[JPeterman]

I recently bought a 2004 and I notice that the consumption screen keeps track of regeneration via 50wH increments. Does anyone have a rough idea what 50wH gets me? i.e., in stealth mode I could drive x feet at y MPH and use roughly 50wH.

 

[clett]

Efficient battery-electric cars can go about 4 miles per kilowatt-hour (kWh). This means that a traditional EV takes about 250 Wh per mile - so your 50Wh could be good for about one fifth of a miles worth of EV mode travel - about 320 metres?

The EV button over here gives about 1.5 miles range - which would tally with about 375Wh from battery maximum to minimum allowed levels, suggesting the safety margin on the battery only allows a range of ~30% full capacity between maximum and minimum allowed soc.

 

[frenchie]

Note that the 2 paragraphs above are perfectly consistent ( 375 / 1.5 = 250 ) , which shows that the Prius can be an efficient battery-electric car from time to time.

 

[JPeterman]

That's exactly what I was looking for. Thanks for the info.

 

[Daniel]

This is very interesting.

Now I would like to extend the original poster's question:

How many watt-hours correspond to one bar on the battery gauge. I.e., how many green 50 wH regeneration leaves does it take to boost the SOC by one bar?

 

[BIF]

And as an extension to Daniel's extended question:

Are all of the battery bars equal in how much energy each bar represents?

 

[frenchie]

According to Wayne Brown, one of the most famous Prius gurus, the available state of charge (SOC) in a 2004 Prius is between 40% and 80% of the total battery capacity. This total capacity is equal to 1.3 kWh (202 V * 6.5 Ah = 1313 Wh). 40% of that equals about 525 Wh, corresponding to eight bars on the display. Therefore, one bar means 65 Wh of energy, or 1.3 leaf (yes, all bars are equal, as far as I know).

PS : Please note that the correct symbol for Watt-hour is Wh. :wink:

 

[BIF]

Thanks, Frenchie, but I'm a little bit confused. I'm sure this is my fault.

The available SOC is 40% to 80%? And the 40% represents 8 bars? I often am able to run my battery down to half or one bar lower than half, which is less than 8 bars.

Or did I somehow misunderstand your explanation? Thanks!

 

[frenchie]

Sorry if I was not clear.

I meant the difference between 80 and 40% (which is also 40% !) is displayed as 8 bars. in other words, when your battery looks empty it is still 40% full, and when it looks full it is at 80% SOC.

 

[ammiel]

I believe Wonderful Wayne has stated that one green car = 1/3mi in stealth better yet use 1/4 to be conservative.

 

[BIF]

Frenchie:

Many thanks for that explanation, my friend! It's definitely "real world" usable information!

 

[PriusPhysics]

RE: What does 50 Wh get me? question

The answer of 250 Wh (watt-hour) per mile on battery (EV or stealth) mode agrees well with other numbers from Toyota. Toyota claims a 2004 Prius maximum "tank-to-wheel" efficiency of 37% on gasoline. Because gasoline has about 121 million joules of energy per gallon (per Chevron), this means that the available energy at the wheels is 45 million joules per gallon of gasoline. Using 50 miles per gallon, and 3600 joules per Wh, this comes out to be 250 Wh per mile. If a fully charged battery holds about 1300 Wh, then this implies a maximum range of about 5 miles on a fully charged battery. Very careful driving, at an equivalent mpg of 70 mpg (between 30 and 40 mph), would imply a 40% longer range. I guess this means "Don't leave home without it" (referring to gasoline).

PriusPhysics

 

[patrickg]

Great stuff! A sort of related question... How many "cars" of regeneration (consumed from the battery) does it take to put enough energy into the motion of the vehicle to regenerate a car when stopping.

If that doesn't communicate... I'm trying to get a handle on storage and retrieval efficiency (along with other losses like friction). Another way to look at it would be to accelerate from a stop using only electricity then stop the car, maximizing regeneration. Repeat the above until you drop from 80% charge to 40%. How far have you gone?

Of course going faster in the sprints prior to braking loses more energy to drag. Only building up to a quite slow speed and stopping also wastes more energy to friction brakes as regeneration cuts off at about 7 mph or so. So since we have poor performance at high speeds and low speeds there must be an optimal speed (or range) for stop and go in all electric mode. I realize this is an artificial example as it assumes equal repetitive sprints and stops but it is a start in understanding the "nature of the beast."

Pat

 

[ehurtley]

So since we have poor performance at high speeds and low speeds there must be an optimal speed (or range) for stop and go in all electric mode.

Well, last night I got stuck in horrendous traffic on the interstate (construction had what was normally 3 lanes down to one restricted lane for a 3-mile stretch with no exits. There were also two cars stalled in that stretch, with very little shoulder, causing traffic to get even worse. Of course, the slowdown didn't become obvious until I had missed the 'last chance' exit before my own.) In that 3 miles (which took 30 minutes,) I averaged a dismal 20-30 mpg. This was with the radio and A/C off, lights on, started with 6 bars of battery. Ended with 6 bars of battery. Never got above 20 mph until right before the end (my exit was within 1/4 mile of the end of the construction, of course.) Came to a complete stop only twice, each time for less than one minute. Never accelerated fast enough that it SHOULD HAVE come out of EV mode, but it kept switching between ICE and EV, even though the battery never dropped below 3 bars. I could coax it back into EV mode, but it wouldn't stay there very long.

The 30-minute history had every bar between 20 and 30 mpg. The five minutes it took to actually reach home after leaving the freeway (accelerate from freeway 20 mph to 45 mph for two minutes, one minute of stopped time at a light, and two minutes of <20 mph in stealth mode,) I got 70 mpg.

 

[clett]

Great stuff! A sort of related question... How many "cars" of regeneration (consumed from the battery) does it take to put enough energy into the motion of the vehicle to regenerate a car when stopping.

I don't think you'll ever get as much back from regenerative braking as you put into it in the first place, regardless of friction etc. The generator is only rated at 21kW, which I think the battery might be able to absorb, but braking events often make more power than this so the rest is lost to the brake rotors (discs).

To take an extreme example, imagine stopping quickly from 60mph in 5 seconds. The kinetic energy is 0.5 x 1300 x 27 x 27 (1300kg mass, 27 metres per second squared) 462 kJ, so to absorb all this energy the generator would need to be able to handle 92kW. Only a gentle stop, taking 22 seconds to come to a complete halt, brings things back down within the 21kW limits of the generator.

With a more powerful generator and battery, however, you'd be able to capture more but it'll never be 100% because the internal electrical losses always add up. Efficiencies of the various parts might be (all guess work!): generator (95%); power electronics (98%); battery (90%); power electronics (98%); motor (95%); drivetrain losses (95%). If these numbers were more or less right, (like I said, pure speculation for the purposes of illustration!) then you'd only ever get 74% of the energy you put in back out again (0.95*0.98*0.90*0.98*0.95*0.95). So, even in a friction free environment (OK, doesn't exist except maybe on a rolling road!) you're looking at a best case scenario of 4 cars out, 3 cars in.

Interestingly, it was partly to avoid these losses that Toyota upped the voltage in THSII to 500V (Ploss~I2R).

 

[Daniel]

Re: RE: What does 50 Wh get me? question

... If a fully charged battery holds about 1300 Wh, then this implies a maximum range of about 5 miles on a fully charged battery...

Note, however, that in order to extend battery life out to the life of the car, the electronics limit battery usage to only about half its capacity, and the EV range is even less, as the ICE will start the moment the SOC drops to 2 bars. And how often do you see 8 bars?

The supermarket is very approximately half a mile from my home, and it seems to consume 2 bars to make that drive in EV mode. That's driving about 25 to 30 mph. Since I almost never see more than 6 bars, I figure a best-case maximum of one mile.

 

[kennyb]

I thought the new Prius battery was 2kwh.

45 wh/kg and there are about 45 kg of batteries.

I think the old Prius was 1.3kwh.

Just my recollection.

Interestingly, if you could have 10kwh, then you could drive for 40 miles in EV only mode. I think this is the next logical step, a "plug in hybrid", but there must be some hold up. Maybe cost of the batteries. Newer lithium batteries are up to 200wh/kg so it isn't really a weight issue.

 

[Canadian Prius]

Yesterday I confirmed with my GPS that the difference in elevation between the base of the hill to my house is 204 feet. It is a steep hill, so to gain that elevation, I only have to travel about 1800 feet. I already tried backing up the hill in reverse, and there was no problem, although it used about four of the battery bars.

This is a good test for the battery because the Prius uses only the motor in reverse. I want to try it again and take more careful measurements.

Can someone help with the calculations? How much energy in Wh is being used to elevate the Prius 204 feet?

Also, by using the battery this intensively, will it cause any harm?

Thanks for any help with this.

 

[clett]

Ep=mgh

so the amount of energy it takes to lift your 1370kg Prius up 205 feet (I'm assuming you're in it!) is 1370*9.8*204*0.3048 = 835 kJ (232 Wh).

But that's just to lift it. In real life, a good bit more than this will be used as there is the friction of driving it 1800ft along the road. That's about a third of a mile, so on the flat at low speed it could add about another 80Wh to the total.

You could be looking at about 310Wh for the job, or about 5 energy bars according to Frenchie's calculations.

 

[ehurtley]

Yesterday I confirmed with my GPS that the difference in elevation between the base of the hill to my house is 204 feet. It is a steep hill, so to gain that elevation, I only have to travel about 1800 feet. I already tried backing up the hill in reverse, and there was no problem, although it used about four of the battery bars.

This is a good test for the battery because the Prius uses only the motor in reverse. I want to try it again and take more careful measurements.

Can someone help with the calculations? How much energy in Wh is being used to elevate the Prius 204 feet?

Also, by using the battery this intensively, will it cause any harm?

Thanks for any help with this.

hehe.. It's like one of those little kid 'wind back' cars. You roll backward up the hill, then rocket back down, right? So going DOWN the hill, how many bars do you gain? (Hrm, I have a similar hill, maybe next time I'll try backing up it. It really threw my mom for a loop the first time I backed out of their steep driveway, she said it sounded like I was coasting, only I was coasting up hill.)