If there was ever a sexy battery, there are 52 of them sitting in my garage. Friday, the batteries arrived in Lacey (near Olympia) and Monday we drove down to get them. Packed into four wooden crates, these blue blocks of plastic and Lithium are hefty; not the dead weight of a lead-acid battery, but you know they pack a punch. (WARNING: the read more link contains technical details which may frighten your children into becoming engineers.)
So: details details details. What did I get? To regurgitate some numbers, each battery has 180 AH of charge, runs at 3.2 volts under load, and has a discharge rating of 4C continuous/12C pulse. To put that into perspective for the ammount of power these can produce lets go into some basic calculations: 52 batteries at 3.2 volts apiece creates a 166.4 volt system. To determine maximum power output, we multiply the capacity of one battery by the discharge rate of that battery by the total voltage of the system to get the maximum wattage from the batteries. To convert to horsepower, simply multiply the wattage by 0.00134102209 hp/watt. So:
180ah × 12C × 166.4v = 359424watts
359424w × 0.001341hp/w = 482.00hp
These batteries can put out the equivalent of 482 hp in electrical current but this has upsides and downsides that lie beyond just the output of the batteries. For instance, the maximum amperage the Controller can take is 1000 amps, not the full 2160 that the batteries can provide. Therefore:
1000a × 166.4v × 0.001341hp/w = 223.15hp
But the motor also has limitations. As a matter of fact, even though the motor is rated to take 192 volts, it is only recommended to use 160 volts with it. This is because as you apply more power to the motor it is actually capable of tearing itself apart and sending pieces of flying metal out though its casing. To avoid this, even at 166.4 volts, we will be forced to dial down the amperage, making the usable horsepower of the motor even less than 223hp.
So if all that potential output power does nothing for us, why are we using such powerful batteries? Well, although they are not capable of dumping all their power out at once, they hold a HUGE amount of charge and if used sparingly, the car will have a range of 120 miles on a single charge. To get maximum power capacity, and therefore the distance your car can theoretically travel, you simply multiply the amp hour rating of a single battery by the total voltage. To get the range, you then divide by the number of watts used per mile. Finally, to protect your lithium battery investment, you'll only discharge the batteries to 20% of their total capacity so we'll have to compensate for that in our equation by multiplying our result by 80%.
180ah × 0.80 × 166.4v / 200 (whr/mi) = 120mi
In this case, 200 whr/mi is an estimation, and an optimistic one at that. This number will grow with lights, sound, computer, etc. which will make our total range worse. Still, other improvements to the car can lower this value. These are the games you play with numbers while working with electric cars.