[mbartosik]

Pricing
Talking with Ed (a GM exec responsible for Chevy brand)...
They are still very unsure about where to price it, I think that applies to a number of topics. He is thinking on the lines of keeping it a "premium vehicle". However, Bob Lutz also talked about if they had to take the idea of a vehicle that would make a loss for a few years to the board that would fly.

Ed asked me what I would pay for a Volt. My answer... first I explained that I've already installed huge amounts of solar power and am in a very small minority so he would have to treat my answer accordingly... my answer was $40K and I pointed out that I was assuming about $4K in tax credits.

Ed was genuinely very interested to hear about marketing issues too.

I also told Ed that I would drop the purchase like a hot potato if there was dealer gouging, and he said there would not be, he looked like the exec to ensure that too. I didn't press him on dealer gouging because he time was short.

He was off to a dinner with dealers so I didn't get to speak with him for long enough.

I also raised the idea of a GM credit card only for the Volt, but to get points for optional extras and/or a place in the queue. Also raised the idea of an option of big flashy decals on the car (a rolling advert) with phrases like "Powered by electrons" to spread the word. The execs are very keen to use word of mouth to spread the word about the Volt.

I also offered him a check for $10K as a deposit, which is what I think sparked his questions about pricing. He said that they would take it, but he appeared to mean that they would in the future, rather than take the check at Volt Nation.

------------

Firmware
I also asked another exec about whether they were making the firmware with an eye to after market accessories, Bob Lutz's favorite accessory is programmable simulated engine sounds (e.g. V12), mine is a whole house generator. The exec said no. But all firmware is flash re-programmable, so GM can add options later, I also suspect that the engineers at GM will naturally make the protocols support a lot of add ons simply out of a desire for separation of design concerns, without deliberate intent. Also it uses standard CAN (car area network) which makes it open to unauthorized accessories.

------------

Size:
The interior (as he called it "green house") will be larger than the concept car this was clearly important for the exec. The seat will be higher, with a little more head room too. It is only a 4 seater, no chance of being a 5 seater the tunnel is too high. It will be bigger than existing Colbalt, closer to Malibu in size maybe a tiny bit smaller than Malibu on the inside.

 

[Dr Mark]

Chevy Volt SS Version

All,
I agree with the questioner who asked about a Volt SS, hotrod sport version, that there really needs to be more than one model of the Volt. It's a great opportunity too, remember that GM's EV1 still holds the electric car land speed record at 183 MPH and many electrics (like the Tesla) turn 0-60 times around 4 sec! But there also needs to be a high-MPG economy version to really push the envelope on achievable fuel economy.

I recently put a 12 kW (i.e. 16 HP) gen-set in my electric Toyota MR2 (AC induction motor, regenerative braking and now range extended, so it is alot like a Volt) and I'm finding, for various reasons, that for Florida driving it could have been about 11 HP. So, I asked John Laukner and Frank Weeber both why (at 71 HP) the generator engine is so powerful (for instance 53kW can charge the entire battery pack in about 15 minutes). The Volt team has apparently discussed this at length since both managers gave me the same answer; that they will optimize efficiency of the generator engine for multiple (probably 3) points on its load curve and select the operating point based on the immediate demand for power.

But then I asked John Laukner when you would ever need a sustained 53 kWatts. Since my experience is in "flat" Florida I assumed he would say for driving in mountains, but his answer surprised me. He said "the Volt is a Global product and he wants it to be able to cruise the Autobahn all day at 160 to 180 kph".

Now after thinking about it, that answer bothers me because it forces me to pay for a bunch of Europeans to go screaming across the German countryside. The fact is that the smaller the engine is in a Series Hybrid the better your fuel economy. I have several discussions and examples of this on our website at www.freedomformula.org and more specifically on a "special article" page at http://serieshybrid.com/FreedomFormula/images/Effic.htm. This oversized genset is probably the difference between 50 and 60 MPG (after the initial 40 miles). Even 70-75 MPG would be possible if they used a tiny turbo-charged diesel generator. All in due time though; I agree that the first 40 miles of gasoline free driving is the priority.

But remember that when the Volt is finally launched gasoline will probably be over $5 a gallon and people won't even read beyond the EPA mileage sticker, and many will be so angry they won't care what it costs either.

Dr Mark

 

[Tagamet]

I see your point

All,
I agree with the questioner who asked about a Volt SS, hotrod sport version, that there really needs to be more than one model of the Volt. It's a great opportunity too, remember that GM's EV1 still holds the electric car land speed record at 183 MPH and many electrics (like the Tesla) turn 0-60 times around 4 sec! But there also needs to be a high-MPG economy version to really push the envelope on achievable fuel economy.

I recently put a 12 kW (i.e. 16 HP) gen-set in my electric Toyota MR2 (AC induction motor, regenerative braking and now range extended, so it is alot like a Volt) and I'm finding, for various reasons, that for Florida driving it could have been about 11 HP. So, I asked John Laukner and Frank Weeber both why (at 71 HP) the generator engine is so powerful (for instance 53kW can charge the entire battery pack in about 15 minutes). The Volt team has apparently discussed this at length since both managers gave me the same answer; that they will optimize efficiency of the generator engine for multiple (probably 3) points on its load curve and select the operating point based on the immediate demand for power.

But then I asked John Laukner when you would ever need a sustained 53 kWatts. Since my experience is in "flat" Florida I assumed he would say for driving in mountains, but his answer surprised me. He said "the Volt is a Global product and he wants it to be able to cruise the Autobahn all day at 160 to 180 kph".

Now after thinking about it, that answer bothers me because it forces me to pay for a bunch of Europeans to go screaming across the German countryside. The fact is that the smaller the engine is in a Series Hybrid the better your fuel economy. I have several discussions and examples of this on our website at www.freedomformula.org and more specifically on a "special article" page at http://serieshybrid.com/FreedomFormula/images/Effic.htm. This oversized genset is probably the difference between 50 and 60 MPG (after the initial 40 miles). Even 70-75 MPG would be possible if they used a tiny turbo-charged diesel generator. All in due time though; I agree that the first 40 miles of gasoline free driving is the priority.

But remember that when the Volt is finally launched gasoline will probably be over $5 a gallon and people won't even read beyond the EPA mileage sticker, and many will be so angry they won't care what it costs either.

Dr Mark

But (other than slightly higher initial cost) wouldn't a somewhat oversized genset, still get good mileage if it was driven more conservatively than at Autobaun speeds? In other words, driving the Volt more slowly would tax the genset motor less, so it should then generate power more efficiently. So driving at 60 mph would result in better mpg than charging while running at full throttle (so that you had tears streaming into your ears.)

 

[BillR]

Current Engine Size is Okay

For conventional drive vehicles, the engine load must match the demand of the vehicle. Thus, as shown in Dr. Mark's link, many engines operate at very low efficiency points, because we typically have oversized engines that allow us to accerate well and climb hills without losing speed. Pretty much necessary driving traits in today's traffic.

We could size the engines smaller so that they operate at a more efficient point most of the time, but obviously, there would be sacrifices.

Also, at their most efficient point of operation, large engines are more efficient than small engines. For instance, if you wanted to generate 250 hp to run a generator for a sawmill, one 250 hp engine at full load would be significantly more efficient than 25 - 10 hp lawnmower engines. So engine sizing isn't the total picture, the point of operation is the key.

With the Volt and its E-Flex platform, most of these inefficiencies can be avoided. The engine doe not need to operate such that it only provides the load to the wheels, but also can provide some power to the battery pack. Thus, the engine controls can be configured such that the engine operates for the bulk of its time in the most efficient operational zone. Therefore, the sizing issue of 73 kW versus a smaller engine is not nearly as critical.

 

[DaV8or]

The interior (as he called it "green house") will be larger than the concept car this was clearly important for the exec.

Just to clarify, the term "green house" refers to the area of glass in the car, so what he was saying was that it would have more glass surface area than it does now, not necessarily bigger interior. I would guess, as we have before, that the roof line will raise and the belt lower resulting in bigger side windows.

 

[Dr Mark]

Generator Output Power Peak vs Average

Bill,
Thinking about a Series Hybrid is difficult because for the last 100 years cars have worked pretty much the same. The key point to this discussion is that the engine size has NOTHING TO DO WITH how fast you can go. In a Series Hybrid, speed and acceleration is determined by the torque and RPM capability of the electric motor, and of course the battery must have enough current capacity ("cranking amps") to not be the limiting factor.

The ONLY job of the gen-set is to keep up with the AVERAGE power requirement of the vehicle (not the PEAK); where average is defined as the discharge time of the battery pack (maybe 15 min to 1 hour). The gen-set just has to catch-up before the battery pack is dead. So accelerating up the on-ramp, passing another vehicle, even climbing a medium sized mountain has nothing to do with power output of the gen-set. That's the point of the article in the link; the beauty of a gen-set is that it can run at the point of peak efficiency, about 33% for a gas engine and as high as 46-48% for a diesel; while a normal automobile operates at 10-12% in town and 15-20% on the highway.

So, to run at peak efficiency you have to load the generator engine down (see the torque-RPM-efficiency curve) and maintain a moderate RPM; then be prepared to soak up the number of Watts that come out of it. You can vary horsepower (1 HP is about 750 Watts) by 2:1 maybe 3:1 without sacrificing efficiency too much, but if the "3" is 53kW you have to be prepared to "soak up" about 20kW to keep it at an efficient generation point, and for most driving scenarios that would force the Volt to cycle the engine on and off, which besides being a little distracting it puts wear and tear on the starter and even the engine block and head since the engine has to go thru the an inefficient "warm-up" time.

Of course a smaller generator cuts weight and cost out of the vehicle too.

Dr Mark

For conventional drive vehicles, the engine load must match the demand of the vehicle. Thus, as shown in Dr. Mark's link, many engines operate at very low efficiency points, because we typically have oversized engines that allow us to accerate well and climb hills without losing speed. Pretty much necessary driving traits in today's traffic.

We could size the engines smaller so that they operate at a more efficient point most of the time, but obviously, there would be sacrifices.

Also, at their most efficient point of operation, large engines are more efficient than small engines. For instance, if you wanted to generate 250 hp to run a generator for a sawmill, one 250 hp engine at full load would be significantly more efficient than 25 - 10 hp lawnmower engines. So engine sizing isn't the total picture, the point of operation is the key.

With the Volt and its E-Flex platform, most of these inefficiencies can be avoided. The engine doe not need to operate such that it only provides the load to the wheels, but also can provide some power to the battery pack. Thus, the engine controls can be configured such that the engine operates for the bulk of its time in the most efficient operational zone. Therefore, the sizing issue of 73 kW versus a smaller engine is not nearly as critical.

 

[Dr Mark]

Generator Output Power Peak vs Average

Bill,
Thinking about a Series Hybrid is difficult because for the last 100 years cars have worked pretty much the same. The key point to this discussion is that the engine size has NOTHING TO DO WITH how fast you can go. In a Series Hybrid, speed and acceleration is determined by the torque and RPM capability of the electric motor, and of course the battery must have enough current capacity ("cranking amps") to not be the limiting factor.

The ONLY job of the gen-set is to keep up with the AVERAGE power requirement of the vehicle (not the PEAK); where average is defined as the discharge time of the battery pack (maybe 15 min to 1 hour). The gen-set just has to catch-up before the battery pack is dead. So accelerating up the on-ramp, passing another vehicle, even climbing a medium sized mountain has nothing to do with power output of the gen-set. That's the point of the article in the link; the beauty of a gen-set is that it can run at the point of peak efficiency, about 33% for a gas engine and as high as 46-48% for a diesel; while a normal automobile operates at 10-12% in town and 15-20% on the highway.

So, to run at peak efficiency you have to load the generator engine down (see the torque-RPM-efficiency curve) and maintain a moderate RPM; then be prepared to soak up the number of Watts that come out of it. You can vary horsepower (1 HP is about 750 Watts) by 2:1 maybe 3:1 without sacrificing efficiency too much, but if the "3" is 53kW you have to be prepared to "soak up" about 20kW to keep it at an efficient generation point, and for most driving scenarios that would force the Volt to cycle the engine on and off, which besides being a little distracting it puts wear and tear on the starter and even the engine block and head since the engine has to go thru the an inefficient "warm-up" time.

Of course a smaller generator cuts weight and cost out of the vehicle too.

Dr Mark

For conventional drive vehicles, the engine load must match the demand of the vehicle. Thus, as shown in Dr. Mark's link, many engines operate at very low efficiency points, because we typically have oversized engines that allow us to accerate well and climb hills without losing speed. Pretty much necessary driving traits in today's traffic.

We could size the engines smaller so that they operate at a more efficient point most of the time, but obviously, there would be sacrifices.

Also, at their most efficient point of operation, large engines are more efficient than small engines. For instance, if you wanted to generate 250 hp to run a generator for a sawmill, one 250 hp engine at full load would be significantly more efficient than 25 - 10 hp lawnmower engines. So engine sizing isn't the total picture, the point of operation is the key.

With the Volt and its E-Flex platform, most of these inefficiencies can be avoided. The engine doe not need to operate such that it only provides the load to the wheels, but also can provide some power to the battery pack. Thus, the engine controls can be configured such that the engine operates for the bulk of its time in the most efficient operational zone. Therefore, the sizing issue of 73 kW versus a smaller engine is not nearly as critical.

 

[Koz]

Dr Mark, I tend to agree with you for my personal driving needs and concerns but GM's reasoning is a little different. They are developing this as a world car to be driven not only in the US. They are thinking of autobahn driving at sustained 100MPH. They are also hung up on the battery lasting at least 10 years. GM's doesn't agree with "The ONLY job of the gen-set is to keep up with the AVERAGE power requirement of the vehicle". They have decided to design a high performance car that will not suffer performance degradation in any situation and that relies as little as possible on the battery once charge sustaining mode is reached. They would rather throttle down the genset rather charge the battery and have enough genset power to meet most power demands. The battery will only be needed for short transient needs. They feel it is a better use of battery life to take power from outside chargins as much as possible and from the genset as little as possible.

For my use, I would be better served by a drivetrain designed around your philosophy since my commute is so short and the biggest hill within 600 miles is 350' high. I would be much better off using the battery less effectively than losing it to calendar life with nothing in return. But alas, GM is designing for the world and not me. I can't blame them for that.

 

[BillR]

Projected ICE Operation

Dr. Mark,

I've put some more thought into this onboard engine genset, and this is my hypothesis. Please see the following link for some background info:

http://www.gm-volt.com/2007/08/29/latest-chevy-volt-battery-pack-and-generator-details-and-clarifications/

The ICE is a 1.0 liter engine with VVT, DI, and turbocharging. I see it as a close cousin to GM's 2.0 Liter engine in the Solistice GXP. More info on that engine at this link (see Solistice GXP 2.0).

http://media.gm.com/us/powertrain/en/product_services/2008/08car.htm

Although the information suggests variable speed, my conjecture is that GM will operate the ICE at 1800 rpm in 60 Hz markets (North America and others) and 1500 rpm (50 Hz) in Europe. With these speeds, and a 4 pole generator, the frequency/power can be made to match the power from an electrical outlet. This may be key, because you can now utilize the power electronics from the charging circuit to recharge the batteries, no additional power electronics req'd. And some information has indicated that the power electronics are expensive.

With this info, how would the engine operate? Although the link above states 25 kW for highway driving, an article I read recently stated that the Tahoe Hybrid only needed 30 hp (22.5 kW) to cruise at highway speeds. This doesn't make sense. Therefore, I will use the 200 kWh per mile number at 60 mph which equates to 12 kW to drive the Volt at highway speed, level surface, dry pavement. This actually equates with numbers for other moderate sized vehicles. I will use 60 mph for my highway analysis as it makes the numbers easy (1 mile per minute).

One hp is 33,000 ft-lbf per minute. A kW is then 44,250 ft-lbf per minute. If the Volt with 4 passengers and gear weighs 4000 lb, then an 11 foot rise over 1 minute will require 1 kW. Likewise, a 55 foot rise over 1 minute equals 5 kW. For climbing a hill, a 1% grade is defined as a 1 foot rise for every 100 feet traveled. For 1 mile (5280 feet), a 1% grade would equate to a 53 foot rise. Therefore, at 60 mph, it will take 12 kW for the Volt to overcome drag forces, and 5 kW for every 1% of grade when going up a hill.

Now let's assume your Volt is charged and your driving from Kansas City to San Francisco. After 40 miles, you are at 30% SOC, the ICE comes on. Since Kansas is somewhat flat, you only need 12 kW of power. I will guess that the ICE will operate at it's most efficient point (about 30 kW) and charge the batteries to 40% SOC. Since the battery pack is 16 kWh, 1.6 kWh is needed to go from 30% to 40% SOC. Since the car is consuming 12 kW, 18 kW is going to the batteries. So the engine runs for about 0.1 hours or 6 minutes to achieve this. At 200 Wh per mile, the car will go for 8 minutes on batteries before being back at 30% SOC. I am not sure whether the engine would cycle on and off, or return to an idle condition when running on batteries. This would apply for steady, level, cruise.

During this cruise, I would expect the ICE to be at full throttle with mild boost from the turbo.

Once you pass Denver, you will begin to climb (you're not in Kansas anymore, Dorothy). At a 6% climb, the Volt will require 12 + 6*5 or 42 kW. Here the engine will max out. At 5000 feet, at 53 kW motor only produces about 83% of its sea level power, or 44 kW. Now all but 2 kW is used to drive the car, and it will take 0.8 hours (48 minutes) in this mode of operation to charge the batteries from 30% to 40% SOC. (Note, as you climb, the air gets thinner and the ICE output decreases further, and you may not be able to maintain 60 mph with a 6% uphill grade at these elevations).

In this max point of operation, its is suggested that the engine speed would change, but that could complicate the power electronics, so I will guess that GM will go to high turbo boost for this condition, and maintain 1800 rpm.

Once at the mountain pass at 10,000 feet, it's snowing, it's below freezing, and you have the heat blasting and the front and rear defroster cranking. Your wife is shivering and has her heated seats on max. The kids are in back seat with their DVD player plugged in to convenience plug watching "Transformers" with the volume at 95 decibels. Your level road power consumption now increases to 18 kW.

At 10,000 foot altitude, your ICE engine output is only 68% of what it is at sea level. Thus at its best operating condition, the ICE only provides 20 kW instead of 30 kW. Again, it will take 0.8 hours to charge the battery pack from 30% to 40% SOC.

Once over the mountains, you will be descending, it would make sense to allow the batteries SOC to exceed 40%, since this is "free" electricity".

Once in San Francisco, you are using less power for city driving, since there is less drag at low speeds, and you get the benefit of regenerative braking. I envison the engine will have a part-load condition of maybe 12 kW. At this point, the engine will use its VVT to operate like the Atkinson cycle with late valve intake closure. This is used on the 6.0 liter Tahoe engine for better efficiency. If city driving takes 8 kW, then with this operation, the engine will charge the battery pack from 30% to 40% SOC in 0.4 hours or 24 minutes. In this scenario, I would expect the engine to cycle on and off.

I obviously am not making guarantees on this analysis, but just trying to paint a picture of how a long trip in the Volt may be with the ICE in operation a significant portion of the time.

 

[Cybereye]

Dr. Mark,

Although the information suggests variable speed, my conjecture is that GM will operate the ICE at 1800 rpm in 60 Hz markets (North America and others) and 1500 rpm (50 Hz) in Europe.

One thing you overlook or I have not find the info yet. What make you says that it generate AC, not DC. I'm assume the engine is going generate DC into the battery. The battery go to the DC/AC converter to the AC motor.

 

[Koz]

I believe GM is trying to minimize the amount of energy going through the battery coming from the genset. Power will go directly to the motor and auxiliary loads after appropriate conversion and excess power may then go to the battery if had been drained below 30% SOC. If the battery doesn't need the charge, then the engine will be throttled to meat the runnning demand. At least that's how I understand their current concept, but who knows, this may not have been decided yet or may change after testing.

 

[BillR]

Cybereye,

I'm only speculating on a synchronous AC generator because they mention the speeds 1500 and 1800 rpm. Synchronous AC generators are typically very efficient, and you can vary the power output without changing speed. Voltage can be regulated.

Probably, you will need someone with more intuition regarding motors, controls, etc. I believe the drive motor for the Volt will be a permanent magnet synchronous motor with a variable frequency drive. Obviously, the genset will need to provide not only the power, but also the proper voltage. With a DC generator, do you need a variable speed to vary power output? Does the voltage change with the speed?

Just some issues that I am not that familiar with.

 

[Dr Mark]

How High Can You Get on 16kW-hrs

**********************************************
Bill,
Your analysis is very good. The 12kW for drag and resistance at 60MPH can be stated as 200W-hrs per mile (12kW-hrs/60miles in 1 hour) and the Toyota Rav-4 EV uses about 250W-hrs/mile so assuming some improvement in aerodynamics (the older Rav4 was shaped like a shipping crate) a 20% drop is probably right.

Also, I worked out the energy vs altitude in kg and meters, and using my figures or yours we are within 1% so that's a good check. We both conclude then that a 5,000ft climb requires about 7.75 kW-hrs of additional energy vs driving the same distance on flat land. At at 60MPH and 5% grade a 5,000 ft climb takes 18.8 minutes. Looking at altitudes in Colorado you really can't go from Denver to any populated town that is more than a 5,000 ft climb and even at that 7.75 kW-hrs only represents half of the battery pack capacity, so if you wanted to get to an uninhabited spot at 14,000 ft you could still make it with about 10% battery reserve assuming your ICE/generator (i.e. gen-set) is covering losses from drag and vehicle systems, but it would be hard to maintain 60 MPH on those roads.

So, if the ICE/generator can overcome the air and road resistance with 12kW plus provide another 4kW for the car's systems, then an additional 8kW would allow the Volt to climb a 5,000ft mountain once per hour (without even considering regenerative charging on the downhills). This total of 24kW isn't even half of the planned genset output, so my point was that for stop-and-go driving on flat terrain (I live in Florida) I only need 6-10 kWatts, so oversizing the gen-set means that when (and if) I DO need it, it will have to either cycle on and off or run at a load-point that makes it inefficient. Or they could shut down cylinders and throw the other valves open like a Northstar engine; at least eventually GM should push this technology to the limit; advertising a 100 MPG Volt would really get everyones attention.

So my conclusion is you don't really need to design the Volt to keep up with this kind of peak load? You can't climb 265 ft/min indefinitely because you run out of hill, and even the initial 16kW-hr pack seems to be enough to get you up the biggest peaks. The purpose of a hybrid is to smooth out the peaks and lulls in power demand, not meet them all in real-time. This is the time for the $10,000 battery pack to pay you back.

Remember, that the acceleration and top speed have nothing to do with how much power the gen-set makes. A Tesla goes 0-60 in 4 sec and it's gen-set puts out ZERO; and the EV1 could go 183 MPH and it's gen-set put out ZERO. I have argued with Martin Eberhardt that replacing 75% of those batteries in the Tesla with a gen-set would cut the 0-60 down to 3 sec, not to mention, cutting $30,000 off the pricetag.

So what the Volt needs to do is make sure it arrives at the bottom of a mountain with a full charge, and manages to show up empty before decending down into Salt Lake City or before arriving home. Hopefully between GPS (or OnStar), a stored terrain grid and voice recognition it will be easy to tell the Volt where you are going and it will manage the battery's state of charge as you travel. Check the following link for altitudes in Colorado:

http://www.tripadvisor.com/Travel-g28927-c3597/Colorado:United-States:Altitude.Sickness.html

And hopefully that overworked ICE will be able to blow some heat on my frozen kids without further taxing the batteries. Believe it or not I wouldn't run the air conditioning on electricity either. But that's for another message.

Dr Mark

 

[Dr Mark]

150 kWatt Audio Amplifier

Bill,
I forgot to mention, don't worry about the Volt's motor controller being able to make household current out of the DC battery pack. An AC motor controller has to make very pure sine waves of varying amplitude and varying frequency and 50 or 60 Hz and 115 Vrms is right in it's mid-range. They have to be pure because any harmonic energy does NOT contribute to torque output, in fact depending on phase it can subtract from the torque, so some effort goes into filtering out steps and switching spikes to apply pure sinusoids to the motor windings. In a 3 phase motor the phase currents are 120 out of phase with each other and if you hooked them up to three HUGE speakers, you could get 50kWatts of audio from each phase.

Dr Mark

 

[Cybereye]

Cybereye,

With a DC generator, do you need a variable speed to vary power output? Does the voltage change with the speed?

Just some issues that I am not that familiar with.

The reasons I view as a DC generator cause it a Series Hybrid, The generator does not care about the AC motor, but the battery. I don't know much about generator itself. I'm going to assume it going to be 310 volt battery pack. I don't know what range for the battery is? But just to make a point. The generator would have to push above the 310 volt. The battery would have a range of voltage that can be 310 to 340 volt to recharge with out damage it. The higher the speed the higher the volt will be. It may be easy on the gas to recharge at 315 volt. If it needed more current into the battery it would push to 330 volt, but it hard on the gas. If the battery get a warm or too hot, it would drop the voltage untill it cool down. I do remember GM says they may have three different RPM point set to recharge. I'm in the same boat as you about some issues that I am not that familiar with or lack of info.

 

[Dr Mark]

Generator for the Volt Gen-Set

Bill R,
I've tried lots of schemes to charge my 312 V battery pack on the fly (i.e. while you drive). You are right that the generator isn't concerned with what kind of electric drive motor you are using. It only has to make a voltage slightly higher than the battery pack voltage (290 to 340 V) then current flows until it's making so much current that it loads down the generator motor and the engine speeds stays at an equilibrium point where it is making the amount of electric power that is being produced by the IC engine minus the generator efficiency (1 HP = 750W).

An alternator is ideal for this kind of generator, because the faster you spin it the higher the output voltage, so for a given throttle setting, the gen-set engine will spin up to the RPM that loads down the engine and it reaches an equilibrium point (which is set by where you put the throttle). For my 16 HP engine, that point is about 30 amps, which is about 10 kWatts into 330V, so the engine is nearly full throttle and runs at about 30% efficiency, vs about 5% when it's near idle speed.

With a variable field alternator you can change the voltage that is made for a given RPM, where for a permanent magnet alternator this relationship is set by the number of windings and the strength of the magnets. But there is no way you can make 350V with a standard car alternator, it has to be designed for High Voltage.

Dr Mark

 

[BillR]

Oversized Genset

Dr. Mark,

Thank you for some of your input on the generator. I don't have enough background to understand all of the power electronics.

Living in FL, I can understand your concern for oversizing the ICE, as I know it is fairly level. But at the VoltNation meeting, GM felt that this car needed to be a car for everyone, and have no compromises, as that would be the first step towards public acceptance of EV's.

I understand what you are saying about using the battery to provide the peak power when climbing a hill, but if you need 40 kW to climb a hill at 60 mph, and the battery only holds 8 kWh, you will delete the complete storage capacity of the battery in 12 minutes. You will have only climbed 3200 ft.

Therefore, what I am saying, is that GM for now is making a car that can be used universally. In the future, they will add improvements such a V2G, solar panels, perhaps GPS integration as you discuss, and even an all EV version. They have mentioned 50 to 60 mpg for this car when using the ICE. See the attached video interview.

http://www.youtube.com/watch?v=H1ACbdTJws0&feature=related

To your point, don't be surprised that in future versions of the car, you can get a smaller ICE integrated with a GPS trip calculator.