Interesting... but not recommended...

[Curious_character]

Most interesting. Do you mean that the Toyota battery is never charged above 60% or discharged below 40% of battery capacity? If so, they're only using 20% of the battery capacity, so the package is five times as large, heavy, and expensive as it would be for a complete charge/discharge cycle. Longevity is important, but that sure is a steep price to pay for it.

Do they have problems with voltage depression with such shallow discharges?

c_c

 

[Battery Guy]

Most interesting. Do you mean that the Toyota battery is never charged above 60% or discharged below 40% of battery capacity? If so, they're only using 20% of the battery capacity, so the package is five times as large, heavy, and expensive as it would be for a complete charge/discharge cycle. Longevity is important, but that sure is a steep price to pay for it.

Do they have problems with voltage depression with such shallow discharges?

c_c

I may be off on the SOC window slightly. It could be 30-70%, but definitely in that range.

And yes, that means that the battery is bigger than it needs to be, but the batteries in those cars are pretty small, and longevity is a huge issue with automotive hybrid batteries. The makers of EVs and extended range EVs (e.g. Chevy Volt) would never be able to get away with this because the battery pack would be huge, but for a straight hybrid the size/longevity trade-off appears to be worth it.

Interesting question on the voltage depression. One might conclude that even if the battery did have voltage depression, you would never see it because you would never discharge the battery outside of its normal operating window. Another thought would be that you don't get voltage depression because you never fully charge the cell. Quite frankly, I don't know the answer. All I know is that those NiMH batteries are incredibly reliable, and everyone I have talked to that business claims that it is because of the narrow SOC window within which the cells are cycled.

Cheers,
Battery Guy

 

[InHisName]

And yes, that means that the battery is bigger than it needs to be, but the batteries in those cars are pretty small, and longevity is a huge issue with automotive hybrid batteries. . . . . .
Cheers,
Battery Guy

You make it sound like this car has a fuel motor and generator to charge the battery. The wheels driven by electric motors. So for example if you had a 14 hp motor driving a 5KW generator as long as you didn't drive so hard to drain the batteries too fast then it should last a few hundred miles. Hwy or city.

Maybe it has an 'idiot' light to say - "Stop and let me catch up the charger". Like while you're at a Mall, shopping etc. I suppose if you were a lane changer and passer on highway driving then your range may be greatly reduced from factory specs.

Now to imagine what size . . . I'm thinking of 1,000 eneloops @ 2000mah x 1.3v = 2.6kwh. If you averaged 5.5kw/hr highway then it would last approx 5 hours till empty with generator running the whole time. Near me are some turnpikes at 65 limit, so thats 325 range. Hmm, kinda interesting. Betcha the battery replacement would be scary!
At Target there are packs of four for $12.99 (I think). So, 1,000 would come to: $3,442.35. Don't forget about the fuel for the generator.

 

[Battery Guy]

You make it sound like this car has a fuel motor and generator to charge the battery. The wheels driven by electric motors. So for example if you had a 14 hp motor driving a 5KW generator as long as you didn't drive so hard to drain the batteries too fast then it should last a few hundred miles. Hwy or city.

Maybe it has an 'idiot' light to say - "Stop and let me catch up the charger". Like while you're at a Mall, shopping etc. I suppose if you were a lane changer and passer on highway driving then your range may be greatly reduced from factory specs.

Now to imagine what size . . . I'm thinking of 1,000 eneloops @ 2000mah x 1.3v = 2.6kwh. If you averaged 5.5kw/hr highway then it would last approx 5 hours till empty with generator running the whole time. Near me are some turnpikes at 65 limit, so thats 325 range. Hmm, kinda interesting. Betcha the battery replacement would be scary!
At Target there are packs of four for $12.99 (I think). So, 1,000 would come to: $3,442.35. Don't forget about the fuel for the generator.

I don't mean to make it sound like something it isn't. I am not a hybrid vehicle guy. All I am saying is that the way Toyota and others get 10+ years of life out of their NiMH batteries is by limiting the SOC window. More information can be found in this article. Here is a key excerpt:

To get maximum life out of the Prius battery pack, the car's computer brain does not allow the battery to fully charge or discharge. Toyota says that for the best service life, the Prius battery likes to be kept at about a 60 percent charge. In normal operation, the system usually lets the charge level vary only 10-15 percentage points. Therefore, the battery is rarely more than 75 percent charged, or less than 45 percent charged.

Hope that helps to clarify.

Cheers,
Battery Guy

 

[bob_ninja]

I may be off on the SOC window slightly. It could be 30-70%, but definitely in that range.

And yes, that means that the battery is bigger than it needs to be, but the batteries in those cars are pretty small, and longevity is a huge issue with automotive hybrid batteries. The makers of EVs and extended range EVs (e.g. Chevy Volt) would never be able to get away with this because the battery pack would be huge, but for a straight hybrid the size/longevity trade-off appears to be worth it.

....

I believe the range is 30% to 80% yielding about half usable capacity.
For instance, Volt has 16 kWh, usable 8 kWh, about 200 Wh/mile giving range of 40 miles.

Older hybrids like Prius and Insight are similar.

 

[TorchBoy]

Do you mean that the Toyota battery is never charged above 60% or discharged below 40% of battery capacity? If so, they're only using 20% of the battery capacity, so the package is five times as large, heavy, and expensive as it would be for a complete charge/discharge cycle. Longevity is important, but that sure is a steep price to pay for it.

I wondered about that, but figured it was only a quirk of the English language.

Here is a key excerpt:

To get maximum life out of the Prius battery pack, the car's computer brain does not allow the battery to fully charge or discharge. Toyota says that for the best service life, the Prius battery likes to be kept at about a 60 percent charge. In normal operation, the system usually lets the charge level vary only 10-15 percentage points. Therefore, the battery is rarely more than 75 percent charged, or less than 45 percent charged.

You did mean that! :huh:

 

[Mr Happy]

I wondered about that, but figured it was only a quirk of the English language.

You did mean that! :huh:

This is actually not as much of a surprise as it might seem. The job of the battery in a Prius is not actually to drive the car or replace the fuel tank. That would serve only to reduce the efficiency and increase the fuel consumption compared to a normal (non-hybrid) car. It would be counter-productive.

What the battery actually does, and what gives the Prius an advantage, is to support regenerative braking and improved power management. When you slow down the excess energy is stored in the battery (like winding up a spring). When you speed up again the energy is released. The actual amount of energy stored and released in this way is not all that large, so the battery can spend most of its time hovering around 50% charge.

Another benefit is to reduce the required size of the engine. In most cars the engine is sized for acceleration from a standstill. When you are driving along at normal speed the engine is using only a fraction of its power and wasting fuel (engines are inefficient when running at low power). With a hybrid car the engine can be sized for steady driving since it can rely on temporary electric assistance to help it get up to speed from a standing start. Since smaller engines have better overall economy this helps the Prius too.

 

[Lynx_Arc]

maybe they are using all the dud 2500mah energizers AAs that are junk and charging them at those rates they don't go bad which would make them from 1000-1500ma. I would also say it is possible that a big brick of batteries if you discharged them all at high rates and charged them up full the heat trapped in a bank would dramatically increase the more capacity you managed as the charging voltage would stay high longer generating more heat.

 

[TorchBoy]

This is actually not as much of a surprise as it might seem. ...

What the battery actually does, and what gives the Prius an advantage, is to support regenerative braking and improved power management. When you slow down the excess energy is stored in the battery (like winding up a spring).

Yes, of course. They need to allow some room to store that braking energy.

 

[Mr Happy]

Most interesting. Do you mean that the Toyota battery is never charged above 60% or discharged below 40% of battery capacity? If so, they're only using 20% of the battery capacity, so the package is five times as large, heavy, and expensive as it would be for a complete charge/discharge cycle. Longevity is important, but that sure is a steep price to pay for it.

This is not necessarily true. You've got to think about all the variables, and capacity may not be the most important performance consideration in the design.

Suppose for instance you are working with a D-size NiMH cell that can supply 10 A while not exceeding its specifications. Suppose furthermore that you wish to augment the engine with 40 hp of electric traction. Then you would have:

(power per cell) = 1.2 V x 10 A = 12 W
(traction power) = 40 hp x 750 W/hp = 30 kW
(number of cells) = (traction power)/(power per cell) = 30 000 / 12 = 2500

Therefore your battery needs 2500 cells to meet the performance requirements. Note that capacity did not come into this calculation.

 

[Mr Happy]

You make it sound like this car has a fuel motor and generator to charge the battery. The wheels driven by electric motors. So for example if you had a 14 hp motor driving a 5KW generator as long as you didn't drive so hard to drain the batteries too fast then it should last a few hundred miles. Hwy or city.

Maybe it has an 'idiot' light to say - "Stop and let me catch up the charger". Like while you're at a Mall, shopping etc. I suppose if you were a lane changer and passer on highway driving then your range may be greatly reduced from factory specs.

It doesn't make any sense to run the car on the electric motors like this. The car will run far more efficiently if the wheels are driven by the gasoline engine rather than the battery. If you run the car on the battery like that, all you will do is increase your fuel consumption, reduce the life of the battery, and increase your running costs from buying more fuel and paying for early battery replacement.

The purpose of a hybrid car like the Prius is to make the most efficient use of gasoline, not to replace gasoline with electricity.

 

[TorchBoy]

The purpose of a hybrid car like the Prius is to make the most efficient use of gasoline, not to replace gasoline with electricity.

Does that have serious ramifications for the Californians I've read about who have converted their Priuses into plug-in hybrids? Is what they're saving in fuel - getting 100+ mpg economy - going to rebound on them when they have to buy a new battery early?

 

[Mr Happy]

Does that have serious ramifications for the Californians I've read about who have converted their Priuses into plug-in hybrids? Is what they're saving in fuel - getting 100+ mpg economy - going to rebound on them when they have to buy a new battery early?

It might have ramifications if they do put too much stress on the battery and have to pay for an early replacement. But I suppose if they are only doing a very short commute each day and can charge the battery up overnight it would work out fine.

 

[core]

It might have ramifications if they do put too much stress on the battery and have to pay for an early replacement.

Not to get too far off topic here (but I think it's too late for that):

Anyone know if the batteries are covered by warranty? Modifications do not have to be permanent.

And I'm also curious about how you change a fundamental behaviour of the car just by keeping the batteries charged at night. (I know nothing about them, just so you know where I'm coming from.) But if everything said in this thread is true, it would use gas when it's designed to and I don't see how a higher state of charge would change that. Do they modify the computer on the car as well?

 

[Battery Guy]

Does that have serious ramifications for the Californians I've read about who have converted their Priuses into plug-in hybrids? Is what they're saving in fuel - getting 100+ mpg economy - going to rebound on them when they have to buy a new battery early?

I believe that those conversions involve replacing the rather small NiMH battery with a substantially larger bank of lithium-ion batteries. So its not like they are using a larger SOC window from the same battery.

Cheers,
Battery Guy

 

[Mr Happy]

I believe that those conversions involve replacing the rather small NiMH battery with a substantially larger bank of lithium-ion batteries. So its not like they are using a larger SOC window from the same battery.

Ah, that makes sense from an electrical point of view. I don't know about the economic point of view...

 

[Battery Guy]

Ah, that makes sense from an electrical point of view. I don't know about the economic point of view...

I understand that the conversions are quite expensive ($20k+), and the batteries are unlikely going to provide similar lifetimes (10+ years) that the unmodified Prius battery does. However, I think that is the price some people are willing to pay to be on the cutting edge.

There are also potential safety issues. A few of these have had fires:

http://blogs.edmunds.com/greencaradvisor/2008/06/plug-in-toyota-prius-catches-fire-explodes.html

I believe that all have been electrical fires resulting from a combination of bad connectors and high voltage.

Cheers,
Battery Guy

 

[WDG]

There are also potential safety issues. A few of these have had fires: http://blogs.edmunds.com/greencaradvisor/2008/06/plug-in-toyota-prius-catches-fire-explodes.html

"...we're kinda hoping things were just a fluke in that car."

Would a statement like this inspire confidence in anyone here, were they an owner or potential purchaser of one of these vehicles?

Given the theatrics we've seen some lithiums being capable of on this forum, I've been wondering what happens when one of these things goes in someone's garage overnight, or worse, with a toddler buckled into a car seat in the back.

 

[Turbo DV8]

Reading that article, and the response of Ann Colcord, part owner of Hybrids Plus, the outfit that does the conversions, I am left with one word which comes to mind ... "PUTZ!" She basically blamed the driver for the car catching on fire, even though there was a prior history of charger problems in their company's conversion of that vehicle. What a dufus.

 

[bob_ninja]

There are different companies using different types of cells. Majority of companies and all of the bigger companies that care about their reputation do not use the Lithium chemistry used in computers and cell phones that can catch fire and explode. Instead they use newer chemistry like A123 Lithium Phosphate which cannot have runaway reactions and fires, etc.

These new chemistries have been tested and are being tested for safety. They are designed to be safe even without protection circuits. So odds of fires and explosions are almost nil.

I am fairly certain that at least one of the companies selling Prius packs does use A123 cells, not sure about all of them, what type they use.

Not to mention many power tool vendors using Lithium packs these days. Consider the risks of vibrations, heat, etc. They wouldn't use Lithum based power packs if there were a significant risk of fire.