Lithium Battery Protection Circuit Schematic

The prominently known lithium-ion batteries have the ideal advantage of having high energy density. However, they demand extreme care when you handle them.

Basically, lithium batteries are capable of being safely charged to about 4.1V or 4.2V, but they cannot go higher than that.

This is because the process of overcharging lithium batteries can result in damages to the battery, and it results in safety hazard such as fire danger. However, all these can be ore went with a battery protection circuit.

Furthermore, lithium batteries can be fully empty when they are discharged to about 2.5V. In discharging a lithium battery cell of such a low voltage, it will not only be stressful to the cell, but it will also decrease the lifespan of the cell.

An ideal battery protection circuit will, however, provide protection for cases of an over-discharge. Also, lithium batteries should never be discharged too fast. This is because lithium-ion batteries have very high discharge current ratings.

As mentioned earlier, the ideal battery protection circuit will take the lithium battery out of the circuit in cases whereby the load current is overly high.

However, the majority of the battery protection ICs make use of MOSFETs to switch lithium-ion cells in and out of its circuit actively.

Basically, the lithium cells of the exact same age, as well as part number, can easily be paralleled and make use of one distinct protection circuit.

Why Does lithium battery Need Protection Circuit

Generally, the protection is actually in the form of a circuit board which is joined to lithium batteries before it is wrapped with the label of the distributor.

Its function is actually to make certain that the rechargeable lithium battery that it is serving never gets to overcharge or discharges below a particular present level.

However, lithium batteries offer about 3.7 volts of power. When they are charging, it is advised and highly recommended that the entire charge current should not exceed 4.2 volts.

When the lithium battery is being discharged, it is also not recommended that the voltage should be allowed to drop below a range of 2.8volts.

Lithium batteries need this protection circuit for the battery to be kept out of danger no matter what. The circuit is needed to shut down the battery whenever a low voltage has been detected.

Additionally, it is highly recommended that you check the lithium battery periodically on a voltage meter when in use and also, instigate another fresh charge when it is getting close for the battery to be shut down by the protection circuit.

Also, note that a named brand charger will stop charging the lithium battery when the battery voltage gets close enough to 4.2V. This aids in ensuring a safe charge because overcharging is just as worse as over discharging for the lithium battery.

Basically, protection circuits work as follow:

· The protection circuit device that is built into the cell takes on the role of a protector to aid in inhibiting increased current surges

· For the circuit interrupt device, it opens up the electrical path should an extremely high charge voltage to raise the inner cell pressure to about ten bar, i.e., 150 psi.

Generally, the safety vents enable a controlled distribution of gas in the event of a swift increase in the pressure of the cell.

In the same vein, the electronic protection circuit that is outside the cells opens up a sturdy state switch if the charge voltage of any of the cells reaches about 4.30V.

A fuse cuts through the current flow if the actual skin temperature of the battery cell gets close to 90°C. In a bid to stop the battery from over-discharging, the quality control circuit cuts off about 2.50V of the current's path.

However, we should keep in mind that every safety precaution are effective if the operational modes come from outside like an electrical short or maybe a faulty charger.

How To Tell If 18650 battery Is Protected

The protected 18650 batteries have a little electronic circuit integrated into its cell packaging. Basically, his circuit protects the battery against some regular dangers like:

· Over-discharge

· Overcharge

· Temperature and;

· Over-current or short circuit

Most protected batteries are more than less likely to spark and cause either property or personal damage. A 18650 battery has some of these components which are:

· CID or the pressure valve

It will disable the cell forever if the pressure is overly high in the battery cell

· Protection circuit

It protects the battery against overheating and indirect overcurrent. It instantly resets.

· The PCB

It will protect the 18650 against an over discharge, over current, and even overcharge depending on its design. PCB will reset instantly or when placed on a charger.

Consideration In Choosing Battery Protection Circuits

The two vital parameters in choosing battery circuits are the under-voltage threshold and the overvoltage threshold. The protection circuit will cut the cell out of the circuit should the cell be over discharged or overcharged.

Lithium batteries basically have more charge during every charge cycle if the batteries are charged to 4.2V. Plus, they have a longer lifespan if charged up to 4.1V.  Meanwhile, for the over discharge protection threshold, it affects both capacity and cell life. Batteries have more capacity for each charge if they are discharged all through. However, this is stressful, and it will reduce the life of the battery.

Moreover, in selecting a battery protection circuit, MOSFETs are the ones usually selected for the protection circuits. This is because they are used to switch the cell in and out of its circuit.

To Wrap It Up

Under some regular circumstances, lithium-ion batteries will just power down when a short circuit takes place.

However, if a defect is inherent to the electrochemical cell-like contamination caused by microscopic metal particles, the anomaly will end up being undetected. Also, neither can the safety circuit end the disintegration immediately the cell is in the thermal runaway mode. Basically, nothing can stop it once it is triggered.