Chargers for NiMH batteries are similar to NiCd systems but require more complex electronics. To begin with, the NiMH produces a very small voltage drop at full charge and the NDV is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and degenerating cell match diminish the already minute voltage delta further ( SONY VGN-FZ battery ).

A NiMH charger must respond to a voltage drop of 8 to 16mV. Making the charger too sensitive may terminate the fast charge halfway through the charge because voltage fluctuations and noise induced by the battery ( SONY Vaio VGN-FZ battery ) and charger can fool the NDV detection circuit. Most of today’s NiMH fast chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.

NiMH batteries that are allowed a brief overcharge deliver higher capacities than those charged by less aggressive methods. The gain is approximately 6 percent on a good battery ( Sony VGP-BPS8 battery ). The negative is shorter cycle life. Rather than 350 to 400 service cycles, this pack may be exhausted after 300.

NiMH batteries should be rapid rather than slow charged. Because NiMH does not absorb overcharge well, the trickle charge must be lower than that of NiCd and is set to around 0.05C. This explains why the original NiCd charger cannot be used to charge NiMH batteries( Sony VGP-BPS8 ).

It is difficult, if not impossible, to slow-charge a NiMH battery. At a C?rate of 0.1C and 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery ( VGP-BPS8 VGP-BPS9) is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100 percent charge. Overcharge could occur even though the NiMH battery feels cool to the touch.

Lower-priced chargers may not apply a fully saturated charge. The full-charge detection may occur immediately after a given voltage peak is reached or a temperature threshold is detected ( Sony VGP-BPS10 battery ). These chargers are commonly promoted on the merit of short charge time and moderate price. Some ultra-fast chargers also fail to deliver full charge.

Charging Lithium Ion

Whereas charges for nickel-based batteries are current limiting devices, Li-ion chargers are voltage limiting. There is only one way to charge lithium-based batteries. The so-called ‘miracle chargers’, which claim to restore and prolong batteries ( Sony VGP-BPS11 battery ), do not exist for lithium chemistries. Neither does a super-fast charging solution apply. Manufacturers of Li-ion cells dictate very strict guidelines in charge procedures.

The early graphite system demanded a voltage limit of 4.10V/cell. Although higher voltages deliver more capacity, cell oxidation shortened the service life if charged above the 4.10V/cell threshold. This problem has been solved with chemical additives ( Sony VGP-BPS11 ). Today, most Li-ion cells are charged to 4.20V with a tolerance of +/?0.05V/cell.

The charge time of most chargers is about 3 hours. The battery remains cool during charge. Full charge is attained after the voltage has reached the voltage threshold and the current has dropped low and leveled off .

Increasing the charge current does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer. Figure 2 shows the voltage and current signature of a charger as the Li-ion cell passes through stage one and two ( SONY VGN-FZ battery  ).

Figure 2: Charge stages of a Li-ion battery. Increasing the charge current on a Li-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer.

Some chargers claim to fast-charge a Li-ion battery ( VGP-BPS9 )n one hour or less. Such a charger eliminates stage 2 and goes directly to ‘ready’ once the voltage threshold is reached at the end of stage 1. The charge level at this point is about 70 percent. The topping charge typically takes twice as long as the initial charge.

No trickle charge is applied because Li-ion is unable to absorb overcharge. Trickle charge could cause plating of metallic lithium, a condition that renders the cell unstable. Instead, a brief topping charge is applied to compensate for the small self-discharge the battery and its protective circuit consume. Depending on the battery, topping charge may be repeated once every 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05V/cell and turns off at 4.20V/cell.

What if a battery is inadvertently overcharged? Li-ion batteries are designed to operate safely within their normal operating voltage but become increasingly unstable if charged to higher voltages. When charging above 4.30V, the cell causes lithium metal plating on the anode; the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up .

Much attention has been placed on the safety of Li-ion to prevent over-charge and over-discharge. Commercial Li-ion battery packs contain a protection circuit that prevents the cell voltage from going too high while charging. The upper voltage threshold is typically set to 4.30V/cell. Temperature sensing disconnects the charge if the cell temperature approaches 90°C (194°F); and a mechanical pressure switch on many cells permanently interrupt the current path if a safe pressure threshold is exceeded. Exceptions are made on some spinel (manganese) packs containing one or two small cells (VGP-BPL8 )The charge process of a Li-ion Polymer is similar to Li-ion. These batteries use a gelled electrolyte to improve conductivity.

Charging at High and Low Temperatures

Rechargeable batteries work under a reasonably wide temperature range. This, however, does not automatically permit charging at these extreme conditions. While hot or cold temperatures cannot always be avoided, recharging a battery is at the control of the user. Efforts should be made to charge at room temperatures. No commercial battery should be charged below freezing.

Nickel-based batteries should only be fast-charged between 10°C to 30°C (50°F to 86°F). Below 5°C (41°F), the ability to recombine oxygen and hydrogen is greatly reduced and the resulting pressure build up may cause the cells to vent.
The charge acceptance of nickel-based batteries  at higher temperatures is drastically reduced. A battery that provides a capacity of 100 percent if charged at moderate room temperature only accepts 70 percent if charged at 45°C (113°F). This explains the poor performance of vehicular chargers in the summer.

The Li-ion batteries offer reasonably good charge performance throughout the temperature range. Below 5°C (41°F), the charge should be with less than 1C. Charging at freezing temperatures must be avoided because plating of lithium metal could occur .

The Cadex Universal Conditioning Chargers (UCC) feature a built-in temperature sensor that applies a trickle charge if the battery is too cold. No charge is applied if too hot. These advanced chargers use reverse load charge and detect the full charge by NDV, dT/dt sensing and timers. Intelligent battery  adapters configure the charger to the correct charge algorithm. The UCC chargers are available in single, dual and six bay (Figure 3) configurations. The two-bay unit is designed for vehicle mounting.

Summary

Commercial fast-chargers are often not designed in the best interests of the battery. The two common battery SONY Vaio VGN-FZ battery ). killers are high temperature during charge and incorrect trickle charge after charge.
Choosing a quality charger makes common sense. This is especially true when considering the high cost of battery replacements and the frustration poorly performing batteries create. In most cases, the extra money invested in a more advanced charger is returned in longer lasting and better performing batteries.

An ASUS laptop quietly on display at CES packed two GPUs, a high-end NVIDIA GeForce 310, and a humble Intel GMA… and intelligently switched, second-by-second, between them. The UL80JT can also re-clock its Intel Core i7 CPU on a second-by-second basis. The result of all this micromanagement: miraculous 12-hour battery life in a high-end laptop, available later this year for just over $1,000.

Laptop design is at least partially a tradeoff between components and VGP-BPS8 SONY VGN-FZ battery life; laptops jammed with high-end components last an hour or two, while power-sipping netbooks can last all day. ASUS is trying to close the gap by allowing its laptops to decide how much power is needed and spend their power budgets more intelligently.

Apple’s solution for dual GPUs on the Macbook Pro requires the user to change settings under “Energy Saver,” which is counterintuitive and makes you log out in order to switch. It wouldn’t surprise us if owners never use this feature, Pavilion TX1000 battery.

ASUS’s solution is different because it’s user-transparent; even a novice user will get the fullest possible benefit because the laptop itself is deciding when to switch.

The same principle applies to the dynamic CPU clocking. ASUS includes a desktop widget to track CPU clock speed. While using the UL80JT, I could see it moving up and down with what I did—up with program openings and CPU-intensive processes, and way down at idle. Between the GPU switching, dynamic clocking, and ASUS’s other power management features, the UL80JT manages to consume less than half as much power as the unibody Macbook while browsing.

When it needs to, though, the UL80JT can call on all the resources of a dual-core i7 and NVIDIA’s latest GPU, holding its own with similarly-specced laptops achieving a fraction of its battery life in casual use. For ASUS, the optimizations involved in battery life planning have really paid off, liberating the user from the choice between performance and battery life in the laptop purchasing decision. Inspiron 6400 battery  dell latitude d630 battery

With the demand for batteries rapidly growing, battery manufacturing may be outpacing the supply of suitable equipment to test them. This void is apparent in the mobile phone market where large quantities of batteries are being returned under warranty. Many are discarded without first checking or attempting to restore them. The dealers are simply not equipped to handle the influx of returned batteries, neither is the staff trained to perform this task on a customer service level. Testing and restoring batteries ( Dell Inspiron 6400 battery ) has become a complex procedure that lies outside the capabilities of most customer service clerks.

With the move to maintenance-free batteries and the need to test larger volumes of batteries, battery test equipment is shifting to quick testing and boosting. In this article we examine the duty of the modern charger and battery (Sony VGP-BPS9 battery)analyzer, and observe how well these units satisfy the current demands.

Conditioning ChargersCharging batteries is often not enough, especially when it comes to nickel-based chemistries. Periodic maintenance is needed to optimize battery life. Some innovative manufacturers offer chargers with conditioning features. The most basic models provide one or several bays with discharge capability. More advanced chargers include a display to reveal the battery capacity. Discharging lithium-based batteries  for the purpose of prolonging life is neither necessary, nor advisable.

Some chargers offer pulse charge methods. This is done to improve charge efficiency and reduce the memory phenomenon on nickel-based batteries. Improved charge performance is achieved by using a pulse charge that intersperses discharge pulses between charge pulses. Commonly referred to as ‘burp’ or ‘reverse load’ charge, this method promotes high surface area on the electrodes and helps recombine the gases generated during charge. Pulse charging benefits mainly Nickel-based batteries (HP Pavilion TX1000 battery).

Some manufacturers claim that the pulse charge method conditions and restores NiCd batteries and makes the periodic discharges redundant. Research carried out by the US Army has revealed that pulse charging does indeed reduce the crystalline formation on the NiCd battery. If properly administered, batteries  charged with these pulse chargers prolong service life. For batteries with advanced memory, however, a full discharge or recondition cycle is needed to break down the more stubborn crystalline formation.

Battery AnalyzersThere are two types of battery analyzers: the fixed current units and the programmable devices. While fixed current units are less expensive and generally simpler to operate, programmable analyzers are more accurate and faster. Programmable units can better adapt to different battery needs and are more effective in restoring weak batteries .

Fixed current analyzers perform well in organizations that use medium size batteries ranging from 600mAh to 1500mAh. If smaller or larger batteries are serviced, the charge and discharge currents are compromised and the program time is prolonged. Here is the reason why.

A fixed current battery analyzer with a charge and discharge current of 600mA, for example, services a 600mAh battery in about three hours, roughly one hour for each cycle starting with charge, followed by discharge and a final charge. Servicing an 1800mAh battery would take three times as long. A very small batteries, say a 400mAh, may not be capable of accepting a charge rate that is higher than 1C and the battery (VGP-BPL8 ) could sustain damage.

When purchasing a battery analyzer, there is a tendency to buy on price. With the need to service a larger volume of batteries of a wider variety, second-generation buyers find the advanced features on upscale models worth the extra cost. These features manifest themselves in reduced operator time, increased, throughput, simpler operation and the use of less trained staff. Adaptation to new battery systems is also made easier. Figure 1 illustrates an advanced battery (HP Pavilion DV9000 battery )analyzer made by Cadex Electronics.

An advanced battery analyzer evaluates the condition of a battery and implements the appropriate service to restore the battery’s performance. On nickel-based systems, a recondition cycle is applied automatically if a user-selected capacity level cannot be reached.

Battery chemistry, voltage and current ratings are user-programmable. These parameters are stored in interchangeable battery adapters and configure the analyzer to the correct function when the adapter is installed. In the Cadex 7000 Series battery (SONY VGN-FZ battery )analyzers, for example, each adapter is preprogrammed with up to ten distinct configuration codes (C-codes) to enable service for all batteries with the same footprint.

Battery-specific adapters are available for all major batteries; user-programmable cables with alligator clips accommodate batteries for which no adapter is on hand. Batteries with shorted, mismatched or soft cells are identified in minutes and their deficiencies are displayed on the LCD panel.

User‑selectable programs service different battery  needs. In the case of the Cadex 7000 Series, Primeprepares a new battery for field use and Auto tests and reconditions weak batteries. Custom allows the setting of unique cycle sequences composed of charge, discharge, recondition, trickle charge or any combination, including rest periods and repeats.

Many battery analyzers are capable of measuring the internal battery resistance. Obtained in only a few seconds, the resistance reading works well with lithium-based batteries because the level of cell resistance is in direct relation to the performance. Internal resistance readings can also be used for nickel-based batteries, however, the readings do not accurately disclose the battery’s condition.

More accurate methods are achieved by using quick test programs. The CadexQuicktest™ is based on fuzzy logic and lasts about three minutes. Good results are achieved with three learn cycles taken from batteries of different SoH readings. The matrices from the learn cycles are stored in the adapters. Most battery adapters are equipped with the matrices when purchased.

New requirements of battery( Pavilion DV9000 battery ) analyzers are the ultra-fast charge and quick prime features. When a battery is inserted, the analyzer evaluates the battery, applies an ultra-fast charge if needed, and prepares the battery for service within minutes. Such a feature helps the mobile phone industry to handle the large number of warranty return batteries. With the right equipment, many of these presumably faulty batteries can be jump-started and given back to the customer instead of being replaced.

To accurately test batteries that power digital equipment, modern battery analyzers are capable of discharging a battery under a simulated digital load. The GSM waveform, for example, transmits voice data in 567 ms bursts with currents of 1.5A and higher. By simulating these pulses, the performance of a battery can be tested under these field conditions. Not all analyzers are capable of simulating such short current bursts. Instead, medium-priced battery  analyzers use lower frequencies.

Another application involving uneven load demand is the so-called 5‑5‑90 program used to simulate the runtime of analog two-way radios. The battery is loaded 5 percent of the time on transmit, 5 percent on receive and 90 percent on standby. Other combinations are 10-10-80. Each stage can be programmed to the appropriate discharge current. Because of the complex load conditions, calculating the predicted runtime in the absence of a battery analyzer would be difficult.

Easy operation is an important attribute of any battery (Thinkpad T43p battery) analyzer. Displaying the battery capacity in percentage of the nominal capacity rather than in milliampere-hours (mAh) is preferred by many. With the percentage readout, the user does not need to memorize the ratings of each battery tested because this information is stored in the system. The percentage readout allows an added level of automation by implementing a recondition cycle if the set target capacity level cannot be reached.

Some analyzers are capable of setting the appropriate battery parameters automatically when a battery is inserted. An intelligent battery adapter reads a passive code that is imbedded in most batteries. The code may consist of a jumper, resistor or specified thermistor value. Some battery packs contain a memory chip that holds a digital code. On recognition of the battery, the adapter assigns the correct service parameters. Automatic battery   identification minimizes training and allows battery service by untrained staff.

Most analyzers are capable of printing service reports and battery labels. This feature simplifies the task of keeping track of batteries. Marking batteries with the service date reminds the user when a battery is due for service. Labeling works well because the basic service history is available where it is needed most — on the battery.

A battery analyzer should be automated and require minimal operator time. His or her task should be limited to scheduling incoming batteries for testing, marking the batteries (VGP-BPS8 ) after service, and replacing those that did not meet the performance criteria. Occasional selection of the correct current rating and chemistry may also be necessary.