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Lead-acid battery - device and principle of operation, varieties

 

The design and functioning of a classic lead-acid battery are based on the reversible electrochemical reactions of lead and lead dioxide with an aqueous solution of sulfuric acid: when the battery is discharged to a load, lead oxide at the cathode and lead at the anode, interacting with sulfuric anions, turn into lead sulfate ( lead dioxide is reduced at the cathode, lead is oxidized at the anode).

Powerful battery for forklifts

When the battery is charging, lead sulfate on the plates decays into ions, lead oxide forms on the cathode, and metallic lead again on the anode. In this case, the concentration of the sulfuric acid solution increases, since the sulfuric acid ions reuniting with hydrogen again form sulfuric acid. Thus, it is possible to use the same battery again and again, simply recharging it from time to time.

Chemical processes in the battery

In the process of discharging the battery, the concentration of sulfuric acid decreases - the density of the electrolyte decreases. And when, at the end of charging, the amount of lead sulfate on the electrodes is almost exhausted, the process of water electrolysis begins to take over. This phenomenon can be observed in the form of an abundance of oxygen and hydrogen bubbles, which is a sign of overcharging a lead-acid battery, and many motorists know firsthand about it.

It is better not to allow such a phenomenon, because in this case, firstly, water is irreversibly consumed, and secondly, there is a danger of explosion. Therefore all normal charging device reduce the charge current upon reaching a certain voltage at the terminals of the rechargeable battery. As for water losses, they are traditionally replenished by adding distilled water to the battery.

Battery diagram

In fact, inside the case of a 12-volt lead-acid battery, there is a battery of six cells connected in series with each other - cells. One cell (the maximum voltage of one such cell is 2.17 volts) consists of two electrodes and separation plates - separators, which do not chemically interact with the electrolyte, but interfere with contact between the electrodes.

The electrodes are pure lead lattices, with lead dioxide powder pressed into the anode lattice and lead powder pressed into the cathodic lattice. Powders are used here in order to maximize the area of ​​interaction of the electrodes with the electrolyte, and thereby obtain the largest possible electric capacity of the battery, since the electrodes are immersed in the electrolyte. Batteries of 3, 6 or 12 cells give 6, 12 and 24 volts at the battery terminals, respectively.


Car starter battery (with liquid electrolyte)

Car starter battery

Classic car batteries - acid batteries, with liquid electrolyte, for a nominal voltage of 12 volts. The lid of such a battery has 6 holes with plugs for easy maintenance - you can check the density of the electrolyte using a hydrometer, if necessary, add distilled water. The range of capacities is from 35 to 230 A * h; they provide starting currents from 330 to 1500 A.

The task of such a battery is to crank the starter at the time of starting the car, as well as power the on-board network (headlights, devices, on-board consumers through the cigarette lighter, etc.) Batteries of this format on liquid electrolyte are gradually becoming a thing of the past, giving way to more modern batteries with thickened electrolyte .


Gel batteries (GEL) for UPS, security systems, etc.

UPS gel battery

In household uninterruptible power supplies (UPS, UPS) (see - How are the UPSs arranged and working?), in the power supply circuits of alarm systems and other similar applications, are sealed lead-acid batteries with a thickened electrolyte - gel batteries.

The liquid acid electrolyte here is thickened to a paste-like consistency with an aqueous alkaline solution of sodium silicates (Na2Si2O4). Batteries of this type do not require maintenance and topping up with distilled water. Gel batteries are available on capacities from 1 to 100 A * h.


AGM Technology

A better version of the gel battery is a maintenance-free lead-acid battery with porous separators made of fiberglass (Absorbent Glass Mat), which allows more severe charging and operating conditions. A distinctive feature of AGM technology is the use of a glass fiber-impregnated porous aggregate-filled porous aggregate.

The micropores of such a material are not completely filled with electrolyte, and the volume free of electrolyte is used here for gas recombination. The battery, manufactured by AGM technology, has several advantages: vibration resistance, normal performance in any position (the main thing is not to have upside down, as there are emergency valves on top).

See also at i.electricianexp.com:

  • How to calculate battery charger settings
  • What is battery self-discharge?
  • Gel batteries and their use
  • The device and the principle of battery operation
  • Popular Battery Types

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