Difference Between Online UPS and Offline UPS - Lento India
Difference Between Online UPS and Offline UPS-A UPS (Uninterruptible Power Supply) is a crucial component of any power backup system. It ensures that critical equipment and systems remain operational in the event of a power outage or other power-related issues. Two main types of UPS systems are available in the market – On-Line UPS and Off-Line UPS. Understanding the difference between these two types of UPS systems is essential for choosing the right one for your needs.
Difference Between Online UPS and Offline UPS
A UPS (Uninterruptible Power Supply) is a crucial component of any power backup system. It ensures that critical equipment and systems remain operational in the event of a power outage or other power-related issues. Two main types of UPS systems are available in the market – On-Line UPS and Off-Line UPS. Understanding the difference between these two types of UPS systems is essential for choosing the right one for your needs.
When it comes to Uninterruptible Power Supply (UPS), there are two main types: Online UPS and Offline UPS. Although both types supply power to devices during power outages, they have distinct differences. The primary difference between Online UPS and Offline UPS is the way they provide power. Online UPS utilizes a rectifier and inverter combination to simultaneously power the load and charge the battery, ensuring that the battery is ready to supply power when needed. On the other hand, Offline UPS supplies AC power directly to the load by switching ON the transfer switch, and only uses the battery backup in the event of a power failure. Another crucial difference is that Online UPS requires a large heat sink.
The rectifier in the Online UPS supplies power directly to the inverter as well as the battery. As a result, heat dissipation will be significant. As a result, an Online UPS requires a larger heat sink than an Offline UPS.
Online UPS
The Online UPS, consisting of a rectifier, battery, and inverter, is directly connected to both the AC mains and the load. The rectifier circuit converts the AC power into DC power, which is used to charge the battery and supply the inverter circuit that powers the load. The transfer switch is always in the ON position, allowing power to be continuously delivered to the load from the rectifier and inverter circuits, without any interruptions in case of a power outage.
Benefits of Online UPS
One of the significant advantages of using Online UPS is that there is no need to switch between the two power paths during a power outage, thus ensuring that power is continuously delivered to the load.
Another benefit is that Online UPS provides proper isolation between the load and input circuits, resulting in distortion-less signals.
Since the inverter is always in the ON position, power is continuously available to the load, resulting in zero transfer time.
Drawbacks of Online UPS
Designing an Online UPS is complex, as it requires a large heat sink.
The instantaneous supply of power to the battery backup and inverter circuit in Online UPS leads to increased power dissipation.
The cost of designing Online UPS is higher than that of Offline UPS.
Offline UPS
The Offline UPS functions by directly providing the AC power to the device connected to the load. During normal operation, the AC power is supplied directly to the load, while the battery is charged with the help of the rectifier circuit.
However, in the event of a power outage, the Offline UPS switches the position of the transfer switch to connect the load to the battery backup path. The charged battery then supplies DC power to the inverter, which converts it into AC and supplies it to the load terminal.
Benefits of Offline UPS
One significant advantage of the Offline UPS is its low design cost in comparison to the Online UPS.
The internal control of the Offline UPS is simple, as there are only two paths, which work at different times according to the position of the transfer switch.
The efficiency of the Offline UPS is high because the battery backup and inverter are not always ON, as they are in the case of the Online UPS.
Drawbacks of Offline UPS
The electric signal obtained from the Offline UPS has poor quality because the inverter is not always ON.
In case of power outage, the transfer time is approximately 5ms, during which there will be no output power. There will be a slight disruption in the output power due to transfer time.
Since the Offline UPS directly supplies AC power when it is available, any spikes or surges present in the input voltage will also be transmitted to the output circuit.
Comparison of On-Line and Off-Line UPS
1. Performance Comparison
Efficiency: On-Line UPS is generally more efficient than Off-Line UPS due to the continuous regulation of the power supply.
Power protection: On-Line UPS provides a higher level of power protection than Off-Line UPS, making it suitable for critical equipment.
Voltage regulation: On-Line UPS can regulate the output voltage, ensuring that the connected equipment receives stable power, while Off-Line UPS cannot regulate voltage.
Switching time: On-Line UPS has a seamless transition between power sources, while Off-Line UPS has a delay in switching to battery power.
2. Cost Comparison
Initial cost: On-Line UPS is generally more expensive than Off-Line UPS due to the higher level of power protection provided.
Operating cost: On-Line UPS consumes more energy than Off-Line UPS, resulting in higher operating costs.
3. Application Comparison
Suitable applications for On-Line UPS: On-Line UPS is suitable for critical equipment such as servers, medical equipment, and industrial machinery.
Suitable applications for Off-Line UPS: Off-Line UPS is suitable for basic power backup needs such as desktop computers and small appliances.
Key Difference Between Online UPS and Offline UPS
The main differences between Online UPS and Offline UPS are in their operation. Online UPS supplies AC power through a rectifier and inverter circuit even when AC mains power is available, whereas Offline UPS directly supplies AC mains power to the load circuit when the power supply is available. Transfer time is a crucial factor that distinguishes the two types of UPS. Online UPS has zero transfer time as there is no switching between the inverter and mains supply path, while Offline UPS has a transfer time of approximately 5ms.
Another significant difference is that the inverter in Online UPS is always ON, while the inverter in Offline UPS is only active during power outages. Online UPS is generally more expensive than Offline UPS. However, the efficiency of Offline UPS is generally higher compared to Online UPS because the inverter and rectifier circuit are not constantly active in Offline UPS.
Conclusion
In conclusion, both Online UPS and Offline UPS are important for providing uninterrupted power supply. The choice between them depends on the specific application requirements. Offline UPS may be suitable for applications where a slight transfer time delay and cost-effectiveness are acceptable. On the other hand, Online UPS may be necessary for critical applications such as medical equipment, industries, and telecommunication, where even a slight transfer time delay is not desirable, despite the higher cost.
Frequently Asked Questions –
1. What is the main difference between online and offline UPS?
The main difference between online and offline UPS lies in their working principles. An online UPS continuously supplies power through the rectifier and inverter circuit, while an offline UPS directly supplies power to the load circuit from the mains and switches to the backup source only when the mains power fails.
2. What is the transfer time difference between online and offline UPS?
The transfer time difference between online and offline UPS is significant. An online UPS has zero transfer time as there is no switching between the rectifier and inverter path and the mains power path, while an offline UPS has a transfer time of about 5ms.
3. Which UPS is more efficient, online or offline?
Offline UPS is generally more efficient than online UPS because the inverter and rectifier circuit in offline UPS are only switched on when the mains power fails, while in an online UPS, they are always on.
4. Which UPS is better for critical applications, online or offline?
Online UPS is better suited for critical applications such as medical equipment, industries, and telecommunication where even a few milliseconds of transfer time can cause significant disruptions. However, offline UPS is a more cost-effective solution for less critical applications.
5. Which UPS is more expensive, online or offline?
Online UPS is more expensive than offline UPS due to its complex design and the need for a large heat sink to dissipate the heat generated by the continuous operation of the rectifier and inverter circuit.
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
ONLINE UPS
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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