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GB Industrial Battery Capacity Ratings and Conversions:
AH (Ampere-Hour) Ratings
6 Hour vs. 20 Hour Ratings:
Rating a battery over a longer time period always means a lower current draw over a longer period of time. The lower the continuous amperage during discharge, the more efficient the battery becomes. The opposite is true when the continuous current draw is increased.
· Forklift applications usually use the 6hr rating.
· Off grid power and specialized power applications usually use the 20hr rating.
· You cannot directly compare a battery rated at 6hrs to a battery rated at 20hrs. Always use the same rate when making comparisons.
· Convert a 6hr rating to 20hr by multiplying: AH @ 6hrs x 1.5764705 = AH @ 20hrs.
· Use the GB Capacity Calculator to convert 6hr through 24hr rates: Battery Capacity Calculator.
The AH rating divided by the number of hours of the rating = continuous amps (current draw) for that number of hours, to a maximum of 80% depth of discharge.
80% Depth of Discharge (DOD): A Fully Charged battery, discharged to 1.75 volts per cell.
· Example: A 600AH battery (rated @ 6hrs) will provide a full 600AH over 6hrs and still have 20% reserve capacity that is never used.
· You are not limited to 80% of the 600AH (480AH) as one might assume.
· Discharging a battery below 80% will drive the voltage below 1.70 volts per cell, which will overheat and damage the battery and any equipment it is powering.
· Sealed batteries usually have a 50% depth of discharge, and will be damaged by an 80% discharge.
· All GB batteries have an 80% depth of discharge, but can be used in 50% (or less) applications.
6hr rate: A fully charged battery discharged 80% over a six-hour period.
6 hour AH rating divided by six hours = continuous amps available over six hours
20hr rate: A fully charged battery discharged 80% over a twenty hour period.
20 hour AH rating divided by twenty hours = continuous amps available over twenty hours
EXAMPLE: 6hr vs. 20hr - Battery Model 6-100-13
600AH @ 6hrs: 600AH divided by 6hrs = 100 amps continuous current for 6 hours.
The same battery rated at 20 hours
945AH @ 20 hours: 945AH divided by 20hrs = 47.25 amps continuous for 20 hours.
Definition: Ampere-hour or AH:
· A measurement of electrical capacity – the amount of energy the battery will store. Current multiplied by time in hours equals ampere-hours. A current of 50 amps for one hour would be 50 AH at the 1hr rate; a current of 30 amps for 5 hours would be 150 AH at the 5hr rate.
· AH ratings will vary with temperature, and with the rate of discharge. For example, a battery rated at 100 AH at the 6-hour rate would be rated at about 135 AH at the 48-hour rate.
Ampere-hours (AH) designate the storage capacity of deep cycle batteries. SLI batteries are not rated in AH, but in "CCA", or cold-cranking amps (marine batteries are often rated in "marine cranking amps"). "6 hour rate" and "20 hour rate" indicate that the battery is discharged steadily over 6 or 20 hours, and the Amp-hour capacity is measured by amperage over time, until the cut-off voltage (usually 1.75 volts per cell) is reached.
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Last Updated: Monday, August 18, 2008 - 10:11 P.M. Eastern Time.
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