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Posted: 2025-09-25 08:09 PM . Last Modified: 2025-09-25 08:24 PM
I have multiple APC UPS's. All of them except the BackUPS 1000 will run on my generator. Onan 15KW gaseous generator, electronic governor for 60Hz (+/- 1/2 Hz), and electronic voltage regulator to keep voltage +/- 5V of 120/240 under any load. Normal load on generator is less than 3 KW.
Parameters on UPS set at widest limits. Unit shuts down after two minutes under any condition. UPS configured to not initiate any shutdown.
Edit: Battery is less than 4 months old. Replaced due to UPS overcharging the first battery, which was only 9 months old. UPS passes "self-test", according to the logs.
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Posted: 2025-09-26 02:50 AM
The APC Back-UPS Series is well known to react poorly when on generator power if the output isn’t clean when compared to the POCO.
You may refer to this APC Resource Link:
https://www.se.com/us/en/faqs/FA158842/
A basic validation is to measure the output while on generator power at different locations using a calibrated and certified oscilloscope / power quality analyzer.
In the ideal situation nothing would be on and powered. At this point you would connect the Back-UPS to the outlet and monitor its behaviour.
If the Back-UPS operates as intended than add more loads to the building. You’ll quickly see the Back-UPS will switch over to battery only mode.
Ask yourself why??
NOTE: You can not simply rely on measuring the voltage / frequency as the final determination.
Questions Ask . . . 👍
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Posted: 2025-09-26 06:13 AM
What does this mean - " if the output isn’t clean when compared to the POCO."? The load on the generator is less than 2KW, and the UPS load is 30%. The waveform of the generator looks identical to that of my POCO.
Can a firmware upgrade remedy this? Is one even available?
The issue is the UPS doesn't even TRY to go back to supplied power, and instead ALWAYS shuts everything down after 2 minutes, regardless of settings. Is this normal?
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Posted: 2025-09-29 04:48 AM
There are no user available firmware on the Back-UPS Series. As it relates to the power output from your generator it’s obviously not clean.
Meaning it’s generating dirty power which the Back-UPS doesn’t like. That can span from voltage, frequency, sine wave, THD, etc.
The litmus test is the fact the Back-UPS operates fine while AC power is provided by the POCO. It obviously doesn’t operate fine while on generator as such the output is not 1:1 in terms of power quality.
In the vast majority of times when it’s not voltage / frequency the primary reason is 3rd harmonic THD.
If you have any high quality filters available you can affirm & test this theory out.
Using a scope would also show how much and the range of frequencies being generated by your Onan.
Lastly, if the system is connected to a computer running APC Power Chute. Provide the following logs for review: Event, Data, UPS during the time the system is on generator power.
Questions Ask . . . 👍
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