How to choose lipo batteries for RC car and the usage note
First, how to choose
The most basic, according to the actual frame of your own, choose a battery of moderate size. The specific size cannot be generalized. Please measure the actual available space of the battery compartment according to the actual situation of your own frame. After obtaining the size of the battery compartment, choose the size of the battery smaller than the battery compartment.
Choose a trustworthy brand. According to the feedback of players, everyone thinks that the one that is good is the one that is good. Such as gens, tattu, ovonic, etc.
Choose according to the withstand voltage of the ESC. The ESC can only use 7.4V but if the car running with 11.1V, it may be burned out. If 22.2V can be used on the car but only use the 7.4V, it will basically not play the best state.
Generally, 1/10 cars use 2s (7.4v) more, and 1/8 cars use 3s (11.v) or 2x 2s (7.4v).
The current lithium battery technology is so mature, basically the energy density of major manufacturers is about the same, the larger the capacity, the longer the available time, but the more expensive the price, appropriate purchase according to the actual situation.
For the battery used in the model, of course, the larger the C-rating, the better, but the C-rating and price increase geometrically. According to actual use, select the appropriate C-rating. The following briefly explains how to know the C-rating.
The inverse principle of C-rating:
According to motor power/battery voltage = required current
Required current/battery capacity (AH) = required C-rating
Summary: Motor power/voltage/capacity=C-rating
This is a very theoretical thing, for example:
A 300W motor is used on a 11.1v 4000mah battery, how much C is suitable?
300 / 11.4 /4 = 6.5C (The capacity is 4 because 4000MAH=4AH)
So: In theory, a 11.1 v 4000mah 6.5C battery can carry a 300W motor.
Note that the above is only a theory, because when the car consumes the most power, it is never when the motor keeps rotating at a constant speed, but when the speed is suddenly increased. At this time, the current tends to increase several times. And even if it keeps rotating at a constant speed, it is impossible to keep your battery working at the limit C number. Take the above example, if the battery is 6.5C and keeps working at 6.5C, the battery will heat up, and overheating will cause the battery to swell. .
So generally we use at least twice the theoretical value. In the above example, it is at least 11.1 v 4000mah 13C battery.
Question: When the speed is suddenly increased, the current will increase several times, but the C-rating is only 2 times? If enough?
Answer: Basically enough, because the lithium battery itself also has the problem of instantaneous burst of C number, basically 1.5 to 2 times the nominal C-rating
Know more about C-rating: https://www.ovonicshop.com/blogs/battery-knowledge/what-does-the-c-rating-mean-on-a-lipo-battery
Can’t overcharge, overdischarge, overcharge, overheat
- Can't overcharge:
This is done by the charger. Basically, the lithium battery charger has this function, otherwise it can't leave the factory, unless it malfunctions after going out (inevitable).
- Can not over-discharge:
This is 100% dependent on players to achieve. There are basically 2 categories of over discharge:
A. Over-discharge during use.
This means that the player did not replace the battery when the voltage drops to the lowest value during use, resulting in over-discharge. Having said that, the lowest limit voltage of lithium battery is about 2.75V. It is recommended to use an ESC with lithium battery protection. If not, it is best to install a lithium battery protector. If not, it is a lithium battery voltage display that checks the voltage regularly. Players don’t think it’s necessary, just change the car as soon as it is unable to accelerate. You can’t wait until the car does not have lithium battery protection and it comes to a complete stop. It’s an absolute over-discharge.
Lithium battery protection value: personally set to 3.0V, that is, when the voltage suddenly drops to 3.0V when accelerating instantly, the ESC starts the lithium battery protection, stopping or changing the speed. The replaced battery measures generally around 3.4V. very safe. )
B.Over discharge in storage
- Do not overload:
That is, do not exceed the power of the lithium battery to use it. Just like the previous example, a 300W motor requires 11.1 v 4000ma 13C batteries, but if only 11.1 v 4000mah 7C batteries are used or even lower, the battery will be overloaded. Overload can easily overheat.
- Do not overheat:
Caused by overload or overcharge. Will cause the battery to swell