Batteries Part 1 – Battery Construction
External Connections
Electrical Connections
Balance port gives access to each individual cell. However, never access individual cells to power loads via the balance port.
Number of Battery cells Vs Terminal Voltage
LiPo batteries used in RC are made up of individual cells connected in series so the battery’s voltage is the sum of the voltage of the cells.
A standard LiPo CELL has a nominal voltage of 3.7V. Battery terminal voltage is therefore how many cells in the battery are connected in series to develop that terminal voltage.
- 1S = 1 cell = 3.7V
- 2S = 2 cells = 7.4V
- 3S = 3 cells = 11.1V
- 4S = 4 cells = 14.8V
- 5S = 5 cells = 18.5V
- 6S = 6 cells = 22.2V
Example:
A 14.8V battery would have 4-cells in series. (4S)
NOTE:- A battery with more cells of the same capacity is heavier since it contains more cells.
Number of Battery cells Vs Battery Current
While the number of cells in series determined the possible battery terminal voltage, it is the number of these series strings in parallel that determine the maximum current the battery can deliver.
The alphanumeric designation for cells is therefore (for example) 3S2P. This means 3 cells in series times 2 strings in parallel. (ALL CELLS SHOULD BE IDENTICAL)
Battery Types – General Battery Types
The majority of batteries will have a sticker or some printed markings upon them, describing what type or technology they use. Relevant battery types/chemistries are listed below with typical uses.
- Alkaline : Not rechargeable. Commonly found in AA batteries and used in transmitters, TV remotes etc.
- Ni-Cd : Nickel Cadmium. Rechargeable, comparatively environmentally unfriendly and suffer from memory effect.
- NiMH : Nickel Metal Hydride. Robustly rechargeable (can be topped off) and easy to maintain.
- LiPo : Lithium-ion polymer. Higher energy density, lighter weights, consistent powerful discharge, shorter lifespan (than NiMH) more volatile than other solutions and require intelligent chargers.
What is actually Inside a LiPo ‘pouch’ cell?
Inside a LiPo ‘foil pouch’ cell you will find a long piece of very thin plastic film – the polymer!
Laminated onto the polymer are the thin lithium carbon coated aluminium & copper anode & cathode electrodes.
These are laminated in an alternating pattern on the front and back side of the polymer separator film.
Everything is saturated with a greasy solvent based organic electrolyte.
The long internal polymer film (which is over 7 feet long in the case of a 5000 mAh cell), is folded accordion style back and forth upon itself.
The entire folded material is then heat sealed into the foil pouch, along with the gelled electrolyte.
For interest:- The gelled electrolyte has a very sweet solvent smell, not dissimilar to nail polish remover, or acetone, and is known to attract dogs!