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Posted
13 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

Hang on?!? Clarence is asking Mooneyspace a question? Where is @M20Doc and what have you done with him?

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Posted
1 hour ago, LANCECASPER said:

Hang on?!? Clarence is asking Mooneyspace a question? Where is @M20Doc and what have you done with him?

I never profess to knowing everything.  I come to share what I can and learn what I can.

Clarence

Posted
12 hours ago, PT20J said:

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

Hi Skip,

You nailed it with the Alt Sense breaker, now a little more digging into the VR.

Clarence

Posted
On 6/13/2022 at 7:44 PM, drifter001 said:

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

On yours you have either a bad breaker, or you were pulling in excess of 50 amps.

‘Do you know the output of your alternator? If it’s in excess of 50 amps and you battery was low enough then it could happen, and nothing is broken.

If that’s it, don’t just put a bigger CB in without verifying the wiring can handle the higher amperage

Field wire is the little control wire, it’s how the voltage regulator, regulates voltage

Posted
1 hour ago, M20Doc said:

Hi Skip,

You nailed it with the Alt Sense breaker, now a little more digging into the VR.

Clarence

It's probably some failure of the over-voltage protection circuit in the voltage regulator. From the description in the POH, the OVP circuit uses a "crowbar" relay to pop the field breaker to shut down the alternator.

Skip

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Posted
8 hours ago, PT20J said:

It's probably some failure of the over-voltage protection circuit in the voltage regulator. From the description in the POH, the OVP circuit uses a "crowbar" relay to pop the field breaker to shut down the alternator.

Skip

Skip do the 12v Js have the same sense circuit? I think I only have an ALT field CB on my 12v 

Posted
56 minutes ago, bradp said:

Skip do the 12v Js have the same sense circuit? I think I only have an ALT field CB on my 12v 

I don't think so, but to know for sure you'd have to look at the schematic for your serial number. My 1978 J was 12V and had an OECO voltage regular with no external sense line. My 1994 J is 28V and has a Mooney voltage regulator with the sense line.

Skip

Posted
14 minutes ago, PT20J said:

I don't think so, but to know for sure you'd have to look at the schematic for your serial number. My 1978 J was 12V and had an OECO voltage regular with no external sense line. My 1994 J is 28V and has a Mooney voltage regulator with the sense line.

Skip

Additionally ( I’m nowhere near as good at this as skip), but some aftermarket VR (like zeph) may have the sense line but not need it hooked up depending on how the original airplane is wired.  So it can be confusing when you read about the vr having that circuit but it’s not connected?

Posted
4 minutes ago, Ragsf15e said:

Additionally ( I’m nowhere near as good at this as skip), but some aftermarket VR (like zeph) may have the sense line but not need it hooked up depending on how the original airplane is wired.  So it can be confusing when you read about the vr having that circuit but it’s not connected?

Good point. :)

Posted
On 6/17/2022 at 8:49 AM, A64Pilot said:

On yours you have either a bad breaker, or you were pulling in excess of 50 amps.

‘Do you know the output of your alternator? If it’s in excess of 50 amps and you battery was low enough then it could happen, and nothing is broken.

If that’s it, don’t just put a bigger CB in without verifying the wiring can handle the higher amperage

Field wire is the little control wire, it’s how the voltage regulator, regulates voltage

Ended up being low voltage on the battery so it was overloading the alternator as it tried charging the batt. Battery tender avionics shop has only produces 4amps and seems like the power and avionics draw is higher so it’d slowly trickle the battery down as he was configuring stuff

Posted
1 minute ago, drifter001 said:

Ended up being low voltage on the battery so it was overloading the alternator as it tried charging the batt. Battery tender avionics shop has only produces 4amps and seems like the power and avionics draw is higher so it’d slowly trickle the battery down as he was configuring stuff

You have a problem though, your alternator can produce more current than your electrical system can accept.

I’d look into increasing the CB size, often that means bigger wiring, but usually it’s not that big a deal

Posted
On 6/16/2022 at 3:38 PM, 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

Please let me know if you solve this. I've had this issue for years on a 1993 J, and I gave up trying to fix it. One A&P did fix it, for a matter of months, by if I remember correctly, replacing a diode.

Posted
10 hours ago, A64Pilot said:

You have a problem though, your alternator can produce more current than your electrical system can accept.

I’d look into increasing the CB size, often that means bigger wiring, but usually it’s not that big a deal

Alternator was putting out the power nut it’s only a 50amp breaker so that’s why it tripped. Running with avionics I only see 10 amps max

Posted
11 hours ago, drifter001 said:

Alternator was putting out the power nut it’s only a 50amp breaker so that’s why it tripped. Running with avionics I only see 10 amps max

Exactly, if it’s a 60 amp alternator (example only) and the breaker is a 50, you should fix that. Otherwise anytime you may find yourself with a depleted or just a bad battery, you will find yourself with no alternator output, and a low or bad battery, a double whammy, which could cause problems. No nav or comms and no lights / pitot heat.

All it takes to get you in the hole is a stubborn to start motor, or extended taxi with landing lights and pitot heat on. I’ve had it happen, the extended taxi with lights and pitot heat on depleted the battery as at taxi speeds the alternator couldn’t keep up, once you takeoff the alternator goes to full output and if that exceeds the 50 amp CB, it opens. It was night VFR, I turned everything off and luckily that was enough to drop the requirement to less than the rated CB rating, and after a few minutes the battery recharged and allowed me to turn everything back on. Watch the ammeter to know when.

I later learned something else from that event, I had a Gill wet cell battery, that boiled out some acid from that big charge and the acid went out the tube supplied for that purpose and bleached out paint on the belly, so even though it was all my fault and the battery operated ad it should, I won’t buy another wet cell aircraft battery

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