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Old 03-23-2017, 12:23 PM   #11 (permalink)
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Quote:
Originally Posted by S Keith View Post
You are confused because you haven't embraced the reality that 100% of the propulsive energy used by the car ultimately comes from gasoline. The battery needs to be just large enough to allow the hybrid system to work. Excess capacity is wasted. Additional electricity use necessitates replenishment with gas power.

You further likely don't realize that the amount of energy stored in any of those batteries listed is TINY... about 1-2 miles of SLOW pure EV driving. The Gen2/3 Prius pack usable capacity is almost identical to the total capacity of the tiny lead acid battery in back.

Lastly, passengers can get in an out of cars. Increasing the car's weight permanently by 40# will have a measurable negative impact.

Case in point:

Gen1 vs. Gen2 Prius

Gen1 capacity: 1.8kWh
Gen2 capacity: 1.3kWh

They deliberately downsized it because they realized it was too big and heavy - overkill for the application. The underlying HSD components are nearly identical. Most of the gains came from the aerodynamic improvements.
Hi, thanks for putting it so bluntly. I feel educated and scalded in equal measure.

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Old 03-23-2017, 12:30 PM   #12 (permalink)
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Hi, thanks for putting it so bluntly. I feel educated and scalded in equal measure.
The former was the goal. The latter is an unintentional consequence resulting from my "engineer voice" and poor social skills. It was not my intent. Please accept my apologies.

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Old 03-23-2017, 12:38 PM   #13 (permalink)
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Originally Posted by pugmanic View Post
My daily drive has a mix of urban and motorway (highway) driving, and so the battery is frequently charged to max (80ish %). The battery capacity currently isn't sufficient to complete all of my town driving, so I assumed that a larger capacity would help this part of the journey.
Are you saying that the battery display is showing about 80%, or that the display is showing 100%, which is actually about 80% at the battery? The car likes to keep the battery at about 80% on the display (6 out of 8 bars on my '05 Prius) in order to have plenty of power if you need it while still having room for regen. The battery only uses approximately the 40-80% range of its charge in order to extend its life. The display only shows that 40-80% range, with 40% at the battery being 0% on the display and 80% at the battery being 100% on the display. Google Image search "prius battery soc" and there's several charts showing the relationship between the battery charge and what is shown on the display.

As mentioned by S Keith, you're not driving an electric car, you're driving a gasoline powered car that used a battery and electric motors to help increase fuel economy and drivability. If you're trying to do all your city driving on battery, you're probably going to get lower mileage (unless it's very slow speeds). This is because the car will use gas to charge the battery when it gets too low, instead of regen from braking to keep it topped off. Generally the best way to drive a hybrid at city speeds is to accelerate using gas and then coast and/or use a small amount of electric power to extend the coast.
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Old 03-23-2017, 05:31 PM   #14 (permalink)
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Quote:
Originally Posted by S Keith View Post
You are confused because you haven't embraced the reality that 100% of the propulsive energy used by the car ultimately comes from gasoline. The battery needs to be just large enough to allow the hybrid system to work. Excess capacity is wasted. Additional electricity use necessitates replenishment with gas power.
Additional electricity use does not necessitate replenishment with gas power if that additional electricity was recaptured from braking and otherwise would have been wasted as heat or used to turn the engine over unnecessarily. At issue here is this: do the braking events encountered by a "typical" hybrid driver justify a larger battery capacity? Toyota decided, after weighing a number of factors, that 1.3kWh was large enough in the Prius for most drivers and was the best compromise of weight, cost, packaging, longevity, etc. Does this mean that a particular driver like the OP can't benefit from an increase in HV battery capacity? Of course not. Perhaps his commute, like my parents', takes him down a mountain to a valley floor, generating more braking energy than the battery has capacity to store and he'd like to take advantage of that.

Without knowing the details of his use case, blanket assertions like "excess capacity is wasted" are inane--precisely because we don't know what constitutes "excess capacity" for his use of the car. It is entirely possible that a 1.9kWh battery would be necessary to store all the braking energy captured before opportunity for discharge on his typical commute, in which case 1.9kWh would not be "excess," just as it is entirely possible that another driver with an otherwise-identical car would be perfectly served by a 0.8kWh battery. We simply don't know. There have been plenty of times, driving in the mountains of Idaho and western Washington, and once in Tennessee, when I could have used a slightly larger battery in my car, and I presume the same is true for the OP.
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Old 03-23-2017, 07:40 PM   #15 (permalink)
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Back when I was starting my Firebrid project, I looked at using a Lexus HS250h instead of a Prius V as the basis. Sadly, the voltage of the HS250h is different than that of the Prius HSD, so I would not have been able to do some of the things that I had wanted if I had gone that route.

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Old 03-23-2017, 09:46 PM   #16 (permalink)
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Quote:
Originally Posted by Vman455 View Post
Additional electricity use does not necessitate replenishment with gas power if that additional electricity was recaptured from braking and otherwise would have been wasted as heat or used to turn the engine over unnecessarily. At issue here is this: do the braking events encountered by a "typical" hybrid driver justify a larger battery capacity? Toyota decided, after weighing a number of factors, that 1.3kWh was large enough in the Prius for most drivers and was the best compromise of weight, cost, packaging, longevity, etc. Does this mean that a particular driver like the OP can't benefit from an increase in HV battery capacity? Of course not. Perhaps his commute, like my parents', takes him down a mountain to a valley floor, generating more braking energy than the battery has capacity to store and he'd like to take advantage of that.

Without knowing the details of his use case, blanket assertions like "excess capacity is wasted" are inane--precisely because we don't know what constitutes "excess capacity" for his use of the car. It is entirely possible that a 1.9kWh battery would be necessary to store all the braking energy captured before opportunity for discharge on his typical commute, in which case 1.9kWh would not be "excess," just as it is entirely possible that another driver with an otherwise-identical car would be perfectly served by a 0.8kWh battery. We simply don't know. There have been plenty of times, driving in the mountains of Idaho and western Washington, and once in Tennessee, when I could have used a slightly larger battery in my car, and I presume the same is true for the OP.
Your first statement would be true if the car was ever plugged in, but it's not. Every Joule of energy used in propelling this car is ultimately from gas. You can isolate portions of a drive and say "that's electric," but when you go back even just one step, you see it comes from gas. Oh, and filling that gas tank up is yet more evidence.

How did the car get to the top of the hill? - gas
What was sustaining the kinetic energy of the car before the energy was captured by braking? - gas

For a Prius, a 1.9kWh battery would capture 225' more potential energy beyond what a 1.3kWh battery will - assuming the entire range of usable capacity is available (typically only half is available), so a 50% increase in battery size will typically capture about 113' more potential energy vs. the standard. That seems pretty insignificant to me.

How do you know you could have used a slightly larger battery? I've just calculated that a 50% larger (way more than slightly) battery would only make a 113' difference in captured energy. Were your ascents/descents all less than 113'? Were you monitoring battery performance data? Do you understand how these cars behave? Are you forgetting that most descents are offset by an ascent in the opposite direction - even if it's a week later on the return drive home?

Math can dispel a lot of myths. It can be used to fill in the "we just don't know" blanks when one is inclined to add a sense of mystique to an engineering problem where none exists.
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Old 03-25-2017, 08:32 PM   #17 (permalink)
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Quote:
Originally Posted by pugmanic View Post
Hi, thanks for putting it so bluntly. I feel educated and scalded in equal measure.
Eh, I think S is just a little grumpy for some reason.

They're right insofar as just adding an extra pack will add weight. The hybrid ECU won't recognize it as extra capacity, and an extra ~100lbs in any Prius would ding mileage by ~3% or so. At the same time, that might be offset by lower internal resistance and more efficient battery use.

If you installed a parallel pack or three and also installed another BCM to take advantage of those extra packs, then it's possible you might see an increase in mpg depending on where and how you drive.

https://sites.google.com/site/nwpriu...-plug-in-prius

Quote:
When driven beyond its CD range (about 12-14 miles), the car will operate as a standard Prius, but with slightly improved mileage (55-60 mpg), due to the extra battery capacity whose lower internal resistance allows for more efficient regeneration, as well as easy access to "super-highway-mode" because of the high SOC.
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Old 04-07-2017, 01:47 PM   #18 (permalink)
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Think of it as a Kinetic Energy Recovery System.

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