Rechargeable batteries, the most common ones are Ni-MH batteries, toys, flashlights, razors, etc., which are essential for families. Even early days can see the use of Ni-MH batteries in professional aircraft models. But now it has been gradually eliminated. The only thing that is still used more on the remote control (transmitter). As power batteries, lithium batteries are generally used instead, as are iron phosphates.
Two, common terms for lithium batteries
1. Battery capacity (mah): The capacity of the battery, usually we use AH (Ampere/Hour) to calculate, because the capacity is usually small in the model aircraft, it is accurate to mAH (Milliamp/Hour). In fact, the correct expression of "mah" is "mA/H". m represents the unit "milli", A represents the current unit "ampere", and H represents the time unit "hour". For example, 2200mah means that the battery can be discharged at a constant current of 2200 mA for 1 hour, and the amount of electricity released is the capacity of the battery.
2. Discharge rate (C number): In addition to the battery capacity, the more important thing is the discharge rate, which is the C number we often say! 1C means double the discharge current. For example, for a 2200mah battery, 1C current=2.2A, then 30C is: 2.2A×30C=66A. This is the maximum output current of the battery.
3. Section (S): Lithium battery cell voltage is 3.7V. A single cell is called CELL or "S" to express. If higher voltage is needed, multiple single cells are needed. Series stack, for example 2S (3.7+3.7=7.4V), 3S (11.1V)...and so on
3. How to use lithium battery
All lithium-ion batteries, whether they are in the past or in recent years, including: polymer lithium-ion batteries, lithium iron phosphate batteries, etc., are very afraid of internal short-circuits, external short-circuits, and overcharge.
Because the chemical nature of lithium is very active and it is easy to burn. When the battery is discharged and charged, the inside of the battery will continue to heat up. The gas generated during the activation process expands, the internal pressure of the battery increases, and the pressure reaches a certain level. , It will rupture, causing leakage, fire, or even explosion.
In order to alleviate the danger of lithium-ion batteries, technicians have added ingredients that can inhibit the activity of lithium (such as cobalt, manganese, iron, etc.), but these do not essentially change the danger of lithium-ion batteries. Therefore, you need to be very careful when using it!
1) Charging: The safe working voltage range of lithium battery is 2.8~4.2V, lower or higher than this voltage range, the lithium ion in the battery becomes very unstable and even causes accidents. To ensure that the battery is in a safe range, a special charger is needed. These chargers will automatically adjust the charging method according to the current state of the battery. Three stages are commonly used in lithium batteries.
①Activation: Before the charger starts charging, it will supply the battery with a small current, and at the same time detect the battery voltage change, and gradually increase the current until the set value. This process can be regarded as an activation or test charge.
②Constant current and variable voltage charging: The charger charges the battery with a constant current. As the battery voltage increases, the charger increases the charging voltage at the same time to speed up the charging speed.
③Variable current and constant voltage charging: When the battery reaches the 4.2V cut-off voltage, the battery will only charge about 70% (not full) at this time. At this time, the charger continues to charge the battery with a constant voltage and a gradually decreasing current, until the value is less than 0.1A and the battery voltage continues to rise when the battery voltage continues to rise before stopping charging. This way the battery is fully charged. Generally, the charging current in the industry is recommended to be 2C charging, that is, 2 spares of battery capacity. For example, your battery is 2200mAh, 2C charging is 2200mAHX2C=4400mAh, and the charger is adjusted to 4.4A. To charge a 350mAh battery, that is, 350mAhX2C=700mAh, the charger adjusts the charging current to 0.7A. And so on. Of course, many batteries now support high-current charging and all support up to 5C.
Let me talk about what is meant by "balance". This is an intelligent operation unique to the use of series charging for batteries above 1S.
In order to obtain a higher voltage output, we use multiple batteries in series, so when charging, there are two ways:
①Tandem charging: For example, 3S (11.1V), the charger will charge 3 cells connected in series at the same time with 11.1V voltage. (Example: IMAX B6)
②Parallel charge: For example, 3S (11.1V), the charger separately charges each cell with 4.2V voltage. (Example: UNA A6)
Obviously, the parallel charging method is independently controlled by each cell. Just like charging a single 1S battery. However, serial charging may encounter a situation. For example, one of the three batteries has reached the 4.2V cut-off voltage, while the other two have not reached the cut-off voltage. What should I do? At this time, it is necessary to "balance" the voltage of the three cells. A typical B6 is this way. It will discharge the high-voltage batteries, and then charge the whole group, and finally reach a balance and fullness.
Understand this charging process, you can understand the difference between a charger of about 10 yuan and a charger of hundreds of yuan. Inexpensive chargers only rely on a few switching tubes to achieve cut-off voltage control, which is either dissatisfied or overcharged. A good charger uses a single-chip microcomputer to detect the battery status synchronously to control the switching of the charging mode.
2) Discharge:
What needs to be paid attention to during discharge is to prevent over-discharge. The safety voltage of lithium battery is 2.8~4.2V. If the voltage is lower than 2.8V, the lithium ion will enter the attenuation state. Once attenuated, it cannot be activated and cannot be charged. But our old model friends all say "Don't go below 3.6", there may be a misunderstanding! We need to distinguish between two voltages:
①: Load voltage: when the battery is under load, such as when an airplane is flying
②: No-load voltage: when there is no power output.
For example, during flight, the battery voltage may be at 3.3V, but after a few minutes after being unplugged, the voltage will rise to about 3.6. In the past, there was no two-way transmission in the old model friends, so you can’t see the battery voltage in flight. It is basically measured after getting off the plane, so "Don’t be lower than 3.6V" has been passed down... to be correct, the load It is reasonable that the voltage should not be lower than 3.2V. Occasionally over-discharge once and a half is actually not so terrible. As long as the load is not less than 2.8, it is basically safe (depending on the battery quality, the battery is less than 3.2V, it is easy to over-discharge. There are some batteries, that is, A few tenths of a second, so it is recommended not to try it lightly)
3) Storage:
Many new chickens threw things into the box after playing the plane. Or some model friends are accustomed to recharging their batteries, and they can fly anytime when they want to fly! ,
Both of these habits are very undesirable. The best storage voltage of lithium battery is 3.7~3.8V. Lithium ions are in the most stable state in this state. Any battery has the characteristic of self-discharge (leakage). If the battery is already almost dead, if you leave it like this for a month, it may all be discharged....
Fully charged is the most damaging battery. After leaving it for 3 days or 1 week, the battery will start to bloat. You will find that the flight is weak, but the measured voltage is normal.
So current chargers, such as B6, have a special storage mode. The charger will automatically discharge or charge according to the battery voltage, and stop the battery after it is at 3.8V.
Note: The above-mentioned things are not authoritative knowledge, but only things that Tutu has learned from all sides and summed up simply by combining his own experience. If you make a mistake, please point me. Please also peers and model friends not to copy or reprint this article... It is not good to mislead the children!
Types of rechargeable batteries
Nickel-cadmium battery (Ni-Cd)
Voltage: 1.2V
Service life: 500 times
The discharge temperature is: -20 degrees to 60 degrees
Charging temperature: 0 degrees to 45 degrees
Remarks: Strong resistance to overcharge.
Ni-MH battery (Ni-MH)
Voltage: 1.2V
Service life: 1000 times
The discharge temperature is: -10 degrees to 45 degrees
Charging temperature: 10 degrees to 45 degrees
Note: The current maximum capacity is about 2100mAh.
Lithium ion battery (Li-lon)
Voltage: 3.6V
Service life: 500 times
The discharge temperature is: -20 degrees to 60 degrees
Charging temperature: 0 degrees to 45 degrees
Remarks: The weight is 30%-40% lighter than Ni-MH batteries, and the capacity is more than 60% higher than Ni-MH batteries. But it is not resistant to overcharging, if overcharging will cause the temperature to be too high and destroy the structure => explosion.
Li-polymer battery (Li-polymer)
Voltage: 3.7V
Service life: 500 times
The discharge temperature is: -20 degrees to 60 degrees
Charging temperature: 0 degrees to 45 degrees
Remarks: The improved type of lithium battery does not have battery liquid, but instead uses polymer electrolyte, which can be made into various shapes and is more stable than lithium battery.
Lead-acid battery (Sealed)
Voltage: 2V
Service life: 200～300 times
The discharge temperature is: 0 degrees to 45 degrees
Charging temperature: 0 degrees to 45 degrees
Remarks: It is a general car battery (it is 6 2V series connected to form 12V), the battery life of the battery without adding water is up to 10 years, but the volume and maximum capacity are the largest.
Explanation of battery charging terms
Charging rate (C-rate)
C is the first letter of Capacity, which is used to indicate the magnitude of the current when the battery is charged and discharged.
For example: when the rated capacity of the rechargeable battery is 1100mAh, it means that the discharge time of 1100mAh (1C) can last for 1 hour. If the discharge time of 200mA (0.2C) can last for 5 hours, the charging can also be calculated according to this comparison.
Cut-off discharge voltage
When the battery is discharged, the voltage drops to the lowest working voltage value at which the battery is no longer suitable for discharging.
According to different battery types and different discharge conditions, the requirements for the capacity and life of the battery are also different, so the specified terminal voltage of the battery discharge is also different.
Open circuit voltage (OCV)
When the battery is not discharged, the potential difference between the two poles of the battery is called the open circuit voltage.
The open circuit voltage of the battery varies according to the materials of the battery's positive, negative and electrolyte. If the materials of the battery's positive and negative electrodes are exactly the same, then the open circuit voltage will be the same regardless of the size of the battery and how the geometric structure changes.
Depth of discharge DOD
In the process of battery use, the percentage of the battery's rated capacity is called the depth of discharge.
The depth of discharge has a deep relationship with the charging life of the secondary battery. When the depth of discharge of the secondary battery is deeper, the charging life will be shorter. Therefore, deep discharge should be avoided as much as possible during use.
Over discharge
If the battery exceeds the battery discharge termination voltage during the discharge process, the internal pressure of the battery may increase when the battery continues to be discharged, the reversibility of the positive and negative active materials will be damaged, and the battery capacity will be significantly reduced.
Over charge
When the battery is charging, if it continues to charge after it reaches a fully charged state, it may cause the internal pressure of the battery to increase, battery deformation, night leakage, etc., and the performance of the battery will also be significantly reduced and damaged.
Energy density
The electric energy released by the average unit volume or mass of a battery.
Generally, in the same volume, the energy density of lithium-ion batteries is 2.5 times that of nickel-cadmium batteries and 1.8 times that of nickel-hydrogen batteries. Therefore, when the battery capacity is equal, lithium-ion batteries will be better than nickel-cadmium and nickel-hydrogen batteries. Smaller size and lighter weight.
Self discharge
Regardless of whether the battery is used or not, due to various reasons, it will cause the phenomenon of power loss.
If calculated in a month, the self-discharge of lithium-ion batteries is about 1%-2%, and the self-discharge of nickel-hydrogen batteries is about 3%-5%.
Cycle life
When the rechargeable battery is repeatedly charged and discharged, the battery capacity gradually decreases to 60%-80% of the initial capacity.
Memory effect
During the charging and discharging process of the battery, many small bubbles will be generated on the battery plate. Over time, these bubbles will reduce the area of the battery plate and indirectly affect the battery capacity.
Does it take 8-12 hours to charge the newly purchased rechargeable battery?
No matter any battery has the characteristic of self-discharge, so when a new rechargeable battery arrives in your hands, the rechargeable battery may have been self-discharged for a period of time. This is that the chemical raw materials inside the rechargeable battery have not been used for a period of time, and the "passivation" state appears, and the chemical reaction cannot be fully exerted to provide sufficient voltage. In this case, when using the rechargeable battery for the first time, be sure to fully charge the rechargeable battery to restore the voltage to its original level. In fact, if your rechargeable battery is not used for a long time, this "passivation" phenomenon will also occur, and the situation will be more serious. It is best to charge and discharge the rechargeable battery three times, which will help the rechargeable battery to activate. Let the chemical substances in the rechargeable battery give full play to its due effect (nickel-cadmium battery). Sometimes when a newly purchased rechargeable battery is put into the charger, the charger will stop charging before it is fully charged. When you encounter this kind of problem, you only need to remove the rechargeable battery from the charger, and then put it in the charger to continue charging. This is a normal phenomenon for new rechargeable batteries, and it is not that you have purchased bad rechargeable batteries (Ni-MH, Li-ion batteries). Generally speaking, the charging time cannot be too long, and up to 12 hours is sufficient. If overcharged, it will cause damage to the rechargeable battery.
How to calculate the charging time?
Charging time (hours) = rechargeable battery capacity (mAh) / charging current (mA) * 1.5 coefficient
If you use a 1600mAh rechargeable battery and the charger uses a current of 400mA to charge, the charging time is: 600/400*1.5=6 hours (note: this method does not apply to newly purchased or long-term unused rechargeable batteries)
Ni-MH rechargeable batteries and Li-ion rechargeable batteries actually have a memory effect, do they really need to be discharged when used?
In fact, the memory effect of the Ni-MH rechargeable battery and the lithium-ion rechargeable battery is very slight, and it is not worth our attention.
(Please note that when you see this, do not use the discharge function of the charger to discharge Ni-MH rechargeable batteries and lithium-ion rechargeable batteries, especially lithium-ion rechargeable batteries. Due to their own material factors, the battery itself is not allowed to withstand The forced discharge of the charger. If you insist on discharging the lithium-ion rechargeable battery, the battery will eventually be damaged.) In addition, if you use a nickel-cadmium rechargeable battery that needs to be discharged, it is recommended that you, regardless of whether the battery is used frequently or not, the most Good to charge and discharge the nickel-cadmium rechargeable battery every two to three months or so, so as to ensure that the memory effect of the nickel-cadmium rechargeable battery is minimized.
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