Intermittent charging issue

[deaston]

I fly a friend's 1998 C182S. He allows several to fly it, so it gets regular use by multiple people, but for some reason, the charging system likes to act up when I fly it.

The first time it happened was on the way home from a short XC. I noticed that the ammeter was showing slight discharge. Thought it was instrument error, but shortly the Aspen reverted to battery power. I unplugged a 12V cigarette lighter charger and everything went back to normal. "Bad Plug" I told myself... After pulling the charger out of the socket, ammeter jumped up to charging significantly (I had already pulled iPad and stratus off of charger). Owner tested the adapter for a short, but found none. Had battery replaced (it tested marginal/bad).

A couple of weeks later, I was waiting for temperatures to come up after start and noticed that the ammeter discharging again. Nothing was plugged into cigarette lighter port. I cycled the Avionics switch and it went back to normal. Hmmm.....

A couple weeks after that, I was outbound on a longer XC and it happened again in flight. I pulled out the 12v charging adapter but it didn't fix it. I started turning electrical load on and off, and cycled avionics master. Finally fixed it by cycling the master. Starting bringing things back online (avionics, Aspen, radios, 530, transponder, etc). Noticed it tarted discharging again. Cycled the master again and then left everything off that I didn't need. Completed the flight without incident. On the way home, slowly brought everything back online and no further problems.

Keep in mind that during all this, others including the owner are logging many hours without incident. They are all looking for it and trying to reproduce it too. Finally the owner told me today it happened to him. He plans to replace the voltage regulator on Monday.

Long story short, does that sound like the right diagnosis? Any other thoughts or suggestions for how to reproduce the problem or pinpoint the cause definitively? I hate problems that you can't duplicate because you end up throwing money at it and you never know if it is really fixed. It just goes away... until it comes back at the worst possible time.

 

[Stewartb]

I had that exact problem for years in my 180. Changed the regulator, then the alternator, traced every wire and checked every wire termination. Mine would cycle off and ultimately no matter what I tried it would come back on-line randomly. I thought I'd found the issue a couple of times but it turned out to be coincidental because the action wouldn't work the next time. I had two of the best aviation electrical guys around scratching thier heads. About 5 years ago I did a panel and interior upgrade and with that re-wired to entire airplane except the wings. I decided to go with a field approved B&C alternator and linear regulator because the certified stuff wasn't very impressive. Problem solved. We all figure there must have been some old wire with a compromised insulator that was causing the problem. Removal revealed many wires with cracked jackets on the engine side of the firewall and concealed in the wire bundle that comes into the cabin through the firewall. Nothing lasts forever.

 

[Dan Thomas]

Nothing lasts forever.

But a 1998 182 shouldn't have aging wiring just yet. I would bet that the alternator brushes are shot and that a new regulator won't fix it.

 

[deaston]

But a 1998 182 shouldn't have aging wiring just yet. I would bet that the alternator brushes are shot and that a new regulator won't fix it.

Would failing brushes cause the alternator to just stop charging intermittently? To me the behavior looks like it just stops charging for some reason, and then changing the amount or state of electrical load will get it charging again. It seems pretty binary - either it is charging strongly, or not charging at all. Yet I can't make seem to make it stop charging on demand...

 

[Dan Thomas]

Worn brushes cock in their holders and will stick a bit and lose good contact with the slip rings. They can't transmit power to the field consistently and so the output is erratic and limited, leading to the conditions you decribed.

Those conditions can also be caused by too much grease in the rear bearing. Kelly and other rebuilders have been bad for that. The excess grease gets squeezed out when the alternator is assembled, and it flies onto the slip rings and gums them up with residue from the brushes, creating a resistive layer that limits field current and therefore output curent. As the rings and brushes heat up it gets worse. It's easy to isolate that: disconnect the field wire at the regulator or alternator and measure the field resistance while turning the propeller a bit. It should remain steady at about 6 or eight ohms (24 volt system) and not be way up at 20 or 30 ohms and/or jumping around.

 

[coloradobluesky]

Gotta be either wiring/connections, voltage regulator, alternator or battery. Have I left something out? Batteries tend not to be intermittent though, and they get worse over time.

 

[Skip Miller]

Exact same symptoms in an Archer II. Replaced the alternator;no further problems. It is a club plane andI am not aware of any exploratory work done inside the old alternator.

Avoid Kelley. Very bad history over on the Red Board.