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M20J Alternator Field Circuit Breaker Pops


Jack46

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About half way from KBTL to KOWB to attend a MAPA PPP session, the alternator field circuit breaker popped. I shut the field switch off, and reset the breaker, turned the field switch back on. In about 5-10 minutes the breaker popped again. I repeated the reset process. I told myself if it happened a third time, I was RTBing to KBTL. In about 5-10 minutes, it popped a third time so I did a 180. On the roughly 45 minute flight back, the breaker never popped again. So, now I'm wondering if I made the right decision.

Is this an issue that is just annoying or is it a safety of flight issue? How can I differentiate? What happens if I just keep re-setting the breaker?

Is this caused by the alternator, voltage regulator, weak circuit breaker, something else?

Has anyone else experienced this?

Jack

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1 hour ago, N201MKTurbo said:

It could be a chafed wire shorting out.

A cheap fix. I’m pulling for you...

The other options are a bad regulator, or a shorted armature.

Or worn brushes in the alternator.

Clarence

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1 minute ago, M20Doc said:

Or worn brushes in the alternator.

Clarence

If the brushes were warn to where they were not making good contact with th3 slip rings, it would draw less current, not more. 

If the field circuit opened up from warn brushes, the regulator would do to full output, but it should correct as soon as contact is mad again.

have you seen a tripped breaker from warn brushes?

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10 minutes ago, N201MKTurbo said:

If the brushes were warn to where they were not making good contact with th3 slip rings, it would draw less current, not more. 

If the field circuit opened up from warn brushes, the regulator would do to full output, but it should correct as soon as contact is mad again.

have you seen a tripped breaker from warn brushes?

Yes, with the brushes worn down to the springs.

Clarence

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All I want to say is that you made a most excellent decision. Better to kick yourself on the ground because it turns out to be something small and harmless, than kick yourself in the air with a cabin full of smoke, and when it is going on in the air you don't really know which is which.  When you get to the PPP,  or the next PPP if you missed that one, they should have you teach a course in how to act to break an accident chain before it becomes an accident. 

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On ‎9‎/‎27‎/‎2018 at 5:30 PM, M20Doc said:

Yes, with the brushes worn down to the springs.

Clarence

I was thinking about this the other day. If the graphite was completely gone, the only contact between the voltage regulator and the alternator armature (field) would be through the bare spring and the slip ring. This would make a high resistance contact point. This could require the voltage regulator to go to its maximum voltage output to get sufficient field current to make the required output voltage. This could blow the circuit breaker.

Not doubting what you said for a second, just trying to get it straight in my head.

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When the carbon is gone...

there may be a small metal support plate remaining riding on the wires...

the extra wear of metal on metal is bad...

Of course, this comes from a generator on an m20C...

getting new brushes is cheap and easy compared to an OH of the alternator...

 

Jack,

Great decision. Resetting the CB once is good... having it cut out a second time is indicating that the problem is real...

There isn’t much sense in pushing the limit unless needed...

CBs trip based on heat... if the CB is worn, it may trip a little early under a heavy load... and even sooner when hot in the cockpit... and even sooner than that when hot, heavy load, and not allowed to cool since the first trip...

A sign of a worn breaker... the click isn’t as strong as a new or less worn breaker...

compare to similar CB switches in the panel... for feel.

PO thoughts only, not a mechanic...

Best regards,

-a-

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There is a procedure to check the alternator and regulator in the maintenance manual. I'd recommend having your IA follow it step-by-step. If you have old wires on your alternator, yesterday is the time to have them all replaced or it will ground you sometime when you don't want it to. 

For the want of a nail the shoe was lost,
For the want of a shoe the horse was lost,
For the want of a horse the rider was lost,
For the want of a rider the battle was lost,
For the want of a battle the kingdom was lost,
And all for the want of a horseshoe-nail.

Here's a story. My batteries in my Rocket were not healthy when I bought it. It would struggle to start. Eventually I remember hearing a cricket in my headset from the alternator -- likely a rectumfrier diode failed. Then I'd occasionally get a hi/low voltage indication, see a high discharge rate, and it would come back. Then the breaker tripped. IA diagnosed a bad Zeftronics regulator, which almost never fail. My guess is that the poorly performing batteries put excess charging load on the alternator, which had a diode fail, which caused the regulator to fail. The end result was new new Concorde batteries, a new alternator, and a new regulator. 

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Sounds like there is a short circuit somewhere in the field circuit causing it to full field.  This is something commonly done to test an alternator and it causes max current in the field circuit, which of course, would trip the breaker.  The short, of course, could be the regulator malfunctioning.

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41 minutes ago, MBDiagMan said:

Sounds like there is a short circuit somewhere in the field circuit causing it to full field.  This is something commonly done to test an alternator and it causes max current in the field circuit, which of course, would trip the breaker.  The short, of course, could be the regulator malfunctioning.

I believe the regulator will sacrifice itself to save your avionics stack. Bad alternator => blows regulator. 

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How's your battery and was it "run down" during start or prior to flight?  I ran a battery flat once and then started it up without charging the battery.  No issues until full power and then it would go for 3 min, and then pop the breaker.  It did this at reduced RPM until the battery was "charged" enough so it didn't need the full capacity of the alternator- about 40 minutes (on the ground).  Not my favorite thing I've ever done, but food for thought if the battery was low/old.  

More likely it's what others are saying with chafing/field/regulator/etc.  

 

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  • 3 years later...

Don’t mean to revive an old thread but I just had the alternator/gen breaker trip today on my m20e. Plane is getting a dual gi275 upgrade. Swung the nose last week for ahrs calibration and everything was running fine. Redid calibration today and breaker kept tripping. Only difference was the backup battery for the 275 was low due to battery test and plane batteries weren’t fully charged due to battery tender timing out. Would the added load of both those cause a trip?

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The 275 battery should be minuscule current draw. I have seen excess load trip the field breaker, so maybe the low ships battery could if low enough ?

The one thing I didn’t see trouble shooting wise is to check all connections, I don’t know why but it seems the field wire likes to fatigue right at its terminal crimp breaking several wire strands and that I believe could cause a tripped breaker as the regulator has to step up current to get enough through a bad connection.

I know why the wire fatigues at the crimp, just saying I don’t know why the field wire seems to do it so often.

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12 minutes ago, A64Pilot said:

The 275 battery should be minuscule current draw. I have seen excess load trip the field breaker, so maybe the low ships battery could if low enough ?

The one thing I didn’t see trouble shooting wise is to check all connections, I don’t know why but it seems the field wire likes to fatigue right at its terminal crimp breaking several wire strands and that I believe could cause a tripped breaker as the regulator has to step up current to get enough through a bad connection.

I know why the wire fatigues at the crimp, just saying I don’t know why the field wire seems to do it so often.

So on mine it’s the 50a “generator” breaker. Previous owner did the alternator stc. Not sure if that’s what you mean by field wire or if it’s a different one. When we ran it on Thursday, everything was working fine though

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On 9/28/2018 at 1:31 PM, mooniac15u said:

FWIW, the FAA recommends against repeatedly resetting circuit breakers in flight due to the risk of electrical fire.

https://www.faasafety.gov/files/notices/2009/Dec/SAIB_CE-10-11.pdf

 

It’s only a recommendation though.  I carry a big roll of 100 mph tape and any breaker popping is getting taped down.   

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Working on a weird issue on a 1994 28 volt J model.  Alternator seems to work fine, but on shut down turning off the field switch causes the field circuit breaker to trip.  Reset the breaker and is stays set.  It does this with or with out the engine running.  Replaced the breaker due to the number of times that it’s tripped, thinking the internal spring may be getting weak.  The new breaker didn’t change anything.

Thoughts?

Clarence

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2 hours ago, M20Doc said:

Working on a weird issue on a 1994 28 volt J model.  Alternator seems to work fine, but on shut down turning off the field switch causes the field circuit breaker to trip.  Reset the breaker and is stays set.  It does this with or with out the engine running.  Replaced the breaker due to the number of times that it’s tripped, thinking the internal spring may be getting weak.  The new breaker didn’t change anything.

Thoughts?

Clarence

The field CB supplies power to the voltage regulator. The field switch supplies power from the voltage regulator to the F1 terminal on the alternator. There is also an ALT SENSE CB that connects the battery bus to the remote sense terminal on the voltage regulator. Some fault in the voltage regulator might be the issue. I would try pulling the ALT SENSE CB (which is the only power connection to the voltage regulator when the field switch is OFF) and see if that keeps the field breaker from tripping.

Skip

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