ICCNexergy

Leaders in Rechargeable Power Systems

Virtual Voltage Termination

ICCNexergy’s VVT Charging Algorithm Eliminates the Effect of Resistive Loses in the Battery Pack and Charges the Cell Stack Inside the Battery Pack

This revolutionary new technology offers several benefits over conventional charging including faster charge, charging at lower peak power and extended cycle life. Virtual Voltage Termination (VVT) looks through the resistive losses of a battery pack’s terminals, PCBA and cell pack to measure Open Circuit Voltage (OCV), the true charge status of the battery. This function is achieved without extra contacts or impact to standard communication signals in smart battery packs. By monitoring OCV, VVT  allows the charger to charge in the constant current mode longer than conventional CC/CV chargers, greatly reducing the time spent in the constant voltage stage of charging.

VVT allows the charge time to stay consistent over the life of the battery pack regardless of degrading conditions or other component aging effects that can increase circuit impedance. This improves overall reliability and durability of a rechargeable device.

Benefits

  • Efficient and reliable method for battery charging
  • Shorter charging time than conventional CC/CV chargers
  • Charges in same time as CC/CV with 25-30% less power
  • Consistent charge time over life of battery pack
  • Implemented through software (no additional hardware cost)

Open Circuit Voltage (OCV) Measurement

The VVT enabled charger performs a low frequency switching (on/off) control of the power supply, allowing for a zero current OCV measurement of the cell/cell pack. Once the cell/cell pack OCV reaches a predetermined maximum voltage, the charger switches to constant voltage and the charger monitors the current level to the battery. Charging at the proper rate reduces stress on the cells and maximizes cycle life.

Charge Termination

Charge termination is predetermined by conventional end-of-charge current measurement and the cell manufacturer’s specification. VVT enables full termination of the charge current to prevent float charging and minimize the stress on the cell/cell pack.

The Difference Between VVT and CC/CV

VVT  incorporates Open Circuit Voltage (OCV) measurements to accurately measure battery cell voltage and eliminate the impact of series resistance. Constant Current/Constant Voltage (CC/CV) chargers do not compensate for series resistance. VVT chargers utilize cell voltage for regulation feedback and improve the CC/CV charging dynamics. By incorporating dynamic cell voltage feedback, VVT can charge with greater tolerance levels than CC/CV and therefore provide better safety characteristics.

Comparisons

Both systems charging at 0.7C, 4.2Vpc, C/10 end-of-charge current termination. Battery cell is Sony 18650GT 3.6V, 2.0Ah capacity, 0.3 Ohm resistance between charger and battery cell. The key advantage of VVT is the active transition from CC to the CV stage. This active control of the charging process enables a longer duration of the CC stage and a more precise transition to CV.

Due to internal resistance stackup, the CC/CV charger reaches the analog transition point at approximately 50 minutes. The current proceeds to taper for an additional 10 minutes until the termination criterion is achieved.

With VVT, the constant current stage extends for approximately 45 minutes longer. Once the transition to the CV stage occurs, the current taper process is significantly shorter. The overall charge is terminated in less than 100 minutes versus the 150 minutes with the CC/CV process.