17/03/10

ELECTRIC PILL No 3

Charge Systems for Electric Cars

Electric cars can basically be “filled up” by means of a standard charge or a “fast charge”.
Standard Charge
A standard charge supplies power without altering its flow as concerns the time taken for the charge or the charge level of the battery. As a rule, a standard charge system takes a lot of time to charge the batteries and it can also degrade them or even damage their capacity. This type of recharge can supply the battery either with a steady voltage or a steady current. With a steady voltage system the current goes down to zero when the batteries are charging, and this operation doesn’t need any monitoring. With a steady current, instead, when the charging operation is nearly at the end, the system has to be equipped with a device that switches it off in order to avoid that the accumulator may be damaged. A smart battery charger, that is equipped with an electronic monitoring device, usually starts up thanks to a steady current and switches off with a steady voltage charge. The smarter the battery charger is, the better the monitoring of the different modes. Furthermore, according to the charge level of the battery different charge modes can be set, thus avoiding to impair the battery pack as little as possible. A standard charge takes about six to eight hours to fully charge a pack of batteries.

Fast Charge
Fast charge systems require complex battery chargers, specifically designed for the use of the battery they have to recharge. General-purpose battery chargers, that is working on all types of batteries, have to be equipped with a device able to identify the type of battery and choose the proper mode of charge. The batteries are charged at a steady rate of current (C-rate) between 0.5 and 1. When the battery voltage is at its peak then it drops, thus causing a fast full charge. To get a fast charge a high current must be let into the battery but on this purpose a high voltage of the battery charger, that is a high delta V, is required. The higher the voltage, the better the current (Coulomb/time) and the shorter the time taken to charge the batteries. This system can charge a battery pack by 80% of its full capacity in less than 30 seconds.