All about Lithium Polymer Batteries (LiPo)
LiPo batteries are very popular batteries when talking about rechargeable batteries, as they are capable of powering up RCs and Quadcopters in a much better way than any other Rechargeable batteries like AAA, Nickel Cadmium, etc.
Lithium Polymer Batteries or LiPo batteries use a polymer electrolyte inside them instead of using a liquid electrolyte hence the name Lithium Polymer. These Batteries are volatile and come in different shapes and sizes depending on the cells inside them. These batteries can provide high output power and are used in applications where weight is a critical feature for operation for eg. Mobile devices like drones, RC cars, etc.
Ratings of the LiPo Battery:
LiPo Batteries have certain ratings on the pack that are vital to an understanding before buying.
There is an “S” rating or the series rating on the batteries that symbolizes, the total number of cells wrapped insides a single battery. So if there is a battery with a rating of 2S it means that it has two cells wrapped inside it. The nominal voltage that 1 cell provides is almost 3.7 volts, so if you have a 3S-rated battery that means it will have a voltage rating of 11.1V or vice versa in the case of the battery shown above. The above figure has specified the rating as 11.1 V that means it has 3 cells rapped in it. Mostly all RC cars and Drones use 3S to 4S LiPo batteries.
The mAh rating is short for milliamps hour, this rating tells you roughly how long will the LiPo Battery Last, how much “juice” it has. It is a unit that tells us about the capacity of the battery, the higher the number, the more energy the battery can store and the more longer it can run
The “C” rating is the maximum safe continuous discharge rate, in the above image the battery is rated 25c it means that the current I can draw safely from the battery without damaging or overheating it is: 25 * 54000 mA = 135 Ampere of current can be drawn from the battery continuously for 1 hour safely without damaging it. So you can rotors at full throttle or can make your drone fly acrobatically using that much current.
How to Choose a LiPo Battery for your Application:
When you are choosing a LiPo battery for your project or application you need to go through the Ratings that are mentioned above that is:
- The Series Rating
- The mAh rating or Ah rating
- The C Rating
Now addition to these three ratings, there is also a Discharge rating which is also measured in “C” which is when you multiply the mAh rating with this discharge rating you will get the amount of current that gets discharged from the battery continuously in one hour.
Now when you are selecting a LiPo you need to also ensure the connectors that the battery comes up with and whether your LiPo charger is capable of Charging the battery that way.
Lastly, the cost factor comes in, which is not the primary concern, because to need the best for your application you need to spend a hefty amount on the battery, but if you need to cut the cost on batteries, you need to compromise on the project’s Performance.
LiPo battery chargers and charging.
Typically the battery Chargers that come with LiPo batteries are 80 W 6 A chargers that can charge 6S batteries these chargers have built monitors on them that show the state of the battery voltage while charging, thus you can use that to plug out the charger to avoid overcharging the battery, also it is advisable to ensure that the battery is not discharged below 20% of its total capacity to avoid it from swelling up, overheating and catching fire or being damaged.
While charging the battery you should always be present near the battery, you should never charge a damaged battery or swollen up battery. You should also ensure that the battery is charging at a low charging rate of up to 1C if you vary the charging rate on your charger. A slower charging rate ensures the good stability of the battery.
If your battery charger does not have a screen to display the voltage levels of cells while charging then you can use a Battery Monitor that tells you the same and even buzzes alarms to let you know about overcharging.
Ensure to always use a balance connector while charging the battery to ensure that the voltage in each cell while charging the battery is balanced or equal, this avoids unnecessary damages to the LiPo.
LiPo Battery health and Lifetime:
The LiPo battery life is fairly nice, but it does not depend on its usage. Typically a LiPo battery works well enough till 300 charge cycles.
To maintain the good health of the Battery you need to ensure a few things:
- Never Discharge your LiPo Battery at a rate more than what it can handle it will make the LiPo swell and might damage its functioning.
- Never Charge a LiPo that is warm from usage or never use a LiPo that is warm from Charging.
- Overcharging your LiPo will not make it increase its energy capacity but only deteriorate it.
- If you are not using the LiPo battery for a couple of days, do not keep it charged, you should discharge it and store it properly. Discharge it to a voltage of 3.7 V per cell.
- When you discharge a LiPo battery do not bring the per-cell voltage level below 3V, this may damage the LiPo’s Health. Keep the Voltage ideally to 3.6 -3.7V per cell.
There LiPo storage Bags that are ideal for storing LiPo Batteries, these are fireproof bags or that might be metallic ammo boxes, these bags ensure that the batteries are safe from external harm and also maintain the battery’s health.
Prolong storage of LiPo battery in a Travel Case is not recommended, as the foam and plastic of the case might cause a fire due to the LiPo.