Schumacher Automatic PSW-70300A User Manual
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General Charging Notes
Fan: The charger is designed to control its cooling fan for efficient operation.
Consequentially, it is normal for the fan to start and stop when maintaining a fully
charged battery. Keep the area near the charger clear of obstructions to allow the fan to
operate efficiently.
Voltage: The voltage displayed during charging is the charging voltage and is usually
higher than the battery’s resting voltage.
CALCULATING CHARGE TIME
13.
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
PERCENT OF CHARGE PERCENT OF CHARGE
NEEDED
1.265
100%
0%
1.225
75%
25%
1.155
25%
75%
1.120
0%
100%
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
2
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:
Find the percent of charge needed. (A battery at 50 percent charge that will be
1.
charged to 100 percent needs another 50 percent (.50)).
Multiply the Amp Hour Rating by the charge needed (.50) and divide by the charge
2.
rate.
Multiply the results by 1.25 and you will have the total time needed, in hours, to bring
3.
the battery to full charge.
Add an additional hour for a deep-cycle battery.
4.
Example:
Amp Hour Rating x % of charge needed x 1.25 = hours of charge
Charger Setting
100 (AH Rating) x .50 (charge needed) x 1.25 = 3.125 hours
20 (Charger Setting)
100 x .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.