How to calculate the capacity and discharge capacity of lead-acid batteries

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author：enerbyte source：本站 click120 Release date： 2024-07-15 08:50:31

abstract：

At present, there are two types of electric vehicle batteries: lead-acid batteries and lithium batteries! Lead acid batteries have capacities of 12AH, 14AH, 20AH, and 24Ah. However, the capacity of lithium batteries may not be the same, as they can be combined to produce high-capacity batteries such...

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The capacity of an electric vehicle battery represents the amount of stored electrical energy, that is, after the electric vehicle battery is fully charged, it is continuously discharged at a certain battery value, from the beginning of discharge until the terminal voltage drops to the specified discharge termination voltage. The product of discharge current and time represents the capacity unit of the electric vehicle battery in ampere hours, usually expressed in "Ah". After the electric bicycle specific battery is fully charged, it should be left to stand in an environment with a temperature of (25 ± 2) ℃ for 1-4 hours, and then discharged at a constant current (A) of 1/2 of the rated capacity of the battery (2-hour rate) until the average voltage of the individual battery reaches 1.6V (4.8V for a 6V battery and 9.6V for a 12 V battery), and the discharge time should be recorded. The new electric vehicle battery is considered qualified if the discharge time exceeds 120 minutes in one of the three tests. The actual discharge current of an electric vehicle multiplied by the actual discharge hours is the actual capacity of the battery.

The capacity of electric vehicle batteries depends on the amount of active substances and electrolyte involved in electrochemical reactions. The manufacturing process, geometric shape and size of the electrode plate, as well as the temperature during battery use, also have an impact on the measured actual capacity. The more plates there are, the larger the relative area, and the more active substances involved in chemical reactions, the larger the electric vehicle battery; The higher the temperature during battery use, the stronger the penetration ability of electrolyte into the plates, and the deeper the active substances involved in chemical reactions, resulting in larger electric vehicle batteries.

The commonly used valve regulated lead-acid batteries on electric vehicles mainly come in two standard specifications: 6-DZM-10 and 6-DZM-20. Here, "6" refers to six clusters connected in series inside the battery. The former has a 2Hr capacity of 10 ampere hours (Ah), while the latter has a 2Hr capacity of 20Ah. Some manufacturers also use 12V10Ah/2Hr and 12V20Ah/2Hr labels. In order to adapt to more designs, after adjusting the shape, thickness, quantity, electrolyte concentration, and ratio of active substance usage of battery plates, there are also models such as 6-DZM-7, 6-DZM-12, 6-DZM-17, 6-DZM-18, and 6-DZM-24.

1. MAh "is a unit of battery capacity, known in Chinese as milliampere hour (for the convenience of measuring large capacity batteries such as lead-acid batteries," Ah "is generally used, and the Chinese name is ampere hour).

1mAh=0.001 ampere * 3600 seconds=3.6 ampere seconds=3.6 coulombs

2. Coulomb is a unit of electricity, not a basic unit of the International System of Units, but a special unit of the International System of Units. 1 coulomb equals 1 ampere second.

The amount of electricity transported within 1 second with a current of 1A, i.e. 1C=1A · s.

3. Power calculation formula: P=UI. The unit of P is watts (W); In a pure resistance circuit, according to Ohm's law, U=IR can be substituted into P=UI to obtain: P=I * IR=(U * U)/R

1、 The most direct algorithm:

1. First, obtain the current of the electrical equipment

2. The usable duration is obtained by dividing the battery capacity by the current of the electrical device

For example:

A 3000mAH battery with a rated voltage of 5V supplies power to an electrical device with a power consumption of 2.5W and a voltage of 5V. Its theoretical usage duration is:

I=P/U=>2.5w/5v=>0.5A=>500MA

3000mAh means a current of 3000MA can discharge for one hour,

3000/500=6 hours

2、 Using the Coulomb algorithm for charge quantity

C=IS=>3A * 3600s=>10800c Coulomb (charge)

10800c * 5v=54000w electrical energy

54000w/2.5w=21600/3600s=6h

Algorithm for UPS backup time 2010-03-25 15:20

Calculation method for UPS battery discharge time

1) Calculate the maximum discharge current value of the battery:

I-maximum=Pcos ф/(η * E critical * N) Note: P → nominal output power of UPS power supply

Cos ф → Output power factor of UPS power supply (usually 0.8 for UPS)

The efficiency of the EPS inverter is generally 0.88-0.94 (0.9 can be taken in actual calculations)

E-critical → critical discharge voltage of battery pack (12V battery is about 10.5V, 2V battery is about 1.7V)

N → Number of batteries per group

2) Based on the backup time of the selected battery pack, determine the required discharge rate value C of the battery pack, and then use:

The nominal capacity of the battery pack=Imax/C time and discharge rate C

15 minutes 30 minutes 60 minutes 90 minutes 120 minutes 180 minutes 1.98C0.92C0.61C0.5C0.42C0.29C

3) For example, a delay of 15 minutes for 400KVA

The maximum discharge current of the battery is 1058A=nominal power 400000VA × 0.8 ÷ (0.9 efficiency * 32 cells * 10.5V discharge voltage per cell)

The nominal capacity of the battery pack is 1058A ÷ 1.98C=534.3AH

The total capacity of the battery pack is 534.3AH × 32 cells × 12V=205171.2AH, therefore the configuration includes 12V150AH and 32 cells

Definition: The electrode is mainly made of lead and its oxides, and the electrolyte is a type of battery with sulfuric acid solution. English: Lead acidity. In the discharge state, the main component of the positive electrode is lead dioxide, and the main component of the negative electrode is lead; In the charging state, the main component of both positive and negative electrodes is lead sulfate. Divided into exhaust type batteries and maintenance free lead-acid batteries.

The battery is mainly composed of a tubular positive electrode plate, a negative electrode plate, an electrolyte, a separator, a battery compartment, a battery cover, a pole, and a liquid injection cover. The electrodes of an exhaust battery are composed of lead and lead oxide, and the electrolyte is an aqueous solution of sulfuric acid. The main advantages are stable voltage and low price; The disadvantages are low specific energy (i.e. the amount of stored electricity per kilogram of battery), short service life, and frequent daily maintenance. The lifespan of old-fashioned ordinary batteries is generally around 2 years, and it is necessary to regularly check the height of the electrolyte and add distilled water. However, with the development of technology, the lifespan of lead-acid batteries has become longer and maintenance has become simpler.

The most obvious feature of lead-acid batteries is that they have a plastic sealing cover that can be unscrewed at the top, and there are also ventilation holes on top. These injection caps are used for adding pure water, checking electrolyte, and discharging gases. In theory, lead-acid batteries need to check the density and liquid level of the electrolyte during each maintenance, and if there is a shortage, distilled water should be added. But with the upgrading of battery manufacturing technology, lead-acid batteries have developed into maintenance free lead-acid batteries and gel maintenance free batteries. Lead acid batteries do not require the addition of electrolyte or distilled water during use. The main purpose is to use the positive electrode to generate oxygen, which can be absorbed at the negative electrode to achieve oxygen circulation and prevent moisture reduction. Lead acid water batteries are mostly used in tractor, tricycle, car starting, etc., while maintenance free lead-acid batteries have a wider range of applications, including uninterruptible power supplies, electric vehicle power, electric bicycle batteries, etc. Lead acid batteries are divided into constant current discharge (such as uninterruptible power supply) and instantaneous discharge (such as car starter batteries) according to application needs.

When discharging, the concentration of sulfuric acid solution will continuously decrease. When the density of the solution drops to 1.18g/ml, it should be stopped for charging

Charging: 2PbSO+ 2H? O=PbO?+Pb+2H?SO? (Electrolytic cell)

Lead acid battery

Lead acid batteries (4 sheets)

Discharge: PbO+ Pb+2H? SO?=2PbSO?+2H? O (primary battery)

Anode: PbSO+ 2H? O－2e‐===PbO?+4H﹢+SO? 2‐

Cathode: PbSO+ 2e‐===Pb+SO? 2‐

Negative electrode: Pb+SO? 2‐－2e===PbSO?

Positive electrode: PbO+ 4H﹢+SO42‐+2e‐===PbSO?+ 2H? O