Re: Diode Warning Light

Posted by Owen Aaland on February 16, 2007 at 19:48:07 from (65.165.246.115):

In Reply to: Re: Diode Warning Light posted by SuperA-Tx on February 16, 2007 at 13:16:36:

The circuit for the light for the alternator works
by being grounded by the regulator. The circuit
starts at the ignition switch, goes through the
lamp and enters the excitation circuit of the
regulator (I terminal). The base must NOT be
grounded. The light works by battery voltage
coming from the ignition switch, passing
through the lamp, and entering the voltage
regulator where it is grounded by the excitation
circuitry. Since the excitation circuitry in the
regulator has some resistance the lamp will
not be as bright as one that has a grounded
base. When the alternator starts to charge
voltage is applied internally to the excitation
terminal. This voltage will be the same as the
other small terminal, the control circuit (A
terminal). Charging voltage from the output (B
post) goes to the ammeter and down to the
ignition switch. Now there is charging voltage
on both sides of the lamp. With both sides of
the lamp at the same voltage the lamp goes
out. An alternator failure would cause the
voltage to drop at the I terminal and the light
would again come on. This is not entirely
failsafe because a failure internal to the
regulator creating an open circuit will cause
voltage to drop at the I terminal and not be
grounded. In this case the alternator will not
work and the light will not come on. This is
one reason to make sure the light is on before
the tractor is started.

When the switch is turned off, the resistance
of the lamp is enough to keep the back feed
amperage below the level needed to run the
ignition system.

In this set up the lamp must be good to
provide the necessary voltage to the I terminal
to excite the alternator. If the bulb fails, the
alternator will not start charging. Usually there
is a small resister across the lamp terminals
to allow the alternator to begin charging even if
the bulb fails. This resister also causes the
lamp to glow less brightly than it would if it
were directly grounded.

Ideally the control circuit (terminal A) should
be connected as close to the battery as
possible, normally at the battery cable on the
solenoid or starter switch. That allows the
alternator output voltage to be higher than the
voltage that actually reached the battery to
compensate for voltage losses between the
alternator and the battery. The electrical load
on these old conversions is so low that the
control circuit can be connected to the
alternator output terminal with no ill effect.

Replies:

• Re: Diode Warning Light SuperA-Tx 10:25:54 02/17/07 (0)

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