A Convenient Response to an Inconvenient Truth - 4

These batteries with the lithium iron phosphate have done some remarkable things. First, we can now charge them down to 13 degrees below zero, which were previous batteries you did not want to charge below freezing or 32 degrees Fahrenheit because it would cause metallic plating on the cathode and you'd have the same problem of diminished life. Life is what these batteries are really about.

In addition to being extremely heavy, the lead acid batteries have a cycle life of between 300 and 350 cycles. If you charged every day, you would be out of the battery pack in a year. If you don't discharge them past about 50% and you don't have to charge every day, you might get two to three years out of a set of lead acid batteries, but then you have to replace them.

And while you're operating costs of the vehicle at a penny a mile for electricity, it's a little bit eaten up if you have to spend $2,500 on batteries every year or so. And so you've moved the problem from the gasoline pump to the battery store. The Thunderskies, the good news is that they have a tested life of about 3,000 cycles.

That's a little bit dependent on how you treat them, but that puts us in the eight or 10 year range. The average lifespan of an automobile in the United States from showroom to reporting to the salvage yard for shredding is 9.2 years. And so we're hopeful we've basically got a battery that will last the life of the vehicle.

And that's a good thing because these batteries for this car cost $9,600, which leads us to the interest in spending $3,000 on a charger that can take care of it. If I'm willing to go down to 2,000 cycles, I can charge this battery at three times its current rating. These batteries are rated for 90 amp hours.

I could charge it at a rate of 270 amp hours in 20 minutes. And in fact, I could charge the whole car then, because I have two strings in parallel, in about 20 minutes at 540 amps. Well, the problem is there isn't any 540 amps.

At 120 volts AC or 240 volts AC, you typically have a 200 or 400 amp service to your whole house. And there's no device I'm aware of that's available for money, less than $100,000, that would produce that amount of power to put it into the batteries. And so the charge time is a function of our charger's abilities, not of the battery's abilities.

We could recharge these batteries in 20 minutes, given enough power. But where would you get that amount of power? In actual practice, I found that it doesn't matter. One of the things about lithium iron phosphate batteries that's quite different from all other battery types, but certainly different from the nickel metal hydride or the nickel cadmium batteries, is there's not only no memory effect, but you can charge them.

You do not have to fully discharge them ever, not even once. And not to condition them, not the first time, not after you've used them for a while. You simply don't have to do a full discharge ever.

And you don't have to do a full charge ever. And they don't develop a range. There's no memory.

In fact, simply by decreasing the finish voltage on the charge, you can extend the cycle rating quite beyond the 3,000 cycles. The manufacturer tells us that simply by dropping it from 4.25 to 4.1 volts, you can extend the life of the battery quite dramatically. Since we can charge it and discharge it at any time without regard to memory effect or cycling ability, any of those notions that have become part of the public consciousness using nickel metal hydride or nickel cadmium batteries, we can plug it in at any time we want.

And with a charger that's programmable and will do a charge process and terminate itself, we basically walk away. And that brings me back to the programmability of the BRUSA. What we found was that the 4.25 volts of the fully charged voltage is a little bit problematical.

The batteries have an unusual charge and discharge curve for a battery. Going from 2.5 to 3 volts, bringing it up, you have a very steep curve. And then it levels off for about 85%, 90% of its charge.

There's really not much change in voltage. And then the last 5% or 6% of the charge, you again have a steep curve going up from about 3.6 volts to the 4.25 volts. The interesting thing is that's an area where a lot of the damage is done.

In dealing with series packages, it's very difficult to charge the whole package up to 4.25 volt without having one of the batteries at the end take off and shoot through 4.25 volt and shortening the life of the battery. What we found is that by charging them to 3.65 or 3.7 volts, we're sacrificing very little battery capacity, not a half mile range out of the whole pack. And many, many, many of the problems associated with these batteries and keeping them in balance simply disappear.

The other end of taking good care of the battery is, of course, not to run the car fully out. And that takes us to range, which, again, is one of the more important questions for most people. And I will say that individuals living in major metropolitan areas with extended commutes, an electric car probably isn't there yet for you.

For most of us, though, it quite is. There's 203 million Americans licensed to drive some 235 million automobiles, which is over half the automobiles existing in the world. Collectively, we drive about 8 billion miles a day, which works out to about 14,000 miles per year per driver.

But on a per day basis, that's 39.4 miles. And that's the average. There are those individuals who do occupying a sales position professionally, et cetera, who drive quite a bit during the day and will drive several hundred miles.

And what that leads us to is that over half of the driving population, the licensed drivers in the country, actually drive less than 20 miles a day. So by building a car that has 75 mile range, I'm probably not going 75 miles. It's more likely that the average driver would be going 40 miles a day.

And that's well within the discharge profile of these lithium ion batteries, where it's at the extreme edge of the discharge profile of a lead acid battery. And we want that pad to gain that lifetime. Without that 3,000 cycle lifetime, the current cost of these batteries doesn't make much sense.

With that lifetime at that cost, they suddenly make electric cars viable in a way that they simply never were. We get tremendously better performance, less problems, and less expense using these lithium ion batteries than we ever did trying to build electric cars with lead acid batteries. The charger does a couple of things.

We can program it for very specific voltages and in very specific charge regimes. How we have this one set up, our pack voltage, 3.6 volts with 32 cells, is about 116 volts. And so we'll set the charger up to do a constant current 30 amp charge on the pack until the batteries themselves reach the 116 volts.

Again, they may have been as low as 96 volts when we brought it in. As I said, it has a very flat charging curve. So by far, the majority, 90% of the charge cycle, is spent in that first phase, simply pumping 30 amps into the batteries.

When they do reach 116 volts, the charger switches to a constant voltage source. And it holds that 116 volts fairly precisely and continues to charge the batteries. But as the batteries become more equal to this 116 volts, the charge current that they'll accept starts to decline.

And so we have a declining current value from the 30 amps down. And the manufacturer recommends 5% of the initial charge current, which is an amp and a half, perhaps.