Voltage is the life blood of drones

Lithium Polymer batteries are the number one power sources for most drones today. They offer high discharge rates and a high-energy storage/weight ratio. Understanding them can save you time, money, and maybe even your home.

Lithium Polymer AKA LiPo’s. Lithium Polymer or LiPo batteries are used in many electronic devices. Cell Phone, Laptops, camera, tablets are just a few of the day to day items we use that operate with LiPos. They are a rechargeable battery that can be used for devices that need to have a larger amount of power. They are similar to lithium ion batteries in that they each have a nominal voltage of 3.7 volts per cell, but a lithium ion battery uses a organic liquid based electrolyte inside that is used to move ions and that’s what provides the charge and they typically have a hard shell that they are encased in. The lithium polymer batteries use a sheet of polymer for the chemical ion transfer instead of liquid. You remember what a polymer is right? A chain of monomers attached to each other. Sorry the nerd tried to escape. What this allows you to do is have a soft shell battery and can be made in many different shapes and are significantly lighter than NiCad or NiMH batteries, which makes our Quads fly longer and with more power.

When you look at a LiPo battery you will notice there are 2 connectors coming off the end. The only exception to the will be a 1S battery. We will get more in to that later. Lets cover the connectors.

1. First up we have a small red connector that has a rectangular shape. This is called a JST connector. You will see these a lot. They are typically for your accessories like cameras, LEDs, and battery eliminator circuits (BEC’s). They are small and can cannot be used for equipment that use a lot of amps.

1. Next you will see Deans connectors AKA “T” connectors. You will see these on batteries occasionally but I have seen them more on electronic speed controls (ESC’s). These used to be very popular but have become less popular since better designs came out. The connector uses a flat “T” style of plug with a spring to keep tension on the plug to avoid it coming apart during flight. The Deans connector can handle higher amps of around 60 amps of continuous load and bursts up to about 75 amps.

1. Next up is the EC3 connector these have a similar rating as the Deans connector that they can handle 60 amps continuous load and burst up to 75 amps. They are much easier to install on wires than Deans because the pins can be removed to make soldering easier. If you really want to try you can also make them work with the next XT60 connector. But I would not advise that.

1. The most popular that I have seen is the XT60 connector. They are comparable with the amp rating to the other two. The solder cups are on the back and require heat shrink to protect the solder joint and prevent shorts. Make sure you get high quality XT60 connectors. There are some out there that do not handle heat very well and can cause the plastic to melt when soldering the wires into the cups.

1. The last connector you will see on a battery does very in size but the size is based on the voltage your battery provides. This connector is called the balance cable. Let’s talk more about balancing in the next section.

Voltage and Cell Count:

So now let’s look at the voltage. The definition of volts is an electromotive force or potential difference expressed in volts. So, you have point A and point B. The difference between the two points is expressed in 12v or 22.2v etc. Voltage, ohms or resistance, and current are the three parts we will discuss.

Now I am a firefighter as well as a drone guy. I will use water to try and describe the parts of electricity. So, we just talked about Voltage. Now if you had a large water tower the pressure that is exerted on system of plumbing pipes by that water is the equivalent to the voltage. As the community uses the water from the tower the pressure goes down. There is less water in the tower pushing down on the system. Same as if you are flying a drone. As you fly the voltage is pushing the electrons through the system and as you use more and more of the energy the voltage goes down. Therefore, when you take off with a 4S battery you have 16.8v and when you land you have ~14.1v. You consume the pressure as you fly.

The flow of the water is like the current. This is the gallons per min of water that you are using when the hose is turned on. So, the amps or amount of energy being used for all the different motors, esc, flight controllers, and camera are using the amps. This can be affected by resistance if you have kinks in your hose you will have less water coming out. This is known as resistance it slows the rate of flow of water/current. Your battery will tell you how many mAh you have in the battery. Could be 10,000 mAh or 1500 mAh. You should look and see what your battery is rated at. When flying as a safety do not use more than 80% of the total amount of mAh. Example, if you use the 10,000 mAh battery do not use more than 8000 mAh of the battery.

LiPo’s act differently than NiCad or NiMH batteries do when charging and discharging. LiPo cells are fully charged when each cell has a voltage of 4.2 volts. They are completely discharged when each cell has a voltage of 3.0 volts. Now, the nominal voltage in the cell is 3.7V. Each battery is given what’s called an “S” rating. Meaning how many cells are together in Series. So, the following list is the ratings and how batteries are classified.

1. 1S = 1 cell at 3.7 V

2. 2S = 2 cells at 7.4V

3. 3S = 3 cells at 11.1V

4. 4S = 4 cells at 14.8V

5. 5S = 5 cells at 18.5V

6. 6S = 6 cells at 22.2V

Yes, you can keep going but 6S is the top of the “common” batteries you will see out in the drone world. Now, to jump back to the balance cable on the battery. On a 1S battery you will see just one connector coming off the battery. Just like the 2 batteries on the far left of the above picture. But a 2S and above you will see two connecters.One charging and one for balancing. As you increase the cell count the larger the balance connector will be.If your cells do not have a similar cell voltage this can be a sign that the battery is bad and should be replaced. Each connector wire has a ground and a wire that goes to each cell. This balance cable reads the voltage of each cell and looks for that nominal voltage of 3.7 volts.

Now, if you take a LiPo battery apart you will have a long fabric of polymers pieced together in series again this is why you have the “S” rating. If you tune in to the VLOG I will be pulling a battery apart to show you what this looks like. This is not safe to do. DO NOT TRY TO TAKE A LIPO BATTERY APART AT HOME.

Next, we have the “C” rating

The “C” rating is the amount of current you can safely pull from that battery. Back to the water analogy you can’t pull 1000 GPM from a garden hose it will collapse and damage the system. Same thing with batteries you can only pull so many amps at a time. If you pull too many the battery will overheat and could damage the system and maybe even start a fire. Because of this, batteries are given a “C” rating. Sometimes they are given 2 or 3 “C” ratings. One for normal use and one for burst use and one for charging use. Burst use is generally 10 seconds or less. Remember from above about mAh for batteries. Let say you have a race quad and the battery is packed with 1800 mAh and has a 45C rating. First you would convert your mAh in to amps by moving the decimal point over to the left by 3. So, we have 1.8 amps X 45C = 81 amps. That means you can safely draw 81 amps continuously from that battery without causing damage. Or if you have a larger Octocopter like the 3DR X8+ that uses 10,000mAh and has a 10c rating. 10amp x 10c = 100-amp safe draw for this battery. Now you can also have a burst rating. Same equation but the burst ratings is only for about 10 seconds at a time.

LiPo’s need to be charged very differently than NiCad or NiMH. It’s my recommendation that you have a good quality built charger. A charger that will show the rate of charge, the balance of each cell, and with an auto shut off. Always stay near your charger when charging and you don’t leave LiPo’s charging unattended. Buy a LiPo bag for charging and storage. The bag is made of fire retarded material that can help contain damage in case of a battery fire. Yes, these batteries can catch fire if they are over charged or discharged too much.

Check the battery health. Are the cells all charged the same or within +/- 0.05V of each other? If your battery is not balanced your charger should have a balance feature that can fix the issue. If the cell is bad say 3 cells are 4.1V and 1 cell is 1V then the battery is bad and should be replaced. Another indicator that your battery is bad is if it begins to puff up. This is a sign your battery is either overcharged or discharged too much. Keep an eye out for this.

Now Smart batteries are the latest and greatest in the LiPo world. The smart battery monitors the health of the battery and balances the battery during charging. The charger is specific to the battery. They do not use the Deans or XT60 connector that we talked about earlier. But the smart battery like the DJI Inspire 1, 3DR Solo, and many others are very reliable but they can have their flaws as well. So always be watching your batteries.

In short inspect your batteries, make sure there is no damage to the outer shell, ensure its charged before flight, and don’t use more that 80% of the total battery capacity.

I hope this was informative and gives you a better understanding of how LiPo batteries work and why such care should be taken with them. Next week we will talk about ESC’s or electronic speed controls remember to fly drones, shoot guns, drink whisky, (but not at the same time) and freedom on.

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