APC Smart-UPS RT 3000 (SURT3000) - 20W Charge Rate & 93V Reading after Manual Calibration

[Aka1ca]

Hi everyone,

I have an APC Smart-UPS RT 3000 (SURT3000) and I am looking for confirmation on its charging behavior.

Current Setup:

• Model: SURT3000 (192V Battery System)

• Batteries: Brand new, installed yesterday.

• Action: I performed a manual runtime calibration with a 600W load. The unit ran for 45 minutes before shutdown, confirming the batteries are healthy.

The Issue: After the calibration, I plugged the unit back into mains power. The unit is currently functioning and online.

However, monitoring the unit via software shows two confusing values:

1. Charge Power: It is steady at 20 Watts.

2. Battery Voltage: It is reporting 92.92 V.

My Questions:

1. Regarding the 20W: Is this a normal "Soft Start" or trickle charge mode because the batteries were drained? At what voltage will it switch to full bulk charging?

2. Regarding the 93V: Since this is a 192V system, is the software reading just half the DC bus (Positive-to-Neutral)? If the total DC voltage were truly 93V, I assume the unit wouldn't be able to stay Online.

I just want to make sure the charger isn't faulted before I leave it alone for 24 hours.

Thanks for any advice!

[Aka1ca]

The batteries are 11.6v each. Maybe the batteries discharged too low and the charger won't accept to charge ?

[Teken]

Is the voltage increasing now along with the battery capacity since you last wrote?!?!

Provide a screen capture of what you’re seeing along with the event, and data logs.

The specifications indicate the unit incorporates a 382 watt charging system.

Keeping in mind the system is temperature compensated as such the charging / float voltage will fluctuate based on the internal temperature seen by the system within the RBC compartment.

Im not sure why you performed a out of band battery calibration vs using Power Chute / NMC?!?!

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[Aka1ca]

Hi, thank you for your reply.

​I performed a manual calibration because I did not have access to a laptop/software at the time. The batteries are brand new, and during the test, they successfully held a 600W load for 45–50 minutes, so I know the cells are healthy.

​However, now that I have plugged it back in, it seems like the charger isn't working. It appears to be slowly draining the batteries rather than charging them, even though the UPS is connected to wall power.

​Current Status:

• ​LEDs: The 'Online' light is solid green, but the bottom battery indicator is flashing. There are no error lights.
• ​Voltage: When I measure with a multimeter while it's plugged in, the voltage is slowly dropping.
• ​Battery Level: The batteries are currently sitting at around 11.6V per block (deeply discharged).

​Is it possible that the voltage is simply too low for the charger to activate? Does the charging circuit fail to recognize batteries when they are discharged this deeply?"

[Teken]

Yes, the RBC must be at a minimum level or (SOC) State of Charge. 

I would suggest you remove the RBC and disconnect all the cells and manually charge all the cells.

Once fully charged reconfigure and insert the RBC into the system.

NOTE: It’s critical to understand when the RBC is replaced the following steps be completed in sequence:

Date: The battery installation date must be updated if available via the following methods if present: LCD, NMC, Power Chute.

Doing so resets internal counters and adjusts charging tables if applicable. 

Self Test: Manually initiate a self test and let pass. Wait for the RBC to return to 100% SOC.

Calibration: Manually initiate the battery calibration with a minimum of 30% load or greater via the following methods if available: LCD, NMC, Power Chute.

Allow the RBC to recover back to 100% SOC. This procedure will help the system learn the battery health and better reflect the operational runtime via LCD, LED, NMC, Power Chute, APCUPSD, NUT.

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[Aka1ca]

Thanks for the detailed advice.

Since I do not have a dedicated lead-acid battery charger available, can I use a variable DC Bench Power Supply to charge the cells individually?

If this is safe, I have two questions:

1. What are the recommended Voltage (CV) and Current/Amperage (CC) limits to use on the power supply for safe charging?

2. Do the batteries need to be manually charged all the way to 100%, or is it sufficient to bring them up to a specific threshold (e.g., 12.3V – 12.5V) just so the UPS charger can detect them and resume normal operation?

Thanks!

[Teken]

1. Charging voltage can range from 14.4 ~ 15 VDC. Float voltage can range from 13.5 ~ 13.8 VDC. 2.7 Amps is the maximum per cell.

2. Ideally the cell s hould be fully charged to 12.8 ~ 12.9 VDC. But, you can bring the cells to at least 12.6 VDC to play it safe.

Given there are 16 cells in each RBC X 2 for a total of 32 cells. I would parallel as many cells together you feel comfortable with to charge.

Four cells in parallel would be a good compromise.

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[Aka1ca]

I will try, will keep update here

Thank you 

[Aka1ca]

I have an update regarding my battery issue.

Since the batteries were deeply discharged, I removed them and manually charged each battery individually to 12.0V using an external power supply. The total string voltage is now nominally 192V.

The Current Behavior:

When I reassembled the pack and turned the UPS on:

The Charge Power spikes to 180 W for a brief moment.

Immediately after that, it drops down to 20 W and stays there.

The Battery Voltage appears to be slowly dropping instead of rising (likely due to the internal load of the UPS fans/logic being higher than the 20W charge).

On the front panel, 2 Battery LEDs are lit solid green.

My Question:

Is 12.0V per battery still too low for the main charger to engage fully? Do I need to take them out again and charge them higher (e.g. to 12.5V or 12.8V), or does this "180W to 20W" drop indicate a different issue with the charging logic?

Thank you.

[Teken]

As stated the RBC must be at a minimum 12.5 ~ 12.6 VDC otherwise you’re just wasting time. 

At this point I would highly suggest you complete a brain dead reset to clear any soft faults / errors before you move forward:

https://www.se.com/ca/en/faqs/FA156611/

Once the above procedure has been completed measure the output voltage from the UPS RBC connector and report the DC voltage. 

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