7
OPM-122
REV C
The drive belt system must be of adequate size and must be tight
enough to power the generator without slippage. Be careful not to
over-tighten to the extent that it puts excessive strain on the bearings.
Doing so can cause bearing failure and other possible damage to the
generator.
Alignment of the generator to the prime mover is important.
Misalignment of the pulleys will cause excessive belt and pulley wear
and unnecessary stress on the prime mover.
The following table shows the effect if carious operating speeds and
electrical loads on a typical generator when matched and mounted to
an adequate prime mover.
LOAD VS. OUTPUT
Generator
Load
Speed
(RPM)
FREQUENCY
(Hz)
Voltage
None
3690
61.5
129V
Half
3600
60.0
120V
Full
3510
58.5
115V
*Note: Required generator speed must be at 3600 +/- 90 RPM under all
load conditions.
Although individual units and models may vary slightly, the normal
voltage and frequency of typical 60 cycle engine-driven generators
described in this manual are approximately as follows when powered
by a typical prime mover (engine) run first with no load applied, then at
half capacity as rated on the nameplate.
All engines have a tendency to slow down when a load is applied.
The governor on the engine is designed to hold engine speed nearly
constant. When the electrical load connected to the generator is
increased, the engine is more heavily loaded and as a result, the
speed drops slightly. This slight decrease in speed together with the
natural “voltage drop” within the generator itself due to load current and
heating of the windings, results in a slightly lower voltage than when
the generator is running idle.
The normal slight variations on speed also directly affect the frequency
of the output current. This frequency variation has no appreciable effect
in the operation of most loads (such as motors, lights, and most small
appliances). However, timing devices and clocks will not keep perfect
time unless the engine can keep the generator at exactly 3600 RPM at
all times. Since this is not usually possible, minor time errors in clock
occur.
The speed of the engine is usually adjusted so that the generator
produces proper voltage. If the adjustment is made “cold”, set the
voltage a little higher than normal since it will drop a few Volts as the
generator warms up.
NOTE: When operating continuously at full load, the generator shell
becomes very warm. It will be uncomfortable to the touch. This is
normal for any high performance inherently regulated generator. Output
voltage should be checked periodically to ensure proper operation of
the generator and appliances.
UNIT INSTALLATION
Plans for installation should be prepared with proper attention to
mechanical and electrical engineering detail to assure a satisfactory
system installation. The information in this manual is offered as a
guide to finalizing your installation plans. The installation sequence is
summarized below.
PLAN THE INSTALLATION
Generally, two-bearing generators are used on portable equipment. For
best service consider the following:
1. All electrical equipment should be protected from excessive
moisture. Failure to do so will result in deterioration of the insulation
and short circuits and grounds.
2. The generator should be installed in a sheltered area. If the unit must
be left in the open, it should always be protected with a weather cover
such as a tarp or large piece of canvas after each use to keep out
water and dust.
CAUTION: EQUIPMENT DAMAGE
Always allow the generator and prime mover to cool before covering
with a flammable weather covering.
MOUNTING
CAUTION: EQUIPMENT DAMAGE
The generator must be mounted with the engine to a common rigid
base to prevent stress on the engine and generator shafts and
bearings do to vibration displacement. For permanent installations,
the engine-generator is usually mounted on a sub-frame which can be
shock mounted with neoprene pads on the main frame.
Before proceeding with installation, be sure that you have completely
read and understood the assembly and installation instructions.
An engine with adequate horsepower and a close regulated (fixed
speed) governor is required for satisfactory operation of this generator.
About 1.4 horsepower is required to produce 1,000 Watts of generator
output power assuming 100% efficiency of both the engine and the
generator. However, due to engine and generator efficiencies of 80
to 90%, the loss of power due to engine driving accessories such as
cooling fans, battery charging alternators, etc., friction losses and
slippage in the drive pulleys and belts, the general conservative rule
of thumb allowing approximately two (2) horsepower for every 1,000
Watts of generator output is much more realistic. For example, the
7,200 Watt generator output will require a 14.4 horsepower engine
for full output, good speed/voltage regulation, and satisfactory load
performance. When determining the prime mover/generator pulley
ratio to drive the generator at the correct operating speed, bear in mind
the power rating of most prime movers (usually an engine) varies with
speed. It produces more power at higher speeds, less when slowed.
The prime mover must be fast enough to reach desired horsepower for
good generator operation.
