needed for the same battery charge at higher speeds or simply higher RPM such as going uphill. If you operate in EV at those lower speeds (having charged the battery at high RPM) the conversion losses for EV still produce more efficient operation than simply running the ICE at low RPM. This would be why the computer switches the car to EV at those lower speeds.

My conclusion would be... Its fine to use EV when the computer allows it. Of course true glide (everything off) is even better if you enjoy wide ranging variable speed driving

 

With that view, my prius is solar powered. All the power it produces came from the sun initially. "100% of the battery charge you are using by driving on battery alone is achieved by the use of gasoline, and there are always energy losses in every system." If this is correct then why have a hybrid in the first place. With the loss in conversion/transfer of energies the engine would get better mileage without the electric addition which it doesn't.

But hey its cool..we all have our own ideas. I prefer to use the electricity when the car deems it necessary and I always get 55+ letting it do its thing.

 

Let the Prius Computer decide when and how to use the battery.

 

Agreed! We really don't have any choice, we can't make it go into EV unless the computer gives us permission.

 

EV absolutely makes sense when you're driving on common 25-30mph streets. ICE is less efficient in this scenario, since it takes relatively little energy when driving at this speed.

Electric motors are most efficient when you're operating within 68-78% of their maximum free speed. On the Prius, this corresponds to about 30mph.

If you're trying to go faster than that, try to engage the ICE during initial acceleration ("punch the pedal" off the line... of course throttle back after).

Although electric motors are great for torque, this is peak power input scenario (and very little power output), so using EV-only to accelerate to 35 mph from a dead stop is a great way to eat a lot of energy inefficiently.

Don't be afraid to use the EV driving in slow streets. That's how the car largely gets such good city MPG. The opposite is true as well, don't over-abuse the EV for high-speed driving.

 

Not if you have to deplete the battery. Use coasting instead.

 

Especially if there are several cars behind you and no way for them to pass

 

When I drive 20-25 MPH, it's between stop signs or traffic lights. Perfect application for pulse and glide.

 

Exactly.

Using EV too heavily is inefficient. I was reminded by this when I let SOC get below 45% last night. The next morning the engine wouldn't shut down in the normal locations and on a long stretch of country road where I normally get 55+mpg I was stuck in the high 30s to low 40s until SOC went back up. Grrr

 

What is wrong with using the battery to near exhaustion? It is a NiMH second generation rechargeable battery with none of the problems NiCAD batteries present. Also, the engine should be warmed throughout the year prior to the first drive of the day so gas spent warming is gas spent charging.

It is presently quite cold in Michigan and thus a pre-drive ICE warm-up is also a battery juice and heat while the car rests. In winter, one of the best methods to preserve some efficiency is through the battery and that includes cycling the battery in/the ICE out by accelerating to speed and releasing the pedal completely. Then drive on battery power to up to 40 MPH. Drains fast! Indeed but that is also why regenerative braking is available.

 

Put the cruise on, in city driving, and watch it eat up the charge...

I've got no qualms in using up a moderate amount of charge. More so if the level is high, or there's a wopping great downhill coming up, to help recharge.

 

It takes longer to recharge the battery than to warm up the ICE such that you get decent fuel economy. While the ICE is recharging the battery, you get worse fuel economy. Better to pulse & glide when possible and keep SOC above 50%.

 

The lower the depth of the discharge, the more cycles you are going to get.

10% Depth of Discharge x 300,000 cycles

60% Depth of Discharge x 10,000 cycles

 

Thanks for posting!
10,000 cycles sounds a lot, but it one does 10 such cycles a day and drives everyday, battery will fail in 3-4 years. My driving with minimal battery use shoots for 300,000 cycles and gives me best MPG. No brainer here.
This also shows pitfalls of all electric cars if one does full discharge. Lithium-ion batteries have similar cycle life from what I understand, 500-1000 cycles with full discharge.

 

With a lot of EV you will probably be operating at or above the 50% discharge level (SOC 2 to 3 bars showing). If your battery warranty is 10 years or 150,000 miles this doesn't seem like much of a concern.

Note: 1 bar showing is 60% discharge.

 

10 seconds full discharge (0-60 mph floored acceleration) will use about 7%. In normal driving conditions, you'll use a few % DOD per day.

Remember, a full battery shown on the screen is 80% and no bar represents 40% so, the swing from "full" to "empty" is 40% DOD. It is impossible to do 60% DOD in a Prius.

40% DOD can get about 40,000 cycles.

NiMH would not be good for PHEV or BEV. Lithium-ion battery used in plugins can last 5,000 cycles or more.

 

I started this morning at continuous 49.9 MPG and noticed, because of battery charging, it dropped to 49.8 MPG. Negligible, in the noise, losses. I was then able to enjoy a semi-heated interior and brought the continuous MPG up to 50.1 travelling city roads over a distance of 15 miles. Fuel economy for a vehicle not in motion is not even measurable -- hence why there is no measure on the display when at rest. I am becoming a hypermiler, willing to turn the flashers on in while at 22 MPH in a 40 MPH zone so I don't need to cycle the ICE in for this hill climb, but even I am willing to concede some losses.

 

I use the battery when the system will let me. My driving situation is such that there's almost always enough highway and/or braking time that it charges back up without the ICE running specifically to do so. I have no data to back it up but my intuition is that as long as the ICE isn't running just to charge the battery (there's an economy killer!), taking advantage of opportunistic charging is the most efficient way to do things.

 

I can always buy a new battery ... right? Point I am making is that increased use of the battery means decreased use of the ICE. If I wanted to be a conscious, conservative user, I could cycle my use of the battery and ICE depending on the day; Every odd day, I drive on the battery and drain that sucker!! On even days, take the highway and be gentle.

At the risk of admitting it, I think I am becoming a hypermiler and beginning to take small risks I probably should not but it is winter and my MPG are definitely in need of some love ... trees are too and they would probably say "yeah, use that battery .. after all the Prius is an appliance! Start button? .. or is it just a confused car?".

 

What was your SOC when you started? I assume you we're watching your iMPG as well? If you lost .1-.2mpg on one trip how much will this drop your average mpg over an entire tank?

That goes against my experience as well as others.

Oops after re-reading your reply I noticed it has nothing to do with what I said. lol