Updated: Feb 21, 2022
The Science of Inverter Batteries
A power inverter or inverter is an electronic appliance that converts DC (direct current) electricity from sources such as batteries or solar cells to AC (alternate current) electricity for use in appliances. When they use batteries, they are referred to as ‘deep-cycle inverters’; when they use solar panels, they are referred to as ‘PV-inverter’ or solar inverters. Most appliances are built to use AC directly from the mains. However, a few of our appliances like phones and laptops will have to change the AC to DC before using them. These devices that use DC but have to take power from AC outlets need an extra piece of equipment called a rectifier, typically built from electronic components called diodes, to convert from AC to DC. Inverters do the opposite. For most Nigerian users of inverters, inverters find their applications in direct use in home appliances, light bulbs, air-conditioner units, refrigerators or to maintain uninterrupted power supply or to harness solar energy. They are used to power ATMs, hospital and laboratory equipment, traffic lights, etc. Batteries, therefore are a very important component of inverters. The DC is drawn from the batteries and converted to AC by the inverter for use in appliances. Conversely, the batteries are charged by being plugged to power source. All inverters perform the dual roles of rectifiers, that is charging the batteries and inverters, converting them to AC for use.
The battery is itself the major component of the inverter. The health and working of the inverter depends on the battery. Except in the case of portable inverters, that come with an in-built battery, batteries are often sold separately from the inverters and have to be bought and installed separately.
Inverter Batteries Protection
Except for locally made and non-branded inverters, all inverters have battery protection technologies which protect the batteries from damage, overheating, overcharging, deep discharge and misplacement of the battery terminals. They also have displays, LED lights and alarms that show and inform the user of the state of the battery.
The capacity of a battery is the amount of wattage in run time that is to be expected from a battery. It is calculated in Ah (Ampere hours). Battery capacity is ascertained like this
[Power (in watts) X back up hours ( in hrs)] / Battery Voltage (in volts)
For instance, purchasing a battery that provides a run time of 3hrs and assuming the standard battery voltage is 12V will require a battery with capacity of (400 * 3) / 12 = 100 Ah.
Depth of Discharge
Depth of discharge is the capacity to which the lead-acid battery is discharged before it is charged again. The recommended depth of discharge for lead-acid batteries is often 50%.
Components of Inverter Batteries
Batteries convert chemical energy directly to electrical energy. All its components are constructed in an arrangement that is described as ‘cell’.
Electrolyte. The electrolyte in most wet-cell batteries is sulphuric acid diluted with distilled water. Inverter batteries are mostly wet-cell batteries. The two types of lead-acid batteries that use an acidic electrolyte are wet cell and sealed. Wet cell use liquid electrolyte; sealed batteries use either a gel or liquid electrolyte absorbed into fibreglass matt.
Terminals. The terminals are the pure lead at the negative side and the PbO2 on the positive side both constructed as ‘plates’. With acid electrolyte and lead plates, wet-cell batteries are therefore known as ‘lead-acid’ batteries.
Separators. Separators between the positive and negative plates prevent short-circuit through physical contact, mostly through dendrites but also through shedding of the active material. Most separators are made of rubber. They are more stable in battery acid and provide valuable electrochemical advantages that other materials cannot.
Cooling Fans. Though they are not part of the ‘battery systems’, they are installed as part of the general inverter system.
Displays, LED lights and Alarms, incorporated into the general inverter system or sometimes as part of ‘battery chargers’, to inform the user on the state of the batteries.
Microprocessor-Based Circuits, incorporated into the general inverter system or part of ‘battery charger’ that regulate charging.
Types of Inverter Batteries
Based on their plate technology, inverter batteries are divided into Flat Plate and Tubular inverter batteries.
The Tubular plate battery is made up of negative plates like in flat plate battery except the positive part is made up of spines put under tube packets.
Flat Plate Batteries
The Flat plate battery is made up of positive and negative plates made up of pasted grids.
Differences Between Tubular Battery and Flat Plate Battery
The definitive features of the tubular battery are the multi-tube bag gauntlet and increased surface area of the positive plate. Due to increased positive plate surface area, tubular batteries have 20% more electrical capacity than flat plate batteries of comparable size and weight. With less positive plate shedding, tubular batteries also provide up to a 30% longer service life than flat plate batteries.
In the battery world, tubular batteries are generally preferred to flat plate batteries for the following reasons:
They have a complex design and manufacturing process, while flat plate batteries have a simple make up.
Tubular batteries have a life span of 4 to 5 years, whereas that of flat plate batteries is not more than 3 years. The reason is because active materials are used up more slowly than in the flat plate arrangement.
With tubular batteries, the water loss is low, whereas with their counterparts need frequent topping up of water.
The cyclic life is high in case of tubular batteries, and low in flat plate ones.
The former operates consistently even when the temperature is high, while the latter operates only at recommended temperature conditions.
Tubular batteries are suitable for high end applications, while flat plate batteries cannot support heavy applications.
The former are also fast charging and heavily priced, while the latter are slow-charging and affordably priced.
The former are highly reliable, and therefore are recommended for highly productive applications, while the latter are recommended for budget-conscious individuals and small homes.
Tubular batteries have 20% more electrical capacity than their counterparts of the same weight and size. This is because of their increased positive plate surface area.
The flat plate batteries are usually more resistant to heat. The heat dissipation is much better optimized due to the flat surface. A poor heat dissipation will cause the battery to deteriorate faster.
Owing to their toughness and durability, tubular batteries can operate at extreme temperatures and are used in high cyclic applications involving frequent and prolonged power outages.
Comparatively, flat plate batteries are cheaper than the tubular.
Tubular batteries are more suited to high and fast charging rates as well as heavy loads that require much higher currents.
Non-Branded Batteries are locally-made batteries without traceable brand names or ISO certification. Though they are cheap and easy to procure, locally made non-branded batteries do not have smartly programmed microchip that control the charge current at various stages of battery charging. Unlike branded inverters, local inverters does not have short circuit protection, over charge protection, reverse polarity protection and MCB switch to safeguard the electronic gadgets connected to it. They simply supply same amperage and voltage right from the beginning to end of the charging schedule. Locally made non-branded batteries are prone to failure on occurrence of lightning attack or high voltage from grid. Generally, users are advised to purchase and install branded, ISO- or SON-certified batteries for their inverters.
On the basis of their maintenance needs, batteries are classified as either Flooded or Wet Cell lead-acid batteries and Sealed Lead-Acid (SLA) or Gel Cell batteries. The former needs maintenance, while the latter are maintenance-free. The Gel Cell batteries are costlier, and are also called as Valve regulated lead-acid (VRLA) batteries.
The Sealed Maintenance-Free (SMF) batteries need no maintenance. They are sealed, do not require watering, can be used in any orientation, and use a valve for gas blow-off. However, they provide less backup time in comparison to the tubular battery, have lesser life expectancy, inferior design technology, less depth of discharge (50%) and are more expensive. They are primarily designed for automobiles. For inverters, tubular batteries are largely preferred.
Batteries emit a corrosive and explosive mix of hydrogen and oxygen gases during the final stages of charging, which when accumulated in large quantities can ignite if exposed to a flame or spark. They must be installed in a well-ventilated enclosure, preferably away from the house.
Also, the batteries get heated up during use. It is advised that they are installed in airy places for cooling. As batteries have provisions for water to cool them, installing them in well ventilated places reduces the frequency of the water-topping requirement.
The batteries are to be installed at places where children cannot reach them or where there is not much disruptive domestic activities.
The area in front of the installation space should be reserved as work space and not used for storage of any kind. Operators should be able to walk up to the inverter equipment without any obstruction.
Have clear instructions laminated and posted on the wall beside the installed system where in your absence, another operator, a friend or family member, may want to use the system.
All electronics are to be kept away from the reach of children.
Advisably, the inverter system if not mounted on the wall should be installed atop a metal rack. In most cases, SolarKobo requires this as a standard installation procedure.
The batteries should be installed properly and by professionals.
SolarKobo has university-trained electrical engineers that provide high-value installation services on order. We also help our clients in Lagos and Nigeria make the best choice of inverter batteries that suit their power needs and fits their budget.