Frequently customers will call asking if they can connect their small UPS units together in a daisy chain to either increase power protection or to lengthen run time. On the surface of it, the idea seems to make sense. However, connecting UPS systems in serial or a daisy chain is highly discouraged and with most manufacturers, will void the factory warranty.
Top 4 Reasons You Should Never Daisy Chain UPS
- You will void the factory warranty of both UPS systems
- You will not increase the capacity of your power protection
- You will not increase run time
- You will jeopardize the proper operation of the data center EPO
#1 If the manufacturer doesn’t think it is a good idea, it usually isn’t.
#2 You will not increase the capacity of your power protection – Plugging one UPS into another does not increase power protection. Because the first UPS is limited in watt capacity, the output will never exceed the capacity rating. The second UPS would only provide additional outlets, not more watt capacity.
#3 You will not increase run time – The most common misconception about connecting UPS units in serial is that you will benefit from additional run time. This is not true. Most UPS systems output a stepped sine wave when on battery power. Almost all UPS equipment interprets a stepped sine wave as bad power. Therefore, as soon as the first UPS goes on battery and outputs a stepped sine wave, the second UPS in the series will read that input as bad power and convert to battery also. With both UPS systems running on battery at the same time, there is no increase in battery capacity.
#4 You will jeopardize the proper operation of the data center EPO – Most importantly, there is a significant safety issue with running larger UPS systems in serial. The wiring used to daisy chain UPS systems can interfere with the operation of the data center EPO (emergency power off) leaving some equipment powered after tripping the EPO and creating a significant safety hazard.
Options for increasing runtime, power capacity, or redundancy
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- Add External battery cabinets or modules to your existing UPS
- Connect equipment to different UPS units with their own input power source
- Install another UPS to run in parallel using a parallel communications box or bridge
- Use dual input power cords and an automatic transfer switch to change power paths
To increase the runtime of small UPS systems, most manufacturers offer external battery cabinets or extended run options. These external battery packs offer users significantly increased run times. Another option is to connect different equipment to different UPS units keeping each UPS connected to its own input power source.
As you consider run time requirements, keep in mind that UPS equipment is intended to provide an opportunity for the proper shut down of equipment in the event of a power failure, they are not designed to operate as a supplemental power source.
When the objective is to add power capacity or redundancy, UPS systems can be configured to run in parallel. This differs from serial connection as the UPS systems in parallel each have their own input power path. UPS systems should only be run in parallel when wired and installed with a configuration that includes a parallel communications box or bridge. The bridge allows the two (or more) UPS systems to synchronize their sine waves so they can stay in phase.
Generally speaking, only larger, three-phase UPS equipment is installed in parallel. For smaller loads where redundancy is needed, consider dual input cords with an automatic transfer switch connecting one power source to the larger facility UPS and the second power source to a smaller rack mounted UPS with a different input power path.
Contact Power Solutions for more information about the Top 4 Reasons You Should Never Daisy Chain UPS. We can help you meet your requirement safely and efficiently.