Alternator dying or dead - or is it something else entirely??

[chris mitchell]

I have previously posted a couple of times about my alternator problems:

http://www.vansairforce.com/community/showthread.php?t=58550

Quick summary is that I have a PlanePower alternator on a Superior IO-360 in my RV-8. After about 15 hours I started having trouble with the field breaker blowing e.g. while doing mag checks, but also more directly related switching like lights or strobes. Only once did the CB blow apparently spontaneously ie with no other switching going on. It was always possible to reset and proceed without further incident. Over time I have changed the CB itself, all the field wiring and the master switch. Like all the best intermittent faults I would think that it was fixed but a couple of hours later it would be back. My most recent change came when I noticed that the field wire was loomed with the fat wire to the starter solenoid over a distance of about 3 inches - I put the field wire on some little standoffs so that the distance was increased to about one inch. Seemed good - every thing was fine for two flights.

Plane is now at 95 hours airborne time. Saturday morning after a flight lasting 1 hour 20 mins I got a flickering low voltage light for about 10 seconds, then solid illumination. Voltage seen on the Dynon at that point was IIRC 12.0 or so. After landing (about 5 minutes later) it was clear that there was no charging i.e. the ammeter readout on the Dynon was -2A with everything off except the master solenoid, rising as one would expect with additional items switched on. Tried master switch fully off then back on, resetting CB with no change in status. Checked belt tension - fine, verified that the field was indeed supplying 12volts (voltmeter plugged into the alternator end of the wire, master switch on, obviously with the engine off.

Left everything a couple of hours so that anything hot could cool off, restarted engine, still no output.

Question: I conclude alternator is dead. Am I right?

Replaced with a Vans alternator, gave battery a quick charge (PC680). Started engine - got an output but LOTS of whine form the new alternator, even with engine off. Amps out fell as the battery continued to charge, but was jumping around a lot.

Question 2: Is it likely that I have damaged the battery? I am told that the PC680 is very tough but the very variable current is not like anything I have seen previously before.

Wiring is basic VFR a la Nuckholls (?sp?).

Any thoughts will be appreciated. Feeling a bit desperate...

Thanks

Chris

 

[Tom Martin]

I would start by letting the battery charge overnight. Odessey reccomends using a specific style of charger for their batteries. Perhaps this is not necessary but I followed their advice.
With a fully charged battery, reading 13.1 to 13.3V resting, go fly the plane and see what happens. You should see 14.1 or .2 volts when alternator is working.
If you do not feel like sending your 1st alternator back take it to your local automative alternator/starter shop and have them test the unit. They can load the unit and see how it reacts.

 

[chris mitchell]

For what its worth I have done a few tests.

Thanks Tom. The Odyssey PC680 is now fully charged without any problems using a C-TEK charger as per Enersys recommendations.

Turning to the alternator ? there is continuity through the field circuit, checked with a test meter at 1.5 volts, i.e. meter between field wire and alternator case. Put 12 volts across the field ? confirmed current is flowing by wiring via the meter ? absolutely no sign of magnetism at the spindle of the pulley ie it won't hold a small screwdriver or even a small bolt - it really out to be detectable there. Repeated without the meter in the circuit ? definitely no magnetism. Verified that the screwdriver and bolt are indeed ferrous.

From my limited knowledge the only way to generate this result would be a short circuit between field supply (somewhere within the casing) and ground either before the brushes or else within the field winding itself.

Guess l'll find an auto place with a test bench tomorrow to verify that the alternator is dead. Then back to the plane, reinstall the battery and see if the new alternator behaves properly. Maybe I just have two dud alternators.....

Chris

 

[Steve Sampson]

? there is continuity through the field circuit, checked with a test meter at 1.5 volts, i.e. meter between field wire and alternator case. ....

Chris I find it quite hard to visualise your set up, but could you have a poor joint somewhere in the field current cct so that while you are seeing the voltage it is NOT allowing any significant current? I think this would result in the symptoms.

Also, do you have anything in the aircraft that draws a tiny current when the master is off. eg a direct feed to a gps backup battery or something?

 

[chris mitchell]

Thanks Steve,

Just to clarify, the alternator is out of the plane and on my work bench. I was checking the field using a 12 volt car battery which is fully charged -the should definitely be enough amps to magnetise the core.

I am going back to the hangar now (at least its a nice day!) to reinstall the battery, run the engine and see what is happening with the new Vans alternator. With the master off there is no current drain as every thing is isolated. I can remove the wires for the two supply busses which will leave the charging circuit only and will check everything again - if OK I'll add things incrementally......

Chris

 

[Steve Sampson]

Chris, hopefully everything is back to normal and you and back up and running again. Otherwise, I have a few observations. Take them as you want.

Are the tests you are running from basic knowledge of electricity or are they diagnostics for your particular brand of alternator? The reason I ask is because many modern auto alternators have so much intelligence on board, probably more than the first space vehicle I was party to, there is very little I would try to deduce about the thing when at rest from the outside, without a diagnostic guide of some sort. Perhaps you have such a thing, in which case I will shut up.

I knew a lot about motors and generators 40 years ago, I had a degree in the subject, but it was not worth a **** when I came to try to work out a problem with the altenator on my -9a. The onboard IC confused everything.

A few observations:

- you have charged the battery. A good first step. Dont worry about it just check that it is holding the appropriate voltage after it has been quiescent for >24 hrs per the Odyssey docs. when you have everything back up and running; no hurry. They are VERY rugged and it wont give up easily.

- unless you know how much field current should be flowing at stationary I would make no conclusion. The onboard intelligence might choose to limit or even turn it off, though you indicate that is not the case. (I have no idea what degree of on board control exists in your alternator.)

- I would not expect the spindle of the unit to be magnetised with field current flowing. Do you think it should be a N pole or a S pole? If designed perfectly (impossible) all the flux lines are flowing at 90 deg. to the axis of the shaft, so they cut through the stator windings. Perhaps simpler to visualise if you think about what you would expect if you touched your ferrous screwdriver to the middle of a bar magnet: nothing.

- if you think you have two dud alternators I would put my money on my first suggestion, an external wire joint problem.

I hope that's a help not a hindrance. Good luck.