Generac Power Systems Portable Generator 941 2 User Manual

Manual Part No. 0D9057  
SERVICE  
MANUAL  
SERIES IMPACT 36 PLUS II  
Models 940-2 & 941-2  
P.O. Box 297 • Whitewater, WI • 53190  
Phone: (262) 473-5514  
Fax: (262) 472-6505  
Printed in U.S.A  
Revision A - 07/15/03  
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TABLE OF CONTENTS  
PART  
1
TITLE  
THE AC GENERATOR  
SERVICE  
MANUAL  
2
3
4
5
6
7
8
ENGINE MECHANICAL  
GASOLINE FUEL SYSTEM  
GASEOUS FUEL SYSTEM  
ENGINE OIL & COOLING SYSTEM  
ENGINE ELECTRICAL SYSTEM  
TROUBLESHOOTING  
SERIES IMPACT 36 PLUS II  
SPECIFICATIONS & CHARTS  
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SECTION  
1.1  
TITLE  
GENERATOR FUNDAMENTALS  
PART 1  
GENERAL  
INFORMATION  
1.2  
1.3  
1.4  
1.5  
1.6  
1.7  
GENERATOR MAJOR COMPONENTS  
OPERATIONAL ANALYSIS  
INSULATION RESISTANCE  
COMPONENTS TESTING  
CONTROL PANEL  
COMPUTER  
CONTROLLED  
VARIABLE  
SHEET METAL  
SPEED RV  
GENERATORS  
Series Impact 36 Plus II  
Page 1  
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NOTES  
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Section 1.1  
GENERATOR FUNDAMENTALS  
NOTE: The "right hand rule" is based on the "cur-  
rent flow" theory which assumes that current  
flows from positive to negative. This is opposite  
the "electron" theory, which states that current  
flows from negative to positive.  
MAGNETISM  
Magnetism can be used to produce electricity and  
electricity can be used to produce magnetism.  
Much about magnetism cannot be explained by our  
present knowledge. However, there are certain pat-  
terns of behavior that are known. Application of these  
behavior patterns has led to the development of gen-  
erators, motors and numerous other devices that uti-  
lize magnetism to produce and use electrical energy.  
See Figure 1. The space surrounding a magnet is  
permeated by magnetic lines of force called "flux".  
These lines of force are concentrated at the magnet's  
north and south poles. They are directed away from  
the magnet at its north pole, travel in a loop and re-  
enter the magnet at its south pole. The lines of force  
form definite patterns which vary in intensity depend-  
ing on the strength of the magnet. The lines of force  
never cross one another. The area surrounding a  
magnet in which its lines of force are effective is  
called a "magnetic field".  
Like poles of a magnet repel each other, while unlike  
poles attract each other.  
Figure 2. The Right Hand Rule  
ELECTROMAGNETIC INDUCTION  
An electromotive force (EMF) or voltage can be pro-  
duced in a conductor by moving the conductor so that  
it cuts across the lines of force of a magnetic field.  
Similarly, if the magnetic lines of force are moved so  
that they cut across a conductor, an EMF (voltage)  
will be produced in the conductor. This is the basic  
principal of the revolving field generator.  
Figure 3, below, illustrates a simple revolving field  
generator. The permanent magnet (Rotor) is rotated  
so that its lines of magnetic force cut across a coil of  
wires called a Stator. A voltage is then induced into  
the Stator windings. If the Stator circuit is completed  
by connecting a load (such as a light bulb), current  
will flow in the circuit and the bulb will light.  
Figure 1. Magnetic Lines of Force  
ELECTROMAGNETIC FIELDS  
All conductors through which an electric current Is  
flowing have a magnetic field surrounding them. This  
field is always at right angles to the conductor. If a  
compass is placed near the conductor, the compass  
needle will move to a right angle with the conductor.  
The following rules apply:  
• The greater the current flow through the conductor,  
the stronger the magnetic field around the conductor.  
• The increase in the number of lines of force is  
directly proportional to the increase in current flow  
and the field is distributed along the full length of  
the conductor.  
• The direction of the lines of force around a conduc-  
tor can be determined by what is called the "right  
hand rule". To apply this rule, place your right hand  
around the conductor with the thumb pointing in the  
direction of current flow. The fingers will then be  
pointing in the direction of the lines of force.  
Figure 3. A Simple Revolving Field Generator  
Page 1.1-1  
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Section 1.1  
GENERATOR FUNDAMENTALS  
Figure 4. Operation of a Simple Generator  
mum negative value. Two reversals of current flow is  
called a cycle. The number of cycles per second is  
called frequency and is usually stated in "Hertz".  
ALTERNATING CURRENT  
A simple generator consists of a coil of wires called a  
Stator and a magnetic field called a Rotor. As the  
Rotor's magnetic field cuts across the Stator coil, a  
voltage is induced into the Stator windings. The  
amount of induced voltage is equal to the strength of  
the magnetic field.  
See Figure 4. The current alternates according to the  
position of the Rotor's poles in relation to the position  
of the Stator. At 0° and again at 180°, no current flow  
is produced. At 90° of Rotor rotation, current flow  
reaches a maximum positive value. Rotor rotation to  
270° brings another maximum flow of current.  
However, at 270° the current flow has reversed in  
polarity and now flows in the opposite direction.  
ELECTRICAL UNITS  
Figure 5. Alternating Current Sine Wave  
VOLT:  
The VOLT is the unit used to measure electrical  
PRESSURE, or the difference in electrical potential  
that causes electrons :o flow. Very few electrons will  
flow when voltage is weak. More electrons will flow as  
voltage becomes stronger. VOLTAGE may be consid-  
ered to be a state of unbalance and current flow as  
an attempt to regain balance. One volt is the amount  
of EMF that will cause a current of 1 ampere to flow  
through 1 ohm of resistance.  
AMPERE:  
The rate of electron flow in a circuit is represented by  
the AMPERE. The ampere is the number of electrons  
flowing past a given point at a given time. One  
AMPERE is equal to just slightly more than six thou-  
sand million billion electrons per second.  
With alternating current (AC), the electrons flow first  
in one direction, then reverse and move in the oppo-  
site direction. They will repeat this cycle at regular  
intervals. A wave diagram, called a "sine wave"  
shows that current goes from zero to maximum posi-  
tive value, then reverses and goes from zero to maxi-  
Page 1.1-2  
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Section 1.1  
GENERATOR FUNDAMENTALS  
If OHMS is unknown but VOLTS and AMPERES are  
known, use the following:  
VOLTS  
AMPERES  
=
OHMS  
REACTANCE IN AC CIRCUITS  
GENERAL:  
When direct current (DC) is flowing, the only opposi-  
tion to current flow that must be considered is resis-  
tance (ohms). This is also true of alternating current  
(AC) when only resistance type loads such as heating  
and lamp elements are on the circuit. In such a case,  
current will be in phase with voltage- that is, the cur-  
rent sine wave will coincide in time with the voltage  
sine wave.  
Figure 6. Electrical Units  
However, two factors in AC circuits called INDUC-  
TIVE and CAPACITIVE REACTANCE will prevent the  
voltage and current sine waves from being in phase.  
OHM:  
The OHM is the unit of RESISTANCE. In every circuit  
there is a natural resistance or opposition to the flow  
of electrons. When an EMF is applied to a complete  
circuit, the electrons are forced to flow in a single  
direction rather than their free or orbiting pattern. The  
resistance of a conductor depends on (a) its physical  
makeup, (b) its cross-sectional area, (c) its length,  
and (d) its temperature. As the conductor's tempera-  
ture increases, its resistance increases in direct pro-  
portion. One (1) ohm of resistance will permit one (1)  
ampere of current to flow when one (1) volt of electro-  
motive force (EMF) is applied.  
INDUCTIVE REACTANCE:  
This condition exists when current lags behind volt-  
age (Figure 8). As current flows in a circuit, magnetic  
lines of force are created at right angles to the con-  
ductor. The continuous changes in current value  
(from positive to negative) cause these magnetic lines  
to collapse and build up continuously.  
The magnetic field around the conductor induces  
electromotive forces that cause current to keep on  
flowing while voltage drops. The result is a condition  
in which voltage leads current. When a conductor is  
formed into a coil, the magnetic lines of force are con-  
centrated in the center of the coil. This increased den-  
sity causes an increase in magnetically Induced EMF  
without increasing current Thus, coils cause inductive  
reactance.  
OHM'S LAW  
A definite and exact relationship exists between  
VOLTS, OHMS and AMPERES. The value of one can  
be calculated when the value of the other two are  
known. Ohm's Law states that in any circuit the current  
will increase when voltage increases but resistance  
remains the same, and current will decrease when  
resistance Increases and voltage remains the same.  
Inductive reactance can also be caused by placing an  
induction motor on the circuit which utilizes the cur-  
rent's magnetic field for excitation.  
Figure 7.  
If AMPERES is unknown while VOLTS and OHMS  
are known, use the following formula:  
VOLTS  
OHMS  
AMPERES =  
Figure 8. Inductive Reactance  
If VOLTS is unknown while AMPERES and OHMS  
are known, use the following formula:  
VOLTS = AMPERES x OHMS  
Page 1.1-3  
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Section 1.1  
GENERATOR FUNDAMENTALS  
CAPACITIVE REACTANCE:  
trolled by the inverter and is maintained at a steady  
60 Hz signal throughout the load range.  
Computer controlled generator units have the ability  
to operate the engine over a wide range of speeds,  
while conventional generators will deliver correct AC  
frequency and voltage only at a fixed rpm.  
Unlike conventional AC generators, the Impact Plus  
unit can match engine speed to load requirements.  
This provides several advantages, as follows:  
This condition occurs when current leads voltage  
(Figure 9). It might be thought of as the ability to oppose  
change in voltage. Capacitance exists in a circuit when  
certain devices are ~a) capable of storing electrical  
charges as voltage increases and (b) discharging these  
stored charges when the voltage decreases.  
• Smaller engines can be used to produce more  
power than on a conventional generator, since it  
can be allowed to run at a higher speed.  
• When the load is reduced, the engine can run at  
slower than the usual speeds. This improves fuel  
economy and reduces engine noise.  
• The Impact Plus unit can be operated closer to its  
peak power point at all times, because output volt-  
age and current are functions of engine speed. This  
allows for a much more compact generator design.  
IMPACT PLUS SYSTEM OVERVIEW:  
Figure 10 is a block diagram of the Impact Plus sys-  
tem. The major elements of the system are represent-  
ed in the diagram. Operation of the system may be  
described briefly as follows:  
Figure 9. Capacitive Reactance  
WHAT IS AN "IMPACT PLUS" UNIT?:  
1. The engine is directly coupled to a permanent magnet type  
Rotor, so the Rotor runs at the same speed as the engine.  
The Impact Plus is a computer controlled generator  
that uses an inverter to create a superior sine wave  
and maintain a steady frequency. These units are dif-  
ferent from conventional generators in that the perfor-  
mance of the engine and AC generator are more  
accurately matched over a wide range of power  
needs. The Impact Plus computer controlled genera-  
tor provides greater efficiency of both the engine and  
the generator while maintaining electrical output with-  
in an acceptable voltage range. The frequency is con-  
2. As the Rotor turns, its magnetic field cuts across the Stator  
windings to induce a voltage into the Stator.  
Figure 10. Block Diagram of the Impact 36 Plus System  
Page 1.1-4  
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Section 1.1  
GENERATOR FUNDAMENTALS  
3. When the generator circuit breaker is turned to the “ON” position,  
AC voltage is delivered to the Full Bridge Rectifier. The AC volt-  
age is rectified to DC and thus becomes DC Link voltage.  
WHY VARIABLE SPEED CONTROL?  
Most electrical loads will operate satisfactorily only  
within a relatively small voltage band. In order to pro-  
vide useful voltage at larger load currents, it is neces-  
sary to increase engine speed.  
4. AC voltage from the stator PS1/PS2 is delivered to the inverter.  
This is used as the power supply for the inverter circuit board.  
In conventional AC generators, some form of voltage  
regulation is needed to provide correct voltage in the  
full range of load current. This is often accomplished  
by regulating excitation current to the Rotor (field)  
which then regulates the strength of the Rotor's mag-  
netic field. The voltage induced into the Stator wind-  
ings is proportional to the strength of the Rotor's mag-  
netic field.  
The Impact Plus computer controlled generator uses  
a Rotor having a fixed and permanent magnetic field.  
The strength of this magnetic field is fixed and cannot  
be regulated.  
5. AC voltage from the stator TIM1/TIM2 is delivered to the system  
controller. This is used for engine speed sensing.  
6. The system controller sends signals to the inverter for inverter  
operation.  
7. The system controller senses load voltage and signals stepper  
motor operation to achieve required engine speed for correct  
voltage output.  
The output voltage on Impact Plus computer con-  
trolled generators tends to droop with increasing elec-  
trical loads. The SYSTEM CONTROLLER maintains  
a constant AC output voltage by increasing engine  
and Rotor speed as the load current increases, to off-  
set this inherent voltage droop.  
Page 1.1-5  
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Section 1.1  
GENERATOR FUNDAMENTALS  
Page 1.1-6  
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