Battery - Design and Function (Convertible): Specifications Volvo C70 I

Capacity

The capacity of a fully charged battery is its ability to give a constant current during a certain time and is stated in the unit ampere-hours (Ah). The time for discharging varies depending on the battery's purpose.

In principle, the capacity is controlled by the plates' area as well as thickness. In a battery there is a big area on the plates, on which chemical reactions can take place, and also where a great amount of electrons (current) can be generated between the plates. This gives them a higher cold-start current value (CCA = Cold Cranking Amperes).

A start battery has big area but thin plates.

For a deep cycle battery, e.g., battery for leisure use, it is important that the chemical process can continue for a long time with lower current use, that is why the plates have to be thick. This gives them many ampere-hours or "spare minutes". Since the plates are thick, they need longer time to charge so that the chemical reaction also takes place deep inside the plates.

For start batteries, 20 hours' capacity (K20) is mentioned. This refers to how much current the battery can deliver during 20 hours in an ambient temperature of +25°C (+77°F) without the terminal voltage going below 10.5 V.

Example: A battery (of open type) with a stated capacity of 70 Ah should be able to provide a constant current of a max. 3.5 A (3.5 A x 20 h = 70 Ah) for 20 hours.

The capacity of a battery is not only dependent on the size and construction of the battery, but also varies considerably for batteries of the same type with the size of the discharge current. The lower the discharge current the higher the capacity and vice versa. The capacity of the battery is also affected by the temperature and the age of the battery. The nominal value is given at +° (+77°F). The capacity of the battery reduces considerably at low temperatures.

The table shows the difference in capacity in a battery at +25°C (+77°F) and -18°C (-0.4°F).

Differences in capacity at +25°C (+77°F) and -18°C (-0.4°F)

Scheme 18

The service life of the battery depends primarily on its construction, maintenance and operating conditions. The following factors may shorten the service life of the battery

1. «High temperatures»(ref-403978-S26154079562011061000000)
2. «Cycling»(ref-403978-S00860112762011061000000)
3. «Low electrolyte level»(ref-403978-S22430896502011061000000)
4. «Deep discharging»(ref-403978-S02790041242011061000000)
5. «Incorrect charging»(ref-403978-S17950361642011061000000)
6. «Sulfation»(ref-403978-S39644140802011061000000)
7. «Corrosion»(ref-403978-S13222959782011061000000)
8. «Vibrations»(ref-403978-S17437574562011061000000)

To maintain the best possible service life and capacity, the battery must be maintained and charged in accordance with Volvo's recommendations.

The capacity is the ability of a fully charged battery to provide a constant current over a certain time and is given in ampere-hours (Ah). The time taken to discharge depends on the intended use of the battery. For starter batteries one refers to 20 hours capacity (K20). This refers to the amount of current the battery can provide over 20 hours at an ambient temperature of +25°C (+77°F) without the pole voltage falling below 10.5 V.

Example: A battery with a listed capacity of 70 Ah should be able to provide a current of a maximum 3.5 A (3.5A x 20h = 70 Ah) for 20 hours.

Reserve capacity, RC

The reserve capacity, RC, is measured in minutes and is, according to the SAE norm, the time taken to discharge a fully charged battery at 25 A to a voltage of 10.5 V at a temperature of +25°C (+77°F). The reserve capacity is the length of time the battery is able to supply necessary components with current when the generator (GEN) in the car is not functioning. Volvo batteries are marked with the RC value according to the SAE norm.