Generator Information; Use Of Electric Motors; Required Operating Speed; Generator Frequency Adjustment - Westerbeke 38B FOUR Service Manual

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 (AC) 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 start-
ed, 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 lIS-volt motors con-
nected to medium starting loads will be approximately as fol-
lows:
AMPS FOR RUNNING AMPS FOR STARTING
MOTOR SIZE (HP) (AMPERES) (AMPERES)
1/6 3.2
6.4 - 22.4*
1/4
4.6
9.2 - 32.2*
1/3 5.2 10.4 -72.8*
1/2 7.2 14.4 29.2
3/4 10.2 20.4 - 40.8
1 13.0 26
52
*NOTE:
In the above table the maximum "Amps for Starting"
is more for some small motors than for larger ones. The rea-
son for this is that the hardest starting types (split-phase) are
not made in larger sizes.
Because the heavy surge ot 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
se90nds. If difficulty is experienced in starting motors, turn
off all other electrical loads and, if possible, reduce the load
on the electric motor.
REQUIRED OPERATING SPEED
Although individual units may vary slightly, the normal volt-
age and frequency of typical 60 (50) hertz engine-driven gen-
erators described in this manual are approximately as fol-
lows: run first with no-load applied, then at half the genera-
tor's capacity, and finally loaded to its full capacity as indi-
cated 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.
GENERATOR FREQUENGY ADJUSTMENT
Frequency is a direct result of engine/generator speed, as
indicated by the following:
D When the generator is run at 1800 rpm, the AC voltage
output frequency is 60 hertz.
D 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.
GENERATOR MAINTENANCE
D
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 excessive heating and reduced life of wind-
ings.
D
For unusually severe conditions, thin rust-inhibiting
petroleum-base coatings should be sprayed or brushed
over all surfaces to reduce rusting and corrosion.
Typical materials suggested are Ashland Tectyle 506
and Daubert Chemical Co. Non-RustAC-410.
D
In addition to periodic cleaning, the generator should be
inspected for (a) tightness of all connections, (b) evi-
dence of overheated terminals, and (c) loose or dam-
aged wires.
D
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 corners of the head.
D
The rear armature bearing is lubricated and sealed; no
maintenance is required. However, if the bearing
becomes noisy or rough-sounding, have it replaced.
D
Examine the bearing at periodic intervals. No side
movement of the shaft should be detected when force is
applied. If side motion is detectable, the bearings are
wearing or wear on the shaft of the bearing socket out-
side bearing has occurred. Repair must be made quickly
or major components will rub and cause major damage
to the generator.
D
Examine the control box at periodic intervals to detect
cracks from engine and generator vibration. If cracks in
the box are seen, engine vibration may be severe,
requiring bracing in the box for additional strength to
resist vibration.
GENERATOR TROUBLESHOOTING
A complete and illustrated text on troubleshooting and ser-
vicing the WMD. and BT generators is furnished in the fol-
lowing pages.
Engines
&
Generators
78 '