1. Part 1 - Internal Resistance Part 2 - Cell Discharge Performance
Data Interpretation
Part 1 - Internal Resistance
Part 2 - Cell Discharge Performance
Rick Tressler
ESSB Technical Symposium
Monday June 11, 2017
Chattanooga, TN

2. Part 1 - Internal Resistance

3. Internal Resistance Problems in Data Center UPS
Typical system - 40, 12V VRLA X 4 strings
Multiple systems all in data center UPS application
Cabinet enclosures
Good operating environment – 72-75°F
Trained technicians
Consistent testing methods

4. Average Internal Resistance Over Service Life (Micro-Ohms)
5/10/2014
3979
Max 20%
3840
Installation 8/16/11
3580
1/7/2014
Warning 15% 3486
Baseline Established 3/6/2012
3032
11/17/11
Baseline

5. Float Voltage History – Non-Temperature Compensated
Manufacturer Recommended Float – – 13.8 Volts (2.25 – 2.30 VPC)
Overall Float Voltage Range Volts

6. Part 1 Summary Problems spanned across many systems in the facility
All systems were of same vintage of manufacture
There was no root cause result provided, post replacement
Different manufacturer was used for replacement systems

7. Part 2 - Cell Discharge Performance

8. Performance Test Results in a Controls UPS
Modular installation
3 years old
60, 2V VRLA x 1 string, 105 AH (8hr capacity)
No testing or previous maintenance - no operating history
Industrial controls UPS application
Good operating environment – 75-80°F
Tested at published 2 hour rate to 1.78 VPC
Test was paused once to bypass 3 cells, resulting in exceeding 6 minute recommendation in IEEE 1188

9. Typical cell behavior during discharge
This dip in cell voltage observed immediately after starting a test, followed by a recovery is normal for lead-acid batteries. Known as Coup de Fouet.
Recovery during a pause in the test.
Typical cell behavior during discharge

10. Abnormal cell behavior on discharge.
Cell failed just over 1 hour into a 2 hour test. This cell was bypassed.
29% capacity
Possible Internal Issue: Metallurgical problem with grids, straps, posts internal to the cell. Characterized by an immediate and sustained drop in cell voltage during discharge. Abnormally high cell resistance was observed pre-test.
00:35:00 min

11. 40% capacity Abnormal cell behavior on discharge.
Cell just under 50 minutes into a 2 hour test. This cell was bypassed so the test could continue.
40% capacity
Possible Internal Issue: Premature dry-out. No indication of high internal resistance. Characterized by a sharp drop in cell voltage during the discharge. Abnormally high cell resistance was not observed pre-test.

12. Overall battery performance showing battery voltage and load current
Overall battery performance showing battery voltage and load current. Three cells failed. Overall capacity was 90% with 3 cells bypassed.
Overall capacity 89.5%

13. Part 2 Summary
Maintenance should have been started sooner than 3 years into life
Actual capacity when new is questionable
The above is an excellent rationale to perform an acceptance test
Ohmic measurements don’t always foretell of cell problems
Unexpected cell behavior can indicate problems but require a post mortem internal inspection to confirm a specific cause

14. Part 1 - Internal Resistance Part 2 - Cell Discharge Performance
Data Interpretation
Part 1 - Internal Resistance
Part 2 - Cell Discharge Performance
Rick Tressler
ESSB Technical Symposium
Monday June 11, 2017
Chattanooga, TN