Flickering Amp meter

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MountainDude

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Intermittent behavior: the amp meter needle flickers to the right (charge). This only started happening after the last annual and has never happened before. During the annual, I got a new starter and a taxi light bulb (no idea if this could be related). We checked the battery connections and all is good.
Sometimes this flickering does not show up for several hours, and sometimes it's very frequent.
Here is a short video of the needle flickering:

IMG_3340.MOV

drive.google.com drive.google.com

Any ideas what how to troubleshoot?
 
Look for a loose wire or corroded connection somewhere in the charging circuit, or a bad ground, possibly the engine ground. It could be the alternator or voltage regulator is going but I'd bet on something disturbed during the annual. The taxi light wouldn't do it if it doesn't happen when switched off, ditto for the starter.
 
I had that flickering needle once, turned out it was a poorly made crimp on the positive power wire terminal that attaches to the alternator output stud. It was maybe five minutes from when the flickering started to when the terminal/wire melted through and I lost alternator power.

No other damage but it did result in a night diversion over the mountains of WV. The battery lasted me most of the way to the landing, the lights went out right as I rolled out onto final at the diversion airport.

No Cessnas were harmed during the making of this event.
 
You are going to have to determine if the needle is telling you the truth or not. A charge/0/discharge
ammeter is not the most precise meter to troubleshoot with. If you put a good voltmeter on the system and see a voltage spike along with the meter movement, then I'd say the alternator regulator is becoming unreliable and throwing over-exitation spikes. No voltage spikes? Likely a meter going bad.
 
Bell206 said:
Does it continue to flicker on the ground once it starts?
Click to expand...
I do not pay attention on the ground, but it's very intermittent, so I would be surprised if it flickers during the 3 min taxi to the hangar.
 
MountainDude said:
I do not pay attention on the ground, but it's very intermittent, so I would be surprised if it flickers during the 3 min taxi to the hangar.
Click to expand...
If it does flicker on the ground, perhaps taxi around a little longer and turn switches on/off or pull CBs if possible, and see what happens to the flicker?
 
MountainDude said:
Any ideas what how to troubleshoot?
Click to expand...
I made a high-tech troubleshooting device for such stuff. It's a piece of half-inch plywood about three inches by ten, with several screws in it, lined up left to right. Long wires (like ten feet long) are soldered to those screws. One wire goes to a good ground. Another goes to the alternator field terminal. A third goes to the regulator field terminal. Fourth to the battery positive. You sit in the pilot's seat with it in your lap and take measurements using an analog voltmeter.

The battery voltage should remain solidly stable, except maybe for a small drop at low idle with lots of lights on. If it flickers there's a problem that can be found by measuring the voltages at the other screws. The field voltage should rise at low RPM and fall as the RPM rises. If it flickers any time, it's either a bad regulator (as noted at the regulator terminal) or bad wiring between the regulator terminal and alternator terminal (flickering at the alternator).

A picture of the regulator would help. If it looks like this......

1736009967796.png

......it's an old electromechanical type, and uses a relay that buzzes constantly to regulate field current flow. The relay contacts get burned and rough and can stick briefly, overvolting the system a little and making the ammeter jumpy. The overvolt condition isn't big enough to make the overvolt sensor shut the regulator off.

And like others have said, loose or dirty or oily or corroded crimp connections are a common source of trouble. Everything in that system need a close look, including at the back of the ammeter. Everything. Alternator switch and breaker and their bus connections, alternator output breaker, everything. Looking is cheap; replacing stuff until the problem goes away is NOT cheap.
 
Check the alternator field wire for a bad crimp and internally broken conductors which is not apparent from the outside. You may simply want to replace the connector prophylactically an be certain the crimp is good. Internally, the conductors often work-harden from incessant vibration. Mucking about may have broken the last tenuous strands, and vibration is making intermittent contact.
 
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Domenick said:
Internally, the conductors often work-harden from incessant vibration. Mucking about may have broken the last tenuous strands.
Click to expand...
If the last strands broke, the alternator wouldn't be charging at all. The ammeter would show a steady discharge. More likely that there's a connection that's intermittent, and comes on once the connection warms up. A connection will heat up due to resistance from oxidation and poor contact.

It might be something as simple as an old alternator switch with oxidized contacts. It would be cutting the regulator in and out, which switches the alternator on and off. Like I said, everything needs looking at.
 
See the post above. Bad contacts on the alternator will do this. If your mechanic has a jumper wire with alligator clips jumper the switch and see it it goes away.
 
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