LiPo batteries are the most popular choice for anyone looking for long run times and high power.
Pros and Cons of LiPo batteries:
- LiPo batteries are much lighter weight, and can be made in almost any size or shape.
- LiPo batteries offer much higher capacities, allowing them to hold much more power.
- LiPo batteries offer much higher discharge rates.
- LiPo batteries have a shorter lifespan than NiMH/NiCd batteries. LiPo’s average only 300–400 cycles.
- The sensitive chemistry of the batteries can lead to fire if the battery gets punctured and vents into the air.
- LiPo batteries need special care in the way they are charged, discharged, and stored. The required equipment can be expensive.
Terminology of LiPo Battery
1. Voltage/Cell Count
A LiPo cell has a nominal voltage of 3.7V. On the battery, the cell count helps us to find the voltage of the battery. S stands for series.
Therefore, if 6S is written on the battery, that means it has 6 cells in series. This means the voltage provided by the battery will be 6 X 3.7V = 22.2V(In series, Voltage gets added).
LiPo batteries are fully charged when they reach a voltage of 4.2V per cell. Some batteries may be described in a different way, for example, 3S3P. This means that there are a total of 6 cells in the battery, 3 in Series and 3 in parallel.
Just like volatge gets added in a series battery, in case of parallel, the capacity gets added. If we assume that capacity of each cell as 5200mAh, 3S3P will mean that the overall battery has 3x3.7=11.1V with overall capacity being 5200+5200=10400mAh.
The voltage of a battery pack is essentially going to determine how fast your vehicle is going to go. Voltage directly influences the RPM of the electric motor (brushless motors are rated by kV, which means 'RPM per Volt'). So if you have a brushless motor with a rating of 3,500kV, that motor will spin 3,500 RPM for every volt you apply to it. On a 2S LiPo battery, that motor will spin around 25,900 RPM. On a 3S, it will spin a whopping 38,850 RPM.
So the more voltage you have, the faster you're going to go.
The capacity of a battery is basically a measure of how much power the battery can hold. Think of it as the size of your fuel tank.
The unit of measure here is milliamp hours (mAh). This is saying how much drain can be put on the battery to discharge it in one hour.
For example, if a battery is rated at 5200mAh capacity, this means that it will get completely discharged in 1 hour if 5.2A is drawn from it continuously(5200mAh=5.2 Amp hour).
3. Discharge Rate
The C Rating is simply a measure of how fast the battery can be discharged safely and without harming the battery.
One of the things that makes it complicated is that it's not a stand-alone number; it requires you to also know the capacity of the battery to ultimately figure out the safe amp draw (the "C" in C Rating actually stands for Capacity).
Once you know the capacity, it's pretty much a plug-and-play math problem. Taking the above example, if the battery has a discharge rating of 35C, it can safely be discharged at 35x5.2=182A.
Most batteries have a separate safe discharge rate and burst discharge rate. So keep this in mind while using a LiPo.
Taking proper care of LiPo batteries
Lipo Batteries require proper care otherwise they can be harmful to the user. Some of these requirements are-
1. LiPo batteries require specialized care, they charge using a system called Constant Current/Constant Voltage. Basically, the charger will keep the current, or charge rate, constant until the battery reaches its peak voltage (4.2v per cell in a battery pack). Then it will maintain that voltage, while reducing the current. On the other hand, NiMH and NiCd batteries charge best using a pulse charging method. Charging a LiPo battery in this way can have damaging effects, so it's important to have a LiPo-compatible charger.
2. The second reason that you need a LiPo-compatible charger is balancing. Balancing is a term we use to describe the act of equalizing the voltage of each cell in a battery pack.
3. We balance LiPo batteries to ensure each cell discharges the same amount. This helps with the performance of the battery.
4. The safest charge rate for LiPo batteries is 1C.
5. A LiPo cell should never discharge below 3V.
6. They should also be stored in a fireproof container of some sort. As I mentioned above, most people tend toward leaving their LiPos in a LiPo bag, as they are portable and protect your workshop from catching fire should the LiPo combust. I have also seen people use empty ammo boxes, fireproof safes, and ceramic flower pots. Whatever you have (or can buy) that will prevent any fire from spreading will be worth it in the unlikely event that anything untoward should happen.
Picking out the right charger
Looking at the above sections, it must be clear by now that LiPo chargers play a crucial role in the proper functioning and affect battery life as well.
You can find the iMAX B6 charger in our store which works adequately with LiPo batteries. The iMAX B6 charger has various modes to charge various kinds of batteries like NiCd, NiMH, LiFe, LiHV, etc. We will be focusing solely on the LiPo balance charge feature of this charger. In the above section we mentioned the Constant volatge/constant current charging method for LiPo batteries. This charger incorporates this feature under the name of balance charge.
- Input Voltage: 11-18v
- Circuit power: Max Charge: 50W / Max Discharge: 5W
- Charge Current Range: .1-5.0A
- Discharge current range: .1-1.0A
- Ni-MH/NiCd cells: 1-15
- Li-ion/Poly cells: 1-6
- Pb battery voltage: 2-20v
- Dimensions: 133x87x33mm
Steps for charging a LiPo battery using iMAX B6 charger:
- Pick a suitable wall adapter for the charger, the output needs to be in the range of 11-18V and it should have a DC barrel connector at the other end which will be inserted into the B6 charger. (Note: The output current rating of the charger decides the charging rate of the battery, hence, if you want to charge the battery at a high charging rate, make sure your wall adapter is up for the task.
- Once the charger is turned on, you should see that the charger is in LiPo charge mode. Do not charge the battery in this mode, this is not meant for LiPo batteries. Press the INC button once and the charger should change to LiPo balance charge mode.
- Each battery comes with a JST-XH connector which is used to monitor the status of the battery using a battery monitor. On the side of B6 charger, you can see ports which can accommodate this connector. B6 charger is capable of charging batteries rated from 2S to 6S. Plug the battery’s JST connector into the charger.
- Using the connector which comes with the box, connect the positive and terminals of the battery to the charger. Always make sure to connect the negative terminal first. There may be minor sparks while connecting the positive terminal but don't worry about it.
- Once connected, enter the START button once, you will see the charging rate blink, set the charging rate appropriately(For example, if your adapter can supply 1A, don't exceed 0.5A charging rate). Once this is set, again press the START button, this will make the battery voltage blink. Increase or decrease this using the INC and DEC buttons and set appropriately. Once done, long press the START button will you can hear a chime and the battery will start charging(Note: If there are any errors with the connection, the error will be displayed).
- To check individual cell charge, press the INC button once while the battery is charging.
- Always monitor a battery when charging and it can be stopped at any point of time using the STOP button.
Disposal of LiPo Batteries
Before disposing off your LiPo, make sure the warranty has expired. Some companies have one-year replacement warranties that you can take advantage of, but most warranties will be voided if you perform the following steps before seeking a warranty replacement.
Steps to safely dispose off a LiPo:
- Discharge the LiPo battery as far down as you safely can: There are various ways to do this. Most computerized LiPo chargers have a discharge feature in them. If you don't have a charger with a discharge feature, you can run down the battery in your vehicle - keep in mind that you risk a fire and potentially damaging your vehicle doing this, so take care to have the necessary safety equipment around.
- Place the LiPo in a salt water bath. Mix table salt into some warm (not hot) water. Keep adding salt until it will no longer dissolve in the water. Ensure that the wires are all entirely submerged. The salt water is very conductive, and it will essentially short out the battery, further discharging it. Leave the battery in the salt water bath for at least 24 hours.
- Check the voltage of the LiPo. If the voltage of the battery is 0.0V, great! Move onto the next step. Otherwise, put it back in the salt water bath for another 24 hours. Continue doing this until the battery reaches 0.0V.
- Dispose of the battery in the trash. That's right - unlike NiMH and NiCd batteries, LiPos are not hazardous to the environment. They can be thrown in the garbage with no problem.
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Also Read - All About Lithium Polymer Batteries (LiPo)