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Suggestions for DIY Lithium Battery Packs

Recently, many customers have consulted and learned how to DIY lithium battery packs, which are used to modify the battery packs of electric toys and electric vehicles. 

In the communication, we found that their understanding of lithium battery technology is not very deep and rigorous. It can’t be successful to DIY the lithium battery packs if not knowing about the related lithium battery technology.

So here we will sort out several important points for DIY lithium battery packs combining the characteristics of lithium battery.

1. Cell selection

1.1 Selection of voltage

  • LiFePO4    3.2V
  • Ternary lithium battery    3.7V

1.2 Energy storage or power

The difference between energy storage and power is the discharge rate.

Power cells have a higher discharge rate than energy storage cells. In theory, the higher the discharge rate, the better, but the price will also be higher.

If your electric product does not require a high discharge rate, then you can choose a cheaper energy storage battery.

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1.3 Other parameters

Test with an internal resistance tester.

(1) Capacity – MH.

Test the nominal capacity and the actual one. The greater the difference between the actual capacity and the nominal parameters, the worse the quality.

(2) Internal resistance – R.

The lower the internal resistance of the battery, the better. Generally speaking, it is less than 50. If it is more than 50, it may be an old battery or a bad battery.

1.4 Battery cycle life

The more cycles, the longer the service life.

2. Requirements for cell consistency

First of all, the battery pack requires the matching consistency of the cells, the more consistent the better and more stable. If the matching of cells is inconsistent, the capacity will be insufficient. And that will seriously cause the detection failure of the battery protection board and the battery pack not working.

2.1 How to choose the consistent batteries?

If possible, use a special machine to screen. If there is no machine, use an internal resistance tester to measure one by one. Put the lithium batteries with the same voltage, internal resistance, and capacity together, and let them stand for a period of time (7~15 days). If they are still consistent, they can be processed. This is also a physical method to judge the stability of the cell.

2.2 Why not assemble and use directly?

Of course, it can be used directly. But in the case of mismatch, the capacity of the battery pack will be limited to the worst battery in the battery pack. Simply put, the capacity of the battery pack will drop by 10-40%. Seriously, if there is one bad battery in the battery pack, the whole pack will not work. This makes the inspection and maintenance work more cumbersome.

3. Spot welding of battery

3.1 For the processing and assembly of the battery pack, it is recommended to use machine processing first and mainly. While the manual assembly is not recommended (The requirements for single parallel are not high).

Spot welding of battery

3.2 Why is manual spot welding not recommended?

If the strength of battery spot welding is not well controlled, it is easy to break and leak, and the spot welding for nickel sheet is not strong.

As for the manual soldering iron, if the soldering temperature is too high, it will damage the pole piece. Low temperature soldering is recommended. However, most households use high-temperature solder.

3.3 The thicker the battery connecting wire, the better. The thicker the nickel sheet, the better.

3.4 The battery is used as a charge and discharge capacity container,it will release heat during energy conversion. Irregular processing may cause problems in the battery pack, and the processing of the battery pack must be cautious and careful.

4. Requirements for the battery packs

4.1 Waterproof

If the waterproof device of the battery pack is not done properly, moisture will easily enter the battery and cause a short circuit.

4.2 Shockproof

Try to use the method – grid bracket + buffer pad + outer box to achieve the shockproof function. If the grid support is not added, the nickel sheet of the battery pack will fall off under the pressure of years of activities!

4.3 Heat conduction channels available

In energy conversion, timely heat conduction can optimize the battery. Steel outer box + fan auxiliary are both conventional solutions.

Besides, power supply glue packaging is also a solution. But the disadvantage is that the later maintenance will be troublesome.

4.4 Anti-corrosion

The battery will rust if left for a long time, and anti-corrosion measures should be taken as much as possible.

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5. Lithium battery protection board selection

The assembly of the battery pack must be equipped with a matching protection board.

5.1 The protection board of 40A or less is enough for two electric wheels.

While the one of more than 80A is enough for three or more electric wheels. Choose the right one according to the specific power of the motor.

5.2 The voltage should match.

60V is mostly conventional. And it is necessary to distinguish ternary and iron-lithium, also the number of connections.

5.3 Try to choose the protection board with low protection voltage.

For example, the protection board of 4.25V is not as well protected as the ones of 4.2V~4.1V. Because the battery will not be charged to 100%, and it will never close to the limit.

6. Charger selection for battery packs

6.1 Match according to the protection voltage of the protection board and how many connections of iron lithium/ternary lithium.

6.2 Choose the charger with suitable A/H according to the total capacity. Now the 8A/H one is recommended on the market.

6.3 The charger should also be protected from water and shock.

7. Electric vehicle brake matching

Try to choose an electric vehicle with dual disc brakes. The lithium battery has a high discharge rate and fast acceleration.

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8. Conclusion

It is supported if battery packs DIY just for learning, interest, and personal use. But for the commercial use, it is necessary to consider a series of issues such as safety and after-sales. At the same time, the cycle life of the battery is also a key indicator to distinguish the quality of battery packs on the market, which is easily overlooked. The capacity of many DIY battery packs is not up to the standard, and the power will be lost quickly after a period of time. These are the common problems in DIY battery packs.

9. Lithium battery recommendation

DLN Energy is a manufacturer specializing in the production of 18650 batteries with the stable quality. Welcome to inquire us and cooperate with us!

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