HEAVY DUTY ALTERNATORS
The rotor is electrically magnetized by a small current flowing
through it via brushes riding on smooth slip rings.
Alternating current is produced as the magnet poles of the
rotor pass through the coil windings of the stator. For
increased capacity, there are twelve (12) magnetic poles
incorporated into the rotor and three (3) separate windings in
the stator. Since alternating current is produced as the rotor
passes the coil windings of the stator, increased engine speed
produces more current.
The battery stores only direct current and cannot use
alternating current. For this reason, rectifier assemblies are
used to convert alternating current produced in the stator to
direct current. Rectifiers consist of silicon diodes which
function as electrical switches and permit current flow in only
The rectifier diodes are mounted in aluminum castings, called
heat sinks, which are finned to dissipate heat.
A built-in solid state voltage regulator controls alternator output
and the batterys state of charge. A lead from the vehicles key
switch provides turn-on voltage to the voltage regulator.
The regulator senses when the battery has received sufficient
charge and then reduces the "field" (magnetizing) current flow
to the rotor. Reducing the field current flow, in turn, reduces
When headlights and/or accessories place a load on the
battery, the regulator increases the field current flow to the
rotor, thereby increasing alternator output.
Mounting hardware including brackets and drive belts must be
periodically inspected and adjustments or repairs performed
as required. It is important that mounting bolts and nuts be
kept securely tightened to maintain belt alignment and prevent
vibration damage which will occur if mounting bolts work loose.
Vehicle wiring must be inspected at periodic intervals for loose
or corroded connections and repairs made as needed.
Check the drive belts, wiring, and mounting hardware,
and make sure that they are in proper working order.
Check the batteries according to manufacturer
specifications to insure that they are in good
condition. The batteries must be at least 75%
charged. If necessary, charge or replace batteries.
To establish if the alternator is functioning properly,
connect an accurate test voltmeter to the alternator
measuring 1/100 of a volt). With all electrical
accessories off, run the engine at approximately 1000
Voltage reading should be within 13.8-14.2 volts.
If the alternator is overcharging, continue with step 7.
If a low output condition is noted, then continue with
Remove and inspect the brushes. If brushes are
cracked, burned or worn to 3/16" or less, then the
brushes must be replaced. Insure that each brush
contact lead has a good connection to the brush and
the contact cap.
Clean each brush contact cap and the two contact
pads on the regulator.
Reinstall the brushes and regulator as shown under
REASSEMBLY, steps 12 and 13.
Repeat the test in step 3. If the output voltage is
below 13.8 volts, the unit should be full field tested as
shown in step 6.
Shut off the engine and all electrical accessories.
Measure the voltage at the alternator output terminals
and make a note of the reading. Connect a short
jumper to the alternator NEGATIVE output terminal
and to a 1.5-2" piece of stiff wire (a piece of paper clip
wire is suitable). Insert the wire in the full field access
hole as far as it will go. See Figure 3.
Figure 3 - Jumper Connections for Full Field Test.
Run the engine at about 1000 RPM and check the
output voltage. If the voltage rises rapidly above the
voltage reading noted when the engine was off, the
alternator is OK, continue with step 7.
If the voltage rises slowly or remains the same, the
alternator is defective. Continue with step 8.
CTS-4043A - Chapter II - Page 3