Lithium Battery Voltage- Introduction, Measurement and Charging

Batteries were once bulky, awkward, and bigger things that only provided a feeble amount of power concerning its size and weight. Luckily, technology has advanced over time, and by 2020 we are blessed with high-performance, high-capacity lithium batteries that can supply any power needed.

Generally, there are two different main types of lithium batteries available in the market. One of them is lithium metal batteries, and the other is lithium-ion batteries. Battery voltage plays an essential role in the performance of the battery. The usual range of voltage in lithium batteries is between 1.5 V- 3.7 V.  The lithium-ion batteries are reusable and rechargeable; thus, they are mostly used in all electronic devices.

Here are some considerations one must know about lithium batteries:-

What is the nominal battery voltage

A function of anode and cathode materials is known as nominal voltage, as well as impedance. During discharge, the voltage of the lithium battery output varies. The nominal voltage is determined between maximum charge and fully discharged at the midpoint, based on a 0.2C discharge (where C is the cell's rated capacity in mAh).  Always consider that a higher voltage is always set arbitrarily and does not affect the working of portable devices or the configuration of the charger. Yet exceptions still exist.

Many LCO architecture of Li-ion batteries features a surface coating and electrolyte additives that boost nominal cell voltage and require higher charge voltages. The charging cut-off voltage for these batteries has to be adjusted accordingly to have the maximum power.

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A single lithium battery cell's nominal voltage is usually shown as either 3.6V, 3.7V, or 3.8V. During discharge, the real voltage profile depends on the cell chemistry used, the rate of discharge, the temperature, and the age of the cells or batteries discharging. A single-cell lithium battery cell nominal voltage is 4.2V, and the cut-off voltage is 2.5V ~ 3V.

How do you measure the voltage of a lithium battery

lithium batteries consist of 4 sets of series-connected Lithium cells that make up most of the lithium battery casing. The cells run longitudinally along the long side of the battery, in vertical layers. The individual lithium battery cells all have a nominal 3.2V and are connected in series to give a nominal total of 12.8V. It can be measured on the V+ and V- labeled central battery terminals. This voltage is not detectable in normal service. The voltage that can be calculated is marked as B+ and B- at the battery terminals above the battery casing.

The positive V+ and B+ are connected directly (fused only). There is no clear relation between the negatives V- and B-. There is a Dual Mosfet Charge / Discharge Controller and a Current Sense Ratio (CSR) unit connecting these two. The Dual Mosfet Controller is the cornerstone of battery safety for overloading current and cut-out of high or low voltage. Depending on the battery Management Unit order, the security unit will open and close the connection between B- and V-. Many more sensors and measurement points are included.

Whenever this V-B- the circuit is opened by the safety unit, although the lithium battery may be fully charged, battery terminals B+ and B- on a multimeter can display only 2-3 V or even zero. (small-voltage capacitors).

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How many voltages do you need to charge your lithium batteries

The lithium-ion charging batteries are based on voltage rather than on current. In this way, lithium-ion battery charging is more similar to lead-acid batteries. One of the advantages of lithium-ion charging batteries is that they have a higher voltage per cell-about 3.7 or 4 volts per cell compared to 1.2 volts.

Lithium-ion batteries often need a much tighter voltage tolerance when fully charged. They do not allow or need trickle or float charging once fully charged. It is particularly necessary to be able to reliably detect the full charge state because the lithium-ion batteries do not tolerate overcharging. They overheat, which reduces their lives, but in extreme situations, it can cause them to catch even burning fire.

Most consumer-oriented lithium-ion batteries charge at 4.2 volts per cell, with a tolerance of approximately ± 50 mV per battery. Charging beyond this usually causes stress and leads to oxidation, which reduces service life and capacity. Sometimes, it can cause health problems. The various types of lithium-ion cells have slightly different voltages. Still, they will all have similar curves of discharge in form.

Simple Precaution For Batteries

Let's look at the mechanism required by the lithium battery voltage for charge and discharge:

Charge current:  For lithium batteries, the charge current must be restricted. The maximum value is usually 0.8C, but lower values are more generally set to provide some margin. Some speedier charging for certain batteries can be possible. Even for batteries or cells that are capable of withstanding higher current charges, lifespan is affected. If the charge rate can be kept lower and fast charging is not used, this will increase the cell's useful life.

Over-voltage: The overvoltage load safety is required to prevent the battery terminal from using too high a voltage. The harm can be done if the charge voltage is allowable to rise too high.

Overcharge protection: The overload protection circuit is required to avoid charging when the voltage is greater than 4.30 volts per cell. The overcharging of lithium in batteries is extremely significant. The device for battery protection will protect against the charge.

Reverse polarity protection: Reverse polarity safety of the lithium battery is required to ensure that the battery is not charged in the wrong direction. It may result in severe harm or an explosion.

Li-Ion over-discharge: Over-discharge protection is necessary to prevent the battery voltage from falling below the manufacturer's 2.3 Volts limit.

Over-temperature:  Overtime safety is also provided to stop the battery's failure if the temperature rises too high.  Temperature above 100 ° C can cause irreparable harm.

The Final Verdict

Lithium batteries can be dangerous, but when used carefully and safely, give you excellent performance. You should know everything about lithium batteries to avoid disasters. Always ensure that you give extra care while measuring the voltage and charging of the lithium battery. Hopefully, this article serves you well to inculcate your lithium power projects.