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Alternator wiring


Davo

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Hi all,

having gone through a recent rewrire of the Robin Hood, it’s mostly all good but I do have an anomaly I think with the alternator I think.  
 

there’s two main circuits, the ignition circuit and accessories on different switches. The anomaly is that once the ignition is running if you switch the accessory circuit off, the gauges etc keep running. 
 

my guess is this is because there is current feed back from the alternator, and I’m guessing this is what keeps that circuit alive. 
 

there are three wires to/from the alternator - two big fat ones which carry the charge back to the battery and the third cable was the excitor to kick start the alternator into making some current. I understand this cable also has a second purpose (and I could be wrong here!), the positive current feeds through that cable but first lights a battery sign, but when charge is made on the other side it evens the current and the battery light goes out. 
 

anyway, the alternator start generating without the wire, so do I really need it? 
 

have I wired this up wrong? 

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The alternator exciter wire allows the alternator to start charging the battery at lower speed. Without it you have to blip the throttle to start charging.

The battery (ignition in old terms) light on the dash has an other function which is to allert you that the battery is not chargeing when the engine is running before the engine stops due to a flat battery, one cause of on charge is a loose or broken fan belt which as it also drives the water pump should cause you to investigate before the cooling system boils dry.

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Thanks ian. Unfortunately I think the loom takes the excitor wire off the accessory circuit which creates this back feed. I’d move it to the main ignition circuit  but I guess then it would be impossible to switch the car off! 
 

as it happens, the car doesn’t currently have any battery warning light so I don’t have that luxury. I get what you’re saying though.   Was my understanding of how the battery warning light works correct? When no charge  is happening the current is lower after  bulb the bulb is lit, and when the alternator returns charge it evens it out so the bulb goes out. And that is exactly the reason why I get feedback to the accessory circuit.  

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Your understanding is right.

Ignition off engine stopped the bulb is at 0 volts both sides bulb off.

Ignition on engine stopped switch side of bulb will be at 12v and the alternator side of bulb at 0v bulb lights and passes a small current (limited by the bulb resistance.)

ignition on engine running both sides of the bulb now at 12v bulb off.

ignition off engine running (for a short while) switch side of bulb now at 0v and alternator side still at 12v (untill engine stops) bulb lights but does not pass enough current to keep sparks going so engine stops.

 

That is how it should work, I hope that this helps.

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It confirms my understanding at least thanks. 
 

Having that wire connected up does mess with other electrical functions though. I noticed with the circuit on the engine became lumpy and the dials were prone to random reboots. I suspect there is a short in my wiring or maybe the voltage from them alternator is unregulated. 

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