Symmetra PX 80kVA Won’t Accept CAT 3306 Generator Input After Outage – Previously Worked for Years

[webservio]

Hello APC community,

We’ve been successfully running an APC Symmetra PX 80kVA UPS (with AP9617 network management card, firmware v3.3.4 AOS, sy3p v3.3.1) alongside a CAT 3306 diesel generator for many years without issue.

Recently, I noticed that during a brief power outage, the UPS remained on battery and did not switch to generator power as it had in the past. The generator started up fine, but the UPS seemed to reject the input. This resulted in a runtime fault and shutdown due to low battery — something that never happened before.

Here’s what I’ve checked so far:

• Input sensitivity settings, but I’m unsure if they were changed or how to view/adjust them via the network card or front panel.

• Generator voltage and frequency are within expected range when tested standalone.

• The event log shows “UPS output turned off due to low battery” and “redundancy lost,” but nothing indicating why it didn't accept generator input.

• Coldstart event logged around the same time suggests a hard reboot was necessary after failure.

My questions:

1. Where exactly can I verify and adjust the Input Sensitivity or enable Generator Compatibility Mode via the AP9617 or front panel for this model?

2. Is it possible the firmware or NMC has reverted or lost settings that made the UPS compatible with the generator?

3. What exact conditions will cause the UPS to reject incoming power, even if voltage/frequency appear within tolerance?

4. Has anyone else experienced compatibility issues with older CAT 3306 generators on a Symmetra PX?

Any insight or recommendations would be greatly appreciated. This system was stable for years, and I’d like to rule out misconfiguration or overlooked settings before calling for major service.

Thanks in advance,

[Teken]

Please supply the following logs from the system: Event, Data, UPS

How old is the UPS & Batteries? As it relates to question three depending how the system is configured and options available the primary reasons for rejecting generator power is input voltage & frequency.

Depending upon the options available a quick test is to adjust the upper & lower input transfer voltages to the widest possible range. 

The system may have two other settings called power quality and sensitivity. Adjust both to the widest range just for testing.

The system may also have a frequency slew rate and if available adjust that too. The only thing you can not compensate is for is THD. 

If the generator is producing dirty power (THD) than the UPS will refuse this input voltage.

A power quality meter will tell you exactly what the generator is producing as it relates to voltage, frequency, THD, and the sine wave produced.

Let’s just assume you have absolutely nothing as it relates to tools right now. You can take an incandescent lamp and plug it into a protected outlet and watch the bulb while on AC Mains and record the same with your cell.

Follow up with transferring power to generator and allow it to power that bulb for 30 minutes.

What does the bulb show in terms of light output / behaviour?!? You may also in concert plug in a AM / FM radio and tune it to a open frequency.

Again, the radio will be plugged into the protected outlet. Use your cell and your ears to listen to any change in audio output once while on normal AC Mains and than while on generator power only.

Both of these tests will affirm / negate voltage, frequency, and noise. Ideally a power quality meter with a scope would be used but field techs need to adapt and use what’s available! 🤣

NOTE: Every generator requires service based on the number of hours in use. Whether it be a PM vs over haul. More often than not you’ll find the output voltage is excessive or there is frequency drift.

Questions Ask . . . 👍

[webservio]

Hi again,

Thanks for the detailed and helpful response.

The UPS batteries are fairly new and reporting no issues, so I’d like to go ahead and test the recommendation of widening the input voltage and frequency thresholds, as well as adjusting power quality/sensitivity settings.

However, I’m having trouble locating those settings in the web GUI (AP9617 with firmware AOS v3.3.4 / SY v3.3.1). Can someone advise:

1. Where exactly to find and adjust input voltage/frequency transfer ranges?

2. Is Input Sensitivity / Generator Compatibility Mode accessible via the web interface on this older model?

3. If not visible in the GUI, do I need to access these settings via the UPS control panel directly or via serial/telnet access?

Would really appreciate step-by-step guidance or confirmation on how to access and safely adjust these thresholds for testing generator compatibility.

Thanks again!

[Teken]

In the NMC Webpage there should be a tab named Configuration -> Power Settings.

Both of the upper / lower transfer voltage and sensitivity should be there. As noted there may also be another tab / option labeled (Power Quality) for extra options like slew rate etc.

The AP9617 NMC is extremely old so perhaps you can upload the tabs and options available for review.

Surprisingly, none of the online APC manuals for your specific model show any mention of where or how to adjust the power quality, sensitivity, transfer voltage?!? 🤦‍♂️👎

Questions Ask . . . 👍

[MorneMeintjes]

Good Morning.

Hope you are well.

It would be great to know what the voltage is from the supply authority, and the voltage and frequency of the generator. First the frequency. If the frequency changes whilst the generator runs with its current load the UPS may not accept the generator power. I would look at the slew rate (UPS Setting) and to increase it. If the generator hunts, set it to 2Hz its normally on 0.5 or 1Hz. The frequency and voltage window that one can set on the UPS relates to bypass, and the bypass window. Not sure it will affect the rectifier/PFC input.

Some Notes:

The NMC firmware does not store the UPS settings, its merely an interface.

Is the generator earthed.

Test the generator with load

Hope these help

Best Regards

[webservio]

In NMC we interface I have the following parameters that are non changable:

Output Voltage: 208 VAC
Vout Reporting: Auto
Output Frequency: 60 +/- 10 Hz

And the following that I have options that I can change:

If UPS Fails:
Alarm If Redundancy Under:
Alarm If Load Over:
kVA
Alarm If Runtime Under:

My question is are there any more parameters to change using the serial connection? I consulted with chatgpt about this and it recommended the following (see below). My question is: has anybody tried to change using this method?

Adjusting Input Sensitivity on APC Symmetra 80k

To ensure your APC Symmetra 80k UPS accepts power from your CAT 3306 generator, you may need to adjust the input sensitivity settings. Here's how:

Using the Front Panel:

1. Access the Main Menu: Navigate to the main menu on the UPS's LCD panel.

2. Navigate to Power Options: Select Setup Menu → Power Options → Input Sensitivity.

3. Adjust Sensitivity: You'll see options such as:

   • High (default): ~±3% voltage, ±2 Hz

   • Medium

   • Low: ~±10% voltage, ±5–10 Hz

4. Select "Low" Sensitivity: This setting allows for greater variance in generator power, accommodating frequency fluctuations.

5. Confirm Selection: Press Enter to confirm your choice.

Note: Changing the sensitivity does not interrupt the load and takes effect immediately.

Using the Serial Interface:

If you prefer using a serial connection:

1. Connect to the UPS: Use a serial cable to connect your computer to the UPS.

2. Access the Terminal: Open a terminal program (e.g., HyperTerminal) with settings: 9600 baud, 8 data bits, no parity, 1 stop bit.

3. Log In: Enter your credentials to access the command line interface.

4. Change Sensitivity:

   pgsql

   CopyEdit

   > ups > sensitivity Current setting: High Set to (H)igh, (M)edium, (L)ow? L New setting: Low

5. Exit: Type exit to leave the interface.

[webservio]

Adjusting Input Sensitivity on APC Symmetra 80k

To ensure your APC Symmetra 80k UPS accepts power from your CAT 3306 generator, you may need to adjust the input sensitivity settings. Here's how:

Using the Front Panel:

1. Access the Main Menu: Navigate to the main menu on the UPS's LCD panel.

2. Navigate to Power Options: Select Setup Menu → Power Options → Input Sensitivity.

3. Adjust Sensitivity: You'll see options such as:

   • High (default): ~±3% voltage, ±2 Hz

   • Medium

   • Low: ~±10% voltage, ±5–10 Hz

4. Select "Low" Sensitivity: This setting allows for greater variance in generator power, accommodating frequency fluctuations.

5. Confirm Selection: Press Enter to confirm your choice.

Note: Changing the sensitivity does not interrupt the load and takes effect immediately.

Using the Serial Interface:

If you prefer using a serial connection:

1. Connect to the UPS: Use a serial cable to connect your computer to the UPS.

2. Access the Terminal: Open a terminal program (e.g., HyperTerminal) with settings: 9600 baud, 8 data bits, no parity, 1 stop bit.

3. Log In: Enter your credentials to access the command line interface.

4. Change Sensitivity:

   pgsql

   CopyEdit

   > ups > sensitivity Current setting: High Set to (H)igh, (M)edium, (L)ow? L New setting: Low

5. Exit: Type exit to leave the interface.

[webservio]

Has anyone tried changing the UPS parameters through serial port?

[Teken]

Not on this specific model but the procedure you outlined is very similar.

Connect via SSH or directly via Serial Connection using the APC Proprietary RS-232 Serial cable.

I would highly suggest you perform this procedure during a maintenance window in case the system must reboot and cycles the outputs.

Questions Ask . . . 👍