LIPO BATTERY OVERALL
1. What is the "lipo" battery?
Lithium Polymer batteries (henceforth referred to as “LiPo” batteries) are a newer type of battery now used in many consumer electronics devices. They have been gaining in popularity in the radio control industry over the last few years, and are now the most popular choice for anyone looking for long run times and high power.
LiPo batteries offer a wide array of benefits. But each user must decide if the benefits outweigh the drawbacks.
2. If there is a 1550mAh 3S 50C battery, what do all the parameters mean?
Capacity(1550mAh) - The capacity of a battery is basically a measure of how much power the battery can hold. 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. [1000mAh = 1 Amp Hour (1Ah)]
Cell count(3s) - As you can see this is a "3S" battery pack - it means that there are 3 cells in Series. A LiPo cell has a nominal voltage of 3.7V. So a two-cell (2S) pack is 7.4V, a three-cell (3S) pack is 11.1V and four cells (4s) is 14.8V.
Discharge rate/”C” Rating (50C) - The C Rating is simply a measure of how fast the battery can be discharged safely and without harming the battery.
BATTERY SELECTION GUIDELINES
1. Knowing what size battery you need
To get the longest flight or running times you should use the largest battery (in terms of capacity) that you possibly can(but still keep within the maximum takeoff weight of your drone). The other thing to take into account is the physical size of the battery, as depending on what drone or car you are using you will only need be able to fit a battery of a certain size.
2. Battery Discharge Rate and Capacity
Probably the most important, but often overlooked factor too is the check the battery discharge C rating is optimum for your drone or car. Using a discharge rate (C rating) that is too low, can result in your battery is damaged, and your drone or car under-performing the battery cant release current fast enough to power your motors properly. Since higher C rating batteries are heavier, if the battery you are using has a C rating that is too high, you will just be carrying extra weight around that you don't need, ultimately reducing the running time.
3. How to calculate the maximum continuous current output for your battery?
In order to know what the total current draw of your drone system is, we cab calculated it based on this simple formula:
Max continuous Amp draw (A)= Battery capacity (Ah) x Discharge rate (C)
For an example, we have a 5100mAh 3 cell Lipo battery with a 10C rating. To find the maximum continuous amp draw, we first convert the 5100mAh to 5.1Ah, and multiply that number by 10C, to give a total continuous output of (5.1 x 10) = 51A
4. How to find the optimum C rating?
As choosing the battery is often the last step to building your own drone, we will already know what motors and ESC we are using. Since the motors will draw the most amount of energy from your battery we can base our calculation around this.
5. The battery C rating depends on the capacity
There is no fixed C rating that you will need to use as the maximum current output of a battery depends on the capacity and C rating. Typically the smaller the capacity of a battery, the higher the C rating needs to be, this is why for many high capacity multi-rotor batteries you will find very low C ratings in the range of 10-15C.
6. How much capacity do I need?
Now that you know the required current draw from your battery, the capacity and C rating can be found. In general, it's best to get the highest possible capacity battery that you can, which still keeping the total weight of your quadcopter including the battery and other equipment at around 50-70% of the maximum motor thrust.
So sticking to our quadcopter example, we know that 50% thrust is around 500g per motor (or 2Kg thrust in total). Our frame, electronics, and motors weight come to 1.2Kg. That leaves 800-1000g that we can use for the battery. So you should try to find the highest capacity LiPo that you can find that weights less than this.
7. Battery Voltage
The battery voltage or cell count is another important decision that you will need to make. Higher voltage batteries allow your motors to produce more power, however, the higher voltage batteries are heavier since they contain more cells.
There is no golden rule to follow when it comes to battery voltage, but the way you can find the best voltage for your drone is to look through your motor thrust data tables and compare the efficiency. You will find that motors are generally more efficient and powerful when using higher cell count lipos (higher voltage), but some of the efficiency bonus is negated by the increase in weight and cost of the battery. So depending on how many motors you are using you will need to choose what is best for your current setup.
One thing to bear in mind is to also make sure that your motors/ESC and other electronics are able to support the voltage of your battery. Some motors will only support a specific cell count lipo or a specific range of voltages which might make the decision easier.
8. Battery Connectors
Soldering battery connectors can be a real pain, so it is a good idea to try to find a battery connector that you like, and stick to it. That allows you to swap batteries easily, and if you decide to build another drone in the future you can use the same batteries. Common connectors include Deans/Tplug, XT60, and also EC3 connectors.
9. Number of batteries
The number of batteries you decide to use on your drone does not ultimately make much difference as there are pros and cons of using more batteries. Firstly using more batteries has an added layer of safety as if one battery should fail, you still have another that you can use to quickly land. Also if you have the flexibility of replacing one battery if one of them gets older than the other. Charging time can be reduced if you have two chargers as each one can charge at the same time. However, using two batteries can be more complex to mount and wire and buying two batteries can sometimes be more expensive than buying one. So ultimately using one or more batteries comes down to the drone you are using and your own preference.
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BATTERY SAFETY GUIDELINES
1. How to store a lipo battery?
- Store lipos in locations as fireproof as possible. Good places are on the concrete in your garage, or in a metal/glass box away from wood or carpet.
- Store in temperature-controlled locations–between 40F to 80F and not in direct sunlight.
- Store the lipos in a container with a bag of sand on top. If something were to happen, the flames would rip a hole in the bag, the sand would fall on the battery and extinguish the flames.
- Lipo batteries should be stored in ammo boxes or non-flammable container.
- Ensure the number of cells and battery type are set correctly on your charger to match the cell count in your battery.
2. How to charge lipo battery safely?
- Try to keep it as far away from flammable materials as possible, you can garages where the floor is concrete.
- You can charge in a metal box which would be able to contain flames in case of a fire.
- Charged within a temperature of 32F to 120F. Charging batteries outside this range may cause extreme heat, leakage, and cell damage.
- Always charge your batteries on a non-flammable surface like steel, cement, stone, glass, etc.
- Do not charge your Lithium Polymer batteries more than 1C.
- Do not charge batteries near flammable products.
- Do not charge the batteries unattended.
3. How to dispose of a lipo battery?
While the battery is in usage, the power drawn out of each cell is not equal. Therefore, at the end of each flight, the cells in the battery will be left out of balance. A non-balancing charger will stop charging the battery pack once the voltage of the overall pack is full without paying any attention to each cell. This causes the battery to be more and more unbalanced with each charge and would also result in diminished performance of the battery pack. The balance charger eliminates any unbalanced-cells symptoms of a battery pack by charging each cell individually; making sure that the cell's voltage remains balanced at the end of each charge. In essence, the balance charger lengthens the life of the battery back and maximizes its performance as well as keep the pack stable and safe to operate.