Electronic Engineering (EE) Times
June 16, 1997

"Battery Charger adapts to various chemistries"

By Ashok Bindra
Norcross, GA. - A novel rapid-charging scheme developed by Advanced Charger Technology Inc. (ACT) promises to cut battery-charging time by more than half for a variety of rechargeable chemistries. ACT has already used its Ultra-Rapid™ technology in a nickel-cadmium-based charger for two-way radios, and it intends to create similar solutions for cellular phones and other portable products.
    Based on charge waveforms, the scheme enables rapid charging without overheating the device. It also eliminates the memory effect-the bane of rechargeable batteries. Whereas conventional chargers require the battery to be fully drained before it is  recharged, the ACT product can charge even a partially drained battery, according to the developer.
    ACT's engineers are in the process of extending the Ultra-Rapid™ charging solution to nickel-metal-hydride (NiMH) and lithium-ion cells. The NiMH system is presently in field test.
   The fast-charging scheme can dynamically adapt to the chemical process, said Karen Robinson, president of ACT. "This efficient, fast and economical charging solution will open the door for battery-powered devices that weren't practical before," she said.

Accommodates larger cells
The base two-way-radio battery charger is designed to handle six NiCd cells with a capacity of 600 mA-hr at 7.2 V. With an adapter, however, the unit is scalable to accommodate larger cells, for battery capacities up to 1.8 A-hr, said Joe Pendergrass, vice president of engineering.
    Typical charging time for the six-cell 600-mA-hr NiCd battery is 20 minutes, rising to about 30 minutes for a battery pack with a capacity of 1,100-mA-hr. The basic Ultra-Rapid charger retails for $140.  The field tests indicate that the batteries continue to maintain full capacity approaching 1,600 cycles, Pendergrass said. According to ACT, the average two-way-radio battery is charged and discharged at about 250 cycles per year. At that rate, and using the Rapid charger, the NiCd batteries would last up to six years, which would almost triple the life of the battery, according to ACT.  The company is currently producing the Ultra-Rapid NiCd charger for two-way radios in its own plant, and is negotiating with contract manufacturers to ramp up production by year's end.
    The company has also licensed the charging technology to Mid-South Product Engineering (Gadsen, Ala.), and is working on similar deals with other manufacturers. The algorithm and its implementation were developed by research scientist Yury Podrazhansky, a Russian emigré who is part of the R&D team at ACT. The implementation is based on the principle of dynamic electrochemical waveform, whereby the charger monitors the battery's voltage, temperature and current levels, and adjusts charge waveforms for optimal battery conditions.
    Unlike conventional constant-current or constant-potentia techniques, Podrazhansky's algorithm exploits pulse-charging schemes, Pendergrass said. It uses a low-end 8-bit micro-controller from Microchip Technology Inc. (Chandler, Ariz.) to implement the algorithm and to keep costs low.
    Furthermore, on-chip memory is sufficient to incorporate the algorithm without the need for any external memory. In addition to the micro-controller, the two-chip solution also uses a de/de buck regulator, according to Pendergrass.

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