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I think my Alternator is Broke

John Tierney

Well Known Member
Sponsor
I need to tap into the VAF brain trust to point me in a direction for further troubleshooting or replacement.

I’d been having an odd electrical issue, usually after touchdown while taxiing to the hangar, where the Alternator (Plane Power AL12-EI60/B) would drop offline and not charge the battery (0 to 5 amps max). Well on Sunday just after starting the charging system failed, so I’ve been troubleshooting. All connections seem solid.

Here are some findings:
Battery Voltage (nothing on) = 12.31 V
Bus Voltage (Master On) = 12.23 V
Alternator Field Voltage (at Alt. Plug) = 12.21 V

It looks like the problem isn’t field voltage, so I checked the Alternator rotation; pulled off the belt and turned the pully by hand. There were no bearing or other awful noises, and the shaft seemed good.
Cleaned up the pulley (found a little oil/grease in the groove), reattached the belt and checked belt tension (read VAF historical documents on belt tension). Started the engine, and again no charging.

I ran through the Plane Power published troubleshooting guide. The engine/alternator has 129 hours since 2019.

Should I bother taking the alternator to a local auto shop for testing, or go directly to Plane Power?
If it needs replacement, I would like opinions on alternate Alternator.
 
Battery?

My first check would have been the belt like you did, then if my battery was over a year or two old, I think I would order a new battery. I have had to replace my pc 680 twice so that would be my second check. After that, I would try taking the alternator to a shop and see what they say.

Good luck.
 
Take a good look at and around the connector where the field wire attaches to the alternator. That has been a trouble spot for some. Make sure engine to airframe ground wires are intact. Otherwise, it sure looks like the alternator. Even at idle power the buss should come to 14.2 (+- 0.2) volts.
 
I had a bad PC-680 wreak havoc with my alternator once. Kept causing all kinds of random issues.
 
You should verify it is the alternator, and you are close.

Call Plane power with your serial number and ask for a RMA for a new one. Save $900.
 
The regulator controls alternator output by varying the current sent to the alternator field coils - and this is done by varying the voltage presented to the field coil, and the amperage follows Ohms law. If you are seeing near-full system voltage at the alternator field coil connector, but not getting full output from the alternator, then you have either an open field circuit inside the alternator, or you have a connector failing to make contact with the field circuit.

I would suggest you test this by putting a wire connected to the field circuit connector in a place where you can measure that voltage (reference to ground) in flight with the engine running. Normally it would be in the 5-8 volt range with most systems holding stable on a 14 volt bus - if you are seeing voltage on that pin at or near the full battery voltage of 12 volts with no charging taking place, then you have your answer - the regulator is feeding all the power it can to the alternator, and the alternator can't use it.
 
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I had two alternators from plane power produce identical systems you are experiencing.
It was determined to be burnt diodes on the bridge rectifier. Plane power was unable to help citing they do not repair alternators.
If you take the back cover off you should be able to determine if any of the diodes appear or smell burnt.
I went on line and ordered two bridge rectifiers and installed them, now both alternators are working fine.
Part number to replace is INR724 and can be ordered from alternatorparts.com.
I did order some cheap ones from eBay, but they were poorly reconditioned parts where alternorparts.com shipped new ones priced at 48.00 plus shipping.
 
You should verify it is the alternator, and you are close.

Call Plane power with your serial number and ask for a RMA for a new one. Save $900.

What Bill said. Certain alternators built prior to 2019 may be replaced free of charge when failure is related to specific issues. Please note I did not say "all", nor do I speak on Hartzell's behalf.

But first...

The plug problem is well known. There is no wire support. The wire fatigues at the socket crimp, or the socket wiggles in the plug body and frets the contact surfaces. Electrical connection becomes unreliable. Plug kits here, with wire support: https://www.ksvlooms.com/products/t...tor-connector-kit?_pos=1&_sid=b579bd566&_ss=r

At every annual, or given any sign of a problem, remove the alternator, clamp the pulley in a good solid vise, and rock the brush end back and forth. Any movement is a rear bearing cavity enlargement failure in progress. I've personally experienced this particular failure twice, on two different airplanes with different engine models and very different belt tensions. The problem is is well known at Hartzell.
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I pulled the alternator and took it to a local automotive starter-alternator-battery shop. They confirmed that it was not producing volts.

Called Plane Power/Hartzell support and when I described the problems, and the serial number (2011 Alt. build but airworthiness not issued until 2019), the support person agreed to send me a brush/regulator assembly to try. I will report back on the results.
 
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