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Charging batteries quickly and safely

22 Jun 2015  | Steve Taranovich

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Limitations of batteries during a charge cycle
There are three intrinsic battery limitations during a charge cycle;

 • Maximum battery voltage
 • Maximum battery temperature
 • Maximum allowable charging current

By exceeding any of these parameters the results can be undercharging, overcharging, overheating or physical degradation. The challenge is to maintain a significant charge acceptance while charging at an elevated current.

Conventional high current charging methods can cause concentration polarisation and electrochemical polarisation.


The challenge
In order To return 51% capacity (71% total capacity) for a 3000mAhr capacity cell in 25 minutes, an average current of 3.7 amps is required:

Average current = 51% x amphour capacity x (60min/25min) = 3.7 amps

The average manufacturer recommended charging current is 0.883 amps.

How does Chargetek's algorithm provide the current required while maintaining battery safety and life? Their algorithm circumvents the battery's physical limitations:

 • Reduces electrochemical polarisation by providing regular rest periods to allow the ions to disperse evenly between the two electrodes
 • Concentration polarisation is eliminated by applying a comparatively short duration reverse pulse, either preceding or following the positive charge pulse
 • Temperature, voltage, and charge acceptance are continually monitored, and from that feedback, the parameters of the charging algorithm adjust continually

The algorithm
By reducing heat generating charge acceptance problems and electrochemical polarisation, Chargetek's algorithm is able to recharge at exceptionally high currents (figure 2).


Figure 2: Critical waveform parameters (Image courtesy of Chargetek)


Chargetek's rapid charge technique is comprised of three fundamental components:

Charge current pulse: The amplitude (IC) and duration (tC) is depicted in red. A charge current of two to three times the amp hour rating of the battery is typically employed.

Discharge current pulse: The amplitude (ID) and duration (tD) is depicted in blue. The magnitude of this current is equal or greater to the magnitude of the charge current. The time duration is a fraction of the charging current.

Rest time: The battery current is zero (tR)

During the entire charging process, battery temperature, rate of temperature change, battery voltage and current are continually monitored and modulated by the proprietary PDI/Chargetek software. The parameters of the algorithm are adjusted in real time during the charge.


Applications
Chargetek's patented fast battery charge technology is the key to the growth of electric vehicles and users of cell phones, laptop computers, power tools, etc. are not stranded without power, fast charging off-the-shelf batteries in minutes, without overheating.

Competitive Advantage:

(1) Electric automobile charging stations need fast battery charge times similar to gas refueling, using off the shelf batteries. Chargetek's 20 minute time is close while the state of the art is 40 minutes.

(2) Among industrial vehicles, 95% of forklift trucks are forced to swap 1 ton batteries between shifts as fast battery charging alternatives require about 3.5 hours but regularly overheat and damage the batteries, releasing toxic fumes. Chargetek eliminate these problems and enable up to 75% savings for industrial rapid charging and double the revenue for automotive charging stations.

(3) Owners of devices such as cell phones, laptops, and power tools are often stranded waiting several hours to recharge. Chargetek's 20 minute fast battery charge can solve that problem from a 110V outlet.


About the author
Steve Taranovich is a senior technical editor at EDN with 41 years of experience in the electronics industry. Steve received his MSEE from Polytechnic University, Brooklyn, New York, and his BEEE from New York University, Bronx, New York. He is also chairman of the Educational Activities Committee for IEEE Long Island. His expertise is in analogue, RF and power management with a diverse embedded processing education as it relates to analogue design from his years at Burr-Brown and Texas Instruments. Steve was a circuit design engineer for his first 16 years in electronics. He then served as one of the first field application engineers with Burr-Brown Corp and also became one of their first global account managers, traveling to Europe, India and China.


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