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The UPS won't operate online when powered by generator.


The UPS won't operate online when powered by generator.

Product Line:

Back-UPS, Smart-UPS


UPS attempting to operate online, while be generator supplied output.


A common characteristic of generators is the normal output voltage distortion when supplying power to nonlinear loads such as computers. This output voltage distortion can be interpreted by the UPS as unacceptable power quality, forcing the UPS to transfer to battery operation. When the load is transferred to the battery, naturally the generator distortion will be reduced or disappear, leading the UPS to attempt to transfer back to line operation. When the load is reapplied to the generator, the distortion will return, leading the UPS to once again transfer to battery. This cycle may repeat indefinitely at intervals of approximately 4 seconds. The answer in this case is to choose a generator which will not distort, when the nonlinear computer load is applied.


In general, the generator should be 3-5x the size of the total load attached to the generator (Not just the load attached to the UPS).

To temporarily correct the issue, please reference the User Manual for your specific UPS model regarding the procedure for adjustment of operating thresholds and sensitivity. Once adjusted to a lower level, the UPS will be capable of tolerating more distortion, as well as a wider voltage range for operation. This will not correct all issues related to your generator and does not apply to all models of UPS. If your UPS does not support sensitivity adjustments you may try removing all load except the UPS (and its attached load) from the generator. This may allow your configuration to function on generator power as desired. An upgrade of the generator or a reduction in the attached load may be the only solution to achieve proper operation. A UPS which does not accept the input power from a generator is not defective, but is protecting the attached load from inappropriate input power.

NOTE: Whenever you choose generator friendly UPS, you may consider upgrading with Online UPS family.
Please click the link for reference: https://www.se.com/sg/en/product-range/61918-smartups-online/?parent-subcategory-id=8020

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