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13.
CALCULATING CHARGE TIME
The Hydrometer or Electronic Method
To find the time needed to fully charge your battery, determine the battery's
charge level with a hydrometer or electronic Percent-of-Charge Tester. The
following table will help you convert hydrometer readings to percent of charge
values.
SPECIFIC GRAVITY
1.265
1.225
1.155
1.120
When you know the percent of charge and the Amp Hour (AH) rating of your
battery, you can calculate the approximate time needed to bring your battery to
a full charge.
To convert Reserve Capacity to Amp Hours, divide Reserve Capacity by 2, and
add 16:
Example:
Amp Hour Rating = Reserve Capacity + 16
NOTE: The Reserve Capacity can be obtained from the battery specification
sheet or the owner's manual.
To calculate the time needed for a charge:
1.
Find the percent of charge needed. (A battery at 50 percent charge that will
be charged to 100 percent needs another 50 percent (.50).)
2.
Multiply the Amp Hour Rating by the charge needed (.50) and divide by the
charge rate.
3.
Multiply the results by 1.25 and you will have the total time needed, in
hours, to bring the battery to full charge.
4.
Add an additional hour for a deep-cycle battery.
Example:
Amp Hour Rating x % of charge needed x 1.25 = hours of charge
100 (AH Rating) x 0.50 (charge needed) x 1.25 = 3.125 hours
20 (Charger Setting)
100 x 0.50 x 1.25 = 3.125
20
You would need to charge your 100-Ampere Hour Battery for a little more than
3 hours at the 20-Amp charge rate using the above example.
PERCENT OF CHARGE
2
Charger Setting
PERCENT OF CHARGE
100%
75%
25%
0%
10
•
•
NEEDED
0%
25%
75%
100%
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