high voltage at alternator exciter wire
Discussion
Hi folks .. ive got a chimaera in and the charge warning light glows when the engine is running ..
the thing is that the output of the alternator is measuring around 13.7 to 14.1 volts .. but the voltage at the exciter wire with engine running is 17 volts .. this voltage difference is making the charge light glow. I can put a test bulb from the exciter wire to the main power out cable on the back of the alternator and with engine running that test light glows also .. so it's at the alternator rather than a wiring fault on the car ??
Now before i go and order an alternator or repair is there anything I can do ? Presumably the exciter wire voltage should equal the main power out voltage otherwise the charge light would never extinguish ..
the thing is that the output of the alternator is measuring around 13.7 to 14.1 volts .. but the voltage at the exciter wire with engine running is 17 volts .. this voltage difference is making the charge light glow. I can put a test bulb from the exciter wire to the main power out cable on the back of the alternator and with engine running that test light glows also .. so it's at the alternator rather than a wiring fault on the car ??
Now before i go and order an alternator or repair is there anything I can do ? Presumably the exciter wire voltage should equal the main power out voltage otherwise the charge light would never extinguish ..
spitfire4v8 said:
Hi folks .. ive got a chimaera in and the charge warning light glows when the engine is running ..
the thing is that the output of the alternator is measuring around 13.7 to 14.1 volts .. but the voltage at the exciter wire with engine running is 17 volts .. this voltage difference is making the charge light glow. I can put a test bulb from the exciter wire to the main power out cable on the back of the alternator and with engine running that test light glows also .. so it's at the alternator rather than a wiring fault on the car ??
Now before i go and order an alternator or repair is there anything I can do ? Presumably the exciter wire voltage should equal the main power out voltage otherwise the charge light would never extinguish ..
If the main alternator positive and negative have proven to be goodthe thing is that the output of the alternator is measuring around 13.7 to 14.1 volts .. but the voltage at the exciter wire with engine running is 17 volts .. this voltage difference is making the charge light glow. I can put a test bulb from the exciter wire to the main power out cable on the back of the alternator and with engine running that test light glows also .. so it's at the alternator rather than a wiring fault on the car ??
Now before i go and order an alternator or repair is there anything I can do ? Presumably the exciter wire voltage should equal the main power out voltage otherwise the charge light would never extinguish ..
You're 100% correct
Exciter voltage should be equal to battery voltage
17 Volts from the field diodes (Exciter) is proof of a short circuit regulator
The chances are that the alternator overcharging has damaged one or more main diodes, could have also started cooking the stator
If the main alternator positive and negative have proven to be good
Hi PS 
As part of my earlier testing I had run jump leads from the alternator mounting bracket and from the main alternator power out direct to the battery, same result. So it looks like repair / replace time. As a garage I will probably put a new unit on - that way it will have a guarantee. Just making sure I hadn't missed anything obvious (can't see the wood for the trees syndrome!)
cheers!
As part of my earlier testing I had run jump leads from the alternator mounting bracket and from the main alternator power out direct to the battery, same result. So it looks like repair / replace time. As a garage I will probably put a new unit on - that way it will have a guarantee. Just making sure I hadn't missed anything obvious (can't see the wood for the trees syndrome!)
cheers!
spitfire4v8 said:
Hi PS
As part of my earlier testing I had run jump leads from the alternator mounting bracket and from the main alternator power out direct to the battery, same result. So it looks like repair / replace time. As a garage I will probably put a new unit on - that way it will have a guarantee. Just making sure I hadn't missed anything obvious (can't see the wood for the trees syndrome!)
cheers!
The fault could easily fool manyAs part of my earlier testing I had run jump leads from the alternator mounting bracket and from the main alternator power out direct to the battery, same result. So it looks like repair / replace time. As a garage I will probably put a new unit on - that way it will have a guarantee. Just making sure I hadn't missed anything obvious (can't see the wood for the trees syndrome!)
cheers!
Keep the faith, always believe your knowledge
Cheers
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