Onan NHC Series Operator's/Service Manual And Parts Catalog page 297

TABLE 2. TESTING SYNCHRO 20 AMP SYSTEM
TEST
Battery voltage - unit
not running
Battery voltage with
unit running at 1800
rpm or more
AC voltage from stator
with plug disconnected
and unit running at
approximately 1800 rpm
VALUE
12 Volts DC
14.2 — 14.8*
Volt DC
17 volts AC
Black to Black
Ohmmeter reading at plug
when checking two AC
stator leads - unit not
running
Resistance values (Ohms) are as follows
between wire pairs.
• B L A C K
. 5 - .7
1.8-2.2x1
• B L A C K
1.3-
1 . 5 A
• R E D
• - 60 Volt minimum at greater than 2000 rpm,
Red to Ground.
Checking Rectifier Assembly: Examine each of the
two diodes for breakdown by connecting ohmmeter
(Rxl scale) from one black lead to white lead. Meter
should read 10 ohms in proper polarity. A shorted
diode would read zero resistance and would cause a
short circuit through the lead winding when in
operation. An open diode would read infinite in both
directions indicating that replacement is necessary.
Testing Regulator Assembly: To check for proper
voltage regulation, attach a DC voltmeter to battery
and operate engine at about 1800 rpm. Battery
voltage will climb to the preset factory setting (14.2 to
14.8 volts).
Some installations may vary due to voltage drop in the length of
ammeter harnesses. Other variations may stem from a loose
connector in the harness or loose or corroded battery leads. Low
voltage readings at the battery mean poor battery connections.
To test regulator, remove connector. Using the
Rxl0,000 scale of your ohmmeter, connect one meter
lead to red leadwire and other meter lead to regulator
base. No deflection should be noted on the ohmmeter
in either polarity. Next connect meter to black
leadwire and base of regulator. Meterwill deflect fully
in one polarity with no deflection in the other.
A L T E R N A T O R S T A T O R
M O U N T E D B E H I N D B L O W E R W H E E L
TO T E R M I N A L
C O N N E C T O R
RECTIFIER
A S S E M B L Y
R E G U L A T O R
A S S E M B L Y
FIGURE 29. 20 AMP SYNCHRO SYSTEM
Full Charge—Will Not Regulate: Check for broken
leads at connection to regulator plates. To be sure
regulator winding operates properly, connect red
lead to ground and start engine. A maximum of 4
amperes should be noted. This would indicate stator
winding is satisfactory. If so, replace regulator.
No Charge: If alternator does not charge when load is
applied to battery, shutoff engineand disconnect one
red leadwire from regulator terminal. Be sure lead is
taped or isolated from conducting engine parts. Once
again, start engine. Alternator should charge to full
output; if it doesn't, replace stator assembly.
15 AMP PHELON SYSTEM
The 15 amp flywheel alternator systems (Figure 30)
have a one piece regulator-rectifier assembly.
Various alternator problems are listed in Table 3.
Testing
With the engine running between 1800-2600 rpm,
observe the panel ammeter (if not already equipped,
connect a test ammeter). If no charging is evident,
proceed with the NO CHARGE TEST. If ammeter
shows a constant higher charge rate, follow the HIGH
CHARGE RATE TEST procedure.
No Charge Test: Perform as follows:
1. Check the B+ to ground voltage using a DC
voltmeter. See Figure 31 for wiring diagram.
2. If voltmeter reads 13.8 volts or higher, add a load
to system (e.g. headlights) to reduce battery
voltage to below 13.6 volts.
3. Observe ammeter. If charge rate increases, con-
sider the system as satisfactory. If charge rate
does not increase, proceed with testing.
4. Disconnect plug from regulator-rectifier and test
the AC voltage at the plug with engine running
near 3600 rpm. If AC voltage reads less than 28
volts, replace the stator. If AC voltage is more than
28 volts, replace the regulator-rectifier assembly.
28