Battery charger noise reduction by frequency switching

1. A method of charging a battery in a charging system having a power convertor that converts AC electrical power to DC electrical power, the method comprising:

operating the power convertor at a first frequency during a first charging phase of the charging system;

monitoring a power output value of the power convertor during the first charging phase, wherein a predetermined criterion is satisfied when the power output value drops below a threshold power output value;

ending the first charging phase upon determining that the predetermined criterion is satisfied; and

subsequent to ending the first charging phase, operating the power convertor at a second frequency during a second charging phase of the charging system, wherein the first frequency is different than the second frequency, and operation of the power convertor the first frequency at a first power output value causes audible noise at a lower level than operation of the power convertor at the second frequency at the threshold power output value.

2. The method of claim 1 , wherein the first frequency is at least one of 20 percent higher or 20 percent lower than the second frequency.

3. The method of claim 1 , wherein the first frequency is at least one of 50 percent higher or 50 percent lower than the second frequency.

4. The method of claim 1 , wherein the first frequency is higher than the second frequency.

5. The method of claim 1 , wherein the first frequency is lower than the second frequency.

6. A method of charging a battery in a charging system having a power convertor that converts AC electrical power to DC electrical power, the method comprising:

operating the power convertor at a first frequency during a first charging phase of the charging system;

monitoring a power output value of the power convertor during the first charging phase of the charging system;

ending the first charging phase upon determining that the power output value of the power convertor has dropped below a threshold value; and

subsequent to ending the first charging phase, operating the power convertor at a second frequency during a second charging phase of the charging system, wherein the first frequency is different than the second frequency and the first frequency is at least one of 20 percent higher than the second frequency or 20 percent lower than the second frequency.

7. The method of claim 6 , wherein operation of the charging system at the first frequency at a first power output value causes audible noise at a lower level than operation of the charging system at the second frequency at the first power output value.

8. The method of claim 7 , wherein the first frequency is at least one of 50 percent higher than the second frequency or 50 percent lower than the second frequency.

9. A method of charging a battery in a charging system having a power convertor that converts AC electrical power to DC electrical power, the method comprising:

operating the power convertor at a first frequency during a first charging phase of the charging system;

monitoring an elapsed time value measured from the time at which the first charging phase commences;

ending the first charging phase upon determining the elapsed time value has reached a threshold value; and

subsequent to ending the first charging phase, operating the power convertor at a second frequency during a second charging phase of the charging system, wherein the first frequency is different than the second frequency and operation of the power convertor at the first frequency at a first power output value causes audible noise at a lower level than operation of the power convertor at the second frequency at the first power output value.

10. The method of claim 9 , wherein the first frequency is at least one of 20 percent higher than the second frequency or 20 percent lower than the second frequency.

11. The method of claim 9 , wherein the first frequency is at least one of 50 percent higher than the second frequency or 50 percent lower than the second frequency.