Alternator Issue

[Pinecone]

252 converted to Encore.

Dual alternators.

After avionics work, #2 alternator is misbehaving.  Start engine, turn on alternator, volts climbs to 32 volts and overvoltage protection trips the breaker.  

Swapped the two voltage regulators and #2 still does the same thing.

Thoughts?  Anyplace good service alternators?  If not, which replacement?  What alternator?  I think I have the Mooney Part Number.  But it is the belt driven one on a TSIO-360-SB

At least it is the one that is easy to get to.

 

[Z W]

Seems odd that the alternator would give out if they didn't work on it and the plane wasn't running.

Have they double-checked the grounds on the regulators, and any other wiring that was disturbed during the panel work?  Maybe they swapped the regulators but kept the same faulty ground or power wire in place.  Just a thought.

[Pinecone]

Good thought.  

[Fly Boomer]

2 hours ago, Pinecone said:

Swapped the two voltage regulators and #2 still does the same thing.

Field wire?

[MikeOH]

If the field wire was disconnected I'd think you would have an under, not over voltage condition.  I'd suspect the voltage sense wire going to the regulator is open; hence the VR "thinks" voltage is low and raises the field current leading to an over voltage output from the alternator.

[RoundTwo]

3 hours ago, Pinecone said:

252 converted to Encore.

Dual alternators.

After avionics work, #2 alternator is misbehaving.  Start engine, turn on alternator, volts climbs to 32 volts and overvoltage protection trips the breaker.  

Swapped the two voltage regulators and #2 still does the same thing.

Thoughts?  Anyplace good service alternators?  If not, which replacement?  What alternator?  I think I have the Mooney Part Number.  But it is the belt driven one on a TSIO-360-SB

At least it is the one that is easy to get to.

 

This sounds peculiarly like my problem from last year. If it’s going over, the regulator is sensing lower voltage. My problem turned out to be a compromised sense wire. Once the sense wire was addressed, it’s been 100%. 
 

Good luck!

[PT20J]

If the OVP is tripping on two different regulators then the problem must either be that the field current is too high and not being controlled by the regulator (maybe shorted to the battery bus) or the sense voltage is too low (maybe disconnected, or shorted to ground or the battery bus). Both field and sense should have breakers and after a major upgrade, goofs at the breaker panel would be where I would start looking.

[Pinecone]

On 5/31/2024 at 7:23 PM, PT20J said:

If the OVP is tripping on two different regulators then the problem must either be that the field current is too high and not being controlled by the regulator (maybe shorted to the battery bus) or the sense voltage is too low (maybe disconnected, or shorted to ground or the battery bus). Both field and sense should have breakers and after a major upgrade, goofs at the breaker panel would be where I would start looking.

Except that both regulators crowbar and shut off the alternator.  So can't see how it is shorted to battery.  I called a aircraft alternator shop and the suggested this or short inside the alternator, until I said the crowbar works and shuts off the alternator.

Sense wire (mentioned be several) sounds like a possibility.

May need to do some voltage measurements with alternators ON, but engine not running.

[PT20J]

I agree that the sense line is more likely. The point is that either the alternator is running without control of the voltage regulator as it would if the field current were higher than commanded by the VR, or the VR is commanding a high field current because it thinks the voltage is too low as it would if the sense line were disconnected. The latter is more likely, but the fact that the OVP works doesn't necessarily rule out a field line shorted to the bus before the CB because the crowbar shorts the field to ground tripping the field CB to remove the field current and shut down the regulator.

With the engine shut down and the master and alternator switches on, the field terminal at the alternator should read something less than bus voltage and the sense line at the VR should read bus voltage.

Edited June 3 by PT20J
Corrected statement that the field line would have to be shorted before the field CB, not after.

[Pinecone]

Update 

Thanks for the help.  It was a disconnected sense wire.

Strangely, the wire was disconnected and capped.   

But it working now.

[MikeOH]

17 minutes ago, Pinecone said:

Update 

Thanks for the help.  It was a disconnected sense wire.

Strangely, the wire was disconnected and capped.   

But it working now.

SWAG: The installers had an unused wire that needed to be capped off...and mistakenly capped the sense wire.  Any chance there's a wire also hooked up to the sense point that maybe shouldn't be?

[Pinecone]

Wasn't their cap.  They don't use those caps.

 

[MikeOH]

10 minutes ago, Pinecone said:

Wasn't their cap.  They don't use those caps.

 

Ok, but now I'm confused.  Wasn't the alternator working properly when you took the plane in for the avionics upgrade?  If so, then, if not them, who had access and capped it off?

[Pinecone]

It seemed to.  That is what is confusing everyone.  

But the shop did say that the voltage ramped up over time, so the normal turn off one then the other before takeoff check might not have seen it.