Choosing the lipo battery charger is one of the most delicate and strategic steps in buying RC equipment because it means ensuring the safety and health of the batteries of our RC cars.
Normally, the lipo battery charger is a tool intended to follow the modeler for several years, so several aspects need to be evaluated to avoid making a hasty and inappropriate purchase. Trying to save as much money as possible in buying the charger may mean, for example, regretting the choice soon and having to replace it shortly after.
We will cover the topic by referring to the features to pay attention to when choosing the LiPo charger, using the specs extracted from a real lipo charger manual.
Electrical specs of a lipo battery charger
Charging voltage
First of all, the charger must be suitable to the number of cells of the LiPo battery to be charged, which is referred to as the S number and is proportional to the rated voltage of a lipo battery: 1S is 3.7V, 2S is 7.4V, and so on.
It is worth pointing out that whether or not the P-number is indicated on the battery has NO bearing on the choice of charger, but only indicates the battery assembly methodology.
Those who have several batteries should consider the battery with the higher number of cells for the charger choice.
Charging current
The charging current provided by the charger is expressed in amperes (A) and should be considered carefully.
In general, LiPo batteries should be charged with a current of 1C, which is the current that equals the battery capacity, allowing the charge to be completed in about 1 hour.
Therefore, the charging current provided by the charger should be at least equal to the capacity of the battery to be charged.
Those who have different types of batteries should consider the battery with the higher capacity for the charger choice.
Some batteries allow charging at 2C and complete the charge cycle in about half an hour. To take advantage of this option, the charger must provide twice the current of the battery rated capacity.
Power
The power of the charger is derived from the charging voltage and current according to the law P=V x I and is expressed in watts (W).
Let us clarify this with an example.
Needing to charge a 4S 5000 mah battery, the charger MUST have a power rating of AT LEAST 14.8 x 5 = 74 watts. If the charger has a lower wattage, the complete charge will take more than 1 hour.
Power supply
Any charger needs to be powered to work. Some models can be powered only by an external DC power supply, while others have an internal power supply to be connected directly to domestic mains (AC).
Finally, other chargers offer dual power options; in this case, careful attention should be paid to the manufacturer's stated data, because the charging performance is normally lower when powered from domestic mains.
According to the example of the previous paragraph, this charger can charge the battery in 1 hour with an external power supply, because it can not exceed 50 W with domestic mains (AC).
Summarizing
Choosing the lipo charger, the electrical characteristics to pay attention to are 3:
The number of cells it can handle, considering the battery that has higher voltage.
The charging current, considering the battery that has the highest capacity.
The power, which must be at least equal to the power required by the most energy-intensive battery (the power for all the batteries should be calculated).
Caution. Charging current and power must double if we want to charge at 2C.
Technical specs of a lipo battery charger
Number of channels
The number of channels is the number of batteries that the charger can handle simultaneously. The considerations made up to this point apply to a single output, so the electrical characteristics provided by the manufacturer should be better considered for chargers with 2 or more channels.
Multi-channel chargers are increasing popularity in the racing world when there are many batteries to be charged and they must be available in a reasonable time.
In some cases, it is wiser to have multiple chargers rather than one multi-channel, to manage equipment more conveniently and flexibly and leave weight at home when it is not needed. Also, having 2 chargers is a good choice in case of failure because one charger remains functional.
Modes of operation
LiPo battery chargers have several charge and discharge options, because LiPo batteries are quite delicate and can be damaged if not handled properly.
Balance during charge
Balancing is critical for LiPo batteries and is used to ensure that the cells sre charged to the same voltage.
The balancing current is a data point for charger performance, although it is not always stated; the higher the value the faster the balancing, in favor of charging time.
Indication of internal resistance
The charger shows the internal resistance of each cell in the pack. It is a very useful function to monitor the health of the cells, which should always be a few milliohm's and not exceed 10 mΩ.
Storage
Some chargers include a storage mode that brings the voltage to a safe level of charge and preserves the battery during a period of inactivity (about 3.85 V/cell). If the battery is not properly managed, it can swell, becoming dangerous and necessitating disposal.
Recovery
This is a recovery mode for batteries that have been over discharged and are no longer recognized by a standard charger.
Discharging batteries below 3 volts/cell can cause them to be permanently damaged, but when the cell is still healthy this mode allows to restore to normal values.
Discharging
Discharge obviously needs to reduce the residual charge of the cells in the battery and is useful for several purposes.
Storage discharge
It is equivalent to the storage mode when starting from a charged battery. In fact, it may happen that you have charged the battery and not used it, and then you need to discharge it to store the battery.
Verification of residual capacity
Discharging the battery to a certain level allows the modeler to check how much actual charge remains in the battery after the training or competition session. This information is useful in understanding the percentage of charge remaining before the battery is fully discharged.
Memories and other features
Almost all battery chargers have the ability to save custom charge/discharge profiles to quickly select the type of pack without setting all the parameters each time.
More advanced chargers also have USB connection options for monitoring and control via computer or app.
Quality and Safety Certifications of a lipo charger
Batteries are extremely delicate items and could be source of danger if not treated with care.
the charger must be reliable and manufactured to high quality standards, guaranteed by rigorous testing and mandatory safety markings.
Conclusions
In this article we have listed most of the useful information for choosing a battery charger for Lipo batteries.
By the way, it is also worth thinking about the future of your hobby in terms of batteries before buying.
In fact, it may be appropriate to choose a charger that can also handle batteries that we don't have yet, but may be part of our equipment in the near future.
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