Electrochemical Accumulators: Types, Parameters & Usage
Electrochemical Accumulators
Electrochemical accumulators store energy. Common types include nickel-cadmium and lead-acid.
Lead-Acid Accumulators
Lead-acid accumulators consist of 2V independent vessels or a 6-cell monoblock (12V total), connected in series. The electrolyte is a diluted sulfuric acid solution (density between 1.1 and 1.30 g/cm³) acting as a conductive element between the battery plates. A single cell has a voltage of 2V (2.6V when loaded, 1.7V when discharged), while a monoblock has 15.6V and 10.2V respectively. Measurements can be taken using an electrolyte density meter or a multimeter.
Gassing State
At the end of the charging process, active materials become scarce, and some current decomposes water into oxygen and hydrogen, which are released as gases.
Electrolyte Stratification
Changes in electrolyte concentration occur during charging and discharging.
Panel Placement
Place accumulators as close as possible to the panels, using appropriate connecting plates to avoid hot spots and voltage drops.
Accumulator Arrangement
Separate batteries with space between them for easy handling.
Safety Measures
Use insulated wrenches, a multimeter, distilled water, cloths, a density meter, caustic soda, neutral petroleum jelly, goggles, and gloves when handling accumulators.
Accumulator Parameters
Nominal Capacity
The amount of electricity (Q) a battery provides until exhausted (Ah). Calculated as H x coefficient x 100.
Depth of Discharge
The percentage of total capacity used. Normal surface discharge is 15-20%, deep discharge is 40-50%, and very deep discharge can reach 80%. Deep discharges shorten battery life. Routine discharge is typically 25-30%.
Discharge-Charge Cycle
This is typically a daily cycle.
Self-Discharge
The daily consumption demand on the battery. The ratio is important for battery performance, which is the useful energy provided.
Temperature Effects
Temperature affects nominal capacity. The ideal range is 15-25°C, with 20°C being optimal. Lower temperatures decrease capacity, while higher temperatures risk gassing. Temperatures below -25°C can freeze the electrolyte.
Nickel-Cadmium Accumulators
Nickel-cadmium accumulators have a voltage of 1.2V and can handle a discharge depth of 85-90%. They are maintenance-free for up to 10 years.
Memory Effect
If the battery is not fully charged before starting the charging process, its capacity may decrease over time. They are not superior to lead-acid batteries due to the memory effect, high self-discharge, cadmium pollution, and lower slow discharge capability.
Accumulator Association
For greater capacity (ampere-hours) and higher voltages, two or more accumulators can be connected in series or parallel.
Parallel Connection
Used to increase capacity (Ah). Cross-connections ensure more homogeneous discharge. It is not advisable to parallel more than two accumulators.
Series Connection
Used to increase the voltage of a single accumulator.
Regulators
The main functions of a regulator are to control charging and discharging. It should be placed near the battery, free from gas emissions, in a ventilated area below 45°C, and protected from leaks. Weather conditions can affect it.
Shunt-Series Regulators
Series regulators are preferred because shunt regulators dissipate more power.
Regulator Parameters
- Nominal Voltage: The voltage for which the regulator was designed.
- Rated Current: The intensity typically handled by the regulator.
- Energy Consumption: The energy consumed by the regulator itself.
- Control System: The regulator’s ability to function at two or three stages.
Two-Level Regulators
These regulators have two stages: a rapid charging stage at approximately 14.7V and a float stage at 13.5V.
Regulator Protections
Regulators offer protections against overload, over-discharge, over-voltage, over-current, temperature issues, short circuits, and polarity inversion. They also provide voltage selection, battery type selection, user information, control voltage for each stage, and storage history.
Inverters
Inverter Types
- Square Wave: Suitable for TVs, PCs, and small equipment.
- Modified Sine Wave: Ideal for lighting.
- Pure Sine Wave: Offers the best quality and performance (over 90%), ideal for induction motors.
Placement
Inverters are placed between the batteries and consumer items.
Inverter Effectiveness
The ratio between power reaching the load and the input power (N = Pout / Pin). It is important to approach the unit to avoid power loss.
High Efficiency
High efficiency maximizes output power.
Auto-Restart
If the inverter disconnects due to excessive load, it will automatically reconnect when the problem is resolved.
Converter Protections
- Short Circuit: The converter opens and stops working.
- Overload: Delayed activation to handle increased overhead.
- Input Surge: The converter disconnects and reconnects automatically after the surge.
- Low Input Voltage: The inverter disconnects and resets when the voltage returns to normal.
- High Operating Temperature: The system disconnects until the temperature drops to a safe level.
Oversizing Converters
It is recommended to oversize converters to accommodate additional electrical elements.
Accumulator Types Based on Use
Lead-Acid Batteries
- Traction Batteries: Deep discharge (80% in 8 hours), cycled for difficult conditions, require frequent maintenance, used in trucks and electric vehicles.
- Starting Batteries: Discharge with high currents, support cycling, used to start cars and trucks.
- Stationary Batteries: Low daily cycle, low maintenance, low self-discharge, used in difficult maintenance facilities and emergency systems.