C.E. Niehoff & Co. C840D Troubleshooting Guides - Manual (Page 2)

Page 2 TG77A
Section A: Description/Operation
CEN C840D Alternator/Regulator Description and Operation
C840D 28 V, 525 A alternator is internally rectified. All windings and current-transmitting components are non-moving,
so there are no brushes or slip rings to wear out. C840D alternator is furnished with an open duct in the anti-drive end
cover plate, which accommodates a 4” duct.
This alternator is externally energized when the battery master switch on the vehicle is turned on and provides power
to the regulator through the IGN circuit (regulator can also operate without vehicle connection to IGN, and instead
provide power by sensing rotation through the regulator’s AC circuit). Field coil is then energized. AC is rectified into
DC output through diodes in anti-drive end rectifier housing and supplied to the battery from the alternator B+ termi-
nal. See Figure 4 on page 3. Alternator output current is self-limiting and will not exceed rated capacity of alternator.
Regulator maintains alternator output voltage at pre-determined regulated setting (see below for setpoints) as vehicle
electrical loads are switched on and off.
A2-346 regulator furnished with some units includes:
• Optional external IGN terminal for energize connection. This regulator can function with or without vehicle ignition.
When necessary, IGN terminal on regulator is connected to vehicle ignition to provide battery voltage when engine is
running. Circuit should be off (no voltage present) when vehicle ignition is off or engine is not running.
• P terminal that can provide optional AC voltage tap.
P terminal signal frequency (Hz) x 10 = alternator shaft rpm.
• D+ terminal that can provide DC voltage signal to vehicle electrical system, confirming alternator operation.
• Overvoltage cutout (OVCO). See page 4.
• Tricolored LED. See page 4.
• Battery type selection and battery maintenance/function are the sole responsibilities of the customer.
• J1939 connector to be used with optional A9-4036 harness.
— When A9-4036 temperature/voltage sense harness is not connected, regulator will operate in fixed voltage setting
determined by the select switch position on the bottom of the regulator. See Column 2 in Table 1.
— When A9-4036 temperature/voltage sense harness is connected, regulator will automatically optimize the charge
voltage for battery type based on temperature. Also, vehicle manufacturer-requested functions of 1939 interface are
available through connector. See Column 3 in Table 1.
Figure 2—Voltage/Battery Switch
Table 1 — A2-346 Regulator Voltage/Battery Switch Position
Switch Position
A9-4036 Harness Not Connected
(Voltage Select)
A9-4036 Harness Connected
(Battery Select)
Position 1 27.5 V Maintenance (D Category)
Position 2 28.0 V Maintenance-free (Group 31)
Position 3 28.5 V AGM
Position 4 29.0 V DO NOT USE POSITION # 4