Battery Charging Circuits consist of three main elements: Battery, Battery management system, charging source. This system could change depending on the battery or charging source but should be a good basis point. This page will go over how to choose the proper battery and BMS system given a charging source.
|Charging Source||Voltage Type||Harnessing Type||Efficiency (1 [worst - 5 [best])|
|Thermoeletric Peltier||DC||Temperature Change||1|
|DC Motor||DC||Mechanical Rotation||4|
|Generator (AC motor)||AC||Mechanical Rotation||5|
|Piezoelectricity||AC||Mechanical lateral Oscillation||3|
The charging source is the most important element and will be the starting point of this project. The charging source device depends on the energy it is trying to harvest. For instance, if there is a huge difference in temperature in a given location, you would use thermoeletric peltier devices. If there is a temperature difference between each side of the device, a constant DC voltage will be made available between the prongs. The chart to the right will give important information on the different types of charging sources. Note: The voltage output depends on many factors and should be tested for each design. The Efficiency factor is an estimated number; the Efficiency factor mostly depends on the device and how the energy is harnessed.
Each storage element has different pros and cons and ultimately depend on the application at hand. For example, if the design is trying to extract solar energy to charge parked electric cars, then the amount of storage should be huge, while weight and size shouldn't be a concern. By knowing that the weight and size is not a concern, the cost of the storage elements can be reduced heavily. A chart to the right will show the pros and cons of each storage element type.
Battery Management System
The Battery management system (BMS) is used so that the battery can be safely charged and discharged. If a BMS isn't used, the battery can be overcharged which will cause the battery to lose capacity and power. A battery is charged when current is forced backwards into the battery. However, when having batteries in series, each battery cell should be monitored in that series configuration. (This is not the same with cells in parallel) That being said, all series connection lithium ion based chemistry cells must be monitored. Furthermore, most BMS systems have a charging port on them which will take care of the charging mechanism. For instance, if wind electricity is being harnessed, if the voltage to charge the cell must be around 4V and the wind turbine is outputting 5V, then the BMS charging circuit will step that down to the appropriate 4V.