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General introduction of Lithium Polymer Battery

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This booklet is intended to provide a set of guide lines for modellers who wish to use Lithium Polymer (LiPo) batteries in model aircraft and associated equipment, particularly when the battery is intended to provide the primary power source for the model. It has been written mainly to emphasise the safety aspects of this area of model flying, but also contains information and guidance on best practise regarding their usage on a day to day basis.

Although lipo batteries have only recently become commercially available (compared to the earlier Nickel Cadmium/Nickel Metal Hydride types), their performance characteristics have quickly taken them to the top of the modellers wish list. The energy density of these cells (the watt minutes/gram) is way above the other cell types we have used, and this, together with their ability to deliver high levels of power, is the reason why they are so attractive to the modeller. Their effect on electric powered model flight has been little short of amazing, and although there is little data to support the statistics, it seems likely that the proportion of powered sports flying using electric power now exceeds 50%. This rate of advance has certain disadvantages, and in this case the main one seems to be a lack of technical information relating to lipos. Whilst some technology is common to all batteries, each particular type has a different chemistry, often a different physical form, and usually quite different procedures in use. Since lipo cells and batteries are the latest to be developed, it is logical to assume that users are less familiar with them than with older types. This text will attempt to remedy that shortfall, at least to some degree.

There may be some confusion over the difference between cells and batteries, but in technical terms it is fairly simple. A cell is a single sealed unit containing an anode, a cathode, and the electrolyte. It has a voltage dependent upon the electrochemistry of the materials used, and in the case of lipo cells this is a mean voltage of 3.7V. To achieve higher voltages, single cells are assembled into series wired sets and these sets are called batteries. The number of cells in a battery is designated by a simple number and the letter S for series, so that a lipo battery 2s or pack has 2 cells and a total mean voltage of 7.4V, a 5S battery has 5 cells and 18.5V.

Electric cells and batteries fall into two broad categories. They are either primary or secondary, dependent upon whether or not they are rechargeable. Primary cells are single use, non rechargeable units, whereas secondary cells are repeated use, rechargeable ones. In modelling, we use both types e.g. the carbonzinc primary cell to power a tachometer, and the nickel metal hydride secondary cell in a glow driver. Lipo cells and batteries are therefore clearly secondary units.

Capacity. If we consider the capacity of a lipo cell/battery then we need to adopt a slightly different system to that used with previous cell types. Whilst the capacity itself is measured in ampere hours (Ah) or milliampere hours (mAh) for smaller packs, we also link this to a C rating for the pack which is actually a measure of rate of discharge (or charge). A 1C rate is equivalent to a complete discharge in one hour so that the current drawn will be the Ah capacity numerically expressed in Amps. Multiples of C (2C, 5C, 20C etc.) would involve a current draw increased by the same multiple with the time period decreased in the same ratio. A theoretical example would be a 3500 mAh lipo battery discharged at 2C when 7000 mA (7.0 Amps) drawn from the pack would last for 30 minutes, or the same battery recharged at 0.5C when the charging current would be 1750 mAh (1.75 Amps) and the pack would take 2 hours to fully recharge from empty. These values are purely theoretical since they take no account of losses during the process.

One additional application of C ratings is in terms of maximum discharge rates. The maximum current which can be safely drawn from a battery is one way of measuring the quality of a pack, so identical capacity packs can be rated differently. A 2200 mAh lipo battery pack rated at 20C should be limited to a maximum discharge current of “20×2 = 40 Amps”, whereas a 2200 mAh lipo battery pack rated at 50C can theoretically be loaded at “50×2 = 100 Amps”. These C ratings are established by the manufacturers and there is some variation in the interpretation of this assessment. Modellers are therefore recommended to approach such maximum currents with caution.

Buying used batteries

Extreme caution should be exercised when considering buying used batteries, as you will usually have no real idea of the history of the battery or its 3 + 3 can provide more than 6 If may be worth buying two smaller batteries instead of one larger one. For example, if you needed a 6S 3,700mAh lipo, consider purchasing two 3S lipo 5000mah 7.4 v battery instead, which would be used in series and dedicated to that model. In this way, if damage occurred to one of the batteries, at least one would still be able to use the other one in a smaller model, thus retaining some of the value of your investment.

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How to Choose Lipo Charger for Lipo Battery

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There are various chargers available in the market but I’ll help you to choose a smart charger to charge your RC’s battery. And which prevent your battery from overcharging, battery heating, charging losses etc. there are two type of chargers available first one is Non-Programmable chargers, Programmable chargers. There are various parameter we have to know about them before further discussion like charging current, power required by charger, maximum output voltage by charger, its input voltage, max power output by charger, USB connecter etc.
Some things to consider when buying a charger
Cell compatibility
There are maximum and minimum LiPo cell count, the battery charger can handle. For example some battery charger supports up to 6S, some even up to 8S, but they might not be capable of charging 14.8 lipo battery. Make sure you know what cell count the charger supports. Some very cheap lipo chargers will only support 2S or 3S, where the fanciers ones will be able to support the full range from 1S to 6S. Other higher end chargers are also able to balance charge more than one LiPo at the same time.
Charge Current Rate
LiPo batteries are often recommended to be charged at 1C current rate for various reasons, although some more expensive LiPo batteries these days are advertised as fast charging, which can be charged at 2C or even higher. The main reason for charging at lower current is safety, and to prevent the battery gets too hot, which might cause the battery to go “puff” and shorter battery life.
Basically, to charge at 1C, it means if you have a RC 2S lipo batteries, your charge current would be 1 x 2000mA = 2A; But to charge at 2C, the charge current is 2 x 2000mA = 4A.
Charger Power
LiPo Charger Power is measured in Watt which is calculated by multiplying voltage (Volts) and current (Amps). If your charger does not meet the power requirement, you might find it charge your battery at a lower current.
For example, to charge a 3S 2000mAh LiPo at 12.6V at 1C (2A), you will need a charger that are rated for 25.2 watts (= 12.6V x 2A). So it’s clear that if you want to charge at 2C (4A), you will need double of the power which is 50.4W. If we want to charge a 3S 2200mAh battery at 1C we will need to use 12.6V x 2.2A = 27.72W. If we want to charge a 3S 5100mAh battery at 1C we will use 12.6V x 5.1A = 64.26W which is actually a little over the standard power rating for chargers. So we an only charge our 5100mAh battery at 50W/12.6V = 3.6A assuming we have a 50W charger.
How A Good Charger Balances Your LiPo
The core reason you need a compatible LiPo charger is because of how efficiently it can balance your LiPo battery during charging.
  1. There is a technical meaning for the word ‘Balancing’. It refers to the act of equalizing the voltage of each cell in a battery pack.
  2. Through balancing, you can ensure that each cell making up a LiPo battery discharges the same amount of voltage.
  3. A direct consequence of such balancing is a LiPo that performs at its optimum, not to mention safely.
  4. There are external stand-alone balancers available on the market but a smart shopper will go for chargers that have built-in balancing capabilities. In these, balancing boards do the ace job of leveling out cell discharge
In addition to keeping things compact (battery and charger in one unit) you simplify the whole charging process with a built-in balancer. Even the price of these particular devices is reasonably lower than a battery and stand-alone charger combo.
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Radio Control Receiver

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The radio control receiver is responsible for transmitting control signals from the safety pilot to the SSC and is responsible for granting or denying control to the on-board processing system.

The receiver is mounted just in front of the network ports on the encloure’s mounting plate. Servo tape is used to secure the recevier to plate. The last step of this installation is to hook the recevier channels to the enclosure’s input channels (block 4 in Figure 20). This requires seven male to male servo cables. In order from pins one through nine (left to right) on the SSC interace board the connection are: channel 8,1,2,3,4,5 and 6. For power, the DSC channel on the receiver is connected to the servo power switch on the Joker Maxi-2. Note that contrary to the output channels, described at the end of Section 3.3.6, the signal wires must be on the bottom row of the connectors.

The last pieces of hardware to be mounted to the USL tested are the batteries. The battery hardware consists of a 37V 10Ah Lipo battery, 11.1V 4.2Ah Lipo battery, 4s lipo batteries, and 4.8V 2000mAh NiMh battery.

The 37V battery is responsible for powering the platform’s main motor and is composed of two heat shruunk 18.5V 10Ah batteries. This battery fits into the frame of the Joker Maxi-2 and is secured from the rear by a small Velero strap. To supply the platform’s Electronic Speed Controller (ESC) with the required 37V a small adapter cable was manufactured in-house. This cable puts the two 18.5V batteries in series and supplies the correct voltage to the ESC.

The 2200mah 3s lipo is used to power both the GPS recevier and the processing system which in turn is responsible for providing power to the remaining sensors. This battery is mounted, using Velcro, to the enclosure’s mounting plate. It is placed just between the enclosure and the square tubing towards the front of the chassis. Due to the location of this battery a small extension cable must be used to reach the SSC interface board. For safety, a small low voltage alarm is wired directly into this extension cable. This alarm constantly monitors the battery and warns the operator when the voltage is reaching a critical level.

The 11.1V 5000mah battery is solely used to power the SSC. This battery is equipped with a 3 pin male Futaba-J connector and is mounted to the top of the enclosure using Velcro. The battery is then connected directly to a HCAM2761 HD power switch. This switch is mounted to the chassis using two zipties. The power output connector of the switch is then connected to the SSC power connector on the enclosure’s faceplate.

Last, the 4.2V 2000mah NiMh battery is solely used to power the servo actuators throughout the testbed. This includes powering the platform’s control servos and the pan/tilt servos. This battery is plugged into the Futaba radio receiver via the Maxi Joker-2’s servo power switch. Power is then naturally routed from the radio receiver to the SSC interface board where it is distributed to all servo connections. A complete assembly of the testbed is detailed in Figure 31.

Before concluding this section, it is noteworthy to mention that Lipo batteries can catch fire and explode if not handled properly. This includes insuring that the individual cells don not immediately be considered a fire hazard and disposed of properly.

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Traveling with Lipo Batteries You Should Notice

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There are several advantages of Lipo batteries but there are also a few risk involved during charging, flying and transporting. We have been traveling across the US and Europe with a a number of our Lipo batteries and we always take special pro caution when traveling. Especially when traveling in an airplane. Before you go on an airplane trip, check your airline’s regulations when it comes to batteries, review if your country’s equivalence to the FAA has any guidelines. And then make sure you follow a few easy steps to improve safety and decrease the probability that something bad could happen.
There used to be some rule of numerous grams of lituim I think it was 11 grams which if i recall was about 7.4v lipo battery 5000mah that put you over the FAA limit. The rule if i recall is not to be in the suitcases in the hold but to go with carry on hand luggage. However some airlines can specifically choose to have their internal own rules and ban any lipos. That’s often targeted at laptops with extra batteries as sometimes those caught fire in the overhead lockers . Those are often the Lipo types 6s 2000mha or the modern 6s 4000 mah.
I’ve brought several Gens Ace 5000mah 3s lipo and 11000 mah as carry on many times. Here is what I do. Wrap the plug and balance terminal in electric tape. Put lipos in gallon ziplocs, usually 2 per bag. Put the ziplocs in my lipo safe bags and all this in a separate tote. At the checkpoint I take the ziplocs out and lay them flat in a tray with nothing on top. I try to make contact with an agent and say ‘hi these are my batteries.’ After I get through the scanner, Usually before my stuff, I think back and try to make eye contact with the agents at the TV, when they get that look, I smile and wave and acknowledge that the suspicious stuff is mine. I then tell them they are for my copters, oblige the extra scan and bomb residue sweep. Then go on my way. Has worked every time, even traveling to other countries.
Quantities
The amount permitted is based on watt-hours (Wh). Wh establishes the lithium content by multiplying voltage with the ampere-hours (Ah). For example, 14.40V x 5Ah battery = 72Wh.
The current IATA dangerous goods regulations and your rights as passenger to carry the LiPos with you in carry-on luggage but not in your checked luggage. There are 3 classes of LiPo batteries. Below 100Wh there are no quantity restrictions as to the amount of batteries you can carry. Between 100Wh and 160Wh you are confined to two battery packs total per passenger. Above 160Wh you are not permitted to carry the packs as carry-on.
Avoiding short circuit
As another safety precaution, though this could not be mandatory according to flight safety regulations is to avoid short circuiting the batteries thus increasing the chance of fire hazard. This is fairly simple, all you need to do is to place each battery into an individual plastic bag. This will come in handy when labeling also, see below. You may also shrink wrap the battery connectors with saran wrap. This process only takes a few seconds and reduces the possibility of electrical arcing and moisture dealing with the battery connectors.
LiPo Bags
Placing your batteries in LiPo safe bags is an absolute necessity, if you don’t have them, do not even attempt to carry them on board an aircraft. This is also for your safety. Obviously you don’t need to have a separate LiPo safe bag for each battery as you have also placed them in separate plastic bags as suggested above. But depending on the number and size of your batteries, be sure to have a bag with enough space for them all, or use multiple bags. This one is a great option, but you can buy larger ones also:
We’ve spent a ton of time combing the internet to know the rules so hopefully this post can help you out when you fly.  Here goes:
1. Do not put LiPos in your checked baggage. Should bad things happen the crew wants to be able to fight a battery fire.
2. Put the LiPos in your carryon baggage. If you’ve still got the original packaging, use it.  If not, put each battery in a separate plastic bag. Tape over the connector and the balancing plug.
3. This isn’t a rule, but I always take the batteries out at the TSA inspections and put them in a separate tub. There is not point in trying to hide them because they stick out like a sore thumb in the X-ray scan.
4. You can only carry 2 batteries greater than 100 Watt-hr (e.g. a 6S 5000 mAh) on the plane.
5. How many less than 100 Watt-hr?  Here the rules are a little ambiguous with verbiage like “a reasonable number.” I’ve carried 6 on international flights successfully.
6. This isn’t a rule, but it’s always a good idea to put the batteries in storage mode (about 50% SOC) to be safe.
7. I wish there was a single site that stated these rules but I haven’t found one. The links below are a collection of them.  I print out the relevant pages and have them with me in case of trouble. At several airports the inspectors were very thankful for this documentation and made copies of it for themselves.
8. Generally, getting through security in the US hasn’t been too bad, although you should allow extra time because they almost always do the extra sniffing tests on them. Internationally is another story because finding an English speaker is often hard.  My most difficult time was in Ulaan Baatar, Mongolia but we eventually prevailed.
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Alkaline vs. Lithium polymer battery Battery Testing

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What Is Alkaline Battery?
Alkaline-manganese, also known as alkaline, is an improved version of the zinc-carbon battery and delivers 1.5V. Lewis Urry invented alkaline in 1949 while working with the Eveready Battery Company laboratory in, Ohio, USA. Alkaline batteries are used in many household items such as MP3 players, CD players, digital cameras, pagers, toys, lights, and radios, to name a few.
What Is Lithium Polymer Battery?
Lithium polymer (Li-poly or LiPo) and lithium ion (Li-ion), is quite different from the more commonly used NiCd and NiMH. There are many things to consider before using lithium cells for eflight. But none is more important than safety. While all cells must be treated with respect due to the energy they contain when fully charged, lithium cells have the highest energy density.
Li-Ion/Polymer Battery Characteristics
The nominal voltage of a Li-Po battery cell is 3.7V (about 4.23 V when fully charged). Two and three cell batteries are available giving us a choice of 7.4 or 11.1 volts. Li-Po batteries can supply substantial current, 6A continuously and 12A for short (30-second) bursts. Li-Po cells have a flexible, foil-type (polymer laminate) case. Since no metal battery cell casing is needed, Li-Po batteries are very light. Because of the lack of metal casing and less space used in intercell spacing, the energy density of Li-Po batteries is over 20% higher than that of a classical Li-ion battery and store more energy than nickel-cadmium (NiCd) and nickel metal hydride (NiMH) batteries of the same volume.
To the left is my Mini Pulse XT aerobatic airplane. It uses the 450 motor and a 7.4v lipo battery 5000mah. Futaba 4-channel radio.
Early lithium batteries had a rather high internal resistance, and had rather low discharge rates. As with all technology that is doggedly pursued, significant improvements have been made to the point that the contemporary Li-Po batteries may be substituted in most systems for the original NiCad or NiMH batteries.
Alkaline vs. Lithium Polymer Testing
We wanted to characterize the batteries for both electronics and pyro uses. The electronics battery must supply between 7 and 12 volts at 100 mA for several hours. (We budgeted 2 hours per launch.) The pyro battery needs to provide higher current for a short period of time. Typical e-matches need 1.5V @ 1A for less than one second. Previous experiments showed that a standard 9V Alkaline could provide power for greater than ten (we stopped at 10, the battery’s charge was still very near full voltage) e-match ignitions. However, the new electronic release device we are developing requires an 18W heating element to be powered for about 15-seconds. The element would draw about 2.3 Amps from a 2s lipo 5000mah.
Batteries tested:
Alkaline Batteries – baseline case
    Three Duracell MN1604 Copper-Top 9V batteries that were new (dated to expire 48 months after the test date).
    Two Duracell MN1604 Copper-Top 9V batteries that were at expiration (dated to expire the month we tested). These batteries were stored for years at room temperature, but never used.
We selected Duracell batteries due to the recommendation of the manufacturer of our flight electronics. Apparently, their welded cell interconnect construction makes these batteries much less prone to drop-outs caused by high G-forces.
Li-Ion/Polymer Batteries
    Four Gens Ace NL606290M-3S 7.4V 800mAh (10C) Li-Po batteries
    One Gens Ace 11.1V  800mAh (10-15C) (no model number printed on battery).
    Recharging was performed with a Tenergy Universal Smart Charger (TLP2000, for 1 to 4 cells, non-balancing).
A concern we have regarding Li-Po batteries is that their technology is evolving very quickly. The battery models that we tested last month may no longer be available this month. For example, we ordered two 11.1V 500mAh (10C) batteries and received the 11.1V  800mAh (10-15C) batteries that had now replaced that “old” product line (at the old price point). We were also concerned that the manufacturer does not label their batteries with model numbers. The rapid advancement in battery technology is great, but it makes it difficult to use components that have been well characterized.
Test Equipment for 100mA discharge test:
West Mountain Radio – CBA II – Computerized Battery Analyzer and supporting software.
Test Equipment for 2.3A discharge test:
Keithley 2100 6.5-Digit USB Digital Multimeter and supporting software.
3.44 Ohm precision power resister
Procedure for the 100 mA test:
The discharge rate of our flight computer (waiting for launch) is 100mA, so that is the discharge rate we programmed into the CBA analyzer. We attached the battery to the analyzer and recorded the discharge data. The test was continued until battery voltage dropped below 7V (9V for the 11.1V batteries). Batteries were rested at least 24 hours between discharge and charge operations. During our first test using the CBA analyzer, the computer attached to it froze, resulting in the deep discharge of 7.4V Li-Po battery #1. The deep discharge damaged the battery (would not take a full recharge) so we excluded it from the results discussed below. A second similar incident occurred with 7.4V Li-Po battery #2. We reset the computer in time to save the battery, but its first test results were lost. After that we monitored the test very closely and were able to detect and correct hangs before they effected the tests. We also switched to a faster dedicated computer. This change eliminated the hang problems.
We tested one new 9V Alkaline battery, one nearly expired 9V Alkaline battery, and all the LiPo batteries using the above method.

Procedure for the 2.3A test:
The thermal element of our pyro event device is equivalent to a 3.4-ohm resistor. We wired the Keithley meter to measure the voltage across the resistor and report it to the computer every 500 milliseconds. The voltage recording was started. We then connected the battery to the resistor for a period of about 20-seconds. Then the battery was disconnected and allowed to rest for 40-seconds. This sequence was repeated 10-11 times.
Our first high current test using Alkaline batteries was performed on the nearly expired Alkaline battery. The 9V Alkaline batteries are not designed for high current use. The 100mA test is at the limit of its rated performance. The battery has a relatively high internal resistance, so trying to draw over an Amp from the battery significantly reduced the voltage at its terminals.
After the first test, it was clear that a single 9V Alkaline battery would not be able to power our 18W heater, so we placed two new 9V Alkaline batteries in parallel for the next test.
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