Any hobbyist can charge a battery quickly, but can you charge it without exploding, overheating, or a significant drop in battery cycle life?
A number of companies already manage fast charging technologies, often using specialized algorithms. These algorithms take into account the battery chemistry and certain non-standard charge rate curves. Many device makers and wireless carriers now offer at least two years of warranty on smartphone devices, setting 800 cycles as the battery cycle life of the battery.
I haven’t seen many (if any) life test results published by any fast charger supplier using popular battery types. Chargetek is one of these companies willing to publish a lifetime test. Together with Potential Difference, Inc., they managed to safely return 51% of the charge in 25 minutes. Their technology is based on proven patents, chemical analysis and above all validation of the technology through extensive testing.
Their technology uses batteries ranging from lithium-ion 18650 cells to 20,000Ahr cells. Their technology is also applicable to lead-based batteries such as Absorbent Glass Mat (AGM), Sealed Lead Acid (SLA) and maintenance-free batteries. Lithium cobalt oxide and lithium iron phosphate can also use this fast charging technology.
I spoke with Chargetek’s CEO, Lou Josephs, and we discussed their proprietary software that they can customize for their customers’ applications. A nice feature of their patented and proven algorithm is that they can quickly charge two large battery packs from a single charger. Each bank will be independently regulated.
Josephs explains how this works:
The battery charger has two ports, one for each battery pack. Battery pack 1 and battery pack 2 are charged and discharged alternately. In the graph below, the battery voltage curve is shown in green, the battery charge current is shown in red, and the battery discharge current is shown in purple.
A positive voltage slope (increase in voltage) occurs during charging. A negative slope (voltage drop) occurs during discharge. The flat areas are the rest periods of the charging cycle. Thanks to our patented algorithm, the magnitude of the positive charging current can be three to four times that of conventional chargers.
Industry standard charge current is based on the battery’s ampere-hour (Ahr) rating and is expressed in C. For example, if each battery pack is 500Ahr, the standard charge rate would be in the range of C/3 – C/5 resulting in a charge current range of 100 – 170 amps. Varies depending on the characteristics of a specific battery.
For this particular application, the charge current will be set at 2C (1000A), with a 50% duty cycle and a charge rate of C or 500 amps. The discharge current is slightly subtracted from it. The resulting charging time is approximately 1.1 hours. This charging time is two to three times faster than that achievable with conventional chargers. With a traditional charger, the charging current will be limited to a maximum of C/3 or 170 amps.
Since only one charger is needed for two battery packs, the savings can be substantial. In addition, at least twice as many battery packs can be charged simultaneously. All in all, our chargers have four times the charging capacity of conventional chargers.
Limitations of Batteries During a Charge Cycle
There are three inherent battery limitations during a charge cycle;
1. Maximum battery voltage
2. Maximum battery temperature
3. Maximum allowable charging current
Exceeding any of these parameters can result in undercharging, overcharging, overheating, or physical degradation. The challenge is to maintain significant charge acceptance while charging at elevated currents.
The traditional high-current charging method will cause concentration polarization and electrochemical polarization.
To restore 51% capacity (71% of total capacity) of a 3000mAhr capacity battery in 25 minutes, an average current of 3.7 amps is required:
Average Current = 51% x Amp Hour Capacity x (60min/25min) = 3.7 Amps
The manufacturer’s recommended average charge current is 0.883 amps.
How does Chargetek’s algorithm maintain battery safety and life while delivering the required current? Their algorithm circumvents the physical limitations of the battery:
· Reduces electrochemical polarization by providing regular rest periods for uniform dispersal of ions between the two electrodes
Eliminates concentration polarization by applying a relatively short duration reverse pulse before or after the positive charge pulse
Continuously monitor temperature, voltage and charge acceptance, and continuously adjust the parameters of the charging algorithm based on feedback
Chargetek’s algorithms enable charging at exceptionally high currents by reducing heat-generating charge acceptance issues and electrochemical polarization.
Chargetek’s fast charging technology consists of three basic components:
1. Charging current pulse: amplitude (I C ) and duration (t C ) are shown in red. Typically a charging current of two to three times the battery’s amp-hour rating is used.
2. Discharge current pulse: amplitude ( ID ) and duration (t D ) are shown in blue. The magnitude of this current is equal to or greater than the magnitude of the charging current. The duration is a fraction of the charging current.
3. Rest time: battery current is zero (t R)
Battery temperature, rate of temperature change, battery voltage and current are continuously monitored and regulated by proprietary PDI/Chargetek software throughout the charging process. The parameters of the algorithm are adjusted in real time during the charging process.
Chargetek’s patented fast battery charging technology is key to the growth of electric vehicles, allowing users of mobile phones, laptops, power tools and more to be freed from power outages and quickly charge off-the-shelf batteries in minutes without overheating.
(1) Electric vehicle charging stations require fast charging with off-the-shelf batteries, similar to refueling. The Chargetek’s 20 minute time is close, and the state-of-the-art is 40 minutes.
(2) In industrial vehicles, 95% of forklifts are forced to replace 1 ton batteries between shifts because the fast battery charging alternative takes about 3.5 hours but often overheats and damages the battery, releasing toxic fumes. Chargetek eliminates these problems and saves industrial fast charging up to 75% and doubles revenue for car charging stations.
(3) Owners of devices such as cell phones, laptops, and power tools often have to wait hours for recharging. Chargetek’s 20-minute fast battery charge can solve 110-volt outlet problems.