APPENDIX A — CHARGING TIMES
To calculate the approximate charging time required to fully charge a battery, it is necessary to determine the specific gravity (or, percent of battery charge) using a hydrometer. Use this technique if battery vent caps can be removed. Check each cell. if there is one cell with a very low specific gravity compared to the other cells, there is probably a shorted cell in the battery. Replace the battery.
The following chart converts hydrometer readings into percent of charge values.
SPECIFIC GRAVITY | PERCENT OF CHARGE PERCENT OF CHARGE NEEDED | |
(HYDROMETER READING) | IN BATTERY | BY BATTERY |
1.265 | 100% | 0% |
1.225 | 75% | 25% |
1.190 | 50% | 50% |
1.155 | 25% | 75% |
1.120 | 0% | 100% |
Refer to the chart below for approximate charging times.
PERCENT OF CHARGE | 75% | 50% | 25% | 0% |
2 AMPS | 7 HRS | 13 HRS | N.R* | N.R* |
6 AMPS | 2.5 HRS | 5 HRS | 7 HRS | 9 HRS |
12 AMPS | 1.2 HRS | 2.5 HRS | 3.2 HRS | 4.6 HRS |
* Not Recommended because over 18 hrs charging time.
The times shown in the chart above are approximate and refer to an average automotive battery. For smaller batteries, the charge time should be adjusted using the formula shown below and adding 1 hour to the time calculated.
To estimate charging time for a discharged battery, divide the AH rating of the battery by the charge rate selected. This is the number of hours required to recharge the battery. For example, a 50 AH (12 volt) battery is discharged (10 volts). How long should it be charged at the 12 Amp rate. Divide the 50 AH by
12.The answer is approximately 4.2 hours. Always round up the charge time by 10% to ensure full charge. In most cases, battery recharge times will vary depending on the age and condition of the battery. Smaller batteries should be charged at a lower rate (2 Amps) and add an extra hour to charge time.
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