Monday, March 29, 2010

Methods of discharge : C-Rate

Methods of discharge : C-Rate

The task of a battery is to store energy and deliver it in a desired time and a controlled way again. In this section, we will discharge the laptop battery at different C-examine the DOD to assess attitudes, in which a battery can be discharged without danger. We will also observe how deep discharges can affect the life expectancy of a battery.

What is the C-rate?

The charging and discharging of a battery is known as the C-coefficient. Most portable batteries are set to 1C. This means that a Dell laptop battery with 1000mAh can submit a current of 1000mA for one hour, when the coefficient is 1C. If the same battery is discharged at 0.5 C, they are at 500mA from 2 hours. At 2C, the 1000mAh battery delivers 2000mA for 30 minutes. 1C is often referred to as 1-hour discharge, a 0.5 C would mean a 2-hour, and a 0.1 C, a 10-hour discharge.

The capacity of a Toshiba PA3535U-1BRS battery is usually measured with a battery analyzer. If the declaration is made for the capacity of the analyzer in percent of rated capacity, 100% would be shown if a 1000mAh battery can deliver this current for 1 hour. If the battery lasts only 30 minutes until shutdown is displayed 50%. A new battery sometimes provides more than 100%.

If a battery is discharged with an analyzer that is capable of using various Entladekoeffizienten C, higher capacitance values are observed when the Toshiba PA3400U-1BRS battery is discharged with a lower C-coefficients and vice versa. When unloading a 1000mAh battery at 2C, i.e. 2000mA, the analyzer is programmed so that he takes the full capacity within 30 minutes. Theoretically, the capacitance measurement should be the same as at a slower discharge, since the same energy is collected only in a shorter time. Due to internal energy losses and a voltage reduction, the battery will quickly reach the lower Spannungsabschalteschwelle and capacity measurement may therefore fall to around 95%. A discharge the same battery of 0.5 C, i.e. 500mA, while 2 hours can increase the capacity resulting measurement of approximately 105%. The differences in the capacity measurements with different C-coefficients have a relationship with the internal resistance of the battery.

A Toshiba PA3421U-1BRS battery that at 1C discharge is not working well, is the portable sealed lead-acid battery. To get a reasonably good capacity measurement, the manufacturers usually recommend one of these batteries Entladekoeffizienten of 0.05 C ie 20 hours. Even at such a slow discharge, it is difficult to reach a capacity of 100%. As compensation for the various measurements at several discharge currents, manufacturers offer a so-called capacity balancing. The capacity compensation is used to correct the reading of the capacity value. He in no way increases the battery life, it corrects only the capacity calculation when using smaller or larger C-coefficients than those that are specified by the manufacturer.

Lithium-Ion/Polymer Toshiba PA3591U-1BRS batteries are electronically protected against high discharge. Depending on the battery model, the discharge current is limited between 1C and 2C. This protective measure will cause lithium-ion batteries for biomedical applications and tools that have a high inrush current that can not be used.

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