how about this --- they get with the Tesla's battery maker for a slightly scaled down battery for the Volt and build it in mass quantities for a decent price instead of spending tons of $$ on R&D?

 

I think you are missing the point that the engine will produce more energy than "just enough to charge the battery". They need to generate *at least* enough for worst case driving conditions. That means in all other circumstances you are generating additional energy that, if not being used to recharge the battery, is being *thrown away*.

Wouldn't you rather use that energy already produced by the wasteful gasoline engine vs. throwing it away?!?

Seriously, not a big deal but I hope you see my point.

 

First GM isn't creating their own battery. They are working with suppliers who spent/spend lots of money on their respective technologies and battery chemistry. There are several different battery technologies that all have different parameters they operate within. No design is "right" for all uses. Some require more space, others require more care with recharging, while others hold great promise but aren't quite there yet.

Don't kid yourself, GM has their fingers in it all. Did you know that Delphi (think GM) owns a fairly significant percentage of EnerDel (the Tesla battery supplier)? They have to keep pushing A123, EnerDel and AltairNano to get a solution that works. There is no clear winner yet so if they want sell a product *now* they will need to make trade-offs.

 

I see where you're coming from but I have a different understanding of how the Volt's generator will be working.

Let's say you reach 30%, which is the Volt's 'effective' empty point.

You seem to believe that the generator will have to be working at, say XX capacity simply because the driver might choose to floor it and if they choose to floor it, the power needs to be available to them... thus the generator is burning more gasoline and creating more electricity than the battery is actually accepting.

That's not how I've come to understand how the Volt's charging system will work. As I understand it once the Volt reaches 30%, the generator kicks in at a constant RPM... by default this will be a set RPM that the engineers have determined most efficiently charges the battery per amount of gasoline burnt with no consideration at all toward if the driver might choose to floor it at the next light. Why? Because in the event of the driver flooring it, the battery still has a 30% reserve... so then what happens? The battery will act like a capacitor in a sense, and feed that power to the drive wheels, giving the driver maximum acceleration. The car will then see that the battery is now down to 26% after that 0-80 run the driver just did, and at that point it will make the decision to either continue to run the engine at the previous constant most efficient RPM in the hopes that the driver won't continue to drive as aggressively, or else increase the RPM of the generator to catch back up to 30% capacity. As to what level the car will allow the car's battery to get down to before getting more aggressive and less efficient in its charging RPM, I'm not sure, but this really is no different than any other gasoline powered car in that if you drive more aggressively, you get worse gas mileage. Actually the Volt could help smooth out the penalties of periodic/occasional aggressive driving a bit seeing as how you might choose to floor it from the light once and then sit idling at the next light for 30 seconds while the Volt's generator is able to continue churning away at its most efficient RPM.

Point being the Volt's generator doesn't need to anticipate your next move and keep the engine running at a higher RPM because of what you might do... it has the luxury of being able to be reactive in nature since the battery acts as a capacitor, even at its effective empty point.

 

I certainly don't claim to understand all the details of the GM charging system but it is fun to speculate. I agree they will run at a constant RPM that is most efficient for the engine when recharging. Don't know if they will be able to vary that to "make up" charge if they start running low. The 30% charge number has been bandied about as a number that the A123 batteries need to stay above to keep their recharge performance (service life) up. My understanding is that the A123 battery is optimized when kept roughly within a 30-80% charge.