“What is transfer time in UPS?”
The definition of transfer time, sometimes also called switchover time, says it is the amount of time a UPS will take to switch from utility to battery supply during a mains failure, or from battery to mains when normal power is restored. What this means is that when the main power supply fails, the UPS will need to switch to a battery mode to provide sufficient power and ensure smooth running of the attached equipment. The transfer time duration differs, depending upon the UPS system attached. It should, however, always be shorter than your equipment’s hold up time. Hold up time is the amount of time your equipment is able to maintain consistent output voltage during a mains power shortage.
Line interactive UPS systems, such as our VIX or VIS series, have transfer time typically between 2-6 milliseconds. For regular computer based systems, where hold up time is approx. 5 milliseconds, line interactive UPS systems are usually sufficient; however some computer systems, as well as other critical sensitive equipment, are more sensitive and require shorter transfer time. Hence in this case you should always choose UPS with zero transfer time like our VFI series.
If your equipment is critical and doesn’t tolerate even slightest power distortion, we recommend choosing online double conversion UPS technology with zero transfer time to ensure your equipment has the highest degree of protection.
Here’s a quick look up of transfer times for Power Inspired UPS systems:
| Product | UPS technology | Typical transfer time | |
| VIX3065 | Line interactive UPS | Typically 2-6 milliseconds | |
| VIX1000N | Line interactive UPS | Typically 2-6 milliseconds | |
| VIX2150 | Line interactive UPS | Typically 2-6 milliseconds | |
| VIX2000N | Line interactive UPS | Typically 2-6 milliseconds | |
| VIS1000B | Line interactive UPS with sinewave inverter | Typically 2-6 milliseconds | |
| VIS2000B | Line interactive UPS with sinewave inverter | Typically 2-6 milliseconds | |
| VFI1500B | Online double conversion UPS | Line to battery | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI3000B | Online double conversion UPS | Line to battery | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI3000BL | Online double conversion UPS | Line to battery* | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI6000BL | Online double conversion UPS | Line to battery* | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI10KBL | Online double conversion UPS | Line to battery* | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI1000T | Online double conversion UPS | Line to battery | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI3000T | Online double conversion UPS | Line to battery | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| VFI10KT | Online double conversion UPS | Line to battery | 0 milliseconds |
| Line to bypass | Approx. 4 milliseconds | ||
| TX1K | Online double conversion UPS with isolation transformer | Line to battery | 0 milliseconds |
| Inverter to bypass | 4 milliseconds | ||
| Inverter to ECO | Less than 10 milliseconds | ||
| TX3K | Online double conversion UPS with isolation transformer | Line to battery | 0 milliseconds |
| Inverter to bypass | 4 milliseconds | ||
| Inverter to ECO | Less than 10 milliseconds | ||
| TX6K | Online double conversion UPS with isolation transformer | Line to battery | 0 milliseconds |
| Inverter to bypass | 4 milliseconds | ||
| Inverter to ECO | Less than 10 milliseconds | ||
| TX10K | Online double conversion UPS with isolation transformer | Line to battery | 0 milliseconds |
| Inverter to bypass | 4 milliseconds | ||
| Inverter to ECO | Less than 10 milliseconds | ||
*unit doesn’t contain internal batteries, requires external battery pack/cabinet
Transfer times are dependent on which stage the power interruption occurs in. That’s why the transfer times stated in the above table are approximate.
As previously mentioned, transfer times also measure the amount of time it takes for the UPS to switch back to mains. The transfer back to mains power is always controlled with minimal interruption as this transfer is planned. As opposed to an unplanned mains failure which happens suddenly and hence a variation in the actual time taken.
We have conducted a transfer time measurement using an oscilloscope (photograph above). For purpose of this exercise, we have used a standard line interactive UPS system and stimulated a power cut. The oscilloscope managed to capture the transfer time which on this occasion lasted 15 milliseconds, due to the original sine wave being interrupted at the peak of the cycle.
“How does transfer time affect my equipment?”
That’s simple – if your equipments tolerance is below UPS transfer time, the UPS will not provide power in sufficient time in order to keep your equipment running.
Let’s say you have highly sensitive laboratory equipment with hold up time of 2 milliseconds. Line interactive UPS will not be sufficient in this case as it will not switch to battery mode quick enough. You will need to invest in an online double conversion UPS or Isolated online double conversion UPS in order to avoid any downtime. On the other hand if your equipment is a very basic computer workstation with approximate transfer time of 10 milliseconds, you can use the line interactive UPS system with peace of mind that your equipment is protected.
Transfer time is definitely one of the things you need to keep in mind while searching for suitable UPS. More factors affecting your choice of UPS technology are covered in this article.
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