Industry News

Aug-10-2009    Can the Lead Acid Battery Compete in Modern Times?

Can the Lead Acid Battery Compete in Modern Times?
Isidor Buchmann/ CadexElectronic
The Lead Acid is the oldest rechargeable battery. Invented by the French physician Gaston Planté in 1859, lead acid serves stationary or wheeled applications where weight and size are of lesser concern. Today, the flooded lead acid battery is used in automobiles, forklifts and large uninterruptible power supply (UPS) systems.

During the mid 1970s, the maintenance-free lead acid battery was developed that could operate in any position. The liquid electrolyte was transformed into moistened separators and the enclosure was sealed. Safety valves were added to allow venting of gas during charge and discharge.

Two designations of sealed lead acid batteries have emerged: the sealed lead acid (SLA), also known as Gelcell, which serves predominantly in wheeled mobility, and the large valve regulated lead acid (VRLA), which is used for stationary applications. This article focuses on the SLA.

The SLA is not subject to memory. Leaving the battery on float charge for a prolonged time does not cause damage. The battery’s charge retention is best among rechargeable batteries. Whereas the NiCd self-discharges 40 percent of its stored energy in three months, the SLA self-discharges the same amount in one year. The SLA is relatively inexpensive to purchase but the operational costs can be more expensive than the NiCd if full cycles are required on a repetitive basis.

The SLA does not lend itself to fast charging — typical charge times are 8 to 16 hours. The SLA must always be stored in a charged state. Leaving the battery in a discharged condition causes sulfation, a condition that makes the battery difficult, if not impossible, to recharge.

Unlike the NiCd, the SLA does not like deep cycling. A full discharge causes extra strain and each discharge/charge cycle robs the battery of a small amount of capacity. This wear-down also applies to other battery chemistries in varying degrees. To prevent the battery from being stressed through repetitive deep discharge, a larger SLA battery is recommended.

The SLA provides 200 to 300 discharge/charge cycles. The primary reason for its relatively short cycle life is grid corrosion of the positive electrode, depletion of the active material and expansion of the positive plates. These changes are most prevalent at higher operating temperatures. Applying charge/discharge cycles does not prevent or reverse the trend.

Among modern rechargeable batteries, the lead acid battery family has the lowest energy density, making it unsuitable for handheld devices that demand compact size. In addition, performance at low temperatures is poor. The high lead content makes the SLA environmentally unfriendly if carelessly disposed

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Lead-Acid Battery Uses

Lead-acid Battery Info

Lead-acid batteries are truly the power behind everyday life. They keep those systems we depend on—cars, boats, public transportation —running as we move through the day. However, perhaps even more important is the function these batteries play in those times when normal life is halted—such as during a blackout or brownout. In these situations, when all other power is cut, lead-acid batteries ensure our safety by providing necessary back-up power for everything from computers to hospital emergency lighting.

In a power outage, lead industrial batteries are what back up wireless and wired telephones and computer systems so that phones stay on no computer data is lost. They power the majority of mobile vehicles both on land and sea. Lead-acid batteries start and power vehicles, back up uninterruptible operations like hospitals, railroad signals, weapons systems, and air traffic controls, and help electric utilities shift loads among grids. On the water they start engines, back up critical systems in submarines, and power navigational signals and devices in boats.

Life without lead-acid batteries would mean everything but muscle-powered transportation would stop. There would be frequent power outages as electric utility companies couldn’t handle rapid fluctuations in the demand for electricity. Every major telephone company in the world uses lead-acid batteries as back up power, keeping telephone systems working during storms, power outages, and earthquakes. They also provide quiet, pollution-free emergency power for critical operations in facilities like air traffic control towers, hospitals, railroad crossings, military installations, submarines, and weapons systems. Lead-acid batteries keep pollution control systems operating during blackouts and brownouts in environmentally sensitive manufacturing operations until the plant can be shut down. These batteries also back up cell phones and two-way radio systems.

Basic Usage Guidelines

Lead-acid batteries typically take 8 to 16 hours to charge and must always be stored in a charged state. Leaving these batteries in a discharged condition causes sulfation, a condition that makes it difficult if not impossible to charge.

Never let the open cell voltage drop significantly below 2.10 volts and be sure to apply a topping charge every six months or when recommended.

The optimum operating temperature for lead-acid batteries is 25 degrees Celsius. It is important to be aware of temperature when using and storing lead-acid batteries for every 8 degrees Celsius rise in temperature will cut the battery life in half. please see the detail lead-acid battery info. (link to: www.leadacidbatteryinfo.org/lead-acid-battery-uses.htm)

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SLA Battery Charging Practices

by Bobby George

SLA batteries are used in many different devices and for many different applications, even though a lot of people never realize they use them. These batteries are often found in devices such as electric wheelchairs, lawn trimmers, portable vacuum cleaners, electric fence generators, and security systems, just to name a few. The reason people rarely encounter one of these batteries is because they are almost completely maintenance free and remain tucked away quietly powering devices until they die or something else goes wrong.

When it comes to SLA battery charging, some folks may get a little confused because they have never had to charge this type of battery. This is often the case with security systems, electric fences, etc. where the battery is mainly used as a backup to another electrical system. In these cases, the main electrical source is used to automatically charge and maintain the battery until the electricity is cut and the battery is needed.

Many other people will need to charge their SLA batteries at one point, if not regularly. Therefore, a basic knowledge of proper SLA battery charging is a good thing to have. Proper charging and maintenance can be the difference between years of use and months of use.

It is important to remember that SLA's are very similar to the battery in your car. Therefore, general maintenance practices performed on your vehicle can usually be applied to SLA batteries as well. For example, most people have discovered that leaving a car in storage for a long period of time without starting it or charging the battery is a recipe for a dead battery in a matter of months. These batteries were designed to have a constant charge without being allowed to run down and stay down for long periods of time. So if someone with an electric wheelchair that uses SLA batteries is no going to be using the chair for an extended time period, it should be placed on a charge occasionally to reduce this effect on the batteries.

It is also important to avoid deeply discharging the batteries very often. This will cause the batteries to wear out much quicker than they should. If you application results in the batteries being drained almost completely on a regular basis, it may be time for an upgrade. With SLA's, one can upgrade the amperage (runtime) to almost any available configuration without having any effect on the use or the device. The only things to remember are that the voltage must stay the same and the batteries will get bigger, heavier, and more costly as the amperage increases. Still, if your batteries are continually drained to a very low level, an upgrade may save you money in the long run.

Bobby George is a technical consultant