Batteries and DC Systems
This form is the record of one capacity discharge test of a stationary lead-acid battery string in standby service. A load at the test rate is drawn from the fully charged string until the terminal voltage reaches the end voltage set by the installation design (the minimum average volts per cell times the number of cells), the actual time to that voltage is compared with the rated time, and the capacity at 25 C is computed by the time-adjusted or the rate-adjusted method with the temperature correction factor from the governing standard or from the manufacturer's published data. The result is graded against the criterion for the test type: acceptance, performance, modified performance (types 1, 2 and 3) or service. Vented cells follow IEEE 450-2020 and valve-regulated cells follow the IEEE P1188/D16 approved draft; fields that belong to the other chemistry are recorded and never graded. Nickel-cadmium, lithium and other chemistries, cycling applications, battery sizing and routine inspections are out of scope. The installation acceptance records for vented and valve-regulated batteries link to this record for their load-test result.
A stationary battery exists for the minutes or hours when the charger and the supply behind it are gone, and nothing but a discharge shows how long it will carry that load. Float voltage, specific gravity and ohmic readings describe the condition of the cells, but ohmic values do not predict capacity. A capacity test under a known load at a known temperature gives one number that can be compared with the rating, with the purchase specification and with the previous test, so a string that is aging normally can be told from one that has dropped more than 10 points since the last test or sits below the point where replacement is indicated. The record also proves the test was run on a basis the standard allows: the right method for the test length, the full published rate on an acceptance test, downtime within the cap, and no cell bypassed where the test type forbids it.
An acceptance test is run on a new string at the full published rate, and on valve-regulated cells by the time-adjusted method; a run at a derated rate leaves the result indeterminate. Performance tests follow as guidance from IEEE 450-2020 and IEEE P1188/D16: the first within two years of installation (within one year for a valve-regulated string that was not acceptance tested on site), then at most every 25 percent of expected service life, and yearly once the string shows degradation (capacity below 90 percent, or more than 10 below the previous test) or reaches 85 percent of its expected life; a vented string at 85 percent of life with capacity of 100 percent or more and no degradation may wait two years. The form computes the months to the next performance test from these entries as guidance only. A modified performance test stands in for a performance test where the battery was sized by the IEEE 485 method, and a service test checks the string against the designer's duty cycle as found, with no temperature or age correction.
The test plan names the chemistry, the test type, the capacity method (kept the same from test to test), the rated time to end voltage and the published rate for that length from the manufacturer's data, and the end voltage from the DC system design. Where the initial average cell temperature lies outside 15 C to 35 C, the rate-adjusted test rate is divided by the standard's temperature factor. Pretest conditions are recorded: an equalize, where one was done, followed by the float window the standard sets (at least 72 hours on vented cells; on valve-regulated cells an equalize ending more than 24 hours and less than 30 days before the test), the graded pretest checks, the terminal float voltage and float current, the average temperature of at least 10 percent of the cells, and whether the charger was disconnected or the load raised by its current. During the run the cell voltages are read across like-polarity posts of adjacent cells, in at least three reading sets on vented strings and five on valve-regulated, connections are watched for abnormal heating, the rate is held to the end terminal voltage, and the actual time, the actual rate and the published rate for that time are entered. Every interruption is logged with the cell or unit, time into test, reason and downtime, and after a bypass the end voltage is recalculated for the remaining cells. On a vented run over 24 hours with a temperature change above 3 C, and at the technician's option on a valve-regulated run over 8 hours, the run-average temperature replaces the initial one for the factor. The end voltage of every cell is recorded and the lowest cells tabulated. Capacity is computed at 25 C and rounded down to 0.01 percent before grading. Restoration closes the test: equipment disconnected, the string recharged and returned to service, with the valve-regulated steps for hot or weak units, the charger reset and replacements installed only after full recharge.
Identification: nameplate data, chemistry and governing document, positive grid alloy, cells or units and cells per unit, nominal string voltage, rated capacity and rating period, installation date, expected service life, strings in parallel, whether sized by the IEEE 485 method and whether acceptance tested on site. Test plan: test type, capacity method, rated time, rate basis and derating factor, published rate and unit, minimum volts per cell and end terminal voltage, purchase specification level, previous performance result and date, duty cycle reference. Pretest: equalize status, date and hours to test, the graded checks, float current and terminal voltage, cells sampled and initial average temperature, charging source. Connection resistance rows. Discharge run: date, start time, load source, reading sets, run checks, connector heating, actual time, actual and published rates, type 3 ampere-hours, run-average temperature and its change. Interruptions with cell, time, reason and downtime; duty-cycle bypass; recalculated end voltage. End voltages of every cell and the low cells. Capacity result with the factor used and the margins, duty cycle met, replacement, degradation and life flags, months to the next test. Restoration checks, ambient temperature, room ventilation, test equipment with calibration date, comments and deficiencies.
The verdict rests on IEEE 450-2020 for vented cells and IEEE P1188/D16 for valve-regulated cells. The result is indeterminate rather than failed when the chemistry, test type or actual time is missing, the capacity cannot be computed, a graded check is left blank, or the basis is not one the standard allows: a time-adjusted test under one hour on vented cells, an acceptance test at a derated rate or by the rate-adjusted method on valve-regulated cells, a rate-adjusted test stopped more than 5 percent short of the rated time without the published rate for that time, a manufacturer factor outside 0.5 to 1.5, a temperature outside 5 C to 45 C, or a ratio that points to a unit mix-up. Graded pass or fail: the pretest checks (connections, float voltages, specific gravity, ohmic values, isolation, temperature compensation) and the run checks (like-polarity readings, rate held to the end voltage, end voltage recalculated after a bypass) must be satisfactory; every interruption needs a reason and a valid duration; total downtime may not exceed the lesser of 10 percent of the test duration and 6 minutes; a vented acceptance test may not bypass a cell; no cell may be bypassed during the duty-cycle portion of a modified performance test; and the string must be restored to service. Capacity, rounded down to 0.01 percent before grading: an acceptance test needs at least 90 percent of rating, or the purchase specification level where it sets a higher one, up to full rating; a vented performance test needs at least 80 percent, 80.00 passing; a valve-regulated performance test must exceed 80 percent, 80.00 failing; a modified performance test needs at least 80 percent on either chemistry and applies only where the battery was sized by the IEEE 485 method; a service test is graded on whether the designer's duty cycle was met, with no capacity percent. Raised as issues without changing the verdict: the equalize window, the temperature sample, the reading-set count, connector heating, a cell near reversal, more than one downtime period, connection resistance triggers, capacity below the replacement point, degradation and expected life.
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