2011年6月17日星期五

Cycle Battery life at elevated charge voltages

Chargers for cellular phones, laptops and digital cameras bring the Li-ion battery to 4.20V/cell. This allows maximum runtime, and the consumer wants nothing less than optimal use of the battery capacity. The industry, on the other hand, is more concerned with longevity and prefers lower voltage thresholds. Satellites and electric vehicles are examples where longevity is important.

We have limited information by how much lower charge voltages prolong battery life; this depends on many conditions, as we have learned. What we do know, however, is the capacities. At a charge to 4.10V/cell, the battery holds a capacity that is about 10 percent less than going all the way to 4.20V/cell. In terms of optimal longevity, a charge voltage limit of 3.92V/cell works best but the capacity would be low. Besides selecting the best-suited voltage thresholds, it is also important that the inspiron 1520 batteryvostro 1500 battery does not stay in the high-voltage stage for a long time and is allowed to drop after full charge has been reached.

The voltage threshold of commercial chargers cannot be changed, and making it adjustable would have advantages, especially for laptops as a means of prolonging battery life. When running on extended AC mode, the user would select the “long life” mode and the battery would charge to only, say, 4.05V/cell. This would get a capacity of about 80 percent. Before traveling the user would apply the “full charge mode” to bring the charge to 4.20V/cell. This saturation charge would take about an hour and would fill the inspiron 1520 batteryvostro 1500 battery to 100 percent capacity.

Realizing the stress on the battery, some laptop and cellular phone manufacturers choose an end-of-charge voltage that is less than 4.20V/cell. A slightly larger pack compensates for the reduced runtime. Another option to extend battery life is removing the pack from the laptop when running on the power grid. The Consumer Product Safety Commissionadvises the public to do this out of concern for overheating and causing a fire. Removing the battery has the disadvantage of losing unsaved work on power failure.

Heat buildup is always a concern and running a laptop in bed or on a pillow may contribute to this by restricting airflow. Not only will heat stress electronic components, elevated temperature causes the electrodes in the battery to react with the electrolyte and this will permanently lower the capacity. Placing a ruler or other object under the laptop to increase floor clearance improves air circulation around the enclosure and keeps the unit cooler.

The question is often asked: Should I disconnect my laptop from the power grid when not in use? Under normal circumstances this should not be necessary because once the lithium-ion battery is full, a correctly functioning charger will discontinue the charge and will only engage when the inspiron 15 battery, inspiron 1525 battery voltage drops to a low level. Most users do not remove the AC power, and I like to believe that this practice is safe.

Everyone wants to keep the battery as long as possible and use it in a way that is least stressful. This is not always feasible. Sometimes we need to run the battery in environments that are not conducive to optimal service life. As a doctor cannot predict how long a person will live based on diet and activity alone, so also does the life of a battery vary, and it can always be cut short by an unexpected failure. Batteries and humans share the same volatility.

To get a better understanding of what causes irreversible capacity loss in Li-ion batteries,inspiron 15 battery, inspiron 1525 battery, several research laboratories* are performing forensic tests. Scientist dissected failed batteries to find suspected problem areas on the electrodes. Examining an unrolled 1.5-meter-long strip (5 feet) of metal tape coated with oxide reveals that the finely structured nanomaterials have coarsened. Further studies revealed that the lithium ions responsible to shuttle electric charge between the electrodes had diminished on the cathode and had permanently settled on the anode. This results in the cathode having a lower lithium concentration than a new example, a phenomenon that is irreversible. Knowing the reason for such capacity loss might enable battery manufacturers to produce future batteries with longer life spans.

Power loss through Protection Circuit
Besides common aging, a Li-ion gk479 , fk890 battery can also fail because of undercharge. This occurs if a Li-ion pack is stored in a discharged condition. Self-discharge gradually lowers the voltage of the already discharged battery and the protection circuit cuts off between 2.20 and 2.90V/cell. Some chargers and battery analyzers (including those from Cadex) provide a wake-up feature, or “boost,” to re-energize and recharge these seemingly dead Li-ion batteries.

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