Generac Power Systems 941-2 - Manual (Page 95)

Section 6.3
ENGINE CRANKING SYSTEM
INTRODUCTION
COMPONENTS:
The engine cranking system is shown schematically
in Figure 1, below. The system consists of the follow-
ing components:
• A 12 volts Battery.
• A Start-Run-Stop Switch (SW1).
• A Starter Contactor (SC).
• A Starter Motor (SM1).
• A6060 Circuit Board.
• Interconnecting wires.
OPERATION:
1. Holding the Start-Run-Stop switch (SW1) at "START" connects
Wire 17 from the A6060 circuit board to frame ground.
a. A6060 circuit board action energizes a crank
relay on the board after a three second delay.
b. Closure of the crank relay's contacts delivers 12
VDC to Wire 56 and to a Starter Contactor (SC).
The Starter Contactor (SC) energizes and its
contacts close.
2. Closure of the the Starter Contractor (SC) contacts delivers
battery voltage to the Starter Motor (SM1). The Motor ener-
gizes and the engine is cranked.
Figure 1. Schematic - Cranking Circuit
BATTERY
RECOMMENDED BATTERY:
The battery is generally supplied by the customer.
Recommended is a battery that meets the following
requirements:
• Use a 12 VDC automotive type storage battery.
• For prevailing ambient temperatures above 32° F.
(0° C.), use a battery rated at 70 amp-hours and
capable of delivering 360 cold-cranking amperes.
• For prevailing ambient temperatures below 32° F.
(0° C.), use a battery rated 95 amp-hours and capa-
ble of delivering 450 cold-cranking amperes.
BATTERY CABLES:
Battery cables should be as short as possible and of
adequate diameter. Cables that are too long or too
small in diameter can result in voltage drop. The volt-
age drop between battery terminals and the connec-
tion point at generator should not exceed 0.121 volts
per 100 amperes of cranking current.
The cables should be carefully selected based on (a)
cable length and (b) prevailing ambient temperatures.
Generally, the longer the cable and the colder the
ambient temperature, the larger the required cable
size. The following chart applies:
CABLE LENGTH CABLE SIZE
Feet (Meters)
0 to 10 (0 to 3) 2*
11 to 15 (3.4-4.5) 0
16 to 20 (4.5 to 6) 000
* For warm weather use No. 2 cable up to 20 feet.
BATTERY CABLE CONNECTIONS:
1. Connect the cable from the large Starter Contactor (SC) lug to the
battery post indicated by a POSITIVE, POS or (+).
2. Connect the cable from its FRAME GROUND connection to the
battery post indicated by a NEGATIVE, NEG or (-).
(continued)
Page 6.3-1