QuestionI'm trying to understand the functioning of the charge light relay on the #2 generator. The wiring diagram doesn't show how the wires are connected to the relay. It looks like 24V is fed to the charge-light and from there to the relay. What is going on in the relay? Which wires are being switched and which are energizing the relay coil?
If I understand your answer to a previous question (and the wiring diagram bears it out) 24 volts are being fed to the 12 volt excitation terminal of the #2 alternator. Is that correct? Is there a resistor, or perhaps a special bulb, to drop the voltage to 12V? I can't seem to wrap my brain around the idea of exciting on a 12V alternator with 24V.
AnswerLets do the relay first.
The pink/black wire is from the ignition switch/fuse block.
It isn't 24 volt. It is 12 volt ignition power.
It powers the pullin coil in the relay.
The black wire is the ground for that relay coil.
The brown wires are what is connected by the relay. They carry the power coming through the gen 2 light, to the #1 terminal on the right (passengers side) alternator. That is the exciting voltage. There is a diode in a connector in that brown wire up under the dash, before it goes through the bulkhead connector.
The relay is needed because that generator,(alternator) is isolated in the 24 volt part of the circuit, although it is a 12 volt alternator.
I know it is confusing, but the negative post on that alternator does NOT connect to the engine or body ground. It connects to what you know as 12 volts, or the output of the other alternator.
Any testing done on the wires to that alternator with a 12 volt test light may burn out your test light bulb unless it is a 24 volt test light, or you connect the ground clip of the test light to 12 volts.
That dash Gen 2 bulb, although it is a 12 volt bulb, connects the same way. What you would think was 12 volts feeding the light, would actually measure 24 volts to the frame, but the alternator, and the bulb, isolated also, see it as just 12 volts.
None of that is important to know, except that normal frame grounding relationships can't be used, and the ignition switch 12 volts cannot be used DIRECTLY for that alternator.
So the relay is used just to keep it isolated. It isn't charging 24 volts...it is just adding another 12 volts to the second battery.
You might think of it like adding a water pump in the middle of a long water line to add some more pressure from the mid point on. Say the pressure would be about 12 to 14 PSI there, from the first pump, but the added pressure would bring it to 24 to 26 PSI beyond the second pump.
The alternators are completely interchangable. They are identical.
Another relay in that same system is a relay to connect the volt meter in the dash, to the batteries. Operates the same way.
Does that wrap your brain around it? Or just tie it in worse knots?
Van
