Calculating Charge Time - Schumacher Electric SE-2254 Owner's Manual

12.

CALCULATING CHARGE TIME

Battery Percent and Charge Time: This charger adjusts the charging time in order to
charge the battery completely, efficiently and safely. The microprocessor automatically
performs the necessary functions. This section includes guidelines that can be used to
estimate charging times.
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
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 setting.
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
Charge Rate Setting
100 (AH Rating) x 0.50 (charge needed) x 1.25 = 3.125 hours
20 (Charge Rate 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.
The Chart Method
Use the following table to more accurately determine the time it will take to bring a
battery to full charge. First, identify where your battery fits into the chart.
CCA = Cold Cranking Amps
RC = Reserve Capacity
Ah = Amp Hour
NR means that the charger setting is NOT RECOMMENDED.
1.265
1.225
1.155
1.120
2
PERCENT OF
CHARGE
100%
75%
25%
0%
10
• •
PERCENT OF
CHARGE NEEDED
0%
25%
75%
100%