GENERATOR
INFORMATION
USE
OF
ELECTRIC
MOTORS
The power required to start
an
electric motor is considerably
more than is required to keep it running after it is started.
Some motors require much more current to start them than
others. Split-phase
(Aq
motors require more current to start,
under similar circumstances, than other types. They are com-
monly used on easy-starting loads, such as washing
machines,
or
where loads are applied after the motor is
started, such as small power tools. Because they require
5 to
7 times as much current to start as to run, their use should
be
avoided, whenever possible,
if
the electric motor is to be dri-
ven by a small generator. Capacitor and repulsion-induction
motors require from 2 to 4 times as much current to start as
to run. The current required to start any motor varies with the
load connected to it.
An
electric motor connected to an air
compressor, for example, will require more current than a
·motor to which no load is connected.
In
general, the current required to start
115-Volt
motors connected
to medium starting loads
will
be
approximately as follows:
MOTOR
SIZE
AMPS
FOR
AMPS
FOR
(HP)
RUNNING
STARTING
(AMPERES)
(AMPERES)
1/6
3.2
6.4
to
22.4*
1/4
4.6
9.2
to
32.2*
1/3
5.2
10.4
to
72.8*
1/2
7.2
14.4
to
29.2*
3/4
10.2
20.4
to
40.8*
1
13
26
to
52
*NOTE:
In the above table the maximum Amps for Starting is
more
for some small motors than for larger ones. The reason
for this is that the hardest starting types (split-phase) are
not
made
in larger sizes.
Because the heavy surge
of
current needed for starting
motors is required for only an instant, the generator will not
be
damaged
if
it can bring the motor up to speed in a few
seconds.
If
difficulty is experienced in starting motors, tum
off
all other electrical loads and,
if
possible, reduce the load
on
the electric motor.
Required
Operating
Speed
Run the generator first with no load applied, then at half the
generator's capacity, and finally loaded to its full capacity as
indicted on the generator's data plate. The output voltage
should
be
checked periodically to ensure proper operation
of
the generating plant and the appliances it supplies.
If
an
AC
voltmeter
or
ampmeter is not installed to monitor voltage and
load, check it with a portable meter and amp probe.
NOTE:
When the vessel in which the generator is installed
contains
AC
equipment
of
120
volts only,
it
is
recommended
that the generator
sAC
terminal block be configured to pro-
vide one
120
voltAC
hot
leg for the
vessels
distribution
panel. This will ensure
good
motor starting response from the
generator.
Generator
Frequency
Adjustment
Frequency is a direct result
of
engine/generator speed, as
indicated by the following:
0 When the generator is run at 1800 RPM, the
AC
voltage
output frequency is
60 Hertz.
0 When the generator is run at 1500 RPM, the
AC
voltage
output frequency is 50 Hertz.
Therefore, to change the generator's frequency, the genera-
tor's drive engine's speed must be changed. Along with a
reconfiguring
of
the
AC
output connections at the generator,
a regulator board voltage output adjustment must also be
made.
See ELECTRONIC GOVERNOR in this manual.
Generator
Maintenance
0 Maintaining reasonable cleanliness is important.
Connections
of
terminal boards and rectifiers may become
corroded, and insulation surfaces may start conducting
if
salts, dust, engine exhaust, carbon, etc. are allowed to
build up. Clogged ventilation openings may cause exces-
sive heating and reduced life
of
windings.
0 For unusually severe conditions, thin rust-inhibiting petro-
leum-base coatings, should be sprayed
or
brushed over all
surfaces to reduce rusting and corrosion. Typical materials
suggested are Daubert Chemical Co.
"Non-RustAC-410"
and Ashland ''Tectyle 506" or equivalent.
0 In addition to periodic cleaning, the generator should be
inspected for (a) tightness
of
all connections, (b) evidence
of
overheated terminals and (c) loose
or
damaged wires.
0 The drive discs on single bearing generators should be
checked periodically
if
possible for tightness
of
screws
and for any evidence
of
incipient cracking failure. Discs
should not be allowed to become rusty because rust may
accelerate cracking. The bolts which fasten the drive disc
to the generator shaft must
be
hardened steel SAE grade
8, identified
by
6 radial marks, one at each
of
the 6 cor-
ners
of
the head.
0 The rear armature bearing is lubricated and sealed; no
maintenance is required. However,
if
the bearing becomes
noisy or rough-sounding, have it replaced.
0 Examine bearing at periodic intervals. No side movement
of
shaft should be detected when force is applied.
if
side
motion is detectable, bearings are wearing
or
wear on
shaft
of
bearing socket outside bearing has occurred.
Repair must
be
made quickly
or
major components will
rub and cause major damage to generator.
Engines
&
Generators
33
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