Hitachi UC 24YJ Manual

TECHNICAL DATA
AND
SERVICE MANUAL
CHARGER
UC 24YJ
SPECIFICATIONS AND PARTS ARE SUBJECT TO CHANGE FOR IMPROVEMENT
LIST No. F889 Oct. 2003
U
MODEL
UC 24YJ
Hitachi 
Power Tools

Page
CONTENTS
1. PRODUCT NAME.............................................................................................................................. 1
2. MARKETING OBJECTIVE ................................................................................................................ 1
3. APPLICATIONS................................................................................................................................. 1
4. SELLING POINTS ............................................................................................................................. 2
4-1. Selling Point Descriptions ...................................................................................................................3
5. SPECIFICATIONS ............................................................................................................................. 5
5-1. Specifications......................................................................................................................................5
5-2. Comparisons with Similar Products ....................................................................................................5
5-3. Explanation of the Specifications........................................................................................................6
5-4. Batteries............................................................................................................................................17
6. PRECAUTIONS IN SALES PROMOTION ...................................................................................... 19
6-1. Safety Instructions ............................................................................................................................19
6-2. Extra Precautions in Sales Promotion ..............................................................................................20
7. QUESTIONS AND ANSWERS ON MODEL UC 24YJ .................................................................... 21
8. GENERAL PRECAUTIONS ............................................................................................................ 24
8-1. Model UC 24YJ.................................................................................................................................24
8-2. Wiring Diagram .................................................................................................................................25
8-3. Pilot Lamp Indications.......................................................................................................................25
9. PRECAUTIONS IN DISASSEMBLY AND REASSEMBLY ............................................................. 26
9-1. Disassembly ....................................................................................................................................26
9-2. Reassembly ......................................................................................................................................26
9-3. Confirmation after Reassembly ........................................................................................................26
10. TROUBLESHOOTING GUIDE ...................................................................................................... 27
10-1. Troubleshooting Based on Pilot Lamp Indications..........................................................................27
10-2. Troubleshooting and Repair Procedures ........................................................................................27
11. STANDARD REPAIR TIME (UNIT) SCHEDULES......................................................................... 29
Assembly Diagram for UC 24YJ

--- 1 ---
1. PRODUCT NAME
Hitachi Charger, Model UC 24YJ
2. MARKETING OBJECTIVE
As higher-power cordless tools have been developed through the years, higher-power and higher-capacity
batteries have also been developed. There is an increasing demand for a charger that can charge such batteries.
The new Model UC 24YJ is a general-purpose rapid charger that has been developed based on the current Model
UC 24YC to meet the market demand. The Model UC 24YJ can charge batteries from 7.2 V to 24 V in shorter
times than the current Model UC 24YC.
3. APPLICATIONS
Recharging of Hitachi batteries
Applicable batteries:
EB 9H 9.6 V 2.2 Ah
EB 12H 12 V
EB 1222HL
EB 14H 14.4 V
EB 18H 18 V
EB 930H 9.6 V 3.0 Ah
EB 1230H 12 V
EB 1230HL
EB 1430H 14.4 V
EB 1830H 18 V
EB 2430H 24 V
EB 7S 7.2 V 1.3 Ah
EB 9S 9.6 V
EB 12S 12 V
EB 14S 14.4 V
EB 7B 7.2 V 2.0 Ah
EB 9B 9.6 V
EB 9M
EB 12B 12 V
EB 1220BL
EB 12M
EB 14B 14.4 V
EB 1820 18 V
EB 18B
EB 24B 24 V
Ni-MH batteries
Ni-Cd batteries
Battery type Model Voltage Capacity

--- 2 ---
4. SELLING POINTS
Capable of charging conventional
7.2 V to 24 V batteries
Capable of charging batteries at low temperatures rapidly
(The charging time required for recharging a battery at a
temperature of -5˚C is shortened from 2.5 hours to 40 minutes.)
Charging status indicator lamp
indicates the charging status.
Charging time indicator lamp indicates the time
up to completion of charging in 3 steps (remaining
charging time can be seen at a glance).
Equipped with the battery revitalizing
(trickle charging) function

--- 3 ---
4-1. Selling Point Descriptions
4-1-1. Capable of charging batteries at low temperatures rapidly
The Model UC 24YJ can charge a battery at a temperature of 5˚C or less. At first, the battery is charged at a low
charging current. When the battery gets warm (over 5˚C), the charging current turns high. Thus a battery at a low
temperature can be rapidly charged. (The time required for charging a 3.0-Ah Ni-MH battery at -5˚C is shortened
from 2.5 hours to 40 minutes.)
4-1-2. Time up to completion of charging is indicated in 3 steps
Voltage and temperature of the battery are detected by the microcomputer during charging. The time up to
completion of charging is assumed according to the result of detection and indicated in three steps by the
charging time indicator lamp (red/orange/green). Thus the remaining charging time can be seen at a glance.
(Refer to the table on page 4 for relationship between the charging time indication and the battery.)
When the charging time indicator lamp lights red continuously:
When the charging time indicator lamp lights red continuously after charging commences, charging will be
completed about 30 minutes later. As charging proceeds, indication of the indicator lamp changes. When the
remaining charging time is about 20 minutes, the charging time indicator lamp lights orange continuously.
When the remaining charging time is about 5 minutes, the charging time indicator lamp lights green
continuously.
When the charging time indicator lamp lights orange continuously:
When the charging time indicator lamp lights orange continuously after charging commences, charging will be
completed about 20 minutes later. As charging proceeds, indication of the indicator lamp changes. When the
remaining charging time is about 5 minutes, the charging time indicator lamp lights green continuously.
When the charging time indicator lamp lights green continuously:
When the charging time indicator lamp lights green continuously after charging commences, charging will be
completed about 5 minutes later.
Charging time lamp indication is only a guide, and may vary depending on the surrounding temperature and
battery conditions.
Charging time lamp indication may switch to a longer indication (e.g. from green lighting (remaining time about
5 minutes) to red lighting (remaining time about 30 minutes)). This is because the Model UC 24YJ makes a
correction according to the battery status when there is an error in the indication. This is not a malfunction of
the charger or the battery.

--- 4 ---
Ni-MH 5˚C or less No power
40˚C or more No power
-5˚C to 50˚C
Ni-Cd -5˚C or less No power or half power
-5˚C to 55˚C
Ni-MH 5˚C or less Half power
40˚C or more Half power
5˚C to 40˚C No power or half power
Ni-Cd -5˚C to 55˚C No power or half power
Ni-MH -5˚C to 50˚C Full power
Ni-Cd -5˚C to 55˚C Full power
Charging time indicator lamp
Lights red continuously:
30 minutes until charging is completed.
Lights orange continuously:
20 minutes until charging is completed.
Lights green continuously:
5 minutes until charging is completed.
Lights red continuously.
(About 30 minutes until
charging is completed)
Lights orange continuously.
(About 20 minutes until
charging is completed)
Lamp indication Battery type Battery temperature Battery status
Fig. 1 Charging time indication
Relationship between charging time indication and battery
4-1-3. Equipped with the battery revitalizing (trickle charging) function
Refer to "5-3-7. Revitalizing the battery (trickle charging)" on page 16 for details.
4-1-4. Capable of charging conventional 7.2 V to 24 V batteries
The Model UC 24YJ can charge conventional 7.2 V to 24 V batteries thanks to the charging controller.
Lights green continuously.
(About 5 minutes until
charging is completed)
Near the end of service life or inactive
due to extensive non-use periods
Near the end of service life or inactive
due to extensive non-use periods
* No power: The battery is dead and has no power.
Half power: The battery has half the full power.
Full power: The battery is almost in the fully charged status.

--- 5 ---
(Inserting type)
5. SPECIFICATIONS
5-1. Specifications
Description
Item
AC single-phase, 50 Hz or 60 Hz
Voltage 230 V
200 W
Constant current charge with switching power source
(1) Detecting the rate of change of the battery voltage ( )
(2) Detecting the rate of change of the battery surface temperature (dT/dt)
(3) Battery surface temperature detection (thermostat or thermistor)
(4) Timer
7.2 V --- 9.6 V --- 12 V --- 14.4 V --- 18 V --- 24 V
1.0 kg
0 ˚C to 40 ˚C
Power source
Charging system
Overcharging protection system
Charging voltage
Product weight
Operating ambient temperature range
5-2. Comparisons with Similar Products
Power input
HITACHI
UC 24YJ
Battery type
Overcharge protection
system
Chargeable battery voltage
C
V
7.2 to 14.4 7.2 to 14.4
7.2 to 14.4
Ni-Cd 2Ah min. Ni-MH: 7
Ni-Cd: 10
16
Charging current A 7.5 9
Chargeable
battery
temperature
range
˚C-5 to 50 0 to 60
--- Peak cut
T
Timer
External dimensions mm 110 x 226 x 75
(4-11/32" x 8-29/32" x 2-31/32") 160 x 202 x 79
(6-19/64" x 7-31/32" x 3-7/64")
140 x 192 x 68
(5-17/32" x 7-9/16" x 2-11/16")
Weight kg 1.0 (2.2 lbs.) 1.0 (2.2 lbs.) 1.0 (2.2 lbs.)
B
V41 7.2 to 14.4
Ni-MH 3Ah min. 25 No applicable battery
Ni-MH 2Ah min. 15 No applicable battery
Charging time
Battery voltage 18 24
27 28 30
No applicable battery
14 18 20
96
24
41
25
18
7.2 to 24
(Inserting type)
Ni-MH
Ni-Cd
7.2 to 24
(Inserting type)
(Inserting type)
(Inserting type)
(Inserting type)
Ni-MH
Ni-Cd ˚C-5 to 55 0 to 60
Cycles 500
Ni-MH
Ni-Cd Cycles 1000
No indication on the
catalog
Maker •Model
Item Unit
Ni-MH: 7
Ni-Cd: 8.5
[ 0 to 45 ]
[ -5 to 55 ]
Indication of the time up
to completion of charging
dT/dt
Timer Peak cut
--- (3 steps)
[ ]: Estimated value
Service life of
battery cycle No indication on the
catalog

--- 6 ---
Fig. 2 Circuit diagram
5-3. Explanation of the Specifications
5-3-1. Charging system (Common to the Model UC 24YC)
Most of rapid type chargers made by Hitachi and competitors are equipped with a switching power source system
that controls constant charging current by turning on and off (switching) the control switch at high frequency (see
Fig. 2). The Model UC 24YJ is also equipped with this system, however, the high frequency may cause noise in a
television or a radio. To prevent this noise problem, avoid connecting the Model UC 24YJ to the same receptacle
where a television or a radio is connected. In addition, keep a distance between the Model UC 24YJ and the
television or the radio during charging. The rapid type chargers made by competitors have the same demerit due
to the switching power source system.
Chargers equipped with the switching power source system (Examples)
Charging
current
detector
HITACHI Competitors
AL 15FC2498 DC 1439
UC 24YJ
UC 24YC
Control switch
Transformer
Constant current
controller
Battery
BC

--- 7 ---
Fig. 3 Relationship between charging time and battery voltage,
temperature and internal gas pressure
Thermistor
Thermostat
Timer
Battery voltage
(Overcharge range)
Battery temperature
Charging time
Battery voltage, temperature and
internal gas pressure
5-3-2. Overcharge protection system
The Model UC 24YJ is equipped with a 4-way overcharge protection system ( , dT/dt, battery surface
temperature sensor and timer) to protect overcharging.
(1) Stops charging after full charging by means of both overcharge protection system and dT/dt overcharge
protection system:
As shown in Fig. 3, voltage and temperature of a battery increase suddenly near the end of charging.
The overcharge protection system detects such a sudden rate of change in the battery voltage and stops
charging just before the overcharge range (*). The dT/dt overcharge protection system detects a sudden rate
of change in the battery temperature and stops charging just before the overcharge range. Normally the
charging stop position by the overcharge protection system is almost the same as that by the dT/dt
overcharge protection system. However, when the battery is inactive due to extensive non-use periods or
near the end of the service life, the battery voltage does not change suddenly and charging may not be
stopped by the overcharge protection system. The Model UC 24YJ is equipped with the dT/dt overcharge
protection system as well as the overcharge protection system in order to prevent overcharge even in
such cases. The Model UC 24YJ always stops charging just before the overcharge range. Thus the charging/
discharging cycles of a battery is increased.
Charging/discharging cycles of a battery (ambient temperature 20˚C)
Ni-MH: about 500 cycles
Ni-Cd: about 1,000 cycles
Battery
internal gas
pressure
(*) In the overcharge range, the battery internal gas pressure rises rapidly due to generation of gas and it
causes high temperature, oxidation of atmosphere that promote degradation. If charging is continued in
such conditions, the safety valve will be activated and the electrolyte will be leaked from the battery.

--- 8 ---
EB 9H
EB 12H
EB 1222HL
EB 14H
EB 18H
EB 930H
EB 1230H
EB 1230HL
EB 1430H
EB 1830H
EB 2430H
Ni-MH batteries
Ni-Cd batteries
Battery type Model When charging a high-temperature battery
(2) Forcefully stops charging by means of battery internal temperature sensor:
As shown in Figs. 4 and 5, each of the applicable batteries is equipped with a built-in thermistor or thermostat
to detect the battery temperature. Charging is stopped when the battery reaches the charging stop
temperature even if the battery is not fully charged.
When charging a high-temperature battery, the thermostat or the thermistor automatically controls to wait
until the battery cools down and then start charging.
In most cases of Ni-MH batteries, charging may stop before the battery is fully charged because the
detecting temperature of the thermistor is set as low as 55˚C and the temperature rise is rapid when the
battery temperature is high (see Fig. 6).
When the battery temperature is over 50˚C, the
charge time lamp flashes red in 0.6-second intervals.
When the battery cools down to 50˚C, the charge time
lamp lights red or orange or green continuously and
starts charging.
EB 7S
EB 9S
EB 12S
EB 14S
EB 7B
EB 9B
EB 9M
EB 12B
EB 1220BL
EB 12M
EB 14B
EB 1820
EB 18B
EB 24B
Control of charging according to battery temperature
When the battery temperature is over 55˚C, the
charge time lamp flashes red in 0.6-second intervals.
When the battery cools down to 55˚C, the charge time
lamp lights red or orange or green continuously and
starts charging.

--- 9 ---
Fig. 4
Thermistor
Thermistor
Terminal
--
Terminal
T
Terminal
+
Terminal
+
Terminal
S
Terminal
(for discharging)
--
Thermal protector
(The charging circuit is interrupted when
the battery temperature is about 80˚C.)
Terminal positions Terminal positions
Terminal positions Terminal positions
Fig. 5
Terminal
T
Terminal
+
Terminal
S
Terminal
--
Terminal
(for charging)
--
Terminal
+
Terminal
S
Terminal
(for discharging)
--
Terminal
T
Thermistor
Discriminating
resistor
Terminal
S
Applicable
battery
models:
EB 7S, EB 9S, EB 12S, EB 7B,
EB 9B, EB 12B, EB 1220BL,
EB 9M and EB 12M EB 14S, EB 14B, EB 1820,
EB 18B and EB 24B
Terminal
(for charging)
--
Applicable
battery
models:
EB 9H, EB 12H, EB 1222HL,
EB 930H, EB 1230H and
EB 1230HL
Applicable
battery
models:
EB 14H, EB 18H, EB 1430H,
EB 1830H and EB 2430H
Thermostat
(Models UC 12Y
and UC 12YA)
Applicable
battery
models:
Models UC 24YJ, UC 24YC, UC 24YFA,
UC 24YF, UC 12YE, UC 12YD and UC 12YB
ThermistorDiscriminating resistor
Thermal protector
(The charging circuit is interrupted when
the battery temperature is about 80˚C.)
Fig. 6 Relationship between battery temperature at the start of charging,
charging time and capacity In the case of Ni-MH batteries
Capacity
Charging time
Battery temperature at the start of charging
Charging time
Capacity
(%)
(Min.)
50
(˚C)

--- 10 ---
(3) Forcefully stops charging by means of timer:
Should overcharge protection system, dT/dt overcharge protection system and battery surface temperature
sensor fail, the timer stops charging.
5-3-3. Discrimination of batteries
A discriminating resistor is provided in each Ni-MH battery to distinguish from Ni-Cd batteries as shown in Fig. 5.
5-3-4. Lamp indications
The indicator lamps show the charging time and status as follows.
Lamp indications Lamp indications
Charging time 30 minutes
Charge time
lamp
(red/orange/
green)
Charge
status lamp
(red/
orange/
green)
Charging time 20 minutes
Overheat standby
Charging impossible
Charging time 5 minutes
Charging complete
Before charging
Status
Lit red
Lit orange
Flashing red
Flashing orange
rapidly
Lit green
Lit green
Flashing red
On 0.3 second, off 0.3 second
On continuously
On continuously
On 0.1 second, off 0.1 second
On 0.5 second, off 0.5 second
20 minutes until charging complete.
Battery or charger malfunction.
Battery overheated. Unable to charge.
(Charging will commence when battery cools.)
Power cord is connected to receptacle.
5 minutes until charging complete.
30 minutes until charging complete.
On continuously
On continuously
5-3-5. Beeper
The beeper sounds when charging is completed and also when the charger or the battery is abnormal as shown
in the following table.
Conditions when the beeper sounds Beeping sound
A 6-second long beep
Short beeps for 5 seconds
When the charger or the battery is abnormal
When charging is completed

--- 11 ---
5-3-6. Switching the charging current
The charging current is switched according to the temperature of the battery or the charger as described in (1) to
(6) below (see Figs. 7 to 12).
(1) 7.2 V to 24 V Ni-Cd batteries
The charging current is switched (9 A/7.5A/6 A/1.3 A) according to the battery temperature at the start of
charging.
Fig. 7 Relationship between battery temperature at the start of charging,
charging time and current
Charging time
Charging current (constant value)
(Min.)
Charging time
Battery temperature at the start of charging
Charging current (constant value)
In the case of 2.0 Ah Ni-Cd batteries Models EB 7B/EB 9B/EB 9M/EB 12B/EB 1220BL/EB 12M/EB 14B
Relationship between temperature of battery/charger and charging current
Temperature
Battery temperature at the start of
charging is between -5˚C and 50˚C.
Battery temperature at the start of charging
is 50˚C or more.
Battery temperature at the start of charging
is -5˚C or less.
Inside of the charger becomes hot during
charging at 9 A (see Fig. 13).
Charging current
Switch from 9 A to 6A
9 A
7.5 A
1.3 A (*)
Purpose
Protection of the charger
Protection of the battery
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it is dangerous.
(2) 18 V Ni-Cd batteries
The charging current is switched (7.5 A/5 A/1.3A) according to the battery temperature at the start of charging.
Charging time
Charging current (constant value)
Battery temperature at the start of charging
Charging current (constant value)
Charging time
Fig. 8 Relationship between battery temperature at the start of charging,
charging time and current
In the case of 2.0 Ah Ni-Cd batteries Models EB 1820/EB 18B
(Min.)

--- 12 ---
Relationship between temperature of battery/charger and charging current
Temperature
Battery temperature at the start of
charging is between -5˚C and 55˚C.
Battery temperature at the start of charging
is -5˚C or less.
Inside of the charger becomes hot during
charging at 9 A (see Fig. 13).
Charging current
Switch from 7.5 A to 5A.
7.5 A
1.3 A (*)
Purpose
Protection of the charger
Protection of the battery
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it is
dangerous.
(3) 24 V Ni-Cd batteries
The charging current is switched (6 A/1.3A) according to the battery temperature at the start of charging.
Charging time
Charging current (constant value)
(Min.)
Charging time
Battery temperature at the start of charging
Charging current (constant value)
In the case of 2.0 Ah Ni-Cd battery Model EB 24B
Temperature
Battery temperature at the start of
charging is between -5˚C and 55˚C.
Battery temperature at the start of charging
is -5˚C or less.
Charging current
6 A
1.3 A (*)
Purpose
Protection of the battery
Fig. 9 Relationship between battery temperature at the start of charging,
charging time and current
Relationship between temperature of battery/charger and charging current
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it
is dangerous.

--- 13 ---
Fig. 10 Relationship between battery temperature at the start of charging,
charging time and current
Charging time
Charging current (mean value)
(Min.)
Charging time
Battery temperature at the start of charging
Charging current (mean value)
In the case of 3.0 Ah Ni-MH batteries Models EB 930H/EB 1230H/EB 1230HL/EB 1430H
Relationship between temperature of battery/charger and charging current
Temperature
Battery temperature at the start of charging
is between 5˚C and 40˚C.
Battery temperature at the start of charging
is between 40˚C and 50˚C.
Battery temperature at the start of charging
is between -5˚C and 5˚C.
Battery temperature at the start of charging
is -5˚C or less.
Charging current
Switch from 9 A to 6A
9 A
Switch from 9 A (6 A) to 4 A
Switch from 1.3 A to 4A
Purpose
Protection of the battery
Protection of the battery
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it is dangerous.
(4) 7.2 V to 14.4 V Ni-MH batteries
The charging current is switched (9 A/6A/4A/1.3 A) according to the battery temperature at the start of
charging. Therefore, the charging time changes as shown in Fig. 10.
Note) Charging times may be longer according to the increase in battery temperature.
However, the thermistor that is a battery surface temperature sensor stops charging before
the battery is fully charged. Thus charging is stopped at an early stage.
Battery temperature becomes over 45˚C
during charging at 9 A or 6 A.
Battery temperature becomes over 5˚C
during charging a low-temperature battery
(5˚C or less).
Inside of the charger becomes hot during
charging at 9 A (see Fig. 13).
Switch from 4 A to 6A
4 A
1.3 A (*)
Saving the charging time
Saving the charging time
Protection of the charger
(Note)

--- 14 ---
Fig. 11 Relationship between battery temperature at the start of charging,
charging time and current
Charging time
Charging current (mean value)
(Min.)
Charging time
Battery temperature at the start of charging
Charging current (mean value)
In the case of 3.0 Ah Ni-MH battery Model EB 1830H
Relationship between temperature of battery/charger and charging current
Temperature
Battery temperature at the start of charging
is between 5˚C and 40˚C.
Battery temperature at the start of charging
is between 40˚C and 50˚C.
Battery temperature at the start of charging
is between -5˚C and 5˚C.
Battery temperature at the start of charging
is -5˚C or less.
Charging current
Switch from 7.5 A to 5A
7.5A
Switch from 7.5 A (6A) to 4 A
Switch from 1.3 A to 4A
Purpose
Protection of the battery
Protection of the battery
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it is
dangerous.
(5) 18 V Ni-MH battery
The charging current is switched (7.5 A/6 A/5A/4 A/1.3 A) according to the battery temperature at the start of
charging. Therefore, the charging time changes as shown in Fig. 11.
Note) Charging times may be longer according to the increase in battery temperature. However, the
thermistor that is a battery surface temperature sensor stops charging before the battery is
fully charged. Thus charging is stopped at an early stage.
Battery temperature becomes over 45˚C
during charging at 7.5 A or 6A.
Battery temperature becomes over 5˚C
during charging a low-temperature battery
(5˚C or less).
Inside of the charger becomes hot during
charging at 7.5 A (see Fig. 13).
Switch from 4 A to 6A
4 A
1.3 A (*)
Saving the charging time
Saving the charging time
Protection of the charger
(Note)

--- 15 ---
Fig. 12 Relationship between battery temperature at the start of charging,
charging time and current
Charging time
Charging current (mean value)
(Min.)
Charging time
Battery temperature at the start of charging
Charging current (mean value)
In the case of 3.0 Ah Ni-MH battery Model EB 2430H
Relationship between temperature of battery/charger and charging current
Temperature
Battery temperature at the start of charging
is between 5˚C and 40˚C.
Battery temperature at the start of charging
is between 40˚C and 50˚C.
Battery temperature at the start of charging
is between -5˚C and 5˚C.
Battery temperature at the start of charging
is -5˚C or less.
Charging current
6 A
Switch from 6 A to 4A
Switch from 1.3 A to 4A
Purpose
Protection of the battery
Protection of the battery
(*) The battery is also charged at 1.3A when the battery is near the end of its service life.
Otherwise, the battery temperature becomes high due to the high internal resistance and it is
dangerous.
(6) 24 V Ni-MH battery
The charging current is switched (6 A/4 A/1.3A) according to the battery temperature at the start of charging.
Therefore, the charging time changes as shown in Fig. 12.
Note) Charging times may be longer according to the increase in battery temperature. However, the
thermistor that is a battery surface temperature sensor stops charging before the battery is
fully charged. Thus charging is stopped at an early stage.
Battery temperature becomes over 45˚C
during charging at 6 A.
Battery temperature becomes over 5˚C
during charging a low-temperature battery
(5˚C or less). Switch from 4 A to 6A
4 A
1.3 A (*)
Saving the charging time
Saving the charging time
(Note)

--- 16 ---
6 A (5 A) range
Switching boundary
9 A range
Fig. 13 Time required to switch from 9 A to 6 A (5 A)
Number of batteries
charged continuously
Ambient temperature
(No.)
5-3-7. Revitalizing the battery (trickle charging)
This is a function to charge a battery further after completion of charging as shown in Fig. 14 (repeats the
following cycle 10 times: 1-hour pause and 15-minute charging at 1.3 A). A new battery or a battery that has not
been used for extensive periods (6 months as a guide) may not be charged completely due to inert internal
chemicals. Leave the battery inserted in the charger for 8 to 12 hours after completion of charging. The charger
automatically "revitalizes" the battery by trickle recharging.
Fig. 14 Revitalizing the battery (trickle charging)
Completion
of charging
Status
Charging current
Charge status lamp lights green continuously.
1-hour
pause
Charging Revitalizing the battery (trickle charging)
{10 times (about 12 hours)}
Completion
of revitalizing
15-minute
charging
15-minute
charging 1-hour pause
1.3 A 1.3 A 1.3 A
Charging time

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5-3-8. Safety device
The Model UC 24YJ is equipped with a safety device that stops charging (and extinguishes the lamp) if any of the
following troubles occurs.
The electrolyte adheres to the thermistor built in the battery. The battery temperature cannot be detected
correctly in this case.
The relay in the charger is at the end of its service life.
How to check whether it is a failure of the battery or the charger
If the lamp goes off, disconnect the power cord plug from the receptacle first. Wait 3 to 5 minutes then connect
the power cord plug to the receptacle again.
In the case of , the lamp lights and the charger operates normally.
In the case of , the lamp does not light and the charger is at the end of its service life.
5-4. Batteries
5-4-1. Types and characteristics of batteries
Two types of batteries are available for electric power tools, Ni-Cd batteries and Ni-MH batteries. The
characteristics of the Ni-Cd batteries and the Ni-MH batteries are described in the table below.
1
2
1
2
Item
Capacity
Relationship between discharging
capacity and temperature
Self-heating during charging
Impact on the environment
Characteristics
Ni-MH batteries have higher capacity than Ni-Cd batteries.
See Fig. 15.
Ni-MH batteries have higher self-heating value than Ni-Cd batteries.
Ni-Cd batteries give impact on the environment as they include a
harmful substance (cadmium).
Ni-MH batteries are environmentally friendly as they do not include any
harmful substance.
Fig. 15 Relationship between battery temperature and capacity
Battery temperature Battery temperature
Capacity
Capacity
Ni-Cd batteries Ni-MH batteries
(*) If a Ni-MH battery is used (discharged) when the battery temperature is 0˚C or less, the battery
performance is extremely low at first but it becomes normal near the end of the operation because the
battery is warmed up. When the battery temperature is -10˚C or less and the capacity is 0, warm up the
battery by charging.
- 10
- 10

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5-4-2. Serial numbers of batteries
The serial number of a battery is indicated on the name plate or marked on the upper case of the battery.
Indication on the name plate of the battery
The numeral indicated at the serial number column means the last digit of the production year and the number
of dots (total of 12) means the production month.
Example) Figure 16 shows the case when the production date is April 1998 (12 - 8 = 4 (April)).
Serial number column
Fig. 16 Name plate
Marking on the upper case of the battery
The serial number is indicated with four digits (the last two digits of the production year + production week) by
marking.
Example) Figure 17 shows the case when the production date is April 1998 (the 15th week = April).
Surface of the upper case
Marking of serial number
Fig. 17 Upper case of battery
9815