What are LiPo rechargeable batteries?
LiPo accumulators (lithium polymer accumulator) are rechargeable batteries that play an important role in model making and embedded and DIY electronics. Wearables and e-textile projects for Arduino and Raspberry Pi often use LiPos to be independent of a fixed power supply. One of the most well-known uses for LiPo batteries is something almost all of us come into contact with on a daily basis - cell phones!
Advantages of LiPos compared to conventional batteries
LiPo batteries have five main characteristics that make them the optimal battery for DIY projects:
- LiPo batteries are lightweight and can be made in almost any shape or size.
- LiPo batteries have large capacities, meaning they store a lot of energy in a small package (high energy density).
- LiPos are very good at maintaining a consistent voltage / output power when discharged. However, the voltage / power drop when they reach a fully discharged state is very rapid compared to NiCd, NiMh or PB.
- LiPo batteries have high discharge rates to power the most demanding electrical projects. LiPos also allow high charge current rates, so charging is possible in a short time.
- Unlike NiCad or NiMh, LiPos have no "memory effect."
What do voltage and cell count mean?
A single LiPo cell has a nominal voltage of 3.7 V. When fully charged, you will see almost 4.3 V on the cell, but this quickly drops to 3.7 V during normal use. When depleted, the cell will have about 3 V. This means that your project will need to handle different voltages if you are working directly from a cell. If you need 5 V, you'll need to combine two LiPos in series to get a 7.4 V pack and regulate it to 5 V.
(Source: ProTalk.net)
For example, the voltage of a battery determines how fast a vehicle will go. The voltage directly affects the speed of the electric motor (brushless motors are rated at kV, which means "speed per volt"). So if you have a brushless motor rated at 3,500 kV, for every volt you apply, that motor will turn 3,500 rpm. With a 2S LiPo battery, that motor will turn 25,900 rpm.
Here is a list of commonly used lipos with cell counts:
- 3.7 volt battery = 1 cell x 3.7 volts (1S)
- 7.4 volt battery = 2 cells x 3.7 volts (2S)
- 11.1 volt battery = 3 cells x 3.7 volts (3S)
- 14.8 volt battery = 4 cells x 3.7 volts (4S)
- 18.5 volt battery = 5 cells x 3.7 volts (5S)
- 22.2 volt battery = 6 cells x 3.7 volts (6S)
By the number in parentheses means, battery manufacturers indicate how many cells in row "S" the battery pack contains.
Batteries can also be wired in parallel to increase capacity. This is indicated by a number followed by a "P". Example: 3S2P would indicate 2 x 3 cell series packs wired in parallel to double the capacity.
What does capacity mean?
Capacity indicates how much current the battery can hold and is expressed in milliampere hours (mAh). This indicates how much load or loss (measured in milliamps) is possible for 1 hour.
For example, a lipo battery rated at 1000 mAh would be fully discharged in one hour if a load of 1000 milliamperes is applied. If a load of 500 milliamperes was applied to the same battery, it would take 2 hours to discharge. If the load was increased to about 15,000 milliamperes (15 amps), the time to discharge the battery would only be about 4 minutes.
What does the C-rate mean?
Almost all lithium polymer batteries you buy today are given a "C" rating. The C in C-Rate stands for capacity. The C-Rate is the maximum, safe, continuous discharge rate of a pack according to the manufacturer's specifications. So if you see 20C printed on your label, it means it can be discharged "continuously" at 20 times the pack capacity. Capacity is usually measured in mAh and a popular cell size is 2200 mAh, for example:
- 2200mAh 20C cell = 2.2A x 20 = 44A continuous discharge.
Along with the continuous discharge rate, some batteries display a 'burst' discharge rate. This is typically twice the continuous discharge rate. This usually means that the battery will allow twice the current, but only for a few seconds.
Connectors
Most LiPos use 2-pin connectors, but they can vary greatly in design. All our LiPo batteries use a 2-pin JST-PH connector with a 2.00 mm pitch(datasheet). This connector is compatible with our lipo chargers and development boards.
Charge and discharge LiPo batteries safely: Lipo Charger
It is important to use a LiPo compatible charger for LiPo batteries, because LiPo batteries need special care and can explode if not handled properly. Basically, the charger keeps the charging current constant until the battery reaches its peak voltage. Then this voltage is maintained while the current is reduced.
There are many inexpensive chargers available for charging LiPo batteries. These often use USB to charge the battery. Do not attempt to charge LiPos without a charger. A LiPo battery can be damaged by overcharging. Therefore, use a specially designed LiPo charger, so-called LiPo Charger. In our category of the same name you will find a large selection of such "Lipo Chargers".
LiPo batteries can also be damaged if they are discharged too far. To protect against this, almost all LiPo batteries have a small safety circuit at the top of the cell that shuts down the battery when the voltage drops below a certain threshold (usually 3 V).
LiPo batteries have a very low internal discharge rate. This makes them a good candidate for projects that have low power requirements and need to run for many days or months.
>>> Buy the right 3.7 V LiPo batteries for your next project!
