Method and apparatus to provide fixed frequency charging signals to a battery at or near resonance
A battery charger with a fixed frequency charging signal at or near the resonant frequency of the battery to be charged is presented. The present invention utilizes a microprocessor to modulate a current source at or near the resonant frequency of the battery to be charged without the use of a PLL. To simplify conventional modulated battery chargers, the PLL or other methods of phase correction are removed, reducing most of the calculation requirements for adjusting the phase angle, thereby reducing the piece count and ultimately cost and complexity. The result is a solution wherein charging occurs at or near the resonant frequency of the battery, and although suboptimal, the results are superior to traditional charging methods.
1. A method of charging a battery, comprising:
establishing a natural resonant frequency of each battery of a group of batteries each having a common characteristic, at least some of the batteries in the group having different resonant frequencies;
establishing a group resonant frequency being a function of the resonant frequencies of the group of batteries, wherein the established resonant frequencies of the batteries in the group are correlated to establish a band of the group resonant frequency; and
applying a charging current to a battery in the group at the group resonant frequency.
2. The method as specified in claim 1 wherein the established resonant frequency of each said battery is a function of the common characteristic of the respective battery when its state-of-charge (SOC) is substantially less than 100%.
3. The method as specified in claim 2 wherein each said battery resonant frequency is established over a range of SOC.
4. The method as specified in claim 2 wherein the established resonant frequency of each said battery is a function of the common characteristic of the battery at a SOC being less than 50%.
5. The method as specified in claim 4 wherein the SOC is less than 40%.
6. The method as specified in claim 5 wherein the SOC is about 30%.