What should be paid attention to when choosing lithium battery and protection board ? Posted by benzoenergy.com
1. Lithium-ion battery type and capacity selection
First,
calculate the continuous current to be provided by the battery
according to the power of your motor (the actual power is required, and
the general riding speed will correspond to the corresponding actual
power). For example, if the continuous current of the motor is 20A
(1000w at 48V), the battery must be able to provide 20A for a long time
and the temperature rise is very low (even if the outdoor temperature in
summer is 35°C, the battery temperature is best controlled below 50°C).
In addition, if the current is 20A at 48V, the overvoltage is doubled
(96V, such as ecpu3), and the current continues to about 50A. If you
like to use overvoltage for a long time, please choose a battery that
can continuously provide 50A current (also pay attention to the
temperature rise). The continuous current of the battery here is not the
nominal battery discharge capacity of the merchant. The merchant claims
that a few C (or a few hundred amperes) is the discharge capacity of
the battery, but when the battery is discharged at this current, the
battery heats up very seriously. If the heat cannot be dissipated
normally, the battery life will be shortened. (Moreover, the battery
environment of our electric vehicles is that the batteries are stacked
and discharged, basically leaving no gaps, and the packaging is also
very tight, not to mention how to do forced air cooling to dissipate
heat). Our use environment is very harsh. The battery discharge current
needs to be derated for use. Evaluating the battery discharge current
capability is to look at the corresponding temperature rise of the
battery at this current.
The
only principle discussed here is actually the temperature rise of the
battery during use (high temperature is the deadly enemy of lithium
battery life). It is best to keep the battery temperature below 50°C.
(Preferably between 20-30°C). This also means that if it is a capacity
lithium battery (discharge below 0.5C), the continuous discharge current
of 20A must be above 40Ah (of course, the most important thing is the
internal resistance of the battery). If it is a power-type lithium
battery, it is normal to continue to discharge according to 1C. Even for
A123 ultra-low internal resistance power lithium batteries, 1C
discharge is usually best (no more than 2C is better, 2C discharge can
only take half an hour, which is not very useful). The choice of
capacity depends on factors such as the size of the car's storage space,
personal expenditure budget, and the expected range of car activities.
(Small capacity generally must be a power type lithium battery)
2. Screening and assembly of batteries
Serious unbalanced battery self-discharge is a taboo for using lithium-ion batteries
in series. As long as everyone is the same, imbalance is fine. The
problem is that this state is extremely unstable. Good battery
self-discharge is small, bad battery self-discharge is large. The
self-discharge is not small, and the state generally changes from good
to bad. The state of this process is unstable. Therefore, batteries with
high self-discharge should be screened out, and only batteries with
small self-discharge should be kept (generally, the self-discharge of
qualified products is small, and the manufacturer has tested it. The
problem is that many unqualified products flow into the market).
On
the basis of small self-discharge, select series with similar capacity.
Even if the capacity is different, it will not affect the battery life,
but it will affect the usable capacity of the entire battery pack. For
example, the capacity of 15 batteries is 20Ah, and only one battery is
18Ah, so the total capacity of this group of batteries can only be 18ah.
At the end of use, the battery is exhausted and the protection board is
protected. The voltage of the whole battery is still relatively high
(because the voltage of the other 15 batteries is normal and there is
still electricity). Therefore, the discharge protection voltage of the
entire battery pack can determine whether the capacity of the entire battery pack
is the same (provided that the entire battery pack is fully charged).
In short, the capacity imbalance will not affect the battery life, but
will only affect the capacity of the entire group, so try to choose
components with similar capacities.
The
assembled battery must achieve good ohmic contact resistance between
the electrodes. That is, the smaller the contact resistance between the
wire and the electrode, the better, otherwise the electrode with high
contact resistance will heat up, and this heat will be transferred to
the inside of the battery along the electrode, affecting the battery
life. Of course, the performance of high assembly resistance is the
large voltage drop of the battery pack under the same discharge current
(part of the voltage drop is the internal resistance of the cell, and
the other part is the assembly contact resistance and line resistance)
BENZO Energy Technology Co.,Ltd
UFine Technology Co., Ltd
Site: www.bz-battery.com / www.benzoenergy.com
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