Strange Alternator Behavior

[GeeBee]

Had an alternator go out again on my Ovation. This time it was dead after 44 hours. Testing showed the alternator dead. So I replaced with a factory rebuilt Continental alternator. I also replaced the regulator. Lucky me I have the VR515GA regulator which is valid for S/N 001 thru 363. After replacing the alternator and regulator we adjusted the voltage with a calibrated VOM to 27.9 volts per the Mooney MM. The MFD was exactly the same as the calibrated VOM at 27.9 volts. The system was rock solid, then all of the sudden threw an over voltage (steady light on the annunciator). No C/Bs popped. I shut it down with the field switch, brought up the standby, then shut that down and brought the main alternator on line. I stressed it with the pitot heat, bringing the voltage down to 27.5. It functioned flawlessly for the next 2 hours until landing. I reviewed the data on Savvy and it shows a solid 27.9 volts until disconnect. There is no indication of over voltage. What I am trying to figure out is why the over voltage disconnect with no over voltage. According to the Lamar Technologies web site the VR will send out a message of over voltage, but what causes the actual field disconnect? Is there a relay within the annunciator? According to the wiring diagram the regulator is wired in without terminal 4 (low voltage) connected because the annunciator takes that off the aircraft bus. The MM and wiring diagram make no mention of how the over voltage is wired up. According to the Mooney MM the annunciator takes it cue from aircraft bus voltage, not the regulator but if so how is there a field disconnect? 

Here is Lamar Technologies wiring diagram

https://irp.cdn-website.com/d25e75f5/files/uploaded/73150901.pdf

 

Here is my Savvy data. As you can see voltage is very steady at 27.9 then disconnect. I bring on the standby (it is all squiggly), then shut it down and bring back the main alternator.

[N201MKTurbo]

Sounds like a wiring issue. Could be a regulator, but you just replaced it. There is little an alternator can do to cause an overvoltage.

[PT20J]

There was no overvoltage as shown by the data. The steady light on the annunciator indicating overvoltage was erroneous causing you to shut down the alternator by pulling the field breaker.

You need to figure out why the annunciator light illuminated.

Regulators have over voltage protection to shut down the alternator in the event of an overvoltage. There are two methods: either by cutting off the field current directly or by shorting the field circuit (via a "crowbar" device) to cause the field CB to trip thus removing the field current. 

[GeeBee]

42 minutes ago, PT20J said:

There was no overvoltage as shown by the data. The steady light on the annunciator indicating overvoltage was erroneous causing you to shut down the alternator by pulling the field breaker.

You need to figure out why the annunciator light illuminated.

Regulators have over voltage protection to shut down the alternator in the event of an overvoltage. There are two methods: either by cutting off the field current directly or by shorting the field circuit (via a "crowbar" device) to cause the field CB to trip thus removing the field current. 

No actually I did not pull the breaker. I shut the alternator off with the alternator switch. The field C/B never popped, never was touched. When the annunciator announced over voltage, the alternator had already dropped off line.

[PT20J]

10 hours ago, GeeBee said:

No actually I did not pull the breaker. I shut the alternator off with the alternator switch. The field C/B never popped, never was touched. When the annunciator announced over voltage, the alternator had already dropped off line.

Sorry, I got the method of shutdown wrong. But you originally said the annunciator illuminated indicating an overvoltage which caused you to shut the alternator down. But now you say that the alternator dropped off line before the annunciator illuminated. If that is the case, then the fault could be in the regulator causing an overvoltage which caused the overvoltage protector to trip, or an errant overvoltage protector that tripped erroneously. The latter seems more likely because the data shows no overvoltage transient. 

[GeeBee]

1 hour ago, PT20J said:

Sorry, I got the method of shutdown wrong. But you originally said the annunciator illuminated indicating an overvoltage which caused you to shut the alternator down. But now you say that the alternator dropped off line before the annunciator illuminated. If that is the case, then the fault could be in the regulator causing an overvoltage which caused the overvoltage protector to trip, or an errant overvoltage protector that tripped erroneously. The latter seems more likely because the data shows no overvoltage transient. 

Yes, I looked over, saw a solid light, looked down saw low volts and a discharge. I shut down the alternator with the switch. Verified the C/Bs in, started the standby. Then I shut down the standby and turned back the alternator on and it worked fine. I left the pitot heat on as the system seemed steadier under load. The G1000 data only records once each second, so it is possible that an over volt spike was not recorded but detected by the regulator. The question is, if the regulator senses over voltage it throws a signal via wire #6. Does that signal go to the annunciator and is it the annunciator that accomplishes the field disconnect upon illumination. The MM and the wiring diagram are not clear on that point or is there a separate relay that accomplishes the field disconnect?

[PT20J]

59 minutes ago, GeeBee said:

Yes, I looked over, saw a solid light, looked down saw low volts and a discharge. I shut down the alternator with the switch. Verified the C/Bs in, started the standby. Then I shut down the standby and turned back the alternator on and it worked fine. I left the pitot heat on as the system seemed steadier under load. The G1000 data only records once each second, so it is possible that an over volt spike was not recorded but detected by the regulator. The question is, if the regulator senses over voltage it throws a signal via wire #6. Does that signal go to the annunciator and is it the annunciator that accomplishes the field disconnect upon illumination. The MM and the wiring diagram are not clear on that point or is there a separate relay that accomplishes the field disconnect?

Do you have a schematic for your serial number? -- it will show the voltage regulator connections. I think all the IAI annunciators have an overvoltage input that comes from the voltage regulator and is activated when the overvoltage protector trips. Since the OVP is located within the voltage regulator, it's really a chicken and egg thing whether there was a regulator failure causing an overvoltage that caused the OVP to trip, or whether the OVP is the problem. Either way, it points to a bad regulator assuming all the connections are good. The only way I can think of to get an overvoltage without the regulator itself initiating it is if the field wire got shorted to the bus somehow.

[GeeBee]

4 hours ago, PT20J said:

Do you have a schematic for your serial number? -- it will show the voltage regulator connections. I think all the IAI annunciators have an overvoltage input that comes from the voltage regulator and is activated when the overvoltage protector trips. Since the OVP is located within the voltage regulator, it's really a chicken and egg thing whether there was a regulator failure causing an overvoltage that caused the OVP to trip, or whether the OVP is the problem. Either way, it points to a bad regulator assuming all the connections are good. The only way I can think of to get an overvoltage without the regulator itself initiating it is if the field wire got shorted to the bus somehow.

Yes I do but the schematic and the MM are a little sketchy. As a matter of fact the Lamar Technologies schematic I posted is better than the Mooney one and the Mooney MM discusses the Zeftronics regulator but not the Lamar Technologies unit. Makes zero mention of it at all. I am going to call Lamar to see what they say.