Types of lead acid batteries

[Korn]

Thought I would start off with a bit of information on types of lead acid batteries, reason for lead acid batteries is because they are still the cheapest technology on the market that is reliable and available

 

Lets first understand the different parts of a battery:

 

Cell

The cell is the basic electrochemical unit in a battery consisting of a set of positive and negative plates divided by separators, immersed in an electrolyte solution and enclosed in a case. In a typical lead-acid battery, each cell has a nominal voltage of about 2.1 volts, so there are 6 series cells in a nominal 12-volt battery. 

 

Active Material

The active materials in a battery are the raw composition materials that form the positive and negative plates, and are reactants in the electrochemical cell. The amount of active material in a battery is proportional to the capacity a battery can deliver. In lead-acid batteries, the active materials are lead dioxide (PbO2) in the positive plates and metallic sponge lead (Pb) in the negative plates, which react with a sulfuric acid (H2SO4) solution during battery operation.

 

Electrolyte

The electrolyte is a conducting medium that allows the flow of current through ionic transfer or the transfer of electrons between the plates in a battery. In a lead-acid battery the electrolyte is a diluted sulfuric acid solution, either in liquid (flooded) form, gelled or absorbed in glass mats. In flooded nickel-cadmium cells, the electrolyte is an alkaline solution of potassium hydroxide and water. In most flooded battery types, periodic water additions are required to replenish the electrolyte lost through gassing. When adding water to batteries it is very important to use deionised water, as even the impurities in normal tap water can poison the battery and result in premature failure.

 

Grid

In a lead-acid battery the grid is typically a lead alloy framework that supports the active material on a battery plate, and which also conducts current. Alloying elements such as antimony and calcium are often used to strengthen the lead grids, and have characteristic effects on battery performance such as cycle performance and gassing. Some grids are made by expanding a thin lead alloy sheet into a flat plate web. Others are made of long spines of lead with the active material plated around them forming tubes, or what are referred to as tubular plates.

 

Plate

A plate is a basic battery component, consisting of a grid and active material, sometimes called an electrode. There are generally a number of positive and negative plates in each battery cell, typically connected in parallel at a bus bar or inter-cell connector at the top of the plates. A pasted plate is manufactured by applying a mixture of lead oxide, sulfuric acid, fibers and water on to the grid. The thickness of the grid and plate affect the deep cycle performance of a battery. In automotive starting or SLI type batteries many thin plates are used per cell. This results in maximum surface area for delivering high currents, but not much thickness and mechanical durability for deep and prolonged discharges. Thick plates are used for deep cycling applications such as for forklifts, golf carts and other electric vehicles. The thick plates permit deep discharges over long periods, while maintaining good adhesion of the active material to the grid, resulting in longer life.

 

Separator

A separator is a porous, insulating divider between the positive and negative plates in a battery, used to keep the plates from coming into electrical contact and shortcircuiting, and which also allows the flow of electrolyte and ions between the positive and negative plates. Separators are made from microporous rubber, plastic or glass-wool mats. In some cases, the separators may be like an envelope, enclosing the entire plate and preventing shed materials from creating short circuits at the bottom of the plates.

 

Element

An element is defined as a stack of positive and negative plate groups and separators, assembled together with plate straps interconnecting the positive and negative plates.

 

Terminal Posts

Terminal posts are the external positive and negative electrical connections to a battery. A battery is connected in a PV system and to electrical loads at the terminal posts. In a lead-acid battery the posts are generally lead or a lead alloy, or possibly stainless steel or copper-plated steel for greater corrosion resistance. Battery terminals may require periodic cleaning, particularly for flooded designs. It is also recommended that the clamps or connections to battery terminals be secured occasionally as they may loosen over time.

 

Cell Vents

During battery charging, gasses are produced within a battery that may be vented to the atmosphere. In flooded designs the loss of electrolyte through gas escape from the cell vents it a normal occurrence, and requires the periodic addition of water to maintain proper electrolyte levels. In sealed or valve-regulated batteries the vents are designed with a pressure relief mechanism, remaining closed under normal conditions, but opening during higher than normal battery pressures, often the result of overcharging or high temperature operation. Each cell of a complete battery unit has some type of cell vent. Flame arrestor vent caps are commonly supplied component on larger, industrial battery systems. The venting occurs through a charcoal filter, designed to contain a cell explosion to one cell, minimizing the potential for a catastrophic explosion of the entire battery bank.

 

Case

Commonly made from a hard rubber or plastic, the case contains the plates, separators and electrolyte in a battery. The case is typically enclosed, with the exception of inter-cell connectors which attach the plate assembly from one cell to the next, terminal posts, and vents or caps which allow gassing products to escape and to permit water additions if required. Clear battery cases or containers allow for easy monitoring of electrolyte levels and battery plate condition. For very large or tall batteries, plastic cases are often supported with an external metal or rigid plastic casing.

 

 

 

 

 

 

 

 

 

[Korn]

Battery Classification:

 

SLI Batteries (Automotive Batteries)

Starting, lighting and ignition (SLI) batteries are types of lead-acid batteries designed primarily for shallow cycle service, most often used to power automobile starters. These batteries have a number of thin positive and negative plates per cell designed to increase the total plate active surface area. The large number of plates per cell allows the battery to deliver high discharge currents for short periods. While they are not designed for long life under deep cycle service, SLI batteries are sometimes used for PV systems in developing countries where they are the only types of battery locally manufactured. Although not recommended for most PV applications, SLI batteries may provide up to two years of useful service in small stand-alone PV systems where the average daily depth of discharge is limited to 10-20%, and the maximum allowable depth of discharge is limited to 40-60%.

 

Motive Power or Traction Batteries

Motive power or traction batteries are a type of lead acid battery designed for deep discharge cycle service, typically used in electrically operated vehicles and equipment such as golf carts, fork lifts and floor sweepers. These batteries have a fewer number of plates per cell than SLI batteries, however the plates are much thicker and constructed more durably. High content lead-antimony grids are primarily used in motive power batteries to enhance deep cycle performance. Traction or motive power batteries are very popular for use in PV systems due to their deep cycle capability, long life and durability of design.

 

Stationary Batteries

Stationary batteries are commonly used in non-interruptible power supplies (UPS) to provide backup power to computers, telephone equipment and other critical loads or

devices. Stationary batteries may have characteristics similar to both SLI and motive power batteries, but are generally designed for occasional deep discharge, limited cycle service. Low water loss lead-calcium battery designs are used for most stationary battery applications, as they are commonly float-charged continuously.

 

 

 

 

[Wetkit]

Great explanation there, thanks Korn.

 

Could you please elaborate on the difference between High Cycle and Deep Cycle batteries?

[Korn]

High Cycle

Typically a flat plate battery that needs to be used frequently but only a small amount of the capacity is removed from the battery but at high currents, ie. 5 to 15% capacity removed and replaced 10 to 20 times a day.

Would typically be used in a hybrid vehicle where the motor starts stops frequently, or a hybrid application where you want your generator to run fewer hours in a day.

 

Deep Cycle

True deep cycle would be a tubular plate. This is a battery that gets discharged 60% to 80% over a period of a day or more. So it is a small amount of power that gets drawn out of a battery over a longer period of time.

[Korn]

Deep cycle batteries for big off grid PV systems:

Maintenance batteries:

OPzS - Tubular Flooded

 

Maintenance free:

OPzV - Tubular Gel

 

Beware of the 12V 100Ah batteries, like the Delkor or Royal, these are good for small camping systems, but will only last for 2 to 3 years. Not good to run houses off!

[Regie]

Hi Korn

Would like to know if you have nay information on the following batteries:  Nortstar NSB 110FT? I cannot find any info on the performance in off-grid application.

It's a year later know but your discussion on batteries is very informative. A lot of people tend to forget that in winter you get less out off your batteries then in summer. Batteries like temperatures between 22 and 27 degrees. Also if you put 60amps in  it does not equate to 60amps out, you should be putting in 30% more than what you take out. (people don't forget rate of charge and rate of discharge=battery bank size) 

It's winter and it's always tough this time of year in off-grid applications.

Thanks