Alternator fault - help please?
Discussion
I have a 94 Chimaera 4.0 with a Magneti Mirelli A127-65 alternator. I have the following faulty condition and need help to resolve:
With ignition off there is 12V across the alternator terminals. Further there is a 3amp drain through the alternator (Yes 3amp i.e. battery flat in hours but alternator nice and warm to the touch).
With ignition switch turned on the red ignition warning light does not come on. With ignition switched on and positive leads to alternator removed red light is on.
Engine will start and alternator charges but voltage appears to fluctuate wildly depending on revs and load (12.2V to 14.6V).
My first thought was that the voltage regulator has gone on the alternator however I am suspicious that there is a relay/regulator somewhere else because:
The positive lead to alternator changed state to 0V after I accidently shorted it when ignition off (multimeter left to read current not volts when connecting accross wire and ground - schoolboy error). The red light would not come on when the positive lead was removed (contrast with above).
Most suprisingly, the positive lead returned to 12V (i.e. original state) after I started the engine (but was not like that after I just turned ignition on). As before I now have 3A current drain and warning light off when ignition on. However, with +ve lead removed and ignition on, light is on again.
For questions see next post.
With ignition off there is 12V across the alternator terminals. Further there is a 3amp drain through the alternator (Yes 3amp i.e. battery flat in hours but alternator nice and warm to the touch).
With ignition switch turned on the red ignition warning light does not come on. With ignition switched on and positive leads to alternator removed red light is on.
Engine will start and alternator charges but voltage appears to fluctuate wildly depending on revs and load (12.2V to 14.6V).
My first thought was that the voltage regulator has gone on the alternator however I am suspicious that there is a relay/regulator somewhere else because:
The positive lead to alternator changed state to 0V after I accidently shorted it when ignition off (multimeter left to read current not volts when connecting accross wire and ground - schoolboy error). The red light would not come on when the positive lead was removed (contrast with above).
Most suprisingly, the positive lead returned to 12V (i.e. original state) after I started the engine (but was not like that after I just turned ignition on). As before I now have 3A current drain and warning light off when ignition on. However, with +ve lead removed and ignition on, light is on again.
For questions see next post.
1. Is it correct to have 12V across the alternator when the ignition is off?
2. Is there a regulator or relay somewhere else that controls the alternator (e.g. only puts power to alternator when ignition turned on)?
3. If I need to get alternator tested, reconditioned or replaced - any suggestions as to where to go/shop.
Many thanks for your help,
TOM
2. Is there a regulator or relay somewhere else that controls the alternator (e.g. only puts power to alternator when ignition turned on)?
3. If I need to get alternator tested, reconditioned or replaced - any suggestions as to where to go/shop.
Many thanks for your help,
TOM
The alternator output is permanently connected to the battery (often via a fusible link). The rectifier in the alternator stops the battery from discharging through the battery. If the rectifier fails you would get the drain you're seeing.
The ignition feed is connected to the alternator through the no-charge warning light, and serves to power up the field coils. Once the alternator is producing power it powers the field coils itself but it needs this small current to get it started. If the light stays on that indicators that the alternator isn't powering up properly. If the light stays on when the ignition is off it shows that the battery is discharging through the alternator.
Basically all these symptoms point to a failed electronic module inside the alternator and you need to get the module replaced. You probably want to have a vehicle electrical specialist take cared of this for you.
The ignition feed is connected to the alternator through the no-charge warning light, and serves to power up the field coils. Once the alternator is producing power it powers the field coils itself but it needs this small current to get it started. If the light stays on that indicators that the alternator isn't powering up properly. If the light stays on when the ignition is off it shows that the battery is discharging through the alternator.
Basically all these symptoms point to a failed electronic module inside the alternator and you need to get the module replaced. You probably want to have a vehicle electrical specialist take cared of this for you.
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