over voltage

[richardZ7]

model 1150P73HY
SERIAL NUMBER 1B851548
150PROXSL

just returning to the ramp and the mercury alarm went off second time in ten years
Shut down the motor and started checking the normal items nothing
Started up no problem started to give it a little gas and noted the voltage went over 16 volts but dropped down to 12/ 13 volts at idle
limped back loaded and back home
At this point i would like say i am an electrical eng with a masters in controls and instrumentation
So when i say the battery is good its good and all terminals are clean and tight they are fused link is good and i have already ordered a new alternator
Now the question
i have never heard of alternator giving over voltage i would love to know more about the circuit but i am unable to find circuit diagram for the charging circuit

hope this post is on the right page if not please move it

[JOE54]

do you have serv manual ????? internaly regulated alternator

[richardZ7]

no i do not have a service manual but right now that sounds like a good idea question what are the control wires red and purple for ? maybe voltage regulator ?
i am ok with big ol red wire

[richardZ7]

thanks to the members
red wire (small) going to Alternator is battery 12V + ref
purple wire (small) is key switched 12V + to activate the regulator

[richardZ7]

not a one wire system so if anyone has a overvolt alarm this should be your check list
check fused link large red wire from alt to terminal other side of motor battery disconnected
check small red wire for battery voltage 12v + battery connected
check small purple wire for 12v+ with ignition on check on and off battery connected

[JOE54]

no sir its not a one wire alt if thats question

[EuropeanAM]

Almost always a failed alternator (regulator failed). Make sure the grounds for the alternator are clean as you replace it.

[richardZ7]

all done and complete going to have the old one repaired and keep it as a spare

[EuropeanAM]

One note to that end: Most of the shops that do these have a device that can spin the alternator at approximately 3500 RPM's for testing.

That's the equivalent of about 1150 RPM's mounted to your engine. Probably not going to fail under those conditions.

At 5000 RPM's, that little alternator is singing along at 15K RPM's.