How do I troubleshoot my Onan electrical system?
This question was originally posted on the club's Discussion
board in the Clubhouse. Read the response from Al Eden, a long-time
Simplicity dealer (see more info). I've posted it here for easy access and reference.
Subject: ONAN MOANIN, charging system
Hi, Hope this is helpful.
I received an e-mail regarding the Onan charging system on the 720. Rather than
to respond only to the e-mail I thought I would address the issue here so it
would become available for discussion by everyone. The first test is to take a
voltmeter and measure across the battery terminals with the engine not running
you should see about 12 volts. Start the engine run it about 1800 to 2000 RPM
and the voltage should come up to about 14 to 14.8 volts DC. If it does the
system is working as it is supposed to. If your ammeter doesnít indicate a
charge, it is probably bad. If it still reads 12 volts. Get to the white wire
coming out of the rectifier and see if you have 14 to 14.8 volts DC. If you do
you probably have a broken connection or an open ammeter between the rectifier
output and the battery, as the voltage from the rectifier is not getting to the
battery. If isnít still isnít charging we will proceed forward. Note: Read
this completely before starting as some of the easiest tests are covered later
and you may want to do them first.
The CCKB engine with the 20 amp. system uses a stator and a ring of magnets
inside the flywheel. These produce an alternating current [AC] power source to
charge the battery. [This goes to a rectifier assy. and a regulator which were
manufactured by PHELON and to the battery.] The AC must be rectified [converted
to DC] to be used. There are 2 black and 1 red wires coming out of the stator.
The 2 black wires are the AC source and the red wire controls the stator output.
To resistance check the stator, you should have .5 to .7 [5/10] of an ohm
between the black leads. [with nothing else connected to the stator] From 1 of
the black leads to the red lead you should have about 1.3 to 1.5 [1+3/10] ohms.
From the other black lead to the red lead you should have 1.8 to 2.2 [1+8/10]
ohms. Next measure from each black lead to ground. Expect to see .1 [1/10] ohm
from each black lead to ground.. If these measurements are normal, the next step
would be to check the AC output.
To check the AC output, the stator needs to be unplugged and the engine running
about 1800 RPM. You should see about 17 or 18 volts AC. [Be sure your meter is
set to AC VOLTS]
The output of the stator goes to the rectifier assy. Typically this will have 2
black and 1 white wire. Use an ohmmeter to check the diodes. Check from each
black wire to the white wire. One direction they should read fairly low
resistance [like 10 ohms] depending on the scale the ohmmeter is on., reversing
the meter leads should read a very high resistance. [like maybe 10,000 ohms] If
either black lead reads near 0 ohms to the white lead and each way with the
meter leads reversed you have a shorted diode. If either one reads very high
both directions you have an open diode in the rectifier assy. Note: [Diodes are
like check valve in a water pipe, they allow electric current to flow in one
direction and not in the other. By reversing the meter leads you are changing
the polarity to the diodes and checking this property.] If the rectifier checks
OK, we will check the regulator.
To test the regulator, which has a black and red lead use an ohmmeter on the r X
10,000 scale and connect one lead to the red wire and the other to the base of
the regulator. There should be NO deflection of the meter reverse the meter
leads and there should be no deflection. In other words there should be NO
leakage from the red lead to the regulator metal base. Next repeat the test
using the black lead and the base. In one direction there should be no
deflection and when the meter leads are reversed should deflect fully.
The logical sequence of events would be to unplug the rectifier and regulator
and do the tests on them first, as this would be the easiest. Note the regulator
base Must be grounded to function properly in the unit. If the off the unit
tests check out we will proceed to a couple of operating tests.
The 2 black wires from the stator connect to the 2 black leads of the rectifier
assy. The white lead from the rectifier goes to the wiring harness to the
battery and to the black lead of the regulator assy. The red lead from the
regulator goes to the red lead that comes out of the stator.
If the tractor doesnít charge shut off the engine and disconnect the red lead
from the regulator. Tape the leads so they donít short out. Start the engine,
the alternator should charge full output, with the engine revved up should go to
or above 14.8 volts if it doesnít the stator is bad. If it does go to full
output do not operate it this way very long or the stator or rectifier may get
If the tractor is overcharging, check the ground on the regulator base, or for a
bad wire on the red lead. If they seem OK, again disconnect the red lead and
tape the regulator red lead and connect a temporary ground to the RED lead coming
out of the stator. Start the engine rev up, using the tractor ammeter or an
ammeter in series with the lead to the battery, the unit should not put out over
4AMPS DC. If it does it indicates the stator is OK and the regulator is bad.
Hope this is not too confusing, I am sorry it is so long, but I donít know how
to shorten it up any more.
Good Luck and Happy New Year,
NOTE: This site is designed to be viewed in at least 1024 x 768
resolution in Internet Explorer v6 or later, Mozilla Firefox v4 or later, and Google Chrome.
It may not display correctly in other resolutions or on other devices.
Links on this site are monetized.
liability or responsibility for the accuracy of
data on this site.
© ô 1998 - 2011 by Simple
trACtors LLC, North Brookfield, MA. All rights reserved.