Monthly Archives: February 2016

The Lipo Batteries for RC Motor Project

Lipo battery is used as a power source for quadcopter due to high power to weight ratio. NiMh is more cost-effective, but heavier than Lipo, hence it is not preferred. Lipo battery can be found in a single cell (3.7 V ) in a pack of over 10 cells connected in series produces 37 V. A popular choice of battery for a quadcopter is the 3SP1 batteries with terminal voltage of 11.1V. Battery has peak discharge rate of 25 times the rated capacity and a capacity of 5000 maAh will deliever maximum current of 25 C × 5000 mAh = 125 A.

gens-ace-lipo-battery-4400mah-60c-6-cells

The batteries for RC motor project can be changed depending on what you want to use. I decided to try and keep this bot relatively lightweight by using Lithium Polymer batteries, abbreviated Lipo. Lipo batteries are typically 3.7v per cell and lightweight compared to lead acid for their charge capacity. These batteries must be charged with a Lipo-specific charger and must not be discharged beyond 3.0v per cell or risk catching on fire;so only use these batteries if you understand how to handle them.

Many online hobby shops have excellent pricing on Lipo batteries and chargers, making them affordable even on a budget. I found Gens ace 4s lipo for only $15 each. They have a 20c discharge rate, meaning that by itself, this battery is capable of discharging approximately 60 Amps continuously (3Ah × 20c = 60 A continuous). If you use two of these packs in the parallel, the discharge rate doubles to 120 Amps (6Ah × 20c = 120A).

To get more power to the motors, I decided to place two packs in series to make 22.2Vdc and 3000mAh. You can buy as many of these as syou can afford and place several 22.2V (series packs) in parallel to achieve 6Ah, 9Ah, 12Ah, and so on. The Lipo battery packs weigh only approximately I pround per set, whereas a comparable SLA battery weighs approximately 6 pounds. Of course, the Lipo batteries are about twice the price of a comparable SLA battery, but you should buy only as many Lipo batteries as you need Amp Hour capacity to decrease the weight on your robot.

Alternatively, you can use Sealed Lead Acid batteries to get around having to buy a Lip charger only or worrying about over-discharging. Two standard 7.4v 2200mah lipo battery would fit nicely in this frame. As you can see from Figure 12-21, either type of battery has plenty of room in this frame.

How to Choose Lipo Battery for RC vehicle

If you call yourself a hobbyist or a kid at heart, you know that remote-controlled vehicles are more than just fun. If you’re a serious R/C man, you’ll know all about doing everything to your model truck or car, like fixing wheels, vamping the pinion gears, waterproofing, troubleshooting, electronic diagnostics, setting up, programming and finally racing. As much as you know about these remote-controlled vehicles, it will never be enough, you’ll always be looking for more. This article tutorial will teach you how to select the right LiPo battery for a remote controlled vehicle.

At first you should know the discharge rate and capacity of lipo battery

Battery Discharge Rate and Capacity

Probably the most important, but often overlooked factor to is the check the battery discharge C rating is the optimum for your drone. Using a discharge rate (C rating) that is too low, can result in your battery being damaged, and your drone 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 dont need, ultimately reducing the flight time.

The battery capacity rating (usually measured in milliamp-hours [mAh] or amp-hours [Ah]) is how much energy a battery can store. Similar to the size of a fuel tank, a battery with a higher mAh rating will last longer on a single charge. A 1000mAh or 1Ah battery can produce 1 amp of current for 1 hour. The discharge rate of a multirotor is much higher than 1 amp, so a more realistic example would be a 2000mAh battery can produce 12 amps for 10 minutes, while a lipo 5000mah battery can produce 12 amps for 15 minutes.

The tradeoff to a higher capacity battery is weight; you can increase a battery’s capacity to increase flight time, but the increased weight will reduce efficiency. At a certain point increasing the battery capacity will not increase the flight time because the battery is too heavy. For a tricopter the size of the TITAN, a 2200mAh (2.2Ah) is a good size to look for.

battery discharge time

Battery Discharge Rate:

This is the final thing that you must consider while choosing the batteries. This actually refers to the amount of time taken by the battery for safe and complete discharge. In case of LiPo batteries, the discharge rate is indicated by “C”.

If the discharge rating for any battery is 10C, this means that the battery will be completely discharged at a rate which is 10 times more than the capacity of the battery. Higher the discharge rate, the better it is.

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.

(MA*3)/BC=C

Where MA is the full throttle current each motor draws in amps, BC is the battery’s capacity in amps, and C is the required discharge rating. For example: let’s say you you’re using the 980kv T-motors from earlier with a 2s lipo 5000mah and a 10×4.7” prop, from the datasheet you can see that at full throttle this configuration will draw 14.4 amps. Since you have 3 motors on a tricopter, you multiply that by three, then divide the result by the battery capacity in amps to determine the required C rating:

(MA*3)/BC=C

(14.4A*3)/2200mA=C

(43.2A)/2.2A=C

19.6=C

So in this case you would want a 2200mAh battery with a C rating of at least 20, but it’s usually better to be safe so I would bump that up by at least 20%.

Battery Unequal Voltages In Series Strings

In a small battery with just a few cells in series, the charger voltage is divided nearly equally among the cells. For example, when charging a standard lead-acid starter battery for a car, a constant voltage of 13.5V is applied to it, and each of the six cells within it sees about 2.25V. If any cell is charged more, its voltage will be a bit higher, taking away some voltage from the other cells. For example, if one cell is at 2.5V, the other celss will be, on the average, at 2.20V. That delta voltage among cells is perfectly acceptable; lead acid cells are much more rolerant to variances in their voltage.

For another example, a small Lipo battery for a consumer product may have two cells in series. When charging with 8.4V, if the cells are balanced, each cell sees 4.2V. If the cells are out of balance, in the worst case the most dicharged cell will be at 3.3V, leaving 4.9V on the most charged one. 4.9V is above the maximum rating for a Lipo cell (4.2V), but it is still low enough that is not going to go in the thermal runawy and catch fire.

In a high-voltage battery with many cells in series, though, there is a much greater chance that the overall pack voltage is not evenly divided among its cells. Here recommend a high security lipo battery for you.

High Security Gens Ace 7.4V 1300mAh LiPo Battery

7-4v-25c-lipo-battery

The security is the most important performance to a rechargeable battery. Without the security concern, battery will never be welcomed by people no matter how nice performance it has. Gens Ace 2s lipo battery 5000mah is the representative of li-polymer batteries. Along with the upgrading of rechargeable batteries, it is popular with more and more copter players. Li-polymer is charged with constant current and voltage. At the same time, it is equipped with a protecting circuit board to prevent the battery over charging or discharging. Besides, the outer of li-polymer batteries is with aluminum materials, which is different from the metal shell of liquid lithium electricity. Therefore, you can see the hidden trouble once the package is in deformation. Also, it will not explode but ballooning if there is any hidden problem.

Consider a 7.4v 2s lipo, charged up to 16.8V. If the cells are perfectly balanced, the total voltage will be equally divided into 4.2V per cell. In practice, the cells will be unbalanced, and one will be the first to be fully charged and then be overcharged. Lipo cells do not deal well with overcharging. Once charged, they cannot take more current as the other cells in series get their needed charge. Instead, their voltage rises rapidly, possibly to dangerous levels. In this example, the second cell is overcharged to 6.3V, while the other ones are around 3.5V. Despite the fact that the total voltage is 16.8V, three of the cells in this battery are not fully charged, and one of its cell is in danger of thermal runawy. Therefore, a system that relies on the total battery voltage to determine when to stop charging the battery gives the user a false sense of security; the system will overcharge some cells, and will create a safety issue as some cells with be overcharged to dangerous levels. It is therefore essential that a BMS monitor such a batter, first and foremost to prevent any cell from being overcharged, and optionally to balance the battery to maximize its performance.

Gens Ace 2S and 3S Lipo Battery Packs Introduction

LiPo batteries changed the RC world when they came out, but they’ve stayed relatively the same for peak voltage. Now Basher Racing by HobbyKing is among a few manufacturers releasing their own version of a high voltage pack labeled LiHV and are available in 6600mAh and 5600mAh hardcase packs. These packs also weigh less and continue to hold higher voltage under load. All of this in a budget-friendly price. Read the official press info from Basher below.

Gens Ace 3S 5000mah Lipo Battery Pack

It is everyone’s dream to run a full race and win the final. In order to do this, you need to get an long lasting lipo battery. Gens has released its Gens Ace, which can give your cars more run time per charge and more power than any other lipo batteries of the same type. Read on to know more about this part!

The Gens Ace lipo 5000mah comes in a hard case lipo 3s 5000mah battery pack. Compared to normal stock batteries, the 5000mah 3 cell 45c 11.1v Lipo can have more than triple of the run time per charge which allows you to run a full race TWICE without pull to the pit stop to change batteries. Comparing to the Ni-Mh’s or NiCd packs, these types of lipo has a much smaller physical size which will easily fit in your RC car and it is also lighter which makes it also a perfect choice for the crawlers that runs on the rocky or hash environments.

Gens Ace 5000mAh 2S 7.4V 60C Hardcase Lipo Battery

The new number one in performance and price! The Gens ace lipo 5000mah deliver the power and and run time needed for high performance models at a price anyone can afford. These hard case packs are 60C continuous with a burst rating up to 120C. Heavy duty 12AWG wire helps deliver this power while keeping resistance to a minimum. Each pack comes equipped with a bullet connector sized perfectly for the vehicle class and a XH style balance connector commonly found on all Gens Ace lipo batteries.

Gens Ace 3S 2200mah Lipo Battery Pack

This Gens Ace 25C 2S 2200mAh 7.4V LiPo Hard Case battery pack is meant to power your remote-controlled model so it achieves peak performance. With features like ultra low resistance 12 AWG soft silicone wire leads and our patented High Current Universal Plug System, you can depend on. Includes plug adaptors to fit Deans, Traxxas, Tamiya and EC3 plug types.

Gens Ace battery packs feature innovative construction and materials including: High impact resistant polymer outer case; Grade A Lithium Polymer Cells; Posi-Weld tabs for the highest durability and conductivity possible. Do not leave anything to chance with your batteries. Trust Gens Ace for long LiFe and consistent durability run after run.

Features

Battery Type: Lithium Polymer (LiPO)
Battery Capacity: 2200mAh
C Rate and Maximum Continuous Discharge (Amps): 25C (125A)
Plug Type: Venom UNI Plug. Compatible with Traxxas Plug, Tamiya Plug, Deans Plug & EC3 Plug.

Gens Ace batteries are lipo batteries which don’t have the memory effect so you can charge and recharge for over 1000 times. It can give your cars triple run time per charge and more power than any other lipo batteries of the same type. You can now run a full race TWICE without pulling to the pit stop to change batteries.

The Connection about ESC and Lipo Battery

Electric RC planes, boats and cars use batteries and Electronic Speed Controls (ESC) to control the motor. The ESC has two sets of leads, one runs to the motor, the other set to the battery pack. While it can be advantageous to solder the motor to the ESC, the same is not true for the battery. LiPo battery packs are rechargeable and need to be removed from the RC vehicle before charging. Some LiPo packs come with a connector already installed, others with nothing but a pair of wires.

What is an ESC?

ESC stands for Electronic Speed Control. Either the flight controller or radio receiver sends signal to the ESC, and the ESC drives the brushless motor by providing the appropriate level of electrical power.

The ESC thinks it is connected to a LiPo battery because it was programmed that way. Low Voltage Cut off (LVC) reduces power to the motor when the voltage drops to a pre determined level (usually 3V per cell for LiPo) to prevent damage to the battery. If you are not using a LiPo you need to disable this functionality. In the manual for the ESC there is a programming procedure which can disable this.

A 3s gens ace 5000mah lipo is 12.6v fully charged, a fully charged 12v lead acid is higher then that, so the ESC probably thinks you connected a 4s lipo. The LVC for a 4s would be 3v x 4 = 12v. When your motor starts pulling amps the voltage drops. It will quickly drop below 12v with how many amps you are trying to pull. This will trigger the LVC which will drastically reduce power to the motor.

gens ace 2200mah

ESC refresh rates vary. For multi-rotors, given the balance of multiple motors critical to the craft’s ability to stay airborne, high refresh rates are more important than many other hobbies where ESCs are used.

The only other major factor to consider is an ESC’s maximum current rating, which must exceed the current draw to each motor. Generally, 30 A for medium/large quads and 10 to 12 A for a small quad is plenty.

Clearly, those are high current draws. But such is the nature of multi-rotors. A medium-sized hex can easily pull 40 A on a steep ascent. As a result, hefty batteries are a necessity for decent flight times.

The industry standard is lithium-ion polymer (LiPo) batteries. Relatively lightweight, compact, and offering high discharge rates, LiPos are well-suited for multi-rotors.

There are three to consider as you start perusing the cyber-aisles of LiPo batteries. The first is voltage. A single cell supplies a nominal voltage of 3.7 V (4.2 V at full charge). Each additional cell wired in series adds 3.7 V to the nominal voltage of that pack. Cell counts are denoted by the number of cells followed by “S”. A 2200mah 3s lipo battery LiPo, therefore, is a battery of four 3.7 V cells at a summation of 14.8 V.

LiPo packs also have C ratings that indicate the maximum rate at which a pack can be discharged, with C standing for capacity. A 20C pack can be discharged at a rate 20 times its capacity.

Capacity, therefore, is the third important factor. It’s measured in milliamp-hours (mAh). Let’s say our 20C pack has a capacity of 4000 mAh. Given what we know about C ratings, we can do the math and determine its maximum discharge at up to 80,000 mA, or 80 A. Similar to ESCs, you need a discharge rate that’s higher than the combined draw current of your motors.

How to Connect ESC to a LiPo Battery

Following the instruction to connect ESC to Your Lipo battery

Instructions

  1. Use your volt meter to determine which lead is positive and which is negative from the battery. If you reverse polarity to the ESC it will either damage the ESC or simply not work.
  2. Look at the wires attached to the ESC, there should be a + and – screened onto the board to indicate the proper polarity. Brushless ESC’s will have three wires running to the motor and two wire to the battery, however, brushed ESC have two wires to each device. Be sure you are working with the battery wires.
  3. Select the type of connector you want to use, most hobbyist use Dean’s connectors. There is a male end (has prongs protruding) and a female end (has sockets that accept the prongs) connectors. It is common to place the female connector on the battery and the male on the ESC.

Strip about a quarter inch of insulation off each of the four wires. Place a 1-inch long piece of heat shrink tubing on each wire. Place the heat shrink as far from the bare end of wire as possible.

Solder the connectors to the wires. Make sure the prongs and sockets align properly to keep the polarity correct. Once the solder has cooled slide the heat shrink tubing over the solder. Use a match or lighter or even your soldering iron to shrink the tubing tight.

Lipo Batteries in Serial and Parallel Connection

Battery packs achieve the desired operating voltage by connecting several cells in series; each cell adds its voltage to the total terminal voltage. Parallel connection attains higher capacity for increased current handling; each cell adds to the ampere/hour (Ah) count.

Serial Connection

Portable equipment needing higher voltages use battery packs with two or more cells connected in series. Figure 1 shows a battery pack with four 3.7v cells in series to produce 7.4V . In comparison, a six-cell lead acid string with 2V/cell will generate 22.2V, and cheap 2s lipo batteries with 3.7V/cell will give 7.4V.

Parallel Connection

If higher currents are needed and larger cells are not available or do not fit the design constraint, one or more cells can be connected in parallel. Most battery chemistries allow parallel configurations with little side effect. Figure 4 illustrates four cells connected in parallel. The voltage of the illustrated pack remains at 1.20V, but the current handling and runtime are increased fourfold.

lipo battery wiringFollowing is some examples for Lipo battery in Series and Parellel, you will know clearly about series and parellel.

Connecting a pair of 2s, 7.4v, 2200mah, 20c LiPo’s in Series:

This will increase the VOLTAGE x 2 but the mAh and Discharge Rate (C rating) will remain the same for a result of 5000mah 3s lipo 20c. Exactly the same as a single 3s, 11.1v, 5000mAh 20c battery.

Connecting a pair of 2s, 7.4v, 2200mAh 10c LiPo’s in Parallel:

This will increase the MAH and C RATING x 2 but the voltage will remain the same for a result of 7.4v, 4400mAh, 20c. Exactly the same as a single 2s, 7.4v, 4400mAh 20c battery.

Batteries in series = add the voltages/# cells together, capacity (mAh) of both must be the same and it doesn’t change.

Batteries in parallel = add the capacities together, voltage/# cells must be the same and doesn’t change.

3S 2200mAh in series with 3S 2200mAh = 6S 2200mAh

3S 2200mAh in parallel with 3S 2200mAh = 3S 4400mAh

For example, a 10C 3S 1500 mah and a 25C 3S 2000 mah pack in parallel should only be expected to put out 35 amps, or 10C of a 3500 mah parallel setup.

When you connect 2 LiPo’s in parallel yourself, you make the tradeoff of Weight and convenience. Your pair of 2s, 7.4v, 2200mah, 10c batteries will double both the mah (to 4400mAh) and the Discharge rate (to 20c) and function the same as a 2s, 7.4v, 2200mah, 20C battery. They will, however, be heavier overall than a single 2s, 7.4v, 4400mah, 20c LiPo. The 2 batteries having 2 power wires and 2 balance/charging wires as well as the wiring you do to connect them also add to your overall weight. You also have to make connectors for it all (or buy them) and plug, unplug and charge the batteries individually instead of dealing with just one.

The Number of Lipo Battery Voltage and Capacity

LiPo batteries act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. {It’s vital|It’s critical} not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can break the battery.

Here is a list of Lipo RC battery pack voltages with cell counts most beginners will be using;

3.7 volt battery = 1 cell x 3.7 volts (1S)
7.4 volt battery = 2 cells x 3.7 volts (2S)
11.1 volt battery = 3 cells x 3.7 volts (3S)
14.8 volt battery = 4 cells x 3.7 volts (4S)
18.5 volt battery = 5 cells x 3.7 volts (5S)
22.2 volt battery = 6 cells x 3.7 volts (6S)

The maximum is 4.2 V/cell, and this ought to be checked on occasion to make sure the charger remains in calibration. When the voltage reaches this point the charge switches from constant current to constant voltage mode, tapering down the current to a cutoff point (usually around 50 mA).

The minimum voltage of 3.0 V/cell is questionable. Usually you don’t want to go even that low if you want your Li-Po’s to last. They suggest to only discharge them to around 80% of capacity. The no load per cell voltage could be much higher then 3.0V. I would say around 3.5 to 3.75V no load after a 80% discharge.

You will find that most average park flying foam/electric airplanes will run on a 3 cell battery. Many micro sized flyers will use 7.4v lipo battery 5000mah, and EDF jets and high performance planes will typically use 4 cell. Some of the really fast EDF setups will use 5S or even 6S setups, but they are relatively rare. Occasionally, the electronics in the plane will actually accept two various kinds of batteries. For example, one model airplane might accept 2S and 3S batteries, while another might accept 3S and 4S batteries. Its very important that you check with your plane’s manufacturer to determine what you can use. In situations where you use a battery with too high a voltage, its very likely that you will burn out the engine probably in mid flight, quickly destroying your entire airplane. Both the ESC and motor need to support the quantity of cells (i.e. the voltage) that you plan to use with them.

Capacity indicates how much power the battery pack can hold, and how long it will take to be flat based on the load you put on it. Capacity is measured in milliamps hours (mAh). On larger capacity batteries (such as 12v car lead acid batteries) this rating is measured as amps hours (ah).

For example, an RC Lipo battery that is rated at 1000 mAh would be completely discharged in one hour with a 1000 milliamp load placed on it. If this same battery had a 500 milliamp load placed on it, it would take 2 hours to drain down. If the load was increased to around 15,000 milliamps (15 amps), a very common current drain in a 400 sized RC helicopter while hovering, the time to drain the battery would be only about 4 minutes.

You can technically get as high of a capacity as you want, it will never harm the electronics in the RC airplane. Just keep in mind that higher capacity batteries have more of the LiPo gel inside of them to store the extra energy. This adds weight, and foam aircraft need to stay relatively light. Usually, the battery is the heaviest thing in the plane, by far, even at low capacities. Once you get too heavy you will fly slower, it will become very easy to stall and you may lose control of your aircraft. For this reason, I suggest you try to keep the size of the battery reasonable. If your airplane comes with a 1800 mAh battery, don’t put a 4400 mAh 7.4 lipo battery in it. You could try a 2200 mAh or 2650 mAh, but be very careful before you go higher.

High Capacity RC Batteries from Gens Ace

Gens Ace RC batteries are specifically designed to deal with the demands of model racing and feature high capacity cells for longer running times. They maintain their voltage even on high current demand, with minimal voltage drop ensuring that the batteries perform when you need it most, and giving you that edge you need when racing. In addition to supplying RC car model batteries to competitive customers we also provide model batteries for the general public and power many RC controlled cars with our batteries country wide. RC cars are a popular hobby for all ages and provide a high intensity and exciting way to race cars from the comfort of your chair.

The Influence Electric-powered Model Airplanes

I’m now learning about many of the factors that influence electric-powered model airplanes. Factors like the weight of materials, gluing techniques, aerodynamics, balancing airplances for flight, why a plane won’t fly, ect. There are several critical factors that make an electric airplane fly well:

RC-Model-Jet-Airplane

* Weight – Keep it light by using light-weight materials. Air weighs less than balsa and balsa weighs less than plastic and glue. Use a light-weight covering if you’re building with balsa. RAMcrolight covering is like Monokonte, but weighs a lot less (035 oz/sq ft for Microlight vs 25 oz/sq ft). Use the correct type of balsa in various parts of the model to botain the best weight-to-strength ratio. You’ll need to a good set of scales to measure the weight of materials you use.
* Motor – Select the proper motor. The less expensive ‘can’type motors are inexpensive, but inefficient. A coreless or brushless or cobalt motor will be more efficient and deliver more battery power to the propeller. The price difference is impressive. A‘can’motor often costs less than $20 for 65% efficiency while the coreless, brushiess or cobalt motors are often $100-$300 for 80-90% effciency, depending on the size of the motor. Another option is a coreless motor. It has no metal core and therefore weighs much less than other motors. A coreless motor may have efficiencies of 80-90%。
* Batteries – select the proper type and capacity battery for the motor. I’ve enjoyed experimenting with batteries for my electric airplanes. NiCd batteries are best for high-current draw (big motors). NiMh batteries are lighter, but have lower current draw capacity. Lithium Ion batteries store more power, but have the lowest current draw capacity. If we define ‘C’as the capcity of the battery, the NiCd batteries can discharge at 10-20 times C. NiMh batteries work best at about 5 times C and Lilon batteries work up to about 2 times C. For a Gens Ace 4s lipo, this translates into discharge rates of 7-14 amps for NiCd, 3.5 amps for NiMh, and 1.4 amps for Lilon. I’ve also developed basic battery info on several types of batteries as they pertain to the electric flight hooby. Today (late 2007), battery vendors are now prodcucing Lithium Polymer batteries that replace the metal can container with light plastic. The current delivery capability has also been increased from about 2C to 20C or more. Cometitive airplaneds are now being powered by electric motors and are winning major competitions.
* Propeller – higher RPM direct-drive motors drive smaller propellers efficiently while geared motors drive larger diameter propeller better. A larger diameter propeller at lower RPM is more efficient than a smaller propeller at higher RPM. However, the application determines the propeller diameter. The propeller pitch also needs to be correct. One can trade pitch for diameter, over a small range. A 10×8 propeller will be nearly equivalent to an 11×4.7 propeller. The 11×4.7 will be more efficient and provide more power while the 10×8 will provide a higher top characteristics. Too large a propeller (diameter or pitch or both) will load the motor more and draw more current with not much performance in return. Too small a propeller will not provied optimum performance.

gens ace 5300mah lipo

A good overview of contemporary battery technology suitable for unmanned vehicle operations can be found. Ultimately the batteries selected for the payload were two 4s 5000mah lipo battery with capacities ranging from 1000 mAh to 2170 mAh. Lithium polymer batteries were selected primarily because of their low weight. They also are commerically available at any hobby store. Downsides with these types of batteries include dangers associated with fires and explosions if they are not charged properly. In addition these types of batteries cannot be carried on board an airplane, which may cause problems with shipping the mobile host. It was determinded the weight saving achieved with lithium polymer batteries far outweghed any disadvantages inherent in this type of battery chemistry. The battery selected to operate the RC car was an 1800 mAh 2S 7.4V lithium polymer battery.

As an example of the tradeoffs, the Tiger Moth uses an‘can’type motor geared at 5.9:1 that draws about 1.5 amps at full speed when driven by a 7 cell battery. The propeller provided with the Tiger Moth is a 9×7, but I’ve found that a 10×4.7 provides better performance. I haven’t noticed that the speed is slower with the 10×4.7 prop, but I have noticed that there seems to be more power for takeoffs and loops. The 650mAh and 720mAh battery packs I use provide me about 20 minutes of flying time each, as expected (figure 720mAh/1.5A = 48hours = 28 minutes on this plane/motor/prop/battery combination by running at about 1/2 throttle. I’ve tried an 11×4.7 and found the performance to be less. The thrust measurements I’ve made show the same difference in thrust with this motor and various propeller combinations – 10×4.7 provides greater thrust.

LiPo Battery Lifetime – Internal Resistance Growth

Battery life can usually only be extended by preventing or reducing the cause of the unwanted parasitic chemical effects which occur in the cells. Ways of improving battery life and hence reliability are also considered below.

Battery Cycle Life is defined as the number of complete charge – discharge cycles a battery can perform before its nominal capacity falls below 80% of its initial rated capacity. Key factors affecting cycle life are time t and the number N of charge-discharge cycles completed. An obvious example is the Depth of Discharge which is a simple reciprocal mathematical relationship, but there are many more complex factors which can also influence performance.

Lifetimes of 500 to 1200 cycles are typical. The actual ageing process results in a gradual reduction in capacity over time. When a cell reaches its specified lifetime it does not stop working suddenly. The ageing process continues at the same rate as before so that a cell whose capacity had fallen to 80% after 1000 cycles will probably continue working to perhaps 2000 cycles when its effective capacity will have fallen to 60% of its original capacity. There is therefore no need to fear a sudden death when a cell reaches the end of its specified life.

My F-22 uses gens ace 4s 2200mAh 25C batteries as the norm. Due to the way I fly the plane I can’t rely on the burst rate of other batteries so I can’t move down much unless I plan on going to very light batteries (1000-1300mAh 20C).

I paid $38 each for them and between the helicopter they were used in previously and the F-22 V1 they are at well over 200 cycles and still going strong. One is showing the early signs of getting tired (has been since a particularly bad crash that required the battery being resoldered) but it’s still got a lot of life left in it yet.

Some of my cheaper lipo 7.4 v 5000mah (I paid about $4 each) have been looked after just as well. ! is going strong, one is dead and the other 4 are beginning to show signs of tiredness after about 80 cycles. These are used in my F-18 V1 that doesn’t have thrust vectoring so they tend not to get run hard either.

All of the above occasionally get charged at the field.

My Gens Ace 1600mAh 20C from my T-50 V1 (get run hard) are at about 40 cycles and going strong but I never charge them at the field. There is another guy at the field using the same batteries being run about as hard and they are beginning to get tired after about 40 cycles.

There are some things you can do to extend your battery investment life:

• Store your batteries at the proper storage voltage of roughly 3.7 vpc. Don’t get hung up on exact voltage as a range of 3.6 to 3.8 vpc is good enough. On the higher side for long term, on the lower side for short term. Point is never ever store them fully charged/ discharged or sit more than a day fully charged up. That will cause swelling and damage.

• Store them in a cool dry space. A good place is in a zip lock bag in the door of your refrigerator, but not freezer. Cool batteries last longer, warm batteries age faster for any battery type. Just don’t confuse that with operation. You want your batteries warmed up before using. Ri decreases significantly as the battery warms up, and Ri rises significantly when cold. Put a cold battery in your plane and you will notice sluggish performance until it warms up. By warm I mean 80ish, not hot above 90.

• Just because you can charge faster than 1C or up to 100% SOC does not mean you should. Current flowing through resistance creates heat and heat is your batteries enemy and causes the swelling. Try to use discipline and charge at no more than 1C. You battery will stay cooler and significantly lessen the chance of thermal runaway where your battery can explode into flames. No reason to take your battery to 100% SOC. You can sacrifice a minute of run time by only charging to 90% SOC or 4.13 volts per cell. Doing so will double your cycle life. Likewise don’t push the discharge to 3 volts. Set LVC to 3.2 vpc. Following this one tip alone will double your battery cycle life.

• Use the right C-Rate for the application and leave a little head room. High C-Rate batteries are expensive. Just make sure you are not pushing the upper limit. If you have a 100 amp ESC and a 3000 mah 35C battery is cutting it to close. Give yourself some breathing room and spend a few extra dollars for that 40C battery. Again this is a heat issue, and heat is the enemy.
What else can Ri tell you? Well for one it has everything to do with C-Rates and heat. If you take two 3000 mah batteries and one has a 20C rating and the other has a 40C rating, the 40 C rating is going to have much lower Ri. For example I have such batteries although they are 3S 2600 mah one group is 25C and the other is 40C. On average the 25C group has an average Ri of 15 mo, and the 40C at 10 mo. The 25C group battery when fully charged up and supply 65 amps are sagging voltage down from 4.2 vpc to 3.2 vpc and burning 65 watts as heat on the battery. The 40C battery at 100 amps voltage sags the same 1 volt but drops 100 watts as heat on the battery. Now if I were to force the 20C battery to 100 amps I would be dropping 150 watts of heat on the battery. That sucker is going to get red hot. However if I limit current to 65 amps on the 40C battery I am only dropping 42 watts and sagging only .65 vpc and that makes for a much cooler higher voltage battery.

What if you race RC cars competitively for prize money and it is the final race. You have 10 batteries to choose from in your box of tricks. Which 1 of the 10 do you choose. Easy, the one with the lowest Ri because it is the strongest healthiest battery you got.

Selecting and Buying a New Battery For Your RC Model

When buying a new battery I suggest you purchase a battery with the greatest reserve capacity or amp hour rating possible. Of course the physical size, cable hook up, and terminal type must be a consideration. You may want to consider a Gel Cell or an Absorbed Glass Mat (AGM)

Be sure to purchase the correct type of battery for the job it must do. Remember that engine starting batteries and deep cycle batteries are different. Freshness of a new battery is very important. The longer a battery sits and is not re-charged the more damaging sulfation build up there may be on the plates. Most batteries have a date of manufacture code on them. The month is indicated by a letter ‘A’ being January and a number ’4′ being 2004. C4 would tell us the battery was manufactured in March 2004. Remember the fresher the better. The letter “i” is not used because it can be confused with #1.

Battery warranties

Battery warranties are figured in the favor of battery manufactures. Let’s say you buy a 60-month warranty battery and it lives 41 months. The warranty is pro-rated so when taking the months used against the full retail price of the battery you end up paying about the same money as if you purchased the gens ace 4s lipo at the sale price. This makes the manufacturer happy. What makes me happy is to exceed the warranty. Let me assure you it can be done.

Battery life and performance

Average battery life has become shorter as energy requirements have increased. Two phrases I hear most often are “my battery won’t take a charge, and my battery won’t hold a charge”. Only 30% of batteries sold today reach the 48-month mark. In fact 80% of all battery failure is related to sulfation build-up. This build up occurs when the sulfur molecules in the electrolyte (battery acid) become so deeply discharged that they begin to coat the battery’s lead plates. Before long the plates become so coated that the battery dies. The causes of sulfation are numerous. Let me list some for you.

  • Batteries sit too long between charges. As little as 24 hours in hot weather and several days in cooler weather.
  • Battery is stored without some type of energy input.
  • “Deep cycling” an engine starting battery. Remember these batteries can’t stand deep discharge.
  • Undercharging of a battery to only 90% of capacity will allow sulfation of the battery using the 10% of battery chemistry not reactivated by the incompleted charging cycle.
  • Heat of 100 plus F., increases internal discharge. As temperatures increase so does internal discharge. A new fully charged battery left sitting 24 hours a day at 110 degrees F for 30 days would most likely not start an engine.
  • Low electrolyte level – battery plates exposed to air will immediately sulfate. Incorrect charging levels and settings. Most cheap battery chargers can do more harm than good. See the section on battery charging.
  • Cold weather is also hard on the battery. The chemistry does not make the same amount of energy as a warm battery. A deeply discharged battery can freeze solid in sub zero weather.
  • Parasitic drain is a load put on a battery with the key off. More info on parasitic drain will follow in this document.

Where to buy LiPo Batteries?

The best retailer of LiPo batteries is www.genstattu.com which sell a huge variety of batteries in many cell configurations and capacitance for very, very low prices. The website sucks, but the prices are great.

Gens Ace High Capacity LiPo Batteries

Gens Ace batteries promises extended flight time with little to no increase in weight vs. the same mAh pack of a different brand. The Gens Ace LiPo batteries allow for an increase in the fuel tank by reducing the discharge rate; a 4s lipo batteries pack has a constant discharge rate of 10a and a burst rate of 20a. These reduced rates can be attained on multirotor platforms, making the Gens Ace LiPo’s a suitable choice.

Gens Ace is claiming increased flight times up to 20%. The packs come prewired with Deans connectors.

The Gens Ace high-capacity LiPo’s are currently available in:

4s 4000 mAh
3s 4000 mAh
3s 5200 mAh
4s 5200 mAh

There are many points and details I have not written about because I wanted to keep this as short and simple as possible. Further information can be found at the links below. If you are aware of sites with good battery maintenance information please let me know.