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• SPECIAL CUSTOMER EDITION •
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WEST SAYVILLE, NEW YORK
EDITION 2 2009
DANGERS OF 3 STEP CHARGING Batteries are a storage medium for energy. When they are charged, energy is stored for use at some future time. A battery
charger converts alternating current to direct current and supplies it to the battery. The charger is preferably automatic,
controlling the current to the battery to recharge the battery as rapidly as possible and then stop charging when the battery is
fully charged.
In order to quickly charge a battery a method known as "3-step charging" has.been developed. The first step, "Bulk Charge",
supplies a constant current until the battery terminal voltage rises to 14.5 to 14.7 volts. At this pOint the charger output voltage
is reduced to the "Absorption" voltage, 13.7 to 13.8 volts and charging continues. As the battery becomes charged it accepts
less current. When near full charge, at a current from 1 to 3 amperes the charger output is reduced to 13.25 volts. This is the
3"' step known as the '110at" step.
Three step charging is preferred for rapid recharging in applications such as golf carts, electric vehicles, fork lifts or any
application that has no parasitic loads. Parasitic loads are those accessories such as radios, medical equipment, air compressors,
lighting, computers or any devices in a vehicle which require constant electrical power. When a battery is being charged these
devices are a load on the charger and will interfere with the 3-step charging process. THIS IS THE DANGER OF 3-STEP
CHARGING It is often possible that the parasitic loads will prevent the charger from completing the "bulk mode" step or
returning to "bulk mode" when accessories are turned "ON". Thus the charger would continuously supply 14.0 to 14.6 volts to
the battery for an extended period of time . This results in overcharging the battery, boiling and out gassing.
A preferred method of charging batteries on emergency vehicles is to use a "float charger". This type of charger has a controlled,
constant output voltage of 13.25 volts and is current limited to the rated charger output. The batteries are charged when their
state of charge is low. Charging continues until the battery voltage rises to the float voltage level. The parasitic loads receive
the same voltage and do not affect battery charging. Kussmaul Electronics Co. , Inc. manufactures both 3-step and float
chargers. For installation in emergency vehicles only the float chargers are recommended.
KUSSMAUL FLOAT CHARGER
091-53-12
KUSSMAUL 3 STEP CHARGER
091-128-12E-20
Authored by Ernesf A. Kussmaul the /ounder a/Kussmaul Electronics Compa,,}', Inc. , 41 years ago in /96 7. He is a degreed engineer, pilot and a
licensed PE who has writ/en numerous artides and technical papers in his fong career, He continually educates the emergency vehicle markel nof
only with articles bul also as a much sought afier speaker and instructor al pre academie.~ throughout the Country.
KUSSMAUL ELECTRONICS CO., INC. WEST SAVVILLE, N.V. 1-800-346·0857
POOR CONNECTIONS CAUSE HIGH HEAT Heat in electrical circuits is caused by current flow
through a resistance. The greater the current the
greater the heat produced. Also, the higher the
resistance the higher the heat. This characteristic
is used in electrical heaters, coffee pots, space
heaters and the like. Sometimes, however, this
heating is not desirable. In wires, switches, and
connections, heating is a sign of trouble .
Often we find that battery chargers are returned
for repair because they no longer charge the
battery due to a "burned out" terminal strip. When
installed , the screws of the terminal strip must be
tight. The wire must be clean and the insulation
stripped to the proper length . Anything on the wire
at the point where it enters the terminal strip can
create a poor connection. The poor connection is
a high resistance to the current and the resistance
creates heat. Poor connections ca n be a
particularly insidious problem because they may
not show up immediately. The heating over time
creates corrosion of the copper wire. Corrosion
of the wire and the terminal increase the electrical
resistance . Higher resistance causes more
corrosion, more heating, more corrosion and more
heating. Eventually the terminal strip insulating
material chars and melts and the individual
terminal becomes so corroded as to be a virtual
insulator. At this point the charger output current
drops to zero.
The photos show examples of overheating. How
long does it take for this to happen? Sometimes
it can occur in 2 weeks while at other times it may
take 6 months. It all depends on how hard the
. charger is working. A vehicle with low utilization
that requires maximum charger output
infrequently will not exhibit the overheating
problem as quickly as one with large batteries
that must be frequently recharged. To prevent the
overheating problem it is absolutely imperative
that the wires are cleanly stripped and inserted
the full length of the terminal. Then the wire clamp
screw must be securely tightened. Periodi c
inspection to ascertain that the screw is tight is
also helpful. At the first sign of heating the wire
should be removed and cleaned and if necessary
the terminal strip replaced. A little preventative
maintenance will go far in ensuring continued
charger operation.