Alternator failure, can’t find cause.

[cdeggz]

Originally Posted by togaflyer

Did you pull the plug from your alternator and check to verify your getting 11.5 is volts at the plug. Just insure power is getting from the switch and/or breaker to the alternator.

Yes, confirmed that as well.

[emsvitil]

Have you tried bypassing the regulator (short, temp test) like we use to do on our old cars?

[cdeggz]

Originally Posted by emsvitil

Have you tried bypassing the regulator (short, temp test) like we use to do on our old cars?

Ed I like this idea. Are you thinking 12V straight to the field? I assume I would need to hook the output (b) up to something that is not the plane?

[Mich48041]

Instead of bypassing the regulator with 12 volts, just measure the field current.

[cdeggz]

Hey Mich. O was seeing a cure t on the field that matched the other alternator. I want to say it was a round 4 amps but I can’t remember exactly.

I guess that is the quick summary:
-Field current seen
-B-lead voltage only at 12 V
-no current from alternator
Those make it look like a faulty alternator, but:
-Alternator shows 7 ohms
-alternator turns with the engine
Which makes the alternator sound like it should be working.

Seems pulling the alternator for further inspection is warranted.

[Mike S]

Craig------as you are also having ignition issues as posted in another thread, I would look for any common link between the two.

Start with the grounds, my $0.02.

It might be time to bring in someone experienced in electrical systems to take a look at your plane.

Good luck, let us know what you end up finding.

[Paul]

Hey Craig,

My 40 amp breaker on the power supply from the alternator had popped and I reset it but had the same type of issue and could not track it down.

Found that there was no continuity across the 40 amp breaker !
Breaker replaced and all was good

[N49ex]

Originally Posted by cdeggz

Hey Mich. O was seeing a cure t on the field that matched the other alternator. I want to say it was a round 4 amps but I can’t remember exactly.

I guess that is the quick summary:
-Field current seen
-B-lead voltage only at 12 V
-no current from alternator
Those make it look like a faulty alternator, but:
-Alternator shows 7 ohms
-alternator turns with the engine
Which makes the alternator sound like it should be working.

Seems pulling the alternator for further inspection is warranted.

If you are seeing 12V at the output, that means the breaker is good and you are seeing the backfeed from the battery, and it is not rising above the static battery voltage because the alternator it in fact not putting out current. Before pulling it out, as others have said, you could force it in place- it's ok to put 12V on the field, disconnect the output from the plane, and put a decent load on the output, something like a heater or a pair of 12V light bulbs in series (with 12V on the field it would put out more than 14V!), and see if it puts out anything. That is the dirt-simplest configuration which should ferret out for sure if the alternator is bad. B&C would probably fix it readily at that short age....

[Mich48041]

Recheck the "B" lead voltage at the alternator. But this time connect a high
wattage lamp in parallel with the voltmeter. Expect to see battery voltage.
A load such as a lamp will make problems show up better.
-
The alternator might NOT be turning fast enough if the drive coupling is slipping.
Field current of 3 or 4 amps is reasonable.

[PilotjohnS]

As was alluded to earlier, there may be common issues that point to something other than alternator.
I would check all the grounds from engine to firewall to battery to alternator's regulator.

Just my $.02