alternator

[bobnoffs]

a month ago my alternator quit charging. it is a n.d. 40 amp , internal reg. and 40 hrs on it. i took it to a shop and the regulator was replaced. i reinstalled it and it put out 14.1 volts again. before a flight i taxied it a little and after a minute it wasn't putting out anything that would show above 13 volts[ batterie's charge]. i ran it up to 2700 rpm [honda engine, redline 55oo rpm] and it started putting out 14.1 volts again. after it sat at the hangar a bit i ran it up to 3500 rpm and no output.
t.t. on the plane is 40 hrs. in all that time it has never put out anything but 14-14.2 volts. and it has always done this at 1700 rpm.
i have checked everything..field wire, relay function in the ovm circuit,etc. i am convinced this is in the alternator. the alt. has had its model number removed so i don't know what model it is. here's my question........the shop has a good reputation. they didn't spin it but tested all components electrically and said all was good but the reg. was bad. can an alt. be tested without actually spinning it? should i just order another alt.? without a model number it's tough.

 

[lr172]

alt stops outputting at 40 hours - odd. Reputable shop tests and repairs with new regulator and it works for a few minutes, then fails again - even more odd. I suppose it is possible that you have just had really bad luck here, but I would not go to round 3 with the alternator before I was absolutely sure that there was not some other issue with the wiring or installation that was causing this. It is quite possible that there is an issue somewhere in the alt that is blowing up the regulators and the shop didn't properly test to identify it. I don't rebuild alternators for a living, but I would expect a shop to look for other internal problems when seeing an IR die at 40 hours, as that is quite unusual. Usually it either fails in a few seconds / minutes or lasts many 100's of hours, with failures between those points rare. That doesn't mean he did it though. Not sue if one can properly test an alternator without spinning it, but my guess is you can't. Pretty sure you also have to heat them up to identify insulation cracks/failures in the windings that cannot be seen when cold.

Not sure I would bring it back for more repair, but would instead work harder at finding a suitable replacement that fit.

 

[qtrmiledan]

ND alternator

If you can find the application and maybe check rock auto and can find an actual ND brand (they’ll usually have numerous brand options) Nippon Denso will be the best quality you can buy IMHO.

 

[bjdecker]

Hang an ammeter current sense around just the field wire between the ALT Field switch and the Alternator connector.

Prove that current is flowing in the wire when it's supposed to be.

We've all seen cases where the field wire has failed open right at the pin in the connector, inside the wires plastic jacket.

 

[N49ex]

Hang an ammeter current sense around just the field wire between the ALT Field switch and the Alternator connector.

Prove that current is flowing in the wire when it's supposed to be.

We've all seen cases where the field wire has failed open right at the pin in the connector, inside the wires plastic jacket.

That said, yes I've also lost an alternator (on an IFR flight!) due to the field wire breaking at the alternator connector.

Two things done in repair and no problem since: 1) Splice in/replace the last few inches from the last support of the field wire a section of high count fine strand silicone insulated wire (Not a typical aviation item, but more flexible and less likely to break; and 2) At the alternator field connector, there are usually two field connections - Use both of them and Y them into the field wire (with the same fine strand silicone wire).

 

[bobnoffs]

today before i dug into the alt. again i did tests on the ovm and the relay it controls on the b line. although everything tested ok when the problem started. today the relay was not activating and completing the circuit when it got its 12 volts. i probed the relay at its male faston connections and got 12 volts at the pos. and continuity to the airframe at the neg. connector. the contacts remained open.
way easier to fix than the alt.
intermittant electrical problems are the scourge of everything.
i have had an electric dog fence that i have maintained for 25 years. for the past year it intermittantly signals''open loop''. a dozen times now the warning goes away before i can find the problem. yes, i have even replaced the transmitter. anyway....