Lead Acid Battery

Overview

Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile starter motors.

Care and maintenance

Lead-acid batteries are a relatively fragile system component. Without diligent care and maintenance, they will become a significant expense. It is important to understand the mechanisms of failure and damage so they can be avoided.

Sulfation and desulfation

It is estimated that 80% of all lead-acid batteries are prematurely discarded because of sulfation .

Sulfation

Sulfation occurs during normal battery operation. When the battery is working properly, a thin layer of sulfate forms on the battery plates during discharge, and dissolves back into the battery acid during charging. Problems from sulfation occur when the sulfate forms a hard crystalline shell that isn't dissolved during charging. Over time, the sulfate crystals grow to cover most of the surface area of the lead plates, reducing capacity. Eventually, the sulfate crystals expand and crack the plates, destroying the battery.

Before complete sulfation occurs, the battery becomes less efficient and is able to hold less charge. The capacity of the battery is reduced to a non-useful level, and the battery is discarded before it is mechanically destroyed.

Causes of sulfation

When batteries do not get a strong enough charging current to dissolve the sulfate frequently enough, sulfation problems can occur. This is primarily a problem in batteries which sit unused for long periods of time. RVs, farm equipment, or a battery left in storage can have this issue.

Another cause of sulfation which may not be obvious is an over-sized battery or battery bank. In this situation the charging current isn't strong enough to fully dissolve the sulfate during the charge cycle. An example here could be an off-grid solar system.

Sulfation will occur especially quickly if the battery is not fully charged for an extended period of time. Higher temperatures will also increase the speed of the sulfation reaction.

Common behaviors which can cause sulfation

Here is a list with some common things that can cause sulfation:

• Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler weather.
• Battery is stored without some type of energy input.
• "Deep cycling" an engine starting battery. Remember these batteries can't stand deep discharge.
• Undercharging of a battery to only 90% of capacity will allow sulfation of the battery using the 10% of battery chemistry not reactivated by the incompleted charging cycle.
• Heat of 100 plus F., increases internal discharge. As temperatures increase so does internal discharge. A new fully charged battery left sitting 24 hours a day at 110 degrees F for 30 days would most likely not start an engine.
• Low electrolyte level - battery plates exposed to air will immediately sulfate.
• Incorrect charging levels and settings. Most cheap battery chargers can do more harm than good. See the section on battery charging.
• Cold weather is also hard on the battery. The chemistry does not make the same amount of energy as a warm battery. A deeply discharged battery can freeze solid in sub zero weather.
• Parasitic drain is a load put on a battery with the key off. More info on parasitic drain will follow in this document.

Desulfation

Battery desulfation is a relatively modern development within the last few decades. Previously the only way to remove sulfation buildup was essentially over-charging the battery, called equalization. This method is still used by some battery chargers. However, this practice shortens the battery life. Another option has been chemicals which dissolve the sulfate.

In the summer of 2000 a circuit for a desulfator was published in Home Power magazine. The article describes pulsing the battery at it's resonant frequency, which is anywhere between 2 - 6 MHz.

Using pulses to remove sulfate is called pulse conditioning. These can be simply current pulses or there can be a frequency component as described by Alastair. Certain patents may prevent all desulfators from using the same method.

Pulse conditioning products

It appears that BatteryMINDer was one of the first companies to produce a pulse conditioning desulfator and they have "patented frequency sweep technology" which may be superior to some other products.

Battery Mossing

Battery mossing is the accumulation of debris on the top edges of the negative plates. Over time, small particles in the electrolyte precipitate, resulting in a layer of sediment being deposited. When this buildup becomes thick enough, it causes a short circuit which results in a defective battery. To help prevent this, some battery manufacturers install a thin plastic shield (battery element protector) on top of the plates.

Research/Construction

• Lead Acid Battery Construction
• http://windpower.org.za/batteries/batteries.html explores the principles of lead acid batteries and how to possibly construct them.

References

• Battery
• Batteries
• Lead-Acid Battery Treatment
• Wikipedia:Lead–acid battery
  • [10] Wikipedia entry on lead-acid battery sulfation and desulfation
  • [11] Industrial Deep Cycle Batteries L16's, T105's, and ForkLift batteries.