Operating instructions

FC Operation & Maintenance Guide (20 & 25 Amp)
7
the high rate. When the charger reaches the boost voltage set point, and current has dropped
to between 50% to 70% of the charger's rating, the charger will revert to the float mode.
The transition from boost to float will result in the battery drawing no c
urrent from the charger.
Once the battery voltage nears the float setting, the charger will again deliver a small amount of
current to the battery to maintain the battery at its fully charged state. Figure 4 is a graph of
how the Autoboost system works.
The battery charger is temperature compensated to match the negative temperature
coefficient of the battery. Thus the float voltage will increase slightly as the temperature
decreases, and decrease as temperature increases. The battery charger is electronically current
limited to 110% of rated output. The charger will decrease its current output when the battery
voltage is lower than nominal.
FIGURE 4
Boost voltage
Float voltage
Point at which charger changes
from current limit to voltage limit
Point at which AUTOBOOST
returns charger to float voltage
100% charger
output current
50% to 75% of
charger current limit
Amps
Volts
Charger output current
Battery voltage
NOTE:
Zero current flow
0
Time
When the charger switches from BOOST to FLOAT mode,
no current will flow into the battery for a while due to the battery's
high state of charge. This is completely normal, and indicates
that the charger is working properly.
4.2 Ammeter and Voltmeter
The voltmeter and ammeter (and alarm LEDs on the FCA models) provide indication of
normal operation. Correct operation is indicated when the voltmeter reads 110% to 120% of
nominal battery voltage. High current flow indicates that the battery has been discharged, and
is being recharged. Low current flow normally indicates that the battery is fully charged. The
charger will at times read 0 amps. This most commonly happens after the charger has reverted