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Get a Charge Out of It: The Ultimate Guide to 3.7V Battery Level Indicators.

In this Instructable I will be going over the basics of proper charging, discharging, handling, usage, storage, and care of lithium polymer batteries so you can use them safely and effectively in your future projects. Now, this is by no means the be-all and end-all of information, and it's always important to consult the instructions for your specific equipment, but I think this Instructable will provide a good basis of knowledge on the subject of these awesome batteries .

If you're new to lithium polymer/LiPo/LiPoly batteries, there are a lot of terms you will need to know before we get started. Everything may seem a bit daunting at first, but with some basic understanding, it's all pretty simple, so let's jump in.

When you look at a LiPo's data sheet or casing, you will notice it has a lot of specs.

Cell arrangement - Described using the format xSyP (where x and y are integers), this tells you how the cells in the battery are wired up. Batteries are made up of cells, whose voltage is determined by cell chemistry and whose capacity is determined by energy density and physical size of the cell. S stands for series and P stands for parallel. As you may know, series adds the voltage of the cells and parallel adds the capacity of the cells, so a combination of cells in series and parallel results in a battery. The battery shown in the second image reads that it has an arrangement of 3S1P, meaning it has 3 cells that are all in series with no parallel wiring. This may seem confusing because it says "1P," but think of the arrangement as a grid. By multiplying the 3

and the 1, you get the total number of cells in the battery, which in this case is 3. If it were a 3S2P battery, there would be 2 sets of 3 series-wired cells in parallel, resulting in 6 cells total. Often times the parallel arrangement is omitted when discussing batteries, because most packs are 1P (so instead of saying you're using a 3S1P pack, you may as well just say 3S).

Capacity - Usually measured in mAh (milliamp hours), this is determined by the cell arrangement (parallel) and tells you how long you can expect the battery to last on a charge (although it's not quite that simple). 2600mAh as shown on the battery in the picture is equal to 2.6Ah (amp hours), a format you may be more familiar with on larger batteries, like the SLA (sealed lead acid) one in your car, which is probably around 50Ah. A capacity of 2600mAh means that the battery can discharge at 2.6 amps for one hour (hence “amp hours”), 1.3 amps for 2 hours, etc., before it runs out of “juice.” Because the battery shown has a 1P arrangement, each cell has a capacity of 2600mAh.

Voltage -The voltage of a battery is also determined by the cell arrangement (series), and there are a few common voltage measurements worth noting:

Charged - the voltage of a fully-charged LiPo cell is 4.20V, and charging above this will damage the cell.

Nominal - this can be considered a type of "half-charged" voltage, as it is 3.70V, in between charged and discharged. Nominal voltage is what manufacturers use when describing the voltage of their batteries.

Discharged - the voltage of a discharged LiPo cell is 3.00V, and discharging below this will definitely damage the cell.

Because the battery shown has a 3S arrangement, it is marked with its nominal voltage of 11.1V (3.70V*3 cells). A fully charged 3S pack is 12.60V and a fully discharged 3S pack is 9.00V.

Constant C Rating (Discharge) - The constant C rating (in relation to discharge) tells you how many amps can be safely drawn from the battery constantly. The “C” in a rating of xC (where x is an integer) actually stands for the capacity of the battery in Ah. By multiplying the C rating's coefficient by the capacity of the battery in Ah, you can determine the sort of amperage you can draw. In the case of this battery, with a capacity of 2600mAh (2.6Ah) and a C rating of 55C (that's pretty high, FYI), I can multiply 55*2.6 and get the max constant output of my battery, which is 143A.

Burst C Rating (Discharge) - In addition to the constant C rating, there is also a burst C rating, which is higher. Most of the time, the "burst" is rated for 10 seconds. Although it is not marked on the battery itself in the picture, it says in the documentation that this battery's 10 second burst rating is 80C. So, 80*2.6 is 208A burst. That's a lot! It's worth noting that your LiPo won't last long when that many amps are being drawn from it. At 208A, a 2600mAh LiPo will last approximately 45 seconds.

C Rating (Charge) - Determined in the same fashion as the C ratings for discharge, the C rating for charge tells you at what amperage you can safely charge your battery. This information is generally listed on the back of the battery with all the safety information. For the battery shown, it happens to be 5C, which means that it can be charged at 13A(2.6*5). We'll be talking a lot more about charge rates later...

Now that we have some battery theory behind us, let's take a look at a few LiPo batteries.

All LiPo batteries (should) have 2 sets of wires coming out of them: discharge leads and balance leads (sometimes called balance taps). The discharge leads are the thicker wires of which there are a positive (red, +, anode) and negative (black, -, cathode), and are used to discharge the LiPo as their name suggests. The balance leads are used when charging the battery to ensure that all the cells in the battery are charged equally. There is generally a common ground connection on one side of the balance connector, as well as a positive connection to each cell in the battery. Therefore, depending on the number of cells the battery has, it will have a balance connector with a different number of pins.

In order to charge LiPo batteries, you must use a LiPo-compatible charger. If you try to charge a LiPo with a non-LiPo charger, something WILL catch on fire. As this isn't a buying guide, I won't go into specific charger models or recommendations, but I will say that 90% of LiPo chargers out there use the exact same UI and have the same basic internals. Let's compare 2 chargers and talk about specs and differences:

Charger #1: Dynam Supermate DC6

Charger #2: Thunder AC6

Power Input - You need to supply more power to your charger than its outputs due to inefficiency. My Thunder AC6 can plug directly into the wall because it has an AC adapter built into it, while by Supermate DC6 requires an external PSU (The Thunder AC6 can take power from an external PSU as well but there's not much point for home use). Both these chargers have 50W max output, which means they need to take more than 50W input... say 60W at least, probably more just to be sure.

Power Output - Like I said, both the Thunder and Supermate feature 50W maximum output. Remember that wattage is the product of voltage and current, so your maximum current you use to charge your battery depends on your battery's voltage and vice versa. However, chargers also have a max/min voltage and max/min current output in addition to their wattage limitations. Both these chargers have a current output range of 0.1-5.0A and a voltage range of 1-6S for LiPo (4.2-25.2V charged). That means that while you'll be able to charge a 2S battery at 5A (8.4V*5A=42W), you won't be able to use that same current to charge a 3S battery (12.6V*5A=63W). For a 3S battery, max charge current on a 50W charger will be 3.9A (50W/12.6V=3.968A).

Balancing - Balancing cells is quite possibly the most important part of charging a LiPo battery. As LiPo batteries are used, their cells may discharge unevenly and become “unbalanced.” To combat this, balancing chargers like these plug into the balancing leads of the LiPo battery as well as the discharge leads, allowing them to individually charge and “balance” the cells within the LiPo battery so that all the cells are the same voltage (4.20 V, remember?) by the end of the charge. Some LiPo chargers don't have balancing capabilities, and when this is the case, it is necessary to buy and use a separate balancer. As I don't have much experience using standalone balancers, I won't go into detail on them.

Extra Features - Some chargers have extra features like temperature sensing or USB connectivity. Both of these chargers have a temperature sensor input, which can be useful if you want to stop charging your battery if temperatures exceed a predetermined value (we'll come back to this later). The Thunder AC6 has USB which works with a Windows application for data logging. Kind of cool, but not especially necessary most of the time.

In addition to batteries and a chargers, there are a few other things you need in order to take care of your LiPos:

Digital Multimeter - Sometimes the voltage readings on chargers aren't totally accurate, so it's good to always be able to fall back on a trusty multimeter to verify. When I'm using a new LiPo battery, I always check the voltage of each cell with a multimeter after I take it off the charger to be sure it's charged correctly.

Low Voltage Alarm/Cutoff - These are used in conjunction with your LiPo battery when its being discharged. A low voltage alarm or cutoff, or LVC as it's more commonly known, plugs into the balance connector on the battery and monitors the voltage of each cell. When any cell below a safe voltage (this threshold depends on the LVC but is generally between 3.3V and 3.0V), the LVC or LVA will either alert you with lights and/or a buzzer, or will cut off power to prevent further discharge . Electronics meant to run off LiPo batteries will generally have this feature built-in, but if you're using a LiPo with something not designed for it, you'll need to use one of these or something equivalent.Charging Case/Bag - LiPos should NEVER be charged in an open space for safety reasons. If something goes wrong within a LiPo, it will quite literally shoot flames out of it, easily setting anything on fire. Most people charge their LiPos in LiPo bags, which are padded, fireproof sleeves that can vent smoke out but keep flames in. I, however prefer the ammo box method, mostly because it looks much cooler and properly scares people. For illustrative purposes of this Instructable, I am charging my LiPos in open air, but I would never do so otherwise, as keeping your LiPos safe while charging is probably the most important thing you can do to.

Charging LiPo batteries, especially balance charging, is a very precise process. If you get it wrong, something bad will happen, but luckily LiPo chargers do their best to not make fires.

When setting up a charger to balance charge LiPo batteries, you're presented with 2 main parameters: current and voltage.

Charge Current - The current at which you should charge your LiPo battery depends on the battery's capacity and charge C rating. Regardless of charge C rating, though, most people charge their LiPos at 1C, as that is the safest rate, both from a fire danger and battery longevity standpoint. Charging your LiPo at a higher rate will make it charge faster, but charging at higher rates will also decrease the life of the battery in the long run.

Charge Voltage - This is the nominal voltage of the battery you want to charge. Often times the charger will state the cell arrangement (such as “3S”) next to its nominal voltage for easier recognition. My chargers check the battery by counting its cells via the balance plug and it will not charge if your selected voltage and the battery's voltage don't match, which is a very good safety feature.

All these charges of their respective batteries are very safe and within the realm of the charger's capability. Additionally, each of these charges, because they are being performed at a 1C charge rate, theoretically takes 1 hour to charge each battery from 3.00V per cell “dead” to 4.20V per cell “full.” In real life, charge time varies depending on the degree of discharge of the battery (most of the time you'll stop using the battery before it hits 3.00V/cell) and the degree of imbalance between the cells (the more imbalanced they are , the longer it takes the charger to balance them).

We can see that the chargers I own are incapable of charging the 2600mAh 3S battery and the 5000mAh 2S battery at 2C, but there are plenty of other chargers that are. Charging at 2C means that each charge would theoretically take just 30 minutes. Never charge your battery at a rate higher than is intended. Even then, I still don't recommend charging any battery above 1C, whether it's rated for it or not. You can do it if your battery is capable and you're in a time crunch, but repeated charges at higher C rates wear down your battery faster than charges at lower C rates do.

Once everything's plugged in, go ahead and start balance charging your LiPo. Like I said, after I tell my charger to start, it checks the battery's cells and asks me to confirm my settings before it starts charging, so yours may do the same.

LiPo chargers follow a 2-part process, using a “constant current” technique first and a “constant voltage” technique second. During the "constant current" portion of the process, the charger ramps up to its specified amperage output and keeps that amperage constant as cell voltage rises. When the cells hit a certain threshold, the charger switches over to "constant voltage." During this portion, the charger varies current output to keep all the cells of the battery at the same voltage. Balancing occurs in this part of the charging process. As the charger nears completion, current drops off significantly until the battery is fully charged at 4.20V per cell, at which point the charger stops.

While your LiPo is charging, watch out for temperatures (I told you I'd come back to it!). A properly functioning LiPo should not exceed 90-100 degrees F while charging. If it does seem to be getting hotter than that (you can feel it with your hand, read it with the temp sensor for the charger, or us

Get a Charge Out of It: The Ultimate Guide to 3.7V Battery Level Indicators.

In this Instructable I will be going over the basics of proper charging, discharging, handling, usage, storage, and care of lithium polymer batteries so you can use them safely and effectively in your future projects. Now, this is by no means the be-all and end-all of information, and it's always important to consult the instructions for your specific equipment, but I think this Instructable will provide a good basis of knowledge on the subject of these awesome batteries .

If you're new to lithium polymer/LiPo/LiPoly batteries, there are a lot of terms you will need to know before we get started. Everything may seem a bit daunting at first, but with some basic understanding, it's all pretty simple, so let's jump in.

When you look at a LiPo's data sheet or casing, you will notice it has a lot of specs.

Cell arrangement - Described using the format xSyP (where x and y are integers), this tells you how the cells in the battery are wired up. Batteries are made up of cells, whose voltage is determined by cell chemistry and whose capacity is determined by energy density and physical size of the cell. S stands for series and P stands for parallel. As you may know, series adds the voltage of the cells and parallel adds the capacity of the cells, so a combination of cells in series and parallel results in a battery. The battery shown in the second image reads that it has an arrangement of 3S1P, meaning it has 3 cells that are all in series with no parallel wiring. This may seem confusing because it says "1P," but think of the arrangement as a grid. By multiplying the 3

and the 1, you get the total number of cells in the battery, which in this case is 3. If it were a 3S2P battery, there would be 2 sets of 3 series-wired cells in parallel, resulting in 6 cells total. Often times the parallel arrangement is omitted when discussing batteries, because most packs are 1P (so instead of saying you're using a 3S1P pack, you may as well just say 3S).

Capacity - Usually measured in mAh (milliamp hours), this is determined by the cell arrangement (parallel) and tells you how long you can expect the battery to last on a charge (although it's not quite that simple). 2600mAh as shown on the battery in the picture is equal to 2.6Ah (amp hours), a format you may be more familiar with on larger batteries, like the SLA (sealed lead acid) one in your car, which is probably around 50Ah. A capacity of 2600mAh means that the battery can discharge at 2.6 amps for one hour (hence “amp hours”), 1.3 amps for 2 hours, etc., before it runs out of “juice.” Because the battery shown has a 1P arrangement, each cell has a capacity of 2600mAh.

Voltage -The voltage of a battery is also determined by the cell arrangement (series), and there are a few common voltage measurements worth noting:

Charged - the voltage of a fully-charged LiPo cell is 4.20V, and charging above this will damage the cell.

Nominal - this can be considered a type of "half-charged" voltage, as it is 3.70V, in between charged and discharged. Nominal voltage is what manufacturers use when describing the voltage of their batteries.

Discharged - the voltage of a discharged LiPo cell is 3.00V, and discharging below this will definitely damage the cell.

Because the battery shown has a 3S arrangement, it is marked with its nominal voltage of 11.1V (3.70V*3 cells). A fully charged 3S pack is 12.60V and a fully discharged 3S pack is 9.00V.

Constant C Rating (Discharge) - The constant C rating (in relation to discharge) tells you how many amps can be safely drawn from the battery constantly. The “C” in a rating of xC (where x is an integer) actually stands for the capacity of the battery in Ah. By multiplying the C rating's coefficient by the capacity of the battery in Ah, you can determine the sort of amperage you can draw. In the case of this battery, with a capacity of 2600mAh (2.6Ah) and a C rating of 55C (that's pretty high, FYI), I can multiply 55*2.6 and get the max constant output of my battery, which is 143A.

Burst C Rating (Discharge) - In addition to the constant C rating, there is also a burst C rating, which is higher. Most of the time, the "burst" is rated for 10 seconds. Although it is not marked on the battery itself in the picture, it says in the documentation that this battery's 10 second burst rating is 80C. So, 80*2.6 is 208A burst. That's a lot! It's worth noting that your LiPo won't last long when that many amps are being drawn from it. At 208A, a 2600mAh LiPo will last approximately 45 seconds.

C Rating (Charge) - Determined in the same fashion as the C ratings for discharge, the C rating for charge tells you at what amperage you can safely charge your battery. This information is generally listed on the back of the battery with all the safety information. For the battery shown, it happens to be 5C, which means that it can be charged at 13A(2.6*5). We'll be talking a lot more about charge rates later...

Now that we have some battery theory behind us, let's take a look at a few LiPo batteries.

All LiPo batteries (should) have 2 sets of wires coming out of them: discharge leads and balance leads (sometimes called balance taps). The discharge leads are the thicker wires of which there are a positive (red, +, anode) and negative (black, -, cathode), and are used to discharge the LiPo as their name suggests. The balance leads are used when charging the battery to ensure that all the cells in the battery are charged equally. There is generally a common ground connection on one side of the balance connector, as well as a positive connection to each cell in the battery. Therefore, depending on the number of cells the battery has, it will have a balance connector with a different number of pins.

In order to charge LiPo batteries, you must use a LiPo-compatible charger. If you try to charge a LiPo with a non-LiPo charger, something WILL catch on fire. As this isn't a buying guide, I won't go into specific charger models or recommendations, but I will say that 90% of LiPo chargers out there use the exact same UI and have the same basic internals. Let's compare 2 chargers and talk about specs and differences:

Charger #1: Dynam Supermate DC6

Charger #2: Thunder AC6

Power Input - You need to supply more power to your charger than its outputs due to inefficiency. My Thunder AC6 can plug directly into the wall because it has an AC adapter built into it, while by Supermate DC6 requires an external PSU (The Thunder AC6 can take power from an external PSU as well but there's not much point for home use). Both these chargers have 50W max output, which means they need to take more than 50W input... say 60W at least, probably more just to be sure.

Power Output - Like I said, both the Thunder and Supermate feature 50W maximum output. Remember that wattage is the product of voltage and current, so your maximum current you use to charge your battery depends on your battery's voltage and vice versa. However, chargers also have a max/min voltage and max/min current output in addition to their wattage limitations. Both these chargers have a current output range of 0.1-5.0A and a voltage range of 1-6S for LiPo (4.2-25.2V charged). That means that while you'll be able to charge a 2S battery at 5A (8.4V*5A=42W), you won't be able to use that same current to charge a 3S battery (12.6V*5A=63W). For a 3S battery, max charge current on a 50W charger will be 3.9A (50W/12.6V=3.968A).

Balancing - Balancing cells is quite possibly the most important part of charging a LiPo battery. As LiPo batteries are used, their cells may discharge unevenly and become “unbalanced.” To combat this, balancing chargers like these plug into the balancing leads of the LiPo battery as well as the discharge leads, allowing them to individually charge and “balance” the cells within the LiPo battery so that all the cells are the same voltage (4.20 V, remember?) by the end of the charge. Some LiPo chargers don't have balancing capabilities, and when this is the case, it is necessary to buy and use a separate balancer. As I don't have much experience using standalone balancers, I won't go into detail on them.

Extra Features - Some chargers have extra features like temperature sensing or USB connectivity. Both of these chargers have a temperature sensor input, which can be useful if you want to stop charging your battery if temperatures exceed a predetermined value (we'll come back to this later). The Thunder AC6 has USB which works with a Windows application for data logging. Kind of cool, but not especially necessary most of the time.

In addition to batteries and a chargers, there are a few other things you need in order to take care of your LiPos:

Digital Multimeter - Sometimes the voltage readings on chargers aren't totally accurate, so it's good to always be able to fall back on a trusty multimeter to verify. When I'm using a new LiPo battery, I always check the voltage of each cell with a multimeter after I take it off the charger to be sure it's charged correctly.

Low Voltage Alarm/Cutoff - These are used in conjunction with your LiPo battery when its being discharged. A low voltage alarm or cutoff, or LVC as it's more commonly known, plugs into the balance connector on the battery and monitors the voltage of each cell. When any cell below a safe voltage (this threshold depends on the LVC but is generally between 3.3V and 3.0V), the LVC or LVA will either alert you with lights and/or a buzzer, or will cut off power to prevent further discharge . Electronics meant to run off LiPo batteries will generally have this feature built-in, but if you're using a LiPo with something not designed for it, you'll need to use one of these or something equivalent.Charging Case/Bag - LiPos should NEVER be charged in an open space for safety reasons. If something goes wrong within a LiPo, it will quite literally shoot flames out of it, easily setting anything on fire. Most people charge their LiPos in LiPo bags, which are padded, fireproof sleeves that can vent smoke out but keep flames in. I, however prefer the ammo box method, mostly because it looks much cooler and properly scares people. For illustrative purposes of this Instructable, I am charging my LiPos in open air, but I would never do so otherwise, as keeping your LiPos safe while charging is probably the most important thing you can do to.

Charging LiPo batteries, especially balance charging, is a very precise process. If you get it wrong, something bad will happen, but luckily LiPo chargers do their best to not make fires.

When setting up a charger to balance charge LiPo batteries, you're presented with 2 main parameters: current and voltage.

Charge Current - The current at which you should charge your LiPo battery depends on the battery's capacity and charge C rating. Regardless of charge C rating, though, most people charge their LiPos at 1C, as that is the safest rate, both from a fire danger and battery longevity standpoint. Charging your LiPo at a higher rate will make it charge faster, but charging at higher rates will also decrease the life of the battery in the long run.

Charge Voltage - This is the nominal voltage of the battery you want to charge. Often times the charger will state the cell arrangement (such as “3S”) next to its nominal voltage for easier recognition. My chargers check the battery by counting its cells via the balance plug and it will not charge if your selected voltage and the battery's voltage don't match, which is a very good safety feature.

All these charges of their respective batteries are very safe and within the realm of the charger's capability. Additionally, each of these charges, because they are being performed at a 1C charge rate, theoretically takes 1 hour to charge each battery from 3.00V per cell “dead” to 4.20V per cell “full.” In real life, charge time varies depending on the degree of discharge of the battery (most of the time you'll stop using the battery before it hits 3.00V/cell) and the degree of imbalance between the cells (the more imbalanced they are , the longer it takes the charger to balance them).

We can see that the chargers I own are incapable of charging the 2600mAh 3S battery and the 5000mAh 2S battery at 2C, but there are plenty of other chargers that are. Charging at 2C means that each charge would theoretically take just 30 minutes. Never charge your battery at a rate higher than is intended. Even then, I still don't recommend charging any battery above 1C, whether it's rated for it or not. You can do it if your battery is capable and you're in a time crunch, but repeated charges at higher C rates wear down your battery faster than charges at lower C rates do.