What is a UPS and What it is for?

An uninterruptible power supply (UPS) is a device that allows your computer or telephone switch or critical equipment that normally runs off the utility power supply, to keep running for at least a short time, when the primary power source is lost. It also provides protection from power surges, spikes, brownouts, harmonics and other unwanted problems that are present on the power lines.

A UPS will convert the DC voltage from a battery pack, to an AC voltage that can be used by the equipment. The time it takes to switch from using the utility power supply, to using the battery for power is typically between 0-20ms depending on the type of UPS.

An “online” UPS typically has 0 milliseconds switchover time from mains to backup because it is always online.

A line interactive UPS may take 20 milliseconds to change over.

The quality of the shape of the sinusoidal AC voltage is what you pay for, with a pure sine wave UPS being more expensive than a modified sine wave UPS.

How long will the UPS run when the power goes off?

This depends on the size of the UPS and the size of the load that is connected to that UPS.

Most UPS’s are only designed to run for a few minutes, giving enough time for you to save important files and perform a controlled shut down, or to keep equipment running until a generator can be started.

In general, for a given load, a UPS with a larger VA rating will also have a longer run time than a smaller one, however it really all depends on the batteries that power the UPS.

Retrofitting in larger batteries will increase the run time, however the UPS could overheat as it may not have been designed to deal with the heat generated from continuous use.

What is the lifetime of a UPS?

Most plug-in UPS’s have a lifetime of at least five years. We’d advise you to change the batteries every three to four years.

How to maintain a UPS?
  • Never overload your UPS.
  • Keep it free from dust and moisture.
  • If the UPS battery has performed a discharge, recharge it as soon as possible.
  • Keep a monthly log of the individual battery/cell voltages.
  • Test the UPS with the system load once a month
What is an Inverter?

An inverter is a unit that consists of large capacitors, chokes, a microprocessor and semi-conductor switches that work together to convert direct current (DC) to alternating current (AC) on a continuous basis, unlike a UPS, which is generally designed for short time operation.

Direct current originates from devices such as batteries and solar panels. An inverter allows these devices to provide electric power for household devices which use AC. The inverter does this through a complex process of electrical adjustment. From this process, AC electric power is produced. This form of electricity can be used to power an electric light, a microwave oven, or some other equipment that uses AC power.

An inverter usually also increases the voltage. Battery systems are normally sized as 12V, 24V, 36V or 48V systems. In South Africa, an inverter will convert that to 220V AC. Power is derived from the equation P = Voltage x Amperes, therefore on the DC side of an inverter high current will flow, because the voltage is low, whereas on the AC side, the voltage is much higher so the current will be much lower.

Inverters are made in many different sizes. They can be as small as 150 watts, or as large as 1 megawatt (1 million watts).

What is renewable energy?

Renewable energy is energy that is collected from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. An example is photovoltaic panels that convert sunlight into electricity.

What is Li-ion/lithium-ion?

A lithium-ion battery or Li-ion battery (abbreviated as LIB) is a type of rechargeable battery that use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. Other elements are nickel, manganese and cobalt in various chemical compositions to form a battery that has very good energy density and charge/discharge efficiency. They have a nominal cell voltage of 3.6V

Lithium Iron Phosphate (LiFEPO4) cells have a nominal cell voltage of 3.2V and are less likely to explode or experience thermal runaway events like typical Li-Ion cells, but have slightly less energy density than Li-Ion.

The important fact regarding any rechargeable lithium battery is that the voltage of each cell needs to be carefully controlled and maintained within certain bounds. Voltages above or below these bounds, just for just a moment, can permanently damage a cell. Each lithium-ion or LiFePO4 battery pack is thus monitored by a battery management system or BMS where the voltages of each cell are measured, and the current flowing through a particular cell can be bypassed if necessary to keep the cell voltage within limits. If the limit of a single cell is exceeded then the entire battery needs to be shut down. Control algorithms within the BMS are put in place to continuously balance all the cells in a battery pack.

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