In a message dated 98-08-08 17:16:05 EDT, ARhodes@compuserve.com writes:
> To the Net, can anybody clarify specifically HOW the regulator
> does its job? I see only a few wires to the generator!
I'll give it a shot. Basically, there are three "relays" in the regulator, at
least in the later units. These relays are generally refered to as bobbins,
but they function exactly as a relay functions.
The first relay is the cut-out relay. The coil of this relay is connected to
the output of the generator, and will only be energized, or turned on, when
the generator is spinning fast enough to generate a voltage. Until the relay
is energized, the generator is dixconnected form the rest of the electrical
circuits. When the generator output voltage reaches a preset level, the relay
is energized, connecting the generator to the remainder of the car, and the to
battery. The generator can now supply the current demands of the automobile's
electrical equipment, and, hopefully, provide a little extra to recharge the
When the engine is shutdown, the generator voltage drops as the rpm drops.
When the output voltage drops below the preset level, the cut-out relay opens,
disconnecting the generator from the car. This is done to prevent battery
drain through the windings of the generator.
Normally, the cut-out relay operates only once per vehicle operation, turning
on when the car has started, and turning off when the engine is shut down.
The other two relays are called the voltage and the current regulating relays.
As the name implies, these relays operate to limit the current, and to
maintain the correct voltage output. The contacts of these relays are wired in
series with the field windings. If either the current or the voltage exceeds
the appropriate setpoint, the contacts open, cutting off the current through
the field windings.
The coil of the current regulating relay is wired in series with the output
windings of the generator. When the output current reaches the preset high
value, the current through the relay coil is sufficient to operate it, opening
the contacts, and stopping the flow of current to the field windings. With the
field current now cut off, the output of the generator drops to a lower
current level. When the output current drops below a preset value, the current
through the relay coil is no longer enough to keep the relay energized, and
the contacts once again close. As long as the demand for current exceeds the
maximum value allowed by the setpoint, the contacts will constantly open and
The average value of the current through the field windings will be determined
by the ratio of opened to closed of the relay contacts. The opened/closed
ratio is determined by the difference in the high current setpoint, which
opens the contacts, and the low current setpoint (reset point), which re-
closes the contacts. When properly adjusted, the opened/closed ratio will
limit the output at or below the maximum output capacity of the generator.
When the average value of the field current is limited, the average value of
the output current is also limited.
The coil of the voltage relay is wired in parallel with the output of the
generator, and, just as in the current relay, the contacts are wired in series
with the field windings. The voltage relay operates just as the current relay,
except it is sensitive to voltage, rather than current. When the generator
voltage reaches the high setpoint, the relay contacts open, and they reclose
when the output voltage drops to the preset low voltage level. The
opened/closed cycle of this relay maintains the voltage at the preset level,
by turning on and turning off the field current, just as the current relay
limits the output current. As this relay is used to *maintain* a constant
voltage, it will operate on/off more often than the current relay, which is
only used to *limit* the current.
That's a gross simplification, but I hope it helps.
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74