Checking the battery.
I. Introduction
One of the common issues related to a starting failure of a generator set is the battery and its associated components, like cable, battery clamps, battery switch, charging alternator, and static battery charger. The purpose of the battery is to provide power to the engine’s starter motor and controller. Therefore, routine battery maintenance is important to ensure the generator starts anytime, and this includes physical checks and electrical tests.
II. Physical checks
This includes cable inspection, connection torque checks, cleanliness, electrolyte condition (in wet lead-acid batteries), leaks, and physical damages. A battery with physical damage must be replaced immediately.
III. Electrical tests
This includes two parts: (1) battery, and (2) DC charging alternator.
(1) Battery: This includes open circuit voltage test (OCV), cold cranking amps (CCA), internal resistance (IR), state of charge (SOC), and state of health (SOH). The engine must be OFF in doing this test.
(2) Charging alternator: This includes DC charging voltage (DCV), and AC ripple voltage test (Vripple). The engine must be running at 1800 rpm in doing this test.
IV. Definition of electrical test criteria
(1) Open circuit voltage (OCV): The measured DC voltage of the battery.
(2) Cold-cranking amps (CCA): The current that a battery can discharge for 30 seconds at -18°C and maintain at least 7.2 volts (for JIS, SAE, and BCI standard); or the current that a battery can discharge for 10 seconds at -18°C and maintain at least 7.5 volts (for EN and DIN standard). A battery that has a higher CCA means it has a better ability to start an engine.
(3) Internal resistance (r): The measured internal resistance of the battery expressed in milliohms (mΩ).
(4) State of charge (SOC): The charge condition of the battery expressed in percent (%).
(5) State of health (SOH): The health condition of the battery expressed in percent (%).
(6) DC charging voltage: The measured DC voltage of the charging alternator.
(7) AC ripple voltage: The measured residual periodic variation of the DC voltage from the charging alternator. The AC ripple is due to incomplete suppression of the AC waveform after rectification and is expressed in millivolts (mV).
V. Electrical test and acceptance criteria
Table 1. Electrical test and acceptance criteria for a single 12-volt battery and the engine’s charging alternator.
| Parts | Test criteria | Acceptance criteria |
| Battery | Open-circuit voltage (OCV) | Should be 12 to 13 volts DC. |
| Cold-cranking amps (CCA) | Should be equal to or higher than the rated CCA of the battery. | |
| Internal resistance (r) | It should be less than 15 mΩ. Note: Replace the battery if (r) is 1.5 x the benchmark.
Example: 7 mΩ (benchmark) 7 x 1.5 = 10 mΩ (replace) |
|
| State of charge (SOC) | Should be at least 80%. | |
| Stage of health (SOH) | Should be at least 80%. | |
| Charging alternator | DC charging voltage (DCV) | Should be 13 to 14 volts. |
| AC ripple voltage (Vripple) | Should be less than 300 mV (0.3 volts). |
VI. Test tool
A typical test tool used by many is a multimeter while others use a clampmeter. In most cases, the OCV of the battery is the only parameter one can check using them. A DC voltage does not tell us all about the condition of the battery. An automotive digital battery analyzer like those shown in Table 2 will provide comprehensive information on battery condition. It can check all the above electrical test criteria and charging alternator performance with just a few presses of a button. Remember that this battery analyzer is for automotive batteries only. It is not appropriate for UPS, telecom, or solar batteries.
Table 2. Automotive digital battery analyzer.
