BaldEagle

Electrical gremlins -- alternator?

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Hi all,

Thought I'd reach out to the forum before I call the shop in the morning.  I was 15 mins out from home base this afternoon and the Aspen PFD starts running off battery and the Low Voltage light is flickering.  Ammeter was showing a very small discharge.  The only other odd behavior is that all of the CHTs on the EDM 700 was showing zero.  I didn't have a lot of time to diagnose: power cycled the Aspen, would run fine for a minute and then would start running off battery again and low voltage light would flicker again.  Pulled the alternator circuit breaker, recycled after a minute, same symptoms, same after pulling Aspen breaker.  When the low voltage light went out the temps started rising on the JPI, and then back to zero when the low voltage light came back on.  This all happened at cruise power settings.  I'm guessing it's the alternator or voltage regulator, but I'd be grateful for any suggestions.  Main battery was replaced a couple of weeks ago.

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You may get lucky and find its just a corroded/ loose contact on the alternator (it was for me).  Check the alternator belt tension also.   Assuming its a Plane Power, the install manual has a detailed troubleshooting procedure- it should be followed before pulling the alternator.  Also note the Aspen pfd will revert to battery with only a small drop in bus voltage - something like 12.3V 

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Hi all,
....Pulled the alternator circuit breaker, recycled after a minute, same symptoms, same after pulling Aspen breaker.

Did you reset the field CB or Alt output CB.
The field is one you want to reset.
But it could be anything including a broken field wire at the alternator.



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7 minutes ago, kortopates said:


Did you reset the field CB or Alt output CB.
The field is one you want to reset.
But it could be anything including a broken field wire at the alternator.



Sent from my iPhone using Tapatalk

Alt. Field

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Good news is that these are usually fairly quick to diagnose. Hopefully it's just a bad/broken connection.


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2 hours ago, BaldEagle said:

Hi all,

.  The only other odd behavior is that all of the CHTs on the EDM 700 was showing zero. 

bad loose ground.  Start at the battery.   Make sure all connections are shiny bright.  Check engine ground strap.

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3 hours ago, DXB said:

 Assuming its a Plane Power

Kelly Aerospace, who I’ve never heard of.  The replacement original listed on Spruce is a Hartzell, with the same part number.  I think my alternator may be rather old.  I did drop the lower cowling this afternoon and poked about, nothing obvious and all the connections to the back of the alternator looked good (nothing broken or loose).  I’ll get it booked in to an avionics shop to get a diagnosis.  I’ve been out of the airplane ownership thing for a while, and the one thing that used to have me pulling my hair out were electrical issues :wacko:

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Kelly aerospace was bought by Hartzell. Its the same company in Alabama, the same employees who cant read, spell, or put accessories together correctly.

Edited by jetdriven
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1 hour ago, BaldEagle said:

Kelly Aerospace, who I’ve never heard of.  The replacement original listed on Spruce is a Hartzell, with the same part number.  I think my alternator may be rather old.  I did drop the lower cowling this afternoon and poked about, nothing obvious and all the connections to the back of the alternator looked good (nothing broken or loose).  I’ll get it booked in to an avionics shop to get a diagnosis.  I’ve been out of the airplane ownership thing for a while, and the one thing that used to have me pulling my hair out were electrical issues :wacko:

My first choice would be an A&P that's good at airframe electrical. An avionics shop would likely swap new parts in - if they'll do the job. These are repairable if you have the patience and not in a hurry. I recently had my rotor in an my alternator short out, but .25 AMU's later I had it repaired with new rotor, brushes and bearings versus over 1 AMU for a replacement alternator.

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10 minutes ago, kortopates said:

 An avionics shop would likely swap new parts in - if they'll do the job.

One local avionics shop wouldn’t take 3 AMU from me for an Aspen Max upgrade.  I know they’re all no doubt overwhelmed with the ADS-B mandate and 2020 coming up, but that was a bit surprising.  And I’ll be lucky to see the upgrade this side of Christmas.  Another shop did take my money, but they made it quite clear that they’re not hurting for business.  Good for them.  Aviation is a really weird industry.

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With the cowls off, turn on the battery master and alternator field switches.  Go the the front of the alternator, the pulley retaining nut should be a strong electromagnet.  If it’s not measure field voltage at the field terminal, it should be very close to battery voltage.

Look for broken, lose or damaged wires and terminal ends on the field power, field ground and output terminals.

How many hours on the alternator? Brushes do wear with time, brush springs fail, brush leads fail, all of these are checked or replaced without alternator removal.  

Clarence

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13 hours ago, Yetti said:

bad loose ground.  Start at the battery.   Make sure all connections are shiny bright.  Check engine ground strap.

I agree.  The loss of those sensors makes it look like a grounding issue.  The engine ground strap is a likely culprit since it was affecting engine sensors and the alternator.

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