SU1400 overheating with swollen batteries

[Anonymous user]

My SU1400 was cooking with no alarms - unless you count the sound of the fan running at top speed.

I only noticed because I went down to the basement. It took a couple of hours for the unit to cool down enough for me to work loose the badly swollen batteries. They measured 12.8V.

My supplier tells me that this indicates a failure of the charging circuitry on the UPS. Is there a way for me to test this without batteries?

I have the AP9605 network interface card installed so I should be able to connect to it.

Thank you for your help.
Keith

[BillP]

If your batteries are more than 3 years old and your setup is a set-it and forget-it type (located in basement) it is possible that the batteries are simply worn out. Regular self test on the UPS ensures that it detects faulty battery, provided that self test is enabled on the unit. Sounds like your batteries have internally their cells shorted. This type of failure can be detected by the ups with briefly transferring the load to battery, if there is no battery capacity, it will indicate battery failure. Without this self test enabled, the UPS assumes the shorted cells to be depleted batteries, thus force charging current in them, without them ever reaching full charge. The charger has obviously not failed since it tries to charge the batteries as we can tell. What is possible though is that the charging voltage is out of range. Too high voltage shortens battery life. Acceptable charge voltage for SU1400 is between 27.1-27.7 VDC, best to be around 27.2-27.3 VDC. 

Unofficially speaking (not being an APC employee).  Try the following only at your own risk, and be wary to not to short circuit the electronics, including battery terminals. Dangerous voltages may be present. Attempt only if you are qualified and have the proper tools and accessories. Do not touch anything inside the unit with bare hands, including battery terminals. The following procedure can be undertaken by service center personnel, take it to an authorized service center if you are unsure. 

Charge voltage can be checked by connecting your faulty batteries just so that you can start the unit. After connecting the batteries, plug in the unit to the mains so that charging may start.  Then disconnect UPS negative battery lead from battery terminal, and use a multimeter to measure DC voltage between UPS battery leads positive and the disconnected negative.

Anyway, a good indication for the need of battery replacement (if it is not indicated by the ups yet)  is by paying attention to UPS internal temperature, which is reported by the UPS when queried. It is usually above by several degrees of room temperature, and should stay consistent apart from battery operation and after it, battery charging, which generates more heat than usual standby float charging mode. If charger forces excessive current for extended periods of time, standby temperature of the UPS increases which is a good way to help determine that it requires attention. 

[Anonymous user]

Thank you Wolf for the detailed reply. I really appreciate you taking the time to help.

My UPS does perform the self test weekly but since it is in the basement, I seldom notice. It is not being monitored by Powerchute though, only by my two QNAP NAS units. I will see if I can write or find a tool to interrogate the temperature and other values so that I can monitor them more closely.

It has been a long time since I have connected to it directly but when it was overheating, there was no indication on the front panel.

The batteries were 28 months old but were not APC batteries. Unfortunately, I left the failed batteries with the company. I will ask if I can get them back for testing.

You wrote:

After connecting the batteries, plug in the unit to the mains so that charging may start

Does this mean I cannot start the unit without batteries? (I haven't tried yet.) I have another smaller Smart-UPS that I can temporarily cannibalize for testing if necessary.

Thank you again,
Keith

[BillP · Accepted solution]

Yes, older units like SU1400 need to have batteries installed, more precisely, they need batteries that measure at least 22-23VDC. Since yours probably has shorted cells, it is possible that voltage has dropped well below that, but it is worth a shot. Also you may try without batteries, but if my memory serves right, it will not do anything even with mains power connected. 

I consider inspecting my UPS unit personally every few weeks or months a good practice, there are times like this when you may notice abnormalities well before the UPS could. Proper monitoring over serial or network is a very recommended thing to do if the UPS is to remain out of sight for extended periods of time. Batteries do not deform that badly in short term, it means they could have been bad for more weeks or months even, which places unnecessary stress on the electronics as well.