IL Corrects Volt Story: Batteries Will NOT Charge When Driving; GM Website Differs

[PhishPhood]

Originally Posted by E. Haskell

Most people buy the Touring model which has a real world price of around $26-29k. If Toyota brings out a plug in Prius, expect it to be $30k+. Lets compare apple to apples here.

Sorry this is absolutely wrong.

The Touring model is by far the least popular. Some regions don't even carry it. The 2008 Package #2 Base Model lists for ~ $24000 on the Toyota website.

I think that the whole point of the presentation was to show all the various options a buyer might have ( including USED vehicles ) to keep total personl transportation costs to a minimum. A bicycle is better yet.

[CaptainDan]

Originally Posted by rob2299usa

That's why the volt only makes sense for people who will mainly be using it 40 miles per day or less.... or if they can charge at work, 80 miles per day or less.

If you have a large commute or regularly take longer distance trips then the volt may not be for you!!!

Even on a longer commute, you STILL get the first 40 miles gas-free. Plus you get about 50mpg after that. Sounds like the Volt STILL could be for you.

[CaptainDan]

Originally Posted by PeterPuck

If the battery isn't used after 40 miles, but the vehicle gets 50 MPG after it's depleted, the whole thing doesn't really makes sense to me.

Why not get rid of the battery, use the gas engine to run the electic motor, and knock at least $10,000 off the price? You'd still get 50 MPG, and you'd have a lot more space.

But then maybe I just don't understand anything in the article, or in what's being posted.

Because without the battery, it would NOT get 50mpg. The gas engine gets 50mpg by running at a max efficiency, smooth speed, using the battery to cover the ups and downs of driving, which aren't so smooth. Plus you get the first 40 miles GAS-FREE. And that part most certainly needs the battery.

You could certainly cut the battery in size some (save that weight), but that would reduce that gas-free 40 mile number. The battery size was selected specifically to deliver that 40 miles. GM figured that to be the best trade off (for most people) between a bigger battery that gave more gas-free miles, but wastefully carries around MORE battery mass - and a smaller battery that would yield fewer gas-free miles, but save on that extra mass.

In the future I'm sure that the Volt, and all the other E-Flex-type vehicles, will offer you the choice, in an optional battery size to suit your personal need.

[CaptainDan]

Originally Posted by goblue

Wow Phish - that's called taking a simple concept and making it complicated. It works like the thermostat in your house. When the temp drops to 68, the furnace comes on and pushes it to +1-2 degrees, depending on the thermostat. Then the furnace shuts off. If you ran your furnace constantly at a low rate it would be horribly inefficient, so it cycles. Same thing.

The generator is hooked to the battery. When the charge hits 30% the generator comes on and runs till it hits some arbitrary percentage GM set. Say, 32%. It could vary depending on how you are driving, the outside air temp, whether the a/c is on, etc, or it could be fixed at say, 31.5% Then when it hits the number the generator shuts off.

To the lay person, the battery isn't being charged because the gauge won't really move. Just like when you set the thermostat to 70, you tell your wife the temp is 70, even though its really somewhere between 69 and 71. In truth - to the engineer - the state of charge of the battery will vary slightly, up and down. Drive aggressively with the A/C - the generator will run more. Cruise at 60 on the freeway, the generator might need only run for 5 minutes out of every 15. Crusing on the freeway uses something like 20hp on average. Its a 150hp motor. Acc'd to GM a 70hp motor would have been sufficient for the VOLT, they used a 150hp motor so it could run slower, and to use an existing design.

For ex: if the car is cruising and using 10 hp on average, but the generator supplies 100hp when running, then it needs to run 10% of the time. Its the average usage that counts. If you floor it and use 150hp for 30 sec, but then cruise at 50 for the next 15min using 10hp, the generator only needs to supply on average, ~15hp.

Which is why GM said the VOLT could get by with a 70hp motor. Lets say you spent 50% of the time with the pedal floored, and 50% of the time braking - thats a crazy scenario - and we know the E-Motor is 150hp. 150/2=75.

Wonder why its speed limited to 100mph? 2 reasons, first - much faster than 100 and you need a trans to keep the electric motor to a reasonable RPM. Second reason, the only way to keep the e-motor floored is to drive it at the speed where wind resistance is the limiting factor, for a 150hp aerodynamic car with 235 ft-lbs avail, thats around 130 or so? Wind resistance goes up to the velocity squared. So 130^2 / 100^2 = 1.69, almost double the power required.

The VOLT is set to run efficiency optimized single speed on the genset, so its probably somewhere between 70-100hp. So, if you drive at 100mph with the A/C on, expect the genset to run constantly once you drain the pack to 30%. Drive at 65, and it might run half the time, or a third of the time. 100^2/70^2 = 2, or half the power needed.

In reality, its more complicated than all this - but hopefully this starts to illustrate how a 70hp motor can keep a 150hp car running as long as there is gas in the tank, and why the battery is integral and why its not going to drive like a Pinto once it hits 30% charge. It will drive like the same exact car with a little intermittent background noise.

Good explanation!

[CaptainDan]

Originally Posted by Hybridized

I'm surprised anybody is trying to justify the Volt in terms of out-of-pocket expenses compared to current alternatives. The table below (if formatting is preserved) was made by me and published in a finance forum recently:

Q: How much will the car cost?
A: Goal is to be less than $30,000, but first versions might be closer to $40,000. [GM Faq]

Fuel cost: First 40 miles of EV only, 8 kWh. As of 2008 a kWh in the US is 8 - 12 cents depending on location.
After 40 miles and until next battery recharge, expect about 50 mpg.

Opportunity Cost Comparison
Opportunity cost is the cost of foregone opportunities.
Assuming that are comparing the cost of these cars against putting the money in the bank for 10 years at 5%.
If you put the 40k in the bank on day 1 instead of buying a car after 10 years at 5% you'll have 65,155k.

Assumptions: [BULLET][LI]You drive the car for 10 years, and for 15k miles a year.
[LI]Electricity costs .08/kWh, and that the Volt gets to only use electricity (a big assumption)
[LI]The gas cars gets 25mpg.[/BULLET]

Therefore, assuming a time value of money of 5% per year, in terms of 10-years-later-dollars, your costs are:

[C]$4/gallon petrol
| Capital Cost | Fuel Costs | Fuel Opport cost | Total cost in 10 years
40k Volt | 65,155 | 3,019 | 882 | 69,056
10k car | 16,289 | 24,000 | 7056 | 47,345
20k car | 32,578 | 24,000 | 7056 | 63,634
30k car | 48,867 | 24,000 | 7056 | 79,923
23K Prius | 37,464 | 12,000 | 3528 | 52,992 (assuming 50mpg)
[/C]

[C]$5/gallon petrol
| Capital Cost | Fuel Costs | Fuel Opport cost | Total cost in 10 years
40k Volt | 65,155 | 3,019 | 882 | 69,056
10k car | 16,289 | 30,000 | 8820 | 55,109
20k car | 32,578 | 30,000 | 8820 | 71,398
30k car | 48,867 | 30,000 | 8820 | 87,687
23K Prius | 37,464 | 15,000 | 4410 | 56,874 (assuming 50mpg)
[/C]

[C]$6/gallon petrol
| Capital Cost | Fuel Costs | Fuel Opport cost | Total cost in 10 years
40k Volt | 65,155 | 3,019 | 882 | 69,056
10k car | 16,289 | 36,000 | 10584 | 62,873
20k car | 32,578 | 36,000 | 10584 | 79,162
30k car | 48,867 | 36,000 | 10584 | 95,451
23K Prius | 37,464 | 18,000 | 5292 | 60,756 (assuming 50mpg)
[/C]

You compare the cheapest possible Prius to the highest estimated Volt price? Sounds fair

Particularly when compounded by a very generous 5% over 10 years.

There is also the battery replacement cost. The Volt's battery is a newer, better (but more expensive) design - the main reason the Volt is more costly. But it is MUCH longer lasting than the Prius type battery, which would never last 10 years. Even if the Volt's battery didn't last ten years, a new one would be free (warranty) - Prius does not offer that after 5 years. So, factor in at least one new battery.

[rob2299usa]

Originally Posted by CaptainDan

Even on a longer commute, you STILL get the first 40 miles gas-free. Plus you get about 50mpg after that. Sounds like the Volt STILL could be for you.

True enough... if I had a 50 mile round-trip commute I may still find the Volt attractive, but the point I was trying to make clear is that this car is not for everyone. The whole point is to use as little gas as possible, not to charge the battery off of gasoline!!!!

No one has yet to answer my question:

Why would you ever want the car to charge the battery off of the gas engine???

[Hybridized]

Originally Posted by rob2299usa

No one has yet to answer my question:
Why would you ever want the car to charge the battery off of the gas engine???

For load leveling, to borrow the phrase from Dan, and in order to have battery assist during periods of power demands that exceed the ICE output.

[fan]

Originally Posted by goblue

Read up on how batteries work. Basically, the arrangement you proposed wouldn't work for a host of other reasons, but its not much stress on the battery - in fact, its 100% necessary to get good performance out of the car.

Gas engines are ill suited to transportation because you use their full capability a very small percentage of the time. So, the VOLT uses its battery as a buffer. The electric motor has full access to max power at any point, but the gas engine can run only when necessary to maintain charge at 30%, and when it does run, it runs at peak efficiency.

Thats the whole point. When the VOLT hits 30% the generator comes on to maintain charge - it doesn't increase charge.

In a previous post :

Originally Posted by fan

The battery could be built not as 'one piece', but at least two parralel batteries. After depleting one, the system could switch to the other and prepare the depleted one only for recharging(not recharging and providing power simultaneously). The other one (the full one)could provide the necessary power.

It may be possible to have the gas engine providing power for the electric motors and also recharging the battery.

To maximize fuel economy, the engine would start runing at optimum rpm when the first battery would be depleted. From this point on, the setup would work like a parallel hybrid. When there's need for more power, the battery would make up for the not-enough power supplied by the engine running at constant rpm.

- At normal speeds:
The surpluss power from the engine would recharge the depleted battery.

-Under stress:
The battery would supply the elctric motors with aditional power.

The scenario could work with 'one' battery but there would be more stress on it. Anyway the battery is likely built from many modules. It would be easy to setup 'two' parralel batteries

So, when the engine is running I don't see why it wouldn't be good to have the power from the generator transfered directly to the emotors bypassing the battery. This would actually be more eficient than transferring the same power through the battery ( in at moment t and out at moment t +3ms).
So, when battery is discharged(35%), the engine would run (at optimal rpm) and:

Normal conditions (most of the time): send directly power to the emotors and recharge the battery .
Under stress(from time to time): power the electric motors and get assistance from the battery when required.

[rob2299usa]

Originally Posted by Hybridized

For load leveling, to borrow the phrase from Dan, and in order to have battery assist during periods of power demands that exceed the ICE output.

I'm sorry let me rephrase my question:

Why would anyone ever want the car to fully charge the batteries off of the gas engine???

[CaptainDan]

Originally Posted by rob2299usa

I'm sorry let me rephrase my question:

Why would anyone ever want the car to fully charge the batteries off of the gas engine???

I think we are all actually in agreement here. You DO want (and need) some minimal battery charging by the gas engine. You do NOT want (or need) the gas engine to fully charge the battery.

You know, most of us in here have a decent understanding of how these things do (or probably will) work. The general car buying public neither knows, nor cares, about the inner workings of this. Be prepared for a TREMENDOUS amount of customer issues related to "how my car works." Try not to look down on those who are "unaware". They aren't idiots (mostly). This stuff is all a huge change from what was. If you see a Volt or Prius, or whatever future model of hybrid/electric at the side of the road, it doesn't mean it's broken. The driver probably ran out of gas. (Wha? Why would my car need gas?) sigh.

[Hybridized]

While waiting for confirmation that Dan's understanding of the Volt is correct, meaning in CS mode the ICE recharges the battery to about 5% above minimum, a quick back of the envelope calc meant to answer: how much vertical climbing is the battery good for over and above ICE use ? I used 2000 Kg to include people, and 800 wH battery capacity availability.

Came out to 2,880,000Joules/9.8*2000 = 147 meters. This isn't bad, but people who drive aggresively in hilly areas are going to "hit the wall", to borrow a metaphor. The Prius works out to be about 65 meters.

[big swede]

Originally Posted by goblue

It works like the thermostat in your house. When the temp drops to 68, the furnace comes on and pushes it to +1-2 degrees, depending on the thermostat. Then the furnace shuts off. If you ran your furnace constantly at a low rate it would be horribly inefficient, so it cycles. Same thing.

The generator is hooked to the battery. When the charge hits 30% the generator comes on and runs till it hits some arbitrary percentage GM set. Say, 32%. It could vary depending on how you are driving, the outside air temp, whether the a/c is on, etc, or it could be fixed at say, 31.5% Then when it hits the number the generator shuts off.


To the lay person, the battery isn't being charged because the gauge won't really move. Just like when you set the thermostat to 70, you tell your wife the temp is 70, even though its really somewhere between 69 and 71. In truth - to the engineer - the state of charge of the battery will vary slightly, up and down. Drive aggressively with the A/C - the generator will run more. Cruise at 60 on the freeway, the generator might need only run for 5 minutes out of every 15. Crusing on the freeway uses something like 20hp on average. Its a 150hp motor. Acc'd to GM a 70hp motor would have been sufficient for the VOLT, they used a 150hp motor so it could run slower, and to use an existing design.

For ex: if the car is cruising and using 10 hp on average, but the generator supplies 100hp when running, then it needs to run 10% of the time. Its the average usage that counts. If you floor it and use 150hp for 30 sec, but then cruise at 50 for the next 15min using 10hp, the generator only needs to supply on average, ~15hp.

Which is why GM said the VOLT could get by with a 70hp motor. Lets say you spent 50% of the time with the pedal floored, and 50% of the time braking - thats a crazy scenario - and we know the E-Motor is 150hp. 150/2=75.

Wonder why its speed limited to 100mph? 2 reasons, first - much faster than 100 and you need a trans to keep the electric motor to a reasonable RPM. Second reason, the only way to keep the e-motor floored is to drive it at the speed where wind resistance is the limiting factor, for a 150hp aerodynamic car with 235 ft-lbs avail, thats around 130 or so? Wind resistance goes up to the velocity squared. So 130^2 / 100^2 = 1.69, almost double the power required.

The VOLT is set to run efficiency optimized single speed on the genset, so its probably somewhere between 70-100hp. So, if you drive at 100mph with the A/C on, expect the genset to run constantly once you drain the pack to 30%. Drive at 65, and it might run half the time, or a third of the time. 100^2/70^2 = 2, or half the power needed.

In reality, its more complicated than all this - but hopefully this starts to illustrate how a 70hp motor can keep a 150hp car running as long as there is gas in the tank, and why the battery is integral and why its not going to drive like a Pinto once it hits 30% charge. It will drive like the same exact car with a little intermittent background noise.

That's the best written explanation I have read. Many of us see it the same way as you have written it but you have done a much better job spelling it out in detail which shows exactly how the Volt will have access to full power 100% of the time and will not fall off dramatically after the first 40miles on the battery.

MonaroSS is conspicuous by his absence. Either he is tired of calling us a bunch of idiots because he still thinks it works completely different or he finally grasps that it might work much differently than he thought.

[rob2299usa]

Originally Posted by CaptainDan

I think we are all actually in agreement here. You DO want (and need) some minimal battery charging by the gas engine. You do NOT want (or need) the gas engine to fully charge the battery.

You know, most of us in here have a decent understanding of how these things do (or probably will) work. The general car buying public neither knows, nor cares, about the inner workings of this. Be prepared for a TREMENDOUS amount of customer issues related to "how my car works." Try not to look down on those who are "unaware". They aren't idiots (mostly). This stuff is all a huge change from what was. If you see a Volt or Prius, or whatever future model of hybrid/electric at the side of the road, it doesn't mean it's broken. The driver probably ran out of gas. (Wha? Why would my car need gas?) sigh.

I am not looking down on anyone. I posed that question to get people thinking. I realize that you have a good understanding of how this system works. That question was not for you it for those people who say,


"What?!?!? the engine DOESN'T charge the batteries?? If this is true then this is a huge mistake on the part of GM."

or

"I live in an apartment and have no where to plug in... How will I charge my volt if not through the gas engine??"


Again, I asked the question to get people thinking. Why would anyone ever want to charge their battery to full charge (80% SOC) on gasoline??

If you thought about it, you would realize that you would NEVER want to do this...

[Dave B]

I have now read (and had explained to me in person at the auto show) so much conflicting info that I am officially and totally confused.

[goblue]

Originally Posted by fan

In a previous post :




So, when the engine is running I don't see why it wouldn't be good to have the power from the generator transfered directly to the emotors bypassing the battery. This would actually be more eficient than transferring the same power through the battery ( in at moment t and out at moment t +3ms).
So, when battery is discharged(35%), the engine would run (at optimal rpm) and:

Normal conditions (most of the time): send directly power to the emotors and recharge the battery .
Under stress(from time to time): power the electric motors and get assistance from the battery when required.

Its automatically does what you suggest. the generator is hooked directly to the battery. The e-motor (via a variable control) is hooked to the battery. Electricity follows the path of least resistance. Here's a few scenarios.

So, lets say the generator (ICE) was running...

and you were accelerating hard. 100% of the power would be flowing from the generator to the e-motor AND more power would be coming from the battery. Again, it follows the path of least resistance.

Now, lets say you were accelerating at exactly the power put out by the generator. Zero power would go into the battery.

Finally, lets say you were accelerating mildly. Some of the generator's power would go to the battery and the rest to the e-motor.

Its all simple physics. Ever use your cellphone while its charging? Works just fine, and the phone has no crazy controller. Power is flowing to the battery and away from it simultaneously, with only the net difference going into or coming from the battery depending on what you're doing.