Fluke 8600A - Page 76

8600A
6-65
.
With
a
fully charged battery pack, the 8600A can
be disconnected from line power and operated for typicallj
8 hours, as a portable instrument.
When
all the display
decimal points flash on and
off, the battery pack
should
be
recharged
by switching
the POWER switch to OFF and
connecting the instrument to the ac power line. The total
charge time
is
approximately 16 hours.
If
desired, the
8600A
can be operated during the charging process, how-
ever,
the
charge time will be extended to approximately
43 hours.
NOTE
Battery manufacturers
recommend
that Ni-cad
batteries
be
recharged at least every
90
days.
Storage temperatures below +25°
Care
recommended.
6-66.
Theory of Operation
6-67.
The
8600A
equipped with the battery
pack
option
(—01)
uses the power
transformer
configuration shown in
Figure
7-2
and the battery power supply pcb shown in
Figure
7-6.
With
the
POWER switch in the ON position,
the batteries are connected to the input of the battery
power
supply
pcb, a
dc-to-dc converter.
6-68. The
+5
volts from the battery
is applied
to
the
primary windings
of T201, causing
transistors
Q201
and
Q202
to alternately
conduct.
The
alternating
current
in
the primary
windings is stepped
up
by the
secondary wind-
ing
and applied
to
a
bridge
rectifier consisting
of
CR203
through
CR206.
The
two halves of
the
rectifier output are
applied to two voltage regulators,
U202 and U203.
The
resulting
+15V and —15V
power
supply voltages provide
the operating
power
for
the instrument.
6-69. Maintenance
6-70. INPUT POWER
6-71
.
The 8600A-01
,
in addition to battery
operation,
is
capable of
operating from
either
100,
1
15,
or
230V ac,
50
or
60 Hz line power. Before connecting the instrument
to
line power, check
and,
if necessary, use the following pro-
cedure to prepare the unit for
operation
at the local
line volt-
age:
a. Remove the
phillips
screw from the rear of the
instrument.
b.
Remove
the case from the unit
by
pulling
it
straight
back from the front
cover.
c.
Locate the Battery Power
Supply
PCB
Assembly
(See Figure
5-1)
and determine the
size of the large
capacitor
C201 on
the
pcb
(See Figure
5-5).
The
relationship of this capacitor to line
power
is
as
follows:
1
.
5.0uF
-
115V ac
60
Hz
2.
6.6uF
-
100V
ac
50 Hz
3. 2.8uF
-
230V
ac
50 Hz
d. Install the
appropriate capacitor. The
capacitors
specifications and John Fluke
part
numbers
are
given in the Lists of
Replaceable Parts, Section 5
.
(Battery Power
Supply PCB Assembly).
e.
Install the unit
in its case and insert the phillips
screw.
6-72.
CHARGING NI-CAD BATTERIES
6-73.
With regard to the charging of nickel-cadmium
bat-
teries, there are
some
phenomena which
should be considered.
For
instance, charging Ni-Cad batteries with cell case temper-
atures
above
25°C will
cause
the cell’s charge capacity to
de-
crease. The
decrease
in capacity is linear from
100%
of
rated capacity at 25°C to only
60%
of rated
capacity at 50°C,
and
as
low
as
45%
at
60°C.
Cell
case temperatures typically
rim
from
5°C
to
10°C above
ambient temperature during
charging
due to heat dissipated
by the charging circuit.
Due to the
enclosed
nature
of the light-weight case
on the
8600A,
the
temperature inside
the case
typically
runs an
additional
10°
to
15°C
above
ambient
temperature. For
most complete
charging and longest battery life,
the
8600
A-01
should be
charged
at less
than 23°C ambient.
Cell
charge
times are also
affected
by
low
temperatures.
Charging the
batteries
at less than 5°C
will reduce
charge
storage capacity and
reduce
battery
life. The battery
manufacturer recommends allowing
the
instrument
to
warm
up
to room temperature before
charging the unit.
6-74.
Charge capacity
may also be
affected
by
a cell’s
charging-discharging routine, due
to a
memory-type
phenom-
enon. For instance, if
a
Ni-Cad battery pack is used in a
daily routine where it is allowed to discharge by
only 30%
before being fully recharged
again, it
will
eventually become
a battery
pack capable
of
delivering
only
30%
of its
rated
capacity. To
return such
a battery pack to its
rated capacity,
connect an external load which will discharge the
battery
completely at a rate
equal to its
capacity
divided
by
20. For
example,
a
pack of
four series-connected
1.2
-volt
cells having
individual capacity
ratings of 3.5 ampere hours should
be dis-
charged at
a
rate
of
3.5A
20
=
.175
A.
This requires a load
resistor of
4.8V
-r
.175A
=
27.5 ohms (approximate)
with
a
6-10
1/77