Power Supply FAQ

To ensure your PC based automation system is working reliably, backup power in the event of utility power outage is important. Recommended is that all PCs (especially the MainLobby Server be connected to a UPS (Uninteruptable Power Supply). The UPS instantly kicks in and runs the PC off of battery power in the event of utility power becoming unavailable.

The UPS should be capacity scaled to the PC (and any peripherals) that are connected to it to ensure there is enough time for when the utility power is typically back online, or until the MainLobby system can be gracefully shut down with proper notices that it is unavailable sent out (like via email or other notification).

Many UPSs provide software for triggering shutdown sequences in the event of power outage that can easily be configured to do some of the above.

Additionally, especially in rural areas, a generator backup to the UPS should be considered if power outages are typically longer in duration than the capacity of the UPS battery. The power coverage would work something like this: Utility power goes out. Instantly the UPS responds and switches to battery. The generator sees the utility power is down, and begins it's startup sequence. When the generator is running and voltage is stable, the generator system switches house power from utility to generator using a Line Transfer switch. This normally happens in under 30 seconds. Once the generator is online, a properly configured UPS will then see that "utility" power is now available and will switch to using the generator's power. Once utility power is resumed, then the reverse sequence occurs.

One problem with generators (especially smaller household scaled ones) is that the UPS sees the generator's power, but it isn't "clean enough" and the UPS stays on battery, even though the generator is online. Below is an article and solution for how APC company addresses this issue (by providing means on some UPS models to desensitize the UPS):


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 attached load.

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. An upgrade of the generator or a reduction in the attached load may be the only solution to achieve proper operation.