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

Part 1 - Internal Resistance

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

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

Float Voltage History – Non-Temperature Compensated Manufacturer Recommended Float – 13.50 – 13.8 Volts (2.25 – 2.30 VPC) Overall Float Voltage Range - 540-552 Volts

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

Part 2 - Cell Discharge Performance

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

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

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

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.

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%

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

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