batteries
Lithium Polymer (LiPo) Batteries
Summary
Lithium Polymer (LiPo) batteries are rechargeable batteries using a polymer electrolyte instead of a liquid one. They are flexible and have a higher specific energy than other lithium-battery types. LiPo batteries are popular in consumer electronics and the radio control industry due to their long run times and high power output.
Key Points
- Nominal Voltage: 3.7V per cell
- Construction: Rectangular cells connected in series and/or parallel
- Voltage Configuration:
- 1S = 3.7V - 2S = 7.4V - 3S = 11.1V - 4S = 14.8V - 5S = 18.5V - 6S = 22.2V - 8S = 29.6V - 10S = 37.0V - 12S = 44.4V
- Power and Voltage Relationship: Higher voltage means more power to drive bigger motors, but does not necessarily mean longer run times. Capacity defines run time.
- Formula: Power (P) = Voltage (U) * Current (I)
Lithium-Ion (Li-Ion) Batteries
Summary
Lithium-Ion (Li-Ion) batteries are a type of rechargeable battery that has been popular since the 1990s. They are used in a wide range of gadgets, from portable cameras to smartphones. Li-Ion batteries are known for their high energy density and lack of the "memory effect."
Key Points
- Electrolyte: Liquid chemical electrolyte, such as ethylene carbonate or diethyl carbonate
- Shape: Mostly rectangular due to chemical composition
- Disadvantages: Capacity decreases over charge cycles, discharges when not in use, and can become unstable at extreme temperatures or if punctured, leading to thermal runaway and fires
- Safety: Uses electronic controllers to regulate charging and discharge power to prevent overheating
Comparison of LiPo and Li-Ion
Summary
LiPo batteries are newer than Li-Ion batteries and use a dry solid, porous chemical, or gel-like electrolyte, allowing for a lower profile and more robust designs. They are safer than Li-Ion batteries but are more expensive and have a shorter life cycle.
Key Points
- Electrolyte: Dry solid, porous chemical, or gel-like electrolyte
- Design: Lower profile, flexible, and more robust
- Safety: Lower chance of leaking electrolytes and thermal runaway
- Disadvantages: Higher manufacturing cost, shorter life cycle, and lower energy storage compared to Li-Ion
- Protection: Uses protection circuits to keep voltages within safe limits
Voltage and Motor Performance
Summary
The voltage of a LiPo battery pack directly influences the RPM of the electric motor. Higher voltage leads to higher motor power and speed.
Key Points
- Motor Rating: Measured in kV (RPM per Volt)
- Example: A 3,500kV motor will spin 3,500 RPM for every volt applied
- Voltage Impact: 2S LiPo battery (7.4V) results in 25,900 RPM; 3S LiPo battery (11.1V) results in 38,850 RPM
- Formula: Power (P) = Voltage (U) * Current (I)