NETA Battery and UPS Systems Testing 4 ā Questions and Answers
Question 1: When performing an AC ripple current test on a VRLA battery, what does excessive ripple current primarily indicate?
- Overcharging from the charger or inverter (Correct answer)
- Normal float charging operation
- Low ambient temperature affecting performance
- High internal resistance within normal limits
Correct answer: Overcharging from the charger or inverter
Excessive AC ripple current on VRLA batteries indicates a malfunctioning charger or inverter is imposing harmful alternating current that accelerates plate corrosion and shortens battery life.
Question 2: According to NETA MTS, what is the recommended maximum acceptable internal ohmic resistance increase for a lead-acid battery cell compared to its baseline before the cell is considered failed?
- 25% above baseline
- 50% above baseline (Correct answer)
- 100% above baseline
- 10% above baseline
Correct answer: 50% above baseline
NETA MTS guidelines indicate a cell with internal ohmic resistance exceeding 50% above its established baseline should be flagged for replacement consideration.
Question 3: A UPS system is tested under a step-load change from 0% to 100% rated load. The output voltage dips by 12% and recovers within 20 ms. This result should be evaluated against which performance specification?
- IEEE 519 harmonic distortion limits
- IEEE 1668 transient response specifications
- NFPA 110 transfer time requirements
- IEC 62040-3 UPS performance classification (Correct answer)
Correct answer: IEC 62040-3 UPS performance classification
IEC 62040-3 classifies UPS performance by output voltage deviation and recovery time under load transients, making it the applicable standard for this test.
Question 4: During a thermal imaging inspection of a battery string, one cell shows a surface temperature 15Ā°C above adjacent cells. What is the most likely cause?
- Cell has lower internal resistance than neighbors
- Cell is in a higher state of charge
- Cell has elevated internal resistance causing excess heat (Correct answer)
- Ambient airflow is directing heat toward that cell
Correct answer: Cell has elevated internal resistance causing excess heat
A cell with elevated internal resistance dissipates more power as heat (P = IĀ²R) during charge and discharge cycles, causing it to run hotter than neighboring cells.
Question 5: What is the primary purpose of equalizing charge on a vented lead-acid battery string?
- To reduce float voltage and extend plate life
- To bring all cells to a uniform state of charge and reverse sulfation (Correct answer)
- To measure true capacity under controlled conditions
- To test the charger's current-limiting ability
Correct answer: To bring all cells to a uniform state of charge and reverse sulfation
Equalization applies a controlled elevated voltage to bring lagging cells up to full charge and dissolve minor sulfation, equalizing the state of charge across the entire string.
Question 6: When sizing a battery string for a UPS, the term 'end voltage' refers to what?
- The maximum float voltage per cell
- The minimum cell voltage allowed before the battery is considered discharged (Correct answer)
- The open-circuit voltage after a full charge
- The voltage at which the charger transitions to absorption mode
Correct answer: The minimum cell voltage allowed before the battery is considered discharged
End voltage is the minimum per-cell voltage threshold established by the manufacturer below which the battery should not be discharged to prevent irreversible damage.
Question 7: A stationary battery capacity test is stopped early when one cell reaches its end voltage while the string voltage is still above the minimum. What action should be taken?
- Continue the test until string voltage reaches minimum
- Record the test as a pass since the string voltage is acceptable
- Stop the test and record the elapsed time and capacity delivered as the actual capacity (Correct answer)
- Replace all cells in the string immediately
Correct answer: Stop the test and record the elapsed time and capacity delivered as the actual capacity
Per IEEE 450/1188, a capacity test must be terminated when any cell reaches its end voltage, and the capacity delivered up to that point represents the true available capacity of the string.
NETA Battery and UPS Systems Testing 4
When performing an AC ripple current test on a VRLA battery, what does excessive ripple current primarily indicate?