Battery configurations (series and parallel) and their protections

A single cell isn't ample for some units. To realize desired voltage, the cells are linked in collection so as to add to the voltage of the cells. To realize the specified capability, the cells are linked in parallel to get excessive capability by including ampere-hour (Ah). This mix of cells is named a battery.

Generally battery packs are utilized in each configurations collectively to get desired voltage and excessive capability. This configuration is discovered within the laptop computer battery, which has 4 Li-ion cells of three.6 V linked in collection to get 14.4 V. Every cell has each other cell linked in parallel to get the double capability of 6800mAh.

Every battery linked within the configuration ought to have the identical voltage and capability as a result of the weaker cell causes an imbalance. In a collection configuration, a battery is as robust because the weak hyperlink within the battery chain, so the upper capability cell can't cost greater than the weaker cell. The weaker cell additionally discharges and expenses first, which might trigger an issue like over-discharge and over-charge within the system.

Single-cell configuration
The one-cell configuration is the best battery pack. This configuration is obtainable in a wall clock, reminiscence backup, and wristwatch. These all are low-power units, in order that they use a 1.5 V alkaline battery. Cellphones and tablets are additionally out there in a single-cell configuration of a 3.6 V Li-ion battery. Determine 2 reveals the single-cell configuration of the li-ion battery.

Determine 2. Single-cell configuration.

As now we have seen, the nominal voltage of a single Li-ion cell is 3.6 V. A nickel-based battery has a nominal voltage of 1.2 V, and an alkaline battery has a nominal voltage of about 1.5 V. The opposite lithium-based battery has a voltage between 3.0 V to three.9 V. Li-phosphate is 3.2 V, and Li-titanate is 2.4 V. Li-manganese and different lithium-based methods typically use cell voltages of three.7 V and better.

Collection configuration
The collection configuration is used the place the voltage of a single cell isn't ample. The collection configuration is achieved by connecting the optimistic of a cell to the unfavorable of one other cell, as proven in Determine 3. The 4 lithium-ion cells of three.6 V linked in collection offers you 14.4 V, and this configuration is named 4S as a result of 4 cells are linked in collection.

The variety of cells might be diverse in line with the voltage of a single cell. A Lead-acid battery has a nominal voltage of two V, so it requires six cells linked in collection to realize 12 V. The six alkaline batteries with a voltage of 1.5 V per cell linked in collection offers you 9 V.

If the system wants an odd voltage, for instance, 10 volts, then three Li-ion batteries might be linked in collection. However when the system wants 8.5 volts from Li-ion, you should know the specification of your system. If it may possibly deal with 10 V, then it may be linked straight; in any other case, a buck or increase is used to realize 8.5 V.

If one cell in collection is defective, cell matching is a problem in an ageing pack on the time of cell substitute. The brand new cell has the next capability than the others, which causes imbalance. That’s why battery packs are generally changed in models.

BMS (battery administration methods) or its controller can decide the defective battery by measuring the voltage at each level of the battery as proven in Determine 4. The one cell is defective, which is giving 2.8 V as an alternative of three.6 V. Resulting from this, the battery voltage collapses, and the system will shut off sooner with a low-battery message. You may restore your battery pack by changing this cell.

Parallel configuration
The cells are linked in parallel to meet greater present capability necessities if the system wants the next present however there's not sufficient area out there for the battery. That system can use the parallel configuration to suit high-current functionality in a small area. The four-cell configuration in parallel is named P4, and three cells linked in a parallel configuration are referred to as P3. Determine 5 reveals a P4 configuration. The voltage within the pack stays the identical, however the present capability (Ah) is elevated.

The cell that develops excessive resistance or opens is much less important in a parallel circuit than in a collection configuration, however the failing cell will cut back the whole present capability. Alternatively, {an electrical} quick is extra severe because the defective cell drains vitality from the opposite cells, inflicting a hearth. The quick happens by way of reverse polarization or dendrite development. The big cell features a fuse to disconnect the failing cell when it shorts. In Determine 6, the third cell within the blue field failed, and the capability is lowered to 1500 mAh. It doesn't have an effect on the voltage, but it surely reduces the whole capability.

Collection  parallel configuration
On this configuration, the cells are linked in each collection and parallel. The series-parallel configuration may give a desired voltage and capability within the smallest attainable measurement. You may see two 3.6 V 3400mAh cells linked in parallel in Determine 7, which doubles the present capability from 3400mAh to 6800mAh. As a result of these parallel packs are linked in collection, the voltage additionally doubles from 3.6 V to 7.2 V. The whole energy of this pack is now 48.96Wh. This configuration is named 2SP2. If the configuration consists of eight cells with the configuration of 4SP2, two cells are in parallel and 4 packs of this parallel mixture are linked in collection. The whole energy produced by this pack is 97.92Wh.

Safety in batteries
The IEC 62133 harmonized the protection necessities for nickel and lithium-based batteries and cells for transportable purposes. The Li-ion batteries are probably the most harmful battery of their class as a result of the battery chemistry has explosive materials. Battery safety is required to forestall any injury as a consequence of excessive present discharge, overcharge, temperature rise, and so on. The safety might be constructed into the construction of the battery or the exterior safety circuit can be utilized to disconnect the battery.

Constructed-in safety in batteries
Some batteries include security options throughout the battery construction. Determine 8 illustrates the protection function of the 18650 Li-ion cells. The PTC (optimistic thermal coefficient) is the resistance that may be very low throughout regular temperature. However when the temperature goes above important situation, its resistance rises to cut back the present circulation. PTC comes beneath regular resistance when the temperature goes under the important vary.

The CID (present interrupt system) is a fuse-type system that completely cuts off the circuit when the vary of cell strain, temperature, or voltage exceeds its limits. If the interior strain will increase by about 1,000kPa, the highest disc disconnects from the metallic foil and disconnects the present circulation. There's a vent on high to launch the gasoline and might be shut once more.

Safety circuit in batteries
Some 18650 Li-ion batteries include a safety circuit. The fundamental perform of the safety circuit is to guard batteries from over-voltage, under-voltage, over-current, and over and beneath temperature. This is part of BMS. The BMS displays the state of batteries for safer operations and sends the sign to the safety circuit if there's any fault within the batteries. When the safety circuit is linked on the battery’s optimistic terminal, it's referred to as high-side safety. When it's linked to the unfavorable aspect of the battery, then it's referred to as negative-side safety.

Determine 9 is the safety circuit block diagram. It is a Excessive aspect safety circuit. The battery configuration is S4 (4 in collection), and a fuse is linked to the optimistic aspect of the battery to close off the battery when the present exceeds the boundaries. There's BMS Monitoring each cell voltage for balancing and fault detection. The present sensing unit will sense the cost and discharge the present it sends it to BMS. If any studying of voltage or present exceeds the boundaries, then BMS sends the sign to the safety circuit that shuts off the cell with a charger or load.

There are some pre-made circuits out there available in the market that are fastened in your voltage or present necessities. You merely need to know the present and voltage specification of battery safety modules, or it's also possible to construct your individual with MOSFETs and BMS out there available in the market.

References
Battery College. BU-302: Collection and Parallel Battery Configurations.
Plainview ISD
Energy Sonic. The best way to Join Batteries in Collection and Parallel.
epec. Battery Pack Configurations.
Robu.In. Collection and Parallel Configuration of Lithium Battery.
Battery College. Security Circuits for Trendy Batteries.