RC systems are high-tech electronic equipment to be used with a proper power source. Separated batteries and cells are not a good option, because the vibrations affect intercellular connections, and so blackout occurs. Another disadvantage is that individual cells can not be sure of their equal capacity, as some cells may be very discharged, resulting reverse polarity or deep discharge.
For safety we recommend you to use packs with welded cell batteries to power the transmitter, receiver or your model.
Batteries are widely used sources of power and easy to maintain. However, there are some basic rules to be followed when using the battery. These rules during their use will make their lives longer.
General Considerations when charging the batteries
Charging equalizing (balancing):
A new package, or one that has been long used, must always be "equalized" (all cells must be leveraged in the charge process) before being used. The same is done for any battery that is in deep discharge, the situation in which one or more cells have reversed polarity.
This operation is giving the package a load of 13-15 hours at a current corresponding to 10% (1/10) of rated capacity.
A quality charger can automatically perform this task, autodetecting the optimal load current.
A classic charger will be suitable for a normal load if it gives a constant current. A good example is UNICHARGER 6. This charger can not prevent the effect of "memory" which can be a problem for the transmitter and receiver batteries, and do not know when the charging process is over.
End of discharge voltage, deep discharge
NiCd and NiMH batteries is considered empty when the voltage is around 0.9 V/cell, measured under load (eg, package 7 cells: 6.3V). If the package is reaching this tension, the cell capacity is low and this can lead to deep discharge and reversed polarity. Reverse polarity destroys the cell, if not corrected in time. The problem can be resolved only by a slow charge for 10-14 hours. It is important to avoid deep discharge of NiMH packages as it can cause irreparable damage. In extreme cases it can open the safety valve, leading to a permanent loss of gas and electrolytes.
Procedures for charging
We need to make a difference between slow and fast charging when working with batteries. It is practically to use the term “charging rate” (C) determining the size of currents charging.
Example: A battery with a capacity of 600 mA is loaded at a rate of 1C if you set a load current of 600 mA.
• Slow Charge: slow charge is the term used for rates of 0.1-0.2C. Charging the battery has not 100% efficiency, so not all the energy inserted in the battery is turned into stored energy. This means that the standard period of charging at 0.1 ° C, is not 10 hours, but 13 hours.
• Accelerated Charge by a current of 0.3-0.5C. Charging batteries packages (especially NiMH) to this trend for a longer period can destroy the battery, because the extra energy has no place in the pack. This action triggers chemical processes and overheated battery, reducing its life. Do not overload batteries !!
At a charge rate higher than 0.2C is essential to monitor the charging process and stop it just in time (immediately after the battery is fully charged). Strong overcharging cause destruction of the battery, having lower voltage, small capacity and short life.
This means that the accelerated charging or fast charging processes must be done with chargers that feature the detection of charge termination.
• Fast Charging - is one of the main characteristics of the battery used in models.
This means that can be loaded from a stream of up to 3C, charging time is 0.5 to 2 hours.
Example: A battery with 1500 mAh capacity is loaded at a rate of 1C setting a load current of 1.5 A.
If you want to quick charge a pack of batteries, it is essential to use a charger to stop charging automatically when the battery is full. The process used is Delta Peak, which monitors the battery voltage increase. Not all processes are good for Delta Peak NiMH batteries. The sensitivity of chargers that use Delta Peak should not be less than 10 mVolts/cell. We recommend you read the instructions of the charger to determine if the charger is suitable or not for NiMH batteries.
All Delta Peak fast chargers have special programs for correct charging of the NiMH battery.
You can do a test alone: charge NiMH pack at 1C, and measure cell temperature. When charge process ends - the temperature must not exceed 450 C. If charger heats package stronger than that, it means it is not good for NiMH batteries, and will destroy the batteries.
Note: Charge the battery in the transmitter
Plugs charging of transmitters can not handle too much current, so keep it under maximum current permitted by the transmitter. If you want to use a modern charger termination detection the emitter charge protection diode must be bypassed, or batteries must be removed and charged separately.
The lifetime of the battery
Batteries can withstand 200 to 500 cycles of charging systems, varying with the quality of charging and style of use. After this period the battery is considered exhausted and can be discarded.
Batteries lose 2-3% of capacity per day, so after about 50 days - depends on the temperature - a fully loaded package is empty. This means that batteries must be loaded before use, if they have been not used for more than 14 days.
Battery storage and preservation
If you don't intend to use a battery in the near future, keep it in a cool dry place, no matter the level of discharge. The only advantage of discharging before storage, is that after the first load it will have full voltage and capacity. If the package is not discharged before storage, it will have only 90-95% of its capacity and voltage; it's maximum performance will be available only after two or three cycles of charging-discharging.