UPS BATTERY-BANKS

[delta4499]

WE HAVE A UPS SYSTEM OF 130 KVA IN 1+1 PARALLEL OPERATION. EACH UNIT HAVE ITS OWN BATTERY BANK OF 192 CELLS OF 2 VOLTS 825 AH (VRLA MAINTENANCE FREE BATTERY) THE INSTALLATION DATE IS OCT.99 AND BATTERY MANUFACTURING DATE IS JUNE 98.

IN THE LAST TWO MONTHS WE FACE THREE NOS. OF BATTERY BANK FAILURE CASE DUE TO FAILURE/BREAKDOWN OF FEW CELL IN EACH BATTERY BANK WE BY PASS THESE CELL AND LATER GONE FOR A CELL HEALTH CHECK-UP. THE HEALTH CHECK-UP REVEALED THAT ANOTHER 20 NOS. OF CELL HEALTH IS NOT GOOD THEY ARE ALSO NEED URGENT REPLACEMENT.
NOW 1)I WANT TO KNOW THAT WHAT IS THE LIFE OF THESE CELLS(2 VOLTS, 825 AH)

2)CAN WE REPLACE THESE FAULTY/DEAD CELLS WITH NEW CELLS IN THE EXISTING SETUP OR WE SHOULD GO FOR A COMPLETE NEW BANK OF 192 CELLS.

ONE MORE THING IS THAT WE HAVE NOT GIVEN ANY BOOST CHARGING TO THESE CELLS DURING THE SAID PERIOD.

THANKS

AJAY

 

[nukeman]

You need to run a capacity test on the remainder of the cells to determine the state of your batteries. The capacity test should be done at a constant current to a end voltage as outlined in the discharge data provided by the manufacture. You need special equipment to perform this test which will monitor each cells voltage over the discharge period.

I suspect that since you have had so many cell failures the whole bank will need to be replaced. VRLA batteries are not maintenance free. Per IEEE 1188 you should be doing internal ohmic readings quarterly along with ICV and temperature readings. Have you been doing any of this? Is there an adverse trend?

If these were my batteries I would first talk with the manufacture, equalize (boost charge) the batteries, put them back on float for another 72 hours and then capacity test them.

The life of VRLA batteries depends on a few important things. Did you purchase a 20, 10 or 5 year battery? No one seems to get the stated life out of the battery. A 20 year battery is more like 7 to 10. What ambient temperature are these cells exposed to? Cell life is greatly impacted by temperature. For every 15 degrees above 77 cell life is cut in half.

 

[DanDel]

I agree with nukeman's recommendation of a battery load test(per IEEE standards, constant current). This test will tell you which cells are defective. In most cases, you can simply replace the bad ones.
Check out my company's web site for an explanation of the IEEE constant current battery test.

http://www.neete.com

Click on 'Battery Testing' in the left column.

 

[alehman]

I agree with the above replies. Before replacing the battery, you should also check some things with the UPS to be sure it isn't damaging the battery:

1. Float voltage is correct. Normally about 2.25V per cell. Voltage either too high or too low will drastically shorten the life of the batteries.

2. Have the UPS service company check the AC ripple current. It is possible for a problem with the rectifier to cause excessive ripple current which can quickly destroy a battery.

3. Make sure the UPS end-of-discharge voltage is set correctly and that the inverter shuts down at the correct battery voltage.

I would recommend checking with the battery manufacturer before equalizing. Some VRLA manufacturers don't recommend equalizing except under certain controlled conditions. They usually have very specific time and voltage level recommendations. Also, you need to monitor cell temperatures during equalize. You need to allow at least 72 hours after equalizing before beginning a load test to allow gas within the cells to dissipate.

Use a cell monitor such as Albercorp BCT-2000 during the discharge test to record voltages on each cell/jar.