Technician Service Guide 33367B
7
charge rate is noted and the findings of the
Test for
battery voltage increase
are normal, an SCR may
have failed. Each charger has two SCRs.
Part A
Does not turn off.
This may be caused by a failed SCR and/or
electronic timer. If the charger is found to be
producing a high finish charge rate, while the
batteries are at or above the typical finish voltage of
2.30 volts per cell or higher, test for a shorted anode
to gate SCR, see
Section 4-SCR Testing
. If an
SCR with a shorted anode to gate is found, the
electronic timer has been damaged and must also
be replaced. Replace with the replacement service
parts specified on the parts list for the specific model
of charger being serviced and retest. If both SCRs
test good, repair or replace the electronic timer.
Part B
Turns off too soon or runs too long.
If batteries have not been used or charged regularly,
they may be sulfated and will not produce their full
capacity. Repeated cycles (at least 5) of a light
discharge, followed by a full charge, will generally
result in the recovery of most of the battery’s
capacity. Do not interpret this reduced battery
capacity as being caused by the charger’s turning off
too soon. The charger is working properly if, after
several charge cycles, the battery capacity increases
to near normal. Sulfation occurs most often when
batteries have been stored without weekly charging.
New batteries may also be sulfated due to extended
shipment or storage time prior to sale.
As batteries age, individual cells may weaken,
causing a reduction in battery capacity. This
condition normally results in a higher finish rate on
conventional wet lead-acid batteries and shorter
charge times for both conventional and sealed types
of batteries. Do not interpret this shorter charging
time and reduced battery capacity as being caused
by the charger’s turning off too soon. The battery is
aging naturally and the charger is working properly.
When the batteries will no longer perform as
required, they should be replaced.
The charger is designed to cease charging when
essentially no further electrochemical reaction is
occurring inside the battery. The electronic timer
senses the progress of the reactions and, when
these reactions virtually cease, turns the charger off.
For conventional wet lead-acid batteries there are
two ways to test if the electrochemical reaction has
actually ceased.
1. An accurate hydrometer can be used to
determine cessation of the electrochemical
charging reaction. If the measured specific
gravity of several cells does not increase in
three (3) consecutive readings taken one hour
apart while the charger continues to charge, the
charger is operating too long.
2. An accurate 5 1/2-digit digital voltmeter can be
used to determine the cessation of the
electrochemical charging reaction. Connect the
voltmeter test leads to the positive (+) and
negative (-) posts of the battery system being
charged. Monitor and record the on-charge
voltage at 30-minute intervals. If the on-charge
battery voltage either begins to decrease
between 30-minute intervals or increases by
less than 0.012 DC volts in two consecutive 30-
minute intervals, the charger is operating too
long.
To test sealed or gel batteries, an accurate digital
ammeter can be used to determine the cessation of
the electrochemical charging reaction. Break the
DC charging circuit and insert the digital ammeter in-
line with the circuit. Monitor and record the on-
charge current at 30-minute intervals when the
battery system voltage is at or above 2.32 volts per
cell. If the on-charge current does not decrease by
0.015 DC milliAMPS in two consecutive readings,
the charger is operating too long.
In the event of an AC power interruption when the
charger is on, the charger will automatically restart
when AC power is restored. This power outage can
make the apparent charge time seem longer than
the actual charge time. To check for AC power
interruptions, plug an electric clock into the same
outlet to which the charger AC cord is connected.
Charge normally and note any time difference
between the test clock time and the actual time.
If battery maintenance has recently been performed,
check the battery system to determine if a battery
has been installed reverse polarity. A common error
is to install one or more 6-volt batteries in a battery
pack in reverse polarity.
If testing indicates the charger is turning off too soon
or operating too long, replace the electronic timer
with the replacement service part specified on the
parts list for the specific model of charger being
serviced and retest.
WARNING: ALWAYS TEST SCRs BEFORE
REPLACING AN ELECTRONIC TIMER. DAMAGE
AND SUBSEQUENT FAILURE WILL OCCUR TO
ALL ELECTRONIC TIMERS INSTALLED IN A
CHARGER THAT CONTAINS A SHORTED
ANODE TO GATE SCR, IF CONNECTED TO AC
POWER.
