Kussmaul Electronics 091-120-12-20 - Manual (Page 3)

PRINCIPLES OF OPERATION
A three-step lead acid battery charger operates in the three stages described below:
1) A discharged battery is recharged at a constant current (bulk charge) until its volt-
age reaches an overcharge level of 2.42 volts per cell (approximately 14.5 vdc for a
12V battery). At this time the charger will switch to Finish Charge. The battery
accepts 75-85% of its capacity during bulk charge.
2) This overcharge voltage is now maintained constant at 2.42 volts per cell (absorp-
tion or finish charge) until the charge current tapers down to {battery capacity/35}
amperes. For the 12 volt, 80 ampere charger this current is 11.9 amperes. The
battery accepts 15-25% of it capacity during absorption charge.
3) Once the charge current reaches the tapered down value (see above), the voltage is
set to a float voltage of 2.24 volts per cell (approximately 13.4 vdc for a 12V bat-
tery), and maintained at float charge. The battery is maintained at full charge during
float charge, and the green indicator labeled “Battery Charged” is illuminated.
Figure 1 depicts the above described operation. Note that the term “absorption charge”
is used interchangeably with “finish charge”. Upon application of AC power, the charger
is placed into bulk charge. When the charger switches to finish charge, a timer starts.
In the event that the charge current did not taper down to approximately C/35 amperes
after 2 ½ hours, the charger will automatically go to float charge, and a timeout will be
indicated. This timeout indicator can indicate an old or leaky battery, or it can indicate
that the charger is undersized for the battery being charged.
A battery fault indicator is provided to indicate the absence of a battery, a battery con-
nected with reverse polarity, or a battery with an open circuit terminal voltage of less
than 1.35 volts per cell.
TEMPERATURE COMPENSATION
Temperature compensation is provided as an optional feature. A temperature probe is
provided which can be placed in the air surrounding the battery or bonded to the battery
case.