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What is the difference between online UPS and ordinary UPS?

Author: Alice
Dec. 06, 2023
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What is a UPS device?

During power surges and failures, Uninterruptible Power Supply (UPS) devices keep computer systems and IT equipment safe and operational. A UPS provides battery backup power when the flow of electricity drops to an inadequate voltage, or if it stops. An uninterrupted power source is vital for the mission-critical environment. Depending on the size and technology of the UPS unit, backup power is provided for a specific period of time, until generators can be activated or network components can be properly shut down. When electricity flows adequately, computers and accessories are protected from damage. A UPS unit can help to shield a single device or an entire data centre effectively. See our review of best UPS devices.

What are the different types of UPS?

There are three main types of UPS systems available to accommodate a complete range of applications, meeting enterprise and consumer needs. A Standby UPS is an offline unit that can detect an electrical failure and switch to battery power automatically. The two other UPS categories are Line Interactive and Online Devices, with online being the more expensive option. Each type of UPS keeps network devices operational when power is unavailable. Features, such as energy metering, vary by model.

What is a Standby UPS?

The basic Standby UPS is an uninterruptible power source that delivers short-term, battery-sourced power during outages. With this category of UPS, hardware receives utility power, under normal conditions, through a direct AC connection. The standby unit and its inverter are essentially on hold until backup power is needed. Depending upon the model, a standby UPS device can also safeguard data and sensitive equipment from surges, spikes, and dips. Compact devices are available for home network protection. A Standby UPS is commonly used to protect computers, modems, VoIP equipment, and other hardware. This category of UPS is the least expensive of the three UPS types.

Battery backup power is initiated with the Standby UPS, which is also referred to as a Backup UPS. Following a blackout, a Backup UPS delivers power for short periods of time. When it detects losses, the transfer switch initiates backup processes. Switchover times occur in milliseconds after failure, with response times varying by a standby UPS unit. The switch time is not instantaneous but should not normally interrupt the flow of power to equipment. If a lengthy outage is expected, the battery backup power of the UPS will allow for safe shutdowns, so equipment and data are protected.

Offline UPS Provides Basic Power for Home and Office

A standby UPS may also be referred to as an Offline UPS, a term that differentiates it from the fully uninterruptible, Online UPS. Though fundamental in design, an offline uninterrupted power source delivers backup runtimes for less demanding home and professional environments. Comms Express representatives have detailed information regarding Offline, Line Interactive and Online UPS models for network, server and desktop UPS applications.

What is Online UPS?

An Online UPS is a type of uninterruptible power supply that utilises either a double or delta conversion technology. With double conversion, network equipment does not receive electricity directly from the AC outlet. Instead, AC power travels to a rectifier, where it becomes DC power. Next, it travels to the battery, and then an inverter. After inversion back to AC, the power is delivered to equipment. With this online UPS device process, computing equipment receives continually clean power. With delta conversion, a certain amount of power is sent to run computers, routers, and other equipment directly. This creates an energy-efficient online UPS system where some of the power skips the processing steps.

If an electrical failure occurs, an Online UPS system maintains consistent current flow for the protection of network equipment. Upon fluctuation or failure, the rectifier within the UPS is automatically bypassed, and power is sourced from the battery until restoration occurs. The online UPS circuity is seamless. This is why Online UPS systems cost more than units in the offline or line-interactive UPS categories.

Double Conversion UPS Technology

Sensitive equipment can be protected with double-conversion UPS technology. Online UPS units are available for a wide range of users. With double-conversion UPS processes, network servers, data centres, and a full scope of environments can be protected, and there is no transfer time in the transition to battery power. Intelligent online UPS systems are available to support demanding loads and run times. More affordable double-conversion UPS units are available to smaller offices. Normally, the larger the unit, the longer equipment can be kept running.

What is Line-interactive UPS?

A Line-interactive UPS is one type of uninterruptible power source that can regulate voltage automatically. The line-interactive technology responds to high and low voltage conditions. Units also support systems during outages without battery drainage. With a line-interactive UPS, the electrical source is the first line of power; however, an inverter/converter technology allows for the unit’s battery to be charged throughout normal operations. During an outage, this UPS converts battery power to AC flow for device delivery.

Line-interactive UPS Systems for IT Applications

Within the category of power protection products, line-interactive UPS systems will safeguard sensitive equipment during brownouts and blackouts. Units in the line-interactive UPS classification are more expensive than standby models but more affordable than an on-line UPS unit. A line-interactive UPS will maintain performance during low voltage situations and short-term power failures. If a lengthy outage is anticipated, its battery power allows devices to be shut down safely. Some live interactive units also offer filtering features.

What is the difference between Online vs. Line-Interactive UPS?

Before buying a power protection unit, you may want to compare on-line versus line-interactive UPS technology. A line-interactive UPS adds an autotransformer to the basic standby design. It has the capability to increase or decrease voltage output. This transformer responds to changes in the AC power and can automatically regulate issues. In comparison, online UPS models use an inverter to transmit all or some of the power, at all times. This means an online UPS can live up to the term “uninterruptible” with a zero transfer time. It takes an interactive UPS a matter of milliseconds to switch into battery backup mode when a failure occurs.

Power Management Solutions with Battery Backup

Reliable power management systems help to ensure that electrical power to valuable equipment is never interrupted. When buying a UPS unit, the volt-ampere (VA) rating of the device should be compatible with the total load that must be protected. This load will include all equipment and network accessories. An advanced online UPS system uses double conversion technology for power management. It delivers consistently clean power, even during the brownout or blackout, for server-grade and data centre systems. Contact Comms Express for questions about VA and wattage ratings on UPS devices.

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Difference Between Online UPS and Offline UPS – Which One is Better?

Main Difference between Online UPS and Offline UPS – Which One to Use?

UPS, Uninterruptible Power Supply is a device that supplies power in case of power failures. A UPS can be either Online UPS or Offline UPS. Both types of UPS can be used as a backup power source but there are many differences between them.

The major point that differentiates between the online UPS and offline UPS is that the online UPS supplies power from the AC mains to the Load through the rectifier and inverter combination while the Offline UPS directly supplies power from AC mains to the load.

Before going to the list of differences between Online UPS and Offline UPS, let’s discuss the basics of Online UPS and Offline UPS.

What is UPS (Uninterruptible Power Supply)?

UPS is an abbreviation for Uninterruptible Power Supply and the reason for its name is that it provides a constant supply of power without any interruption. In Normal operation, it draws current from the AC mains and during a power outage; it draws current from its backup source.

A UPS system utilizes a DC power stored in the battery as its backup source. The UPS charges the battery from the AC mains through a Rectifier and charge controller circuit. At the same time, it supplies power to the output AC load. In case of power failure, the UPS utilizes this charged DC power in the battery and converts it into AC using an inverter and supplies it to the AC load.

Now the switch over between the sources (AC mains and the battery in case of power failure) is instantaneous. But it does take some time. This time delay during the switching may affect some sensitive electronic equipment while other devices may tolerate it in a specific range. This is where Online UPS and Offline UPS comes into play.

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What is Online UPS?

The Online UPS is a type of UPS that supplies power to the AC load through the Rectifier and Inverter Combo in normal operation and uses an inverter to supply AC power during a power failure. Therefore, the output power supply always stays ON and there is no need for switching. Hence, there is no time delay in switching between its sources. There is no interruption in the case of power failure even for a nanosecond.

During normal operation, it converts the AC supply from the AC mains into DC using a rectifier and charges the battery using a charge controller circuit. Now at the same time, the DC power from the charged battery is being converted into AC using an inverter to supply it to the output AC load.

In case of power failure, the UPS will stop drawing current from the AC mains, and stops charging the battery. But the AC load will continuously draw current from the battery through Inverter.

Therefore, Online UPS has a zero time delay when switching its power source. It is also why it is known as Online UPS because it stays ON even during its normal operation.

Since the current drawn by the AC load is continuously flowing through its whole circuit, the temperature of the system increases. Therefore, it needs comparatively larger heat sinks and the components that can withstand high temperature and it can tolerate current flow for very long duration. Due to such a requirement, the cost of Online UPS increases significantly.

It continuously draws current from the battery which quickly reduces the lifetime of the battery compared to offline UPS. They are more inefficient because they continuously stay ON even in normal operation.

On the other hand, it does offer high-quality output because there is no gap during the switching between the source supplies. It completely isolates the output from the AC mains. Therefore, it helps in protection against the distortions or fluctuations in the AC mains.

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What is Offline UPS?

The offline UPS is a type of UPS that directly supplies the power to the AC load from the AC mains in normal operation and uses an inverter to power the AC load from the DC battery. Since there are two separate lines of supplies, the output supply must be switched between the two sources.

The switching speed of an Offline UPS is around 5ms which is enough to keep a computer from shutting down. But not fast enough to keep a smooth operation of sensitive equipment in hospitals.

During normal operation, the power from AC mains is directly supplied to the output through a static transfer switch. At the same time, the AC is converted into DC using a rectifier to charge the battery using a charge controller. But unlike Online UPS, the inverter does not draw current from the battery until the primary supply (AC main) is interrupted.

When the primary supply breaks, the battery stops charging and the static switch transfer the output line to the inverter side very quickly. At the same time, the inverter starts drawing current from the battery which is then supplied to the AC load.

Since it stays off when it draws current from the AC line during normal operation, it is known as Offline UPS.

The Offline UPS mostly stays off in normal operation and because of that, the temperature of the components stays low. Therefore, it requires smaller heat sinks and the components with a lower tolerance can be used which also decreases the overall cost of the offline UPS.

Since it stays off in its normal operation and does not use the battery continuously, the efficiency of the system increases.

But the downside of offline UPS is that the directly supplied AC is not completely isolated from the load. Therefore, there is no protection between the load and source and the distortion or fluctuations in the Ac mains can damage the connected load.

Differences between Online UPS and Offline UPS



The UPS that supplies power from the AC mains to the load through the rectifier and inverter combination

The UPS that supply the AC mains power directly to the load.

It continuously draws current from the battery.

It only draws current from the battery during primary source failure or power outage.

It requires a large battery charger circuit because it carries the entire load current.

It requires a small charger circuit because it only charges the battery.

The input supply and the load is completely isolated.

There is no isolation between the input supply and load.

It has high-performance output because it protects the output load from input voltage spike and distortion.

Its performance reduces with the input voltage distortion; which is directly connected to the load.

There is not switching between the source, hence no time delay

It uses a static transfer switch to switch between its source with a time delay of 5ms

It stays ON almost at all times.

It turns ON only at power failure.

Due to its continuous ON condition, it is inefficient and unreliable.

It is more efficient and reliable because it mostly stays off.

It requires large heat sinks because of the high operating temperature

It requires smaller heat sinks because of low operating temperature due to its off state mostly.

The components used must have the tolerance to withstand high temperature

There is no need for the components to have high-temperature tolerance.

It is expensive than Offline UPS.

It is cheaper than Online UPS.

It is used for very sensitive electronics that cannot tolerate any gap between supplies such as in-hospital ICUs

Offline UPS is used for electronic equipment that can tolerate a delay of 5ms such as Computer etc

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Which one to Use, Online or Offline UPS & Why?

Is online or offline UPS Better? and When to use it? it totally depends on multiple factors such as cost, usage and specific conditions etc. For example,

When to Use Online UPS:

  • When to operate the sensitive and important devices and equipment with continuous power supply without switching operations.

  • When the the main power supply fluctuates frequently or daily scheduled load shading and power outage

  • When there is no concerns about the operation, installation and maintenance cost as the online UPS system is costly than offline UPS system due to the additional parts in online uninterruptible power supply.

  • When you need the simultaneous operation of connected devices for longer time duration.

When to Use Offline UPS:

  • When cost is the major and considerable factor.

  • When switching is not a big issue i.e. you are OK to use it with auto or manual change-over or transfer switch between main power, portable generator or emergency generator set , solar or battery power.

The conclusion of this article showing the key difference between ONLINE & OFFLINE UPS systems is that the online UPS has zero time delay between the switching and they are expensive. while the Offline UPS has a time delay of 5ms but they are inexpensive. Based on efficiency, the offline UPS is far better than Online UPS and it should be used for domestic purposes. The Online UPS should be only used for very sensitive electronic equipment.

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What is the difference between online UPS and ordinary UPS?

Difference between Online UPS and Offline UPS

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