How DIY 36v 10Ah Lithium Battery Pack with Protection Circuit?

- Feb 02, 2019 -

How DIY 36v 10Ah Lithium Battery Pack with Protection Circuit?

As we shared DIY method in previouse article, now let's give an example to illustrate the method of installing overall protection circuit for a group of 36V/I0A lithium battery packs.

1) Current protection

The picture above shows the overcurrent protection device. E is 36V/1OAh lithium battery pack; BX is 10A insurance; J is relay (replaced by YE-KDC-A04:8 color TV switch): C is dry reed tube; LlR is current limiting resistance; C is energy storage capacitor; D is diode; TK is a temperature switch, operating temperature 45 C, M is electric vehicle motor.

When the JK is closed, the. M runs normally. E charges to C through D, and the electric vehicle runs normally. When I (> 14A), the strong magnetic field emitted by L closes the contacts in G. The stored electric energy in C is absorbed by the internal resistance R and R of J winding. J makes Jl (release, cut off the circuit. E) stop supplying power to M. This ensures that E is not burnt down by high current.

The relationship between the action current I of the protector and the number N of L turns of the sampling coil is shown in the attached table.

The protection device has the following advantages

  • 1 The sampling circuit coil L is a 1.2mm enameled wire with a length of llcm, and its energy consumption tends to be 0; 

  • 2. The protection action is sensitive and crisp.

2) When over-voltage protection is used to charge 36V lithium battery pack, when the voltage reaches 42V, the charging power supply must be cut off automatically. The circuit shown below meets this requirement. Three diodes Dl, D2 and D3 (1N5408x3) are connected in series at the positive output terminal of SP-70A charger in the car (second stage). When charging 36V lithium battery pack E at the beginning (first stage), the voltage at point A is 44.4V.D1~D3, and the up voltage drops to 2.6V. When charging 36V lithium battery pack E at constant current of 1.5A, the voltage drops to 2.6V. As time goes by, the voltage of E keeps rising (as shown in figure a below). When the voltage rises to 41.8V, SP-70A moves to the second stage of charging. The output voltage of point A suddenly changes to + 41.7V. O.lV.DI~D3 is in reverse bias lower than point B. The charging current is automatically blocked and the charging ends (as shown in Figure B below).

In this way, lithium oil can not be overcharged under any circumstances.

3) The rated discharge termination voltage of overdischarge protection single lithium battery is 3.0V. For electric vehicles, the discharge termination voltage should be increased to 3.15V. 36V lithium battery pack, discharge termination voltage set to 315V has the following advantages: 1. It is compatible with the original vehicle lead battery discharge termination voltage 31.5V, so that the original vehicle controller can be applied to both lead-lithium batteries at the same time, which reduces the cost and improves the reliability; 2. The lithium electric discharge depth becomes shallow and benefits its life.

Therefore, the 31.5V over-discharge protector in the original controller is decided to be used as the over-discharge protector of lithium battery pack. When the lithium battery discharges to 31.5V, the protector acts (green undervoltage lamp is on). The power supply to motor M of electric vehicle is automatically cut off. This protects the lithium battery pack from damage due to overdischarge.

For lithium battery pack of 36V/IOAh, the overload protection circuit of on-board controller is used to protect lithium battery pack. When the voltage is discharged to 31.5V, the power is automatically cut off and the work stops. There is no problem in using it for one and a half years.

Then, a full discharge experiment was carried out. The lithium battery pack discharged to 31.5V was removed from the vehicle for a long time and continued to discharge to 30.OV for recharging. As a result, the charging termination voltage could only reach 37.6V instead of 41.8V.

The lithium battery pack was dismantled and inspected. Nine of the 10 small lithium battery packs had a voltage of 4.18V, while the other small lithium battery was an o.5v. Aluminum-plastic membrane bulging, which was seriously damaged and lost 80 yuan. Damage reason: When the lithium battery discharges to 31.5V, the voltage of the lithium battery reaches the discharge termination voltage. When the discharge continues, the voltage is put to Ov. After the discharge continues, the current is reversed and the polarity is reversed, and the battery is completely damaged.

Practice has proved that increasing discharge termination voltage to 31.5V is an effective method to protect lithium battery packs from damage caused by over-discharge.

PS: When the overtemperature protection lithium battery is used improperly, the internal temperature increases and the internal pressure increases. When the pressure increases to an unbearable level, the explosion occurs. Therefore, setting temperature protection circuit inside the left lithium battery pack can greatly reduce the probability of lithium battery explosion.

METHODS: A temperature switch of 45 C (1OA) was embedded in the central position of the lithium battery pack, and TK was connected in series to the lithium battery circuit, as shown in Fig. I. TK is a normally closed contact type. When the temperature of TX in lithium battery is lower than 45 C, the normally closed contacts in TK are closed, but the motor of electric vehicle runs normally from the power supply electric vehicle. When the ambient temperature is high or the high current is discharged for a long time, the internal temperature of lithium battery rises to 45 C, the normally closed contacts in TK are separated and broken. Electricity. Lithium battery pack E stops discharging. Thus, the explosion accident of lithium battery caused by high temperature can be avoided.

After cooling for a period of time, when the temperature drops below 45 C, TK contacts are usually closed, and the lithium battery pack is restored to work.

What does SINOLI can do for you?

SINOLI battery producing 36v 10Ah lithium ion battery pack for years. Taking battery expertise and experience in battery production, SINOLI endeavour in making good quality lithium ion batteries with protective circuirt board as well. More and more people find a lot of problems in DIY process, because they do not have systematic testing device, PCB and battery cell on market quality is uneven. if you do not have experience, it's hard to justify which one is good or not. SINOLI is making efforts to save efforts for you.