Charger technology uses improved ion balancing
A new algorithm for recharging waveforms leads to short duty times and decreased deterioration of the electrochemical processes in batteries.
Today, even the smallest company can conduct global business with the right equipment. Laptop computers and cellular phones, two-way radios and hand-held scanning devices are no longer luxuries for top executives or mega-companies_they are required equipment, enabling workers at every level to produce efficiently. However, this mobile equipment, while becoming more powerful every day, still has an Achilles’ heel_undependable battery performance.
Batteries designed to power mobile equipment seldom perform to manufacturers’ standards after the first few uses_a weakness that can render the best business tools in the world useless. Because of this increased use of mobile technology, rechargeable batteries have accounted for a larger share of the battery market in recent years and have become a multibillion-dollar business.
Batteries are a dependent commodity_useless without chargers. Many chargers are so inefficient, they actually destroy the batteries slowly, or contribute to performance problems that have become the nemesis of portable convenience.
Original equipment manufacturers (OEMs) want to replace their nickel cadmium (NiCd) batteries with a lighter, higher-capacity, and most importantly, reliable battery. Battery research in recent years has developed nickel metal hydride (NiMH) batteries, lithium-ion (Li-ion) batteries and a few other smaller players. However, these improvements are not without drawbacks_high costs, short cycle life, limited power capabilities and, with NiMH, a memory effect of its own. In spite of the emergence of these new battery types offering increased power density, NiCd batteries still hold the lion’s share of the market and will continue to do so because of cost, potential life cycles and proven performance. Although it is true that they can demonstrate problems such as memory effect_which reduces charge capacity and cycle life with proper handling and charging_NiCd batteries can continue their role as the affordable, rechargeable workhorse.
Ironically, even though OEMs improve and release new products every year and billions are spent on battery research, little attention is being paid to the charger. This “little companion box” that comes with these products may be the cause, and eventually the solution, to many of these battery shortcomings.
A patented dynamic electrochemical wavelength (DEW) charging technology improves battery performance, recovers lost capacity and turns cumbersome battery-care procedures into a simple, one-step process.
For professional users of all portable products, dependable battery power is critical to staying on the job. A suitable charger was developed in response to the frustrations heard from the field. Public safety, transportation, government, military and utilities professionals, service and field personnel alike have asked for a solution to battery woes that hinder productivity and compromise safety. The charger was designed to provide a new technology that not only charges more efficiently, and thus faster, than other products, but that provides a dependable, maximum-capacity charge every time while extending battery life.
The standard OEM or consumer-priced battery charger is a “constant-current trickle charger.” A trickle charger operates by delivering a steady, low-level, positive current for as long as it is connected to a power supply. Ions are generated at one electrode in a battery cell and must move to the other electrode. If the current is sustained over an extended period, the ions concentrate on one side and create polarization, which causes heat generation, inadequate charging capacity and a shorter life for the battery.
These slow, “overnight chargers” rely on the user to stop them when the battery has reached its maximum capacity. They generally charge a battery fully in about 10 hours. They are inexpensive and simple to design, but they do not optimize the performance of the battery. In fact, they actually contribute to premature disposal of the batteries. The low charge rate allows the chemical reactions to be localized on the electrode surface, leading to dendrite growth. There is a high likelihood of overcharging and, in the case of NiCd and NiMH, voltage depression, or “memory effect.”
Memory effect is the great “imposter” that causes the premature demise of batteries. When NiCd batteries are recharged before they are fully discharged, electrodes passivate, decreasing the ability of the cells to accept a charge. When a battery is repeatedly charged without being fully discharged, operating time and performance deteriorate, and it appears to die before its time. Most electronic equipment will stop operating before the battery can reach a low enough per-cell voltage to recover the voltage depression, so few batteries are fully discharged before they are recharged. This practice and the standard OEM constant-current chargers combine to sabotage NiCd and NiMH battery performance.
Most OEM-upgrade fast chargers operate by increasing the constant current rate, charging the battery in only two or three hours. They either have rudimentary circuitry that terminates when the battery is fully charged, or they decrease the charge current when the battery reaches a certain voltage, usually about 80%-90% charged. However, charging at a high constant-current rate ignores the electrochemical process within the battery, which, over time, causes significant deterioration, similar or worse than that caused by the trickle charger. The result is reduced capacity with each charge, untimely wear-down and an abbreviated life cycle for the battery.
Pulse-charging, introduced in the 1960s, was the first improvement to the constant-current trickle charge. Pulse-charging operates on the principle of surging power into the battery in pulses of electrical current. One-second pulses of power are interspersed with rest periods, lasting a fraction of a second. Interrupting the pulse current gives ions a chance to diffuse and distribute more evenly throughout the battery and return to normal levels routinely, thus reducing some of the negative effects of trickle charging. Although it was developed to address the chemical process of batteries, pulse charging still ignores the chemical reaction and physical phenomenon taking place in the battery. It provides short-term fixes, i.e., charged batteries, but the costs are heavy_shortened battery life and shorter charged cycles, which translates into inadequate power to support equipment for the recommended duration.
The second generation of pulse-charging emerged in the 1970s to counter the problem of recharging batteries that aren’t fully discharged. This method, used only in selected commercial chargers, augments the rest period by adding a short negative discharge pulse (depole pulse) interspersed with the positive charging pulses. The depole pulse is 2.5 times as strong as the charge pulse and is followed by another rest period. This method seemed to solve some of the problems of traditional charging. Batteries return to balance more quickly, speeding up charging rates to as quick as one hour for a 700mAh battery and improving performance. The shortcoming to this approach is that the ion transport problem gets progressively worse as the battery is charged. The single-discharge-pulse method can only gain limited information about the state of the battery, and the charge current cannot exceed the level that is acceptable at the end of the charge, when conditions are most limiting.
A new algorithm Even those OEM chargers that perform a discharge function do not discharge the voltage low enough to recapture all the hidden capacity lost to memory effect. However, a new algorithm, discovered by Yury Podrazhansky and patented by Advanced Charger Technology, discharges to the lowest possible level to return hidden memory capacity. Podrazhansky, a Russian immigrant with a background in electrical and radio frequency engineering, was busy searching for a solution to the problems plaguing his rechargeable batteries when he developed the DEW technology.
Podrazhansky, Advanced Charger Technology’s vice president of research, discovered that the negative discharge in pulse charging can cause negative effects in the reverse direction. Single, high-magnitude negative pulses cause ion transportation problems in the negative direction as well as excessive discharge of the battery, which increases charge time.
Podrazhansky found that applying even shorter, multiple, negative pulses with a higher magnitude eliminates charging problems and actually benefits battery chemistries. The higher-magnitude discharge pulses are inherently focused in the area of dendrites and help to remove them. When allowed to build up, dendrites can short-circuit a battery’s electrodes. The brief, high currents rapidly balance the ion concentration and improve the crystalline structure of the electrodes. In NiCd batteries, the currents momentarily pull the battery voltage down, resulting in a reversal of voltage depression. The improved balancing of ion concentration leads to an efficient charge process that enables a higher charge current, yielding the shortest charge times possible and actually conditioning batteries as they are charged, eliminating the need to discharge first. Podrazhansky used his discovery to develop DEW technology_a charging waveform that intersperses variable length positive charging waves with multiple negative discharge waves.
Since receiving his first patent, Podrazhansky has refined the DEW charging process [or algorithm], and, together with ACT, has developed it for commercial availability. The commercial DEW chargers come in single- and six-bay versions as shown in Photo 1 on page 24. The charge rate is faster than other fast chargers_about 30 minutes per 1,000mAh. That is about 10 times faster than a conventional trickle charger. Although one might think that with such fast charging times, chemical problems in the battery would increase, quite the opposite is true. Using microcontroller intelligence, the charger monitors each individual battery and provides the appropriate charging characteristics for that battery.
How the charger works The charger is a smart charger that provides the benefits of a conditioner. A microcontroller, as shown in Figure 1 on page 26, manages the charging process, which begins automatically when the user inserts the battery. After the battery is installed, the microcontroller determines the condition of the battery. Based on this condition, different processes can transpire, as shown in Figure 2 on page 28.
If the battery is in nominal condition_used and discharged but otherwise fine_ the charger will switch straight into rapid charge mode, conditioning the battery as it charges. The microcontroller monitors voltage and current levels as the battery is being charged, adjusting the charging algorithm to condition the battery throughout the entire process. When charging is complete, a light-emitting diode (LED) illuminates, and the charger halts automatically, delivering the battery in peak condition without overcharging. If the battery is left on the charger, the charger will maintain the battery using a proprietary process. This allows batteries to be left on the charger indefinitely.
At the beginning of the charging process, if the charger detects that the battery condition is below nominal, it will test the battery and, if necessary, slow the charge until the battery is brought into nominal range and then resume rapid charging. When a new or badly abused battery is charged for the first time, it will be reformatted by the technology.
Battery chemistries The sealed lead-acid (SLA) battery was the only game in town for more than a century. It was joined by the NiCd battery in the 1950s, and the two types still dominate the rechargeable market today. Research into new chemistries has developed NiMH, Li-ion, alkaline magnesium and zinc air batteries_all designed to give the consumer lighter-weight, longer-lasting cells. While serving their intended purpose of better performance, each of these new chemistries has its own advantages and disadvantages, and all operate on the same basic electrochemical process.
A battery is a combination of chemicals that are devoid of excess energy in their natural state. However, these chemicals are capable of storing and releasing energy through chemical reactions. Energy-storing ions are generated by an influx of electrons from an external source. Chargers provide these electrons. When they are released, electricity is generated, excess electrons are consumed and the battery slowly deteriorates to its natural state.
A battery consists of two electrodes, a negative anode and a positive cathode, with a porous separator in between. If the electrodes contact each other, the battery shorts out and becomes useless. The electrodes and separator exist in an electrolyte solution that has an initial concentration of ions that supports the chemical reaction rate and provides a medium for ion transport.
As a battery is discharged, its internal electrochemical process results in the transfer of ions from one electrode to the other through the electrolyte. When the battery is charged, the process is reversed, and the ions travel in the opposite direction. During this electrochemical process, each electrode goes through a chemical reaction that generates these ions at one electrode and consumes them at the opposite electrode.
How well this process is carried out has an effect on the overall performance of the battery. The chemical reaction rate at the electrode that is consuming ions is limited by the concentration of the ions at its surface. This concentration is related to how well the ions are able to move through the supporting electrolyte and separator. If the ion concentration across the surface of an electrode is uneven, the chemical reaction rate will not be uniform, leading to the development of dendrites_outgrowths of material from the electrode. Unchecked, dendrites can eventually grow through the separator, and the electrodes can come into contact, shorting out the battery. The charger addresses these problems by preventing dendrite buildup and maintaining even ion concentration.
Another factor in the performance of a battery centers on the crystal structure of its electrodes. A fine-grain structure reduces internal resistance and increases surface area. Under extended, low-current conditions, the slower chemical reaction rates can cause the size of the crystals to increase, reducing the surface area per unit of volume and causing a potential drop in overall battery capacity and an increase in internal resistance. This increase in internal resistance will result in lower battery capacity.
For ideal rechargeable battery performance, the charging regime should work with the electrochemical process to ensure a high uniform crystal structure at the electrode. Ion transfer should be smooth, with minimum resistance, so dendrites cannot grow and crystals remain fine. Like air flowing through a tunnel, the path should be free of obstructions that can slow it down.
Conclusion The charger, applying the DEW algorithm, is designed to work in harmony with both the electrochemical process and composition of batteries. The proven technology, which can charge a NiCd cellular phone battery in as little as five minutes, provides the breakthrough in battery charging awaited by a mobile workforce. Two-way radio users, the first to benefit from this technology, are learning that batteries no longer have to be the Achilles’ heel in job performance_and charging regimes are finally as simple a routine as putting on a uniform or taking a coffee break.
Steinberg is communications manager, and Pendergrass is vice president of engineering for Advanced Charger Technology, Norcross, GA. The company’s product, the Activator battery charger, uses the dynamic electrochemical wavelength technology described in the article.