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Power Outage

What is the Difference Between a UPS and an Inverter?

Power outage is a common phenomenon with multiple causes. Storms, lightning, snow, earthquakes, etc. can all cause power failure. This sudden loss of power is both annoying and dangerous. Crucial lifesaving equipment in hospitals, that need to work 24/7, could risk someones life when power fails. When the power is out, we use a UPS or inverter to provide backup power.

While they both provide backup power their function, circuitry and features are very different. Before going further into the difference, let’s look into what is a UPS and what is an Inverter.

What is a UPS?

UPS is an abbreviation for Uninterruptible Power Supply. It is a device capable of providing backup power in case of power failure. When connected with a battery it acts as the source of power. It draws current from the AC utility to power any electronics and continuously charges the battery.

Once the power is cut off, the UPS switches the power source and starts drawing current from the battery. The switching speed is very fast – almost below 10ms. Such fast switching does not affect the operation of electronic devices such as a computer.

Block Diagram of UPS

A UPS is composed of sophisticated circuitry. It includes an inverter and a charge controller (usually referred to as the rectifier). The inverter switches the DC power from the battery into AC. The rectifier converts the AC utility into DC and also controls the charging parameters.

The intelligent circuit is the most crucial part of the UPS and it is what differentiates it from an Inverter. It is responsible for sensing any interruption in the power source. It switches between the primary power supply (AC utility) and the backup supply (battery). But the most important part is the switching speed. It instantly switches power sources without interrupting the power supply. This the reason it is named an uninterruptible power supply.

It continuously draws current from the battery but at a very low amount. As soon as the circuit senses a break in the power supply from the utility, the circuit switches to draw full current from the battery.

This fast switching allows smooth operation of sensitive electronic devices. When critical equipment is abruptly shut down, data can be lost. The UPS provides enough backup time to save the data and safely shut down the equipment.

The UPS also includes circuits for protection against abnormal conditions such as voltage surges and sags, and power fluctuations.

What is an Inverter?

An inverter is an electronic circuit or device that converts DC into AC. It provides a backup supply to non-sensitive electronic devices where a delay in switching time does not matter, such as lights, fans etc. The switching speed of an inverter is very slow as compared to a UPS and because of this critical equipment may get damaged.

Block Diagram of Inverter

An inverter is basically a DC to AC converter connected with a DC supply such as a battery. It draws current from the battery and converts it into AC supply to power AC appliances. There is no rectifier so it cannot charge the battery. To charge the battery, you need an external charge controller.

It also does not offer protection against abnormal current and voltages. These voltage spikes and surges are one of the drawbacks of an inverter, as it can damage sensitive electronics.    

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The main difference between a UPS and an Inverter is switching time. The switching time of an Inverter is somewhere between 300 and 500ms (milliseconds) while a UPS is below 10ms. This much delay can cause a shutdown in critical equipment and loss of data. But, it does provide a longer backup time.

Inverters can also be used for variable voltage and frequency outputs which is why a Variable Frequency Drive (VFD) or Variable Speed Drive (VSD) is also called an inverter. These drives are designed for variable speed operation of motors.

Comparing the Differences between an Inverter and a UPS


UPS Inverter
A device that provides AC backup power in case of power failure A device that converts DC supply into AC supply.
Converts DC into AC and vice versa at the same time. Only converts DC into AC.
It is made of an Inverter and a rectifier. It is one of the parts inside of a UPS.
The switching speed is 2 to 5ms. The switching speed is 200 to 500ms.
It can also charge the battery from AC utility. It needs an external charge controller to charge the battery.
The supply is not interrupted even after removal of the battery (it then draws from AC utility) Removing the battery will interrupt its power supply.
It provides protection against abnormal voltages and current. It does not offer protection against abnormal conditions.
It also includes AVR (Automatic Voltage Regulator) that provides a fixed output voltage of 220V or 120V. There is no AVR. The output voltage may drop on heavy demand.
Its circuitry is more complex than an Inverter It is a simple circuit which is an AC to DC converter
It is smart and more expensive than an Inverter It is simple and cheaper than a UPS
It provides less backup time than an Inverter It provides a longer backup time than a UPS.
It is used in houses, offices and commercial industries where the delay in power interruption can cause problems. It is used in an application where the delay in power interruption is not a problem such as lights, fans, homes and offices.

Both a UPS or Inverter can be used to provide backup power. The UPS is more expensive and designed for critical equipment. The Inverter is cheaper and cost-effective providing backup power to equipment that is not affected by voltage abnormalities and longer switching times.

Can a UPS be Used as an Inverter and Vice Versa?

A UPS can be used as an inverter while an inverter cannot be used as a UPS. To use a UPS as inverter, simply don’t connect the input supply voltage to the UPS. You may connect the battery only, as a source for the UPS, and it will act as an inverter, i.e. it will convert the DC from the battery into AC and you can feed it to any electrical appliances rated for AC voltages.

Good to know: A UPS can be an inverter but an inverter can’t be a UPS as an Inverter is part of a UPS.

Modified from the original which can be found Here

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