Lithium Polymer Battery FAQ(2)

Q3.) How fast can I charge my batteries?

Different cells can withstand different charging rates. Check with the manufacturer to make certain you don't damage your pack.
For fast charging, most packs can be safely charged in 15 minutes, which requires a charging current of 4 times the capacity of the pack.
Trickle charging is usually done at a rate of 1/10th the capacity, or C/10. Cell manufacturers list this as the charge rate in which the cells will not vent (release gases that build up from overcharging). However, even this charge rate can reduce the life expectancy of a cell if left on after the cell is fully charged.

Q4.) What is Cell reversal?
In a battery, not all cells are created equal. One will be weaker than the others. So, as the battery is discharged, the weakest cell will use up all its active material. Now, as discharge continues, the current through the dead cell becomes a charging current, except that it is reversed. So, now reduction is occurring at the positive terminal. As there is no more nickelic hydroxide, it reduces the water, and produces hydrogen. Cell pressure builds, and it vents. The cell has lost water and the life of the cell has been shortened
This is the big danger of battery cycling to prevent memory. Invariably, unless one is very careful, one ends up reversing a cell. It does much more harm than the cycling does good. Also, keep in mind that cells do have a finite life. Each cycle is a bit of life.

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Lithium Polymer Battery FAQ(1)

Q1.) Does Temperature Affect Lithium Polymer Batteries?

Yes, lithium polymer batteries are affected by temperature. All batteries use a chemical reaction to provide electricity, and a low temperature slows this reaction down significantly. You cannot harm a lithium battery by running it at a low temperature, but you will notice a significant decrease in performance. Allowing lithium polymer batteries to freeze is generally not recommended, so be sure to store the lithium battery in a cool, dry location over the winter months.

Q2.) How can I calculate theoretical flight time?

In order to calculate the maximum theoretical flight time of your models, you will need to know some information about your battery and motor equipment:
#Motor Amperage
#Pack capacity in Mah (milliamp hours)

After you have that information, you can use the following formula to compute the maximum theoretical flight time of your model:
Time (hours) = (battery capacity (amps) / (motor current (amps)

Notice how the battery capacity must be given in amps. To find your battery capacity in amps, divide the capacity in milliamps by 1000. You will probably want the result expressed in minutes. so multiply the time you just calculated by 60.

By this formula, a 33.5 amp motor powered by a 5000 Mah battery would have a run time of a run time of 8.96 minutes. This is a theoretical maximum, if you actually ran the above set up for the calculated maximum time you would destroy the battery. Most lipo batteries shouldn’t be discharged below 80%, so multiply the calculated time by .8 to account for this.

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How To Safely Use, Charge, and Discharge Lithium Polymer (Lipo) Batteries

Lithium polymer batteries are great for RC aircraft, but they have an explosive chemistry that must be treated with caution.

Prevent this from happening to your batteries by following these tips:

1. Store lithium polymer batteries in a flame proof LipoSack while charging. - Charging your lithium polymer batteries in a flame proof LipoSack can contain a fire should it occur. It could mean the difference between a minor clean up and the loss of your house or car. Also make sure that the storage area is well ventilated.
   
2. Read the manual – The importance of reading your battery and chargers manual cannot be emphasized enough. The battery manual will state the proper charging rates and times.
   
3. Use common sense – Don’t charge batteries unsupervised. Even when you do everything right, incidents can occur. Also, do not charge lithium polymer batteries in your car. A flame out can be disasterous if it occurs inside a vehicle.
   
4. Use the right battery charger – Charging a lipo battery with a charger designed for other batteries will cause problems, and will probably result in a fire.
   
5. Charge lithium polymer batteries on a fire proof surface – It’s really important to charge lithium polymer batteries on a flame proof surface such as concrete. In the event of a fire, a fire proof charging surface will stop it from spreading, or at least slow it down significantly.
   
6. Keep a fire extinguisher, or bucket of sand near the charging area – If a fire does occur, you don’t want to be running around looking for something to put it out with. Water will not help put out a lipo fire. Being a conductor, it will cause a short circuit and could even make the fire worse.
   
7. Don’t charge lithium polymer batteries near flammable substances – lithium polymer batteries are flammable enough as it is. Don’t make the problem worse by storing flammable substances near charging batteries.
   
8. Check lithium polymer batteries for swelling prior to charging and each use – A puffed battery is unstable, and can be in danger of exploding. If you see a puffed battery, immediately disconnect it from the charger or aircraft and put it in a bucket of water. Dissolve a few tablespoons of salt in the water to aid conductivity, and leave the battery in the bucked for about 4 days. The salt water depletes any power remaining in the battery by creating a short, and it can’t catch fire while underwater. After the four days are up, take the battery out and cut off the connectors (which may come in handy for other projects). You can then dispose of the battery in the trash. The battery no longer contains toxic metals, won’t harm the environment, and by using the salt water you’ve guaranteed that it won’t catch fire. This should be done as soon as you see a puffed battery. You can’t salvage a puffed battery, the best you can do is to dispose of it safely.
   
9. Never charge a lithium polymer battery in a model – If you charge a lipo battery in your RC airplane or helicopter, you are risking the total loss of your model. Only charge lithium polymer batteries on a flame proof surface, in a LipoSack.
   
10. Make sure the charging leads are connected properly – Connecting positive to negative and negative to positive can cause a major fire.
    
11. Don’t overcharge batteries – By their very chemistry, lithium polymer batteries cannot be discharged to a potential of less than 3 volts without damage. For the same reason, don’t charge them to over 4.2 volts. This means that you have to land your rc aircraft before the motors stop turning. Some aircraft come equipped with a voltage cut-off, others do not. If you don’t have a voltage cut-off, then land as soon as you sense the propeller or rotors slowing down.
    
12. Double check that the charger settings are correct – Lithium polymer battery chargers require you to set the battery configuration. Ensure that this configuration matches the battery you’re charging, or else your lipo could get overcharged and explode. Some chargers automatically sense the battery configuration, but make sure that the setting is correct regardless. They have been known to be wrong on occasion.
    
13. Balance lipo batteries – Lithium polymer batteries have balance connectors, designed to make sure that each cell in the pack has the same charge. If this isn’t the case, some cells can become overcharged and explode.
    
14. Never let the battery leads touch – If the battery terminals touch each other, the battery will short circuit and, in most cases, be destroyed. If this happens and you get a puffed battery, dispose of it by following tip 9 above.
    
15. Don’t ever store / charge lithium polymer batteries in your car – Unless you hate your car. Batteries can and do explode, and if this happens inside a vehicle the result is usually catastrophic. On a hot day, temperatures can rise inside the car and cause stored packs to rupture.
    
16. In the event of a crash, remove the battery and supervise it for at least 4 hours – A crashed plane’s battery can appear fine, but can have an internal short circuit. This short circuit can cause an explosion, even hours after the crash occurred. A LipoSack is a great place to keep a battery that’s been in a crash. If enough time elapses and nothing happens, then your battery is probably fine. If you see puffing, dispose of it immediately following the instructions in tip 9 above.

Always use common sense, read the manual, and know the risks associated with lithium polymer batteries. Handled properly, the risk of a fire is relatively small. Store lithium polymer batteries in a LipoSack for additional saftey.

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Recommend battery chargers

My friend is planning to buy a Li-polymer Battery balance charger. But he does not know choose which one is better. His intention is to get a reasonably good charger with sufficient function to take good care of the Li-polymer Battery.

He ask me what is my suggestion. I recommend two Battery balance chargers for him to choose.

- iMAX B5 Intelligent Digital Li-polymer Balance Charger

- G.T.POWER A6 Digital LiPo Li-polymer Balance Charger

I will discuss this two Battery balance chargers in next time ~bye

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knowledge of Li-polymer Battery (2/2)

Storage temperature and charge of Li-polymer Battery

Storing a Li-Po battery at the correct temperature and charge makes all the difference in maintaining its storage capacity. The following table shows the amount of permanent capacity loss that will occur after storage at a given charge level and temperature.

It is significantly beneficial to avoid storing a Li-Po battery at full charge. A Li-Po battery stored at 40% charge will last many times longer than one stored at 100% charge, particularly at higher temperatures.

If a Li-Po battery is stored with too low a charge, there is a risk of allowing the charge to drop below the battery's low-voltage threshold, resulting in an unrecoverably dead battery. Once the charge has dropped to this level, recharging it can be dangerous. An internal safety circuit will therefore open to prevent charging, and the battery will be for all practical purposes dead.

In circumstances where a second Li-Po battery is available for a given device, it is recommended that the unused battery be discharged to 40% and placed in the refrigerator or freezer to prolong its shelf life. Batteries should be allowed to completely warm to room temperature over up to 24 hours before any discharge or charge.

Permanent Capacity Loss versus Storage Conditions

Storage Temperature	40% Charge	100% Charge
0 °C (32 °F)	2% loss after 1 year	6% loss after 1 year
25 °C (77 °F)	4% loss after 1 year	20% loss after 1 year
40 °C (104 °F)	15% loss after 1 year	35% loss after 1 year
60 °C (140 °F)	25% loss after 1 year	40% loss after 3 months

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knowledge of Li-polymer Battery (1/2)

Serious Safety Issues of Li-polymer Battery

If LiPo batteries are improperly charged they can cause an explosive fireball. We cannot over-emphasize the importance of using a charger specifically designed to charge LiPo batteries, and to be positive that the manual cell count (if the charger has one) is correctly set for the specific battery being charged. If you use a good quality LiPo charger, these batteries are totally safe.

LiPo Do's and Don'ts
Do: Only use a charger that is specifically designed to charge LiPo batteries. Using other types of chargers can cause an extreme fire hazard!

Do: LiPos don't develop memory or voltage depression characteristics like Ni-Cds. Do charge them without the worry of cycling or discharging them.

Do: Store LiPos at least partially charged. LiPos will maintain their performance levels over time, even during non-use, much better than Ni-Cds and there's no need to cycle them.

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Don't: Use any type of charger that is not specifically designed to charge LiPo batteries. Using non-LiPo-specific chargers can cause an extreme fire hazard!

Don't: Fully discharge your LiPo battery pack. Most speed controller have a voltage cut off that will prevent over-discharging the battery. Discharging a LiPo beyond it's critical minimum voltage will cause damage to the battery.

Don't: If you have a crash and the battery is damaged, don't put the battery in your car or house immediately after a crash. It's possible that a chemical reaction can take place in the damaged battery that could cause a fire. Put the battery in a safe place for a least one hour.

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What Battery should I use?

What Battery should I use?



When in doubt, use your airplane manufacturer’s recommended battery. This is generally a good starting point, although with experience you will probably have your own ideas about the best battery to use. Here is some basic info about battery types.

There are three main types of batteries currently (no pun intended) in use for electric airplane motors. These are Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH) and Lithium Polymer (LiPo).

NiCads are the oldest generation of these batteries. They pack more power but are heavier than the NiMH. The NiMH voltage (power) tends to fall off fairly fast during the flight. The wonder batteries LiPos have great power for little weight and hold that power well throughout the flight. However, LiPos tend to be much more expensive than NiCad or NiMH. Again, go with the recommended battery, you will have time to experiment after you learn to fly.

Note that more cells in the battery means more voltage, which means more power.

Power (Watts) = Current (Amps) x Voltage (Volts)

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RC Lithium-ion Polymer batteries

Let you can learn more about RC Lithium-ion Polymer batteries

LiPo batteries are very different from previous generation batteries and understanding how they work, and especially how to charge them, is the key to getting the best performance.

Series
Individual Lithium Polymer cells have a nominal voltage of 3.7 volts (vs. 1.2volts per cell for Ni-Cds or NiMHs). Cells are wired in series to give the following pack voltages:
1 cell = 3.7 volts
2 cells in series = 7.4 volts
3 cells in series = 11.1 volts

Parallel
Unlike Ni-Cd and Ni-MH batteries that self-discharge when wired in parallel, LiPo cells can be hooked up, charged and discharged in parallel with no detrimental effect. Wiring two LiPo cells in parallel doubles the capacity (more run time), plus an important advantage of wiring in parallel is that each cell only sees half the total current.

3S 2P
A battery pack that has three cells in series (giving 11.1 volts) and 2 of these 3-cell packs are wired in parallel is commonly referred to as a 3S, 2P (3 series, 2 parallel).

C Rating
LiPo cells are also commonly given a C or current rating. This is the maximum average recommended discharge current for the cell. For example, the VP2150/20C packs have a 20C rating. To determine the maximum recommended discharge rate multiply the capacity times the C rating. 2150mAh x 20C = 43,000. So the maximum recommended discharge rate would be 43,000mA or 43 amps. If your application has a higher amp draw, remember that LiPo cells can be wired in parallel, and with 2 cells in parallel each cell sees half the total current. With 3 cells in parallel, each cell see one third the current.
By wiring packs in a combination of series to get the voltage and parallel to achieve the capacity and individual cell current to an acceptable level, LiPo cells can be used to power nearly every type and size of model.

Charging
Charging LiPo batteries requires a very different charge method than other types of cells. It's imperative to use a battery charger designed specifically for LiPo batteries, and with most LiPo-specific chargers it's necessary to correctly select the cell count (1, 2 or 3 cells) manually.

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Li-polymer Battery

When we play RC Model , we will use different type of battery, for example,Li-polymer Battery ,Receiver Battery, Transmitter Battery, etc.

Do you understand their use?
Today i want to share some knowledge of Lithium Polymer Battery to you~~

About Lithium Polymer Batteries
In a nutshell, a battery consists of two metals immersed in an electrolyte solution. A chemical reaction takes place that causes electrons to flow from one metal to the other. This produces a voltage difference between the positive and negative poles. When a load (such as a motor) is placed between the two poles, electrons will flow through the circuit until the metals are chemically neutralized (battery dead).

The voltage produced between the two metals is called the electrochemical potential. This energy is directly related to the types of metal used in the battery.

Lithium is the lightest metal in the universe and has the highest electrochemical potential. Lithium would be perfect for making lightweight powerful batteries right?

Well, almost... Because lithium metal is very unstable, battery manufacturers began using non-metallic lithium-ions.

Using Lithium Polymer Batteries
Lithium ion polymer batteries harness an enormous amount of energy in a very small space. These batteries will explode if used improperly. I don't say this to scare you. When proper LiPo battery safety precautions are followed, these batteries are completely safe. Lithium polymer battery care can be broke down into three categories, which are discharging, charging and storage.

Storing LiPo Battery Packs
LiPo batteries should always be stored in a cool environment. In other words, don't leave them in your car with the windows up on a hot summer's day. Keep the battery in a cool location out of the direct sunlight. It is highly recommended that Lipo batteries be kept in a charging bag while be charged and while not in used. A charging bag is a very cheap form of insurance!

Advantages of LiPo Batteries
#1
Have nearly double the capacity with half the weight of NiCad or NiMH battery packs
#2
Retain charge significantly longer than NiCad or NiMH batteries when not being used
#3
Do not develop a "memory" as NiCad batteries do
#4
With LiPo cells in combination of series and parallel, LiPo packs can be built to power most all RC aircraft

Disadvantages of LiPo Batteries
#1
Have very short shelf life of two to three years
#2
Very sensitive to high temperatures
#3
Very sensitive to high and low voltages. Exceeding either will damage the battery
#4
Prone to explode if exposed to heat, or charged/discharged improperly


LiPo Battery Safety
LiPo Battery Packs are safe as long as they are used properly. The video below is an example of what will happen when a LiPo battery is used improperly.

#1
Always let your LiPo batteries cool to ambient temperature before charging
#2
Make sure your charger is designed specifically for Lipo battery packs
#3
Double check that your charger has counted the cells correctly and is charging at or below 1C charge rate
#4
Always charge your batteries on a solid non-flammable surface in a well ventilated area
#5
Always check your LiPo batteries for any damage after a crash. If the LiPo back is punctured or damaged in any way, don't use it.
#6
Always charge and store your LiPo batteries in a charging bag! Charging bags are relatively inexpensive and could potentially prevent your housing from burning down.
#7
Never, under any circumstances, leave your batteries charging unattended
#8
Never leave your batteries inside RC aircraft while charging

Hope u have a greating and safe memory with playing Rc Model.

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