Amp meter needle jiggle

cgrab

cgrab

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cgrab
On my flight today I noticed the amp meter needle moving back and forth rather rapidly around zero. Is this an indication of something amiss? Background: '68 Cardinal, O-320, 150hp, original Cessna meter-about 4500 hours on the frame and 300 on the O/H engine.
 
Mine does this and I was told to not worry about it by my mechanic. Never been an issue for me in 3 yrs. Curious to know what other folks have to say.
 
Google "galloping ammeter".

It can be caused by increased resistance in older connections and components in the charging system.
 
Tail strobe current drain? I doubt a needle could respond to a bad alternator diode. It could also be caused by the rotor brushes in the alternator being nearly worn out.
 
An open alternator diode can cause noise in the headset and reduced alternator output. A shorted diode will cause a much-reduced outout and maybe battery drain.It's not likely to cause ammeter jiggle.

A loose connection at the alternator can cause ammeter jiggle. Engine vibration shakes the alternator and disturbs the loose connection, causing a make-and-break that interrupts the current flow. It doesn't much matter whether it's the field wire or output wire, either. Or the regulator has loose connections, or the regulator itself is loose on the firewall or whatever else it's mounted to. Or the alternator is loose on the engine's mounting bracket.

I think it needs looking into.
 
Happened right before I lost the alternator on a night flight. Turned out to be corrosion causing high resistance at the terminal on the alternator. Ended up burnging through the wire.

Sad thing is an A@P had just worked on the connection a few weeks before. Grrrrrrr........
 
Could always be the simple answer of a failing ammeter, too :)

I imagine the most appropriate response would be to inspect the alternator, ammeter, shunt, and leads.
 
mkosmo said:
Could always be the simple answer of a failing ammeter, too :)

I imagine the most appropriate response would be to inspect the alternator, ammeter, shunt, and leads.
Click to expand...

Especially the connections. A little corrosion or a little loose will raise havoc on a low voltage system. (Or even a high voltage one.)
 
Keep in mind with all of the talk about loose connections: the most dangerous effect of a loose connection is significant heat. A high amperage connection that is loose will generate LOTS of heat, and potentially a fire.

I don't think this bears going into full panic mode, but I know I would certainly feel better after checking all of the alternator, battery, and bus connections, just to be sure. I'd care a lot less about losing power... it's the fire I'd be concerned with.
 
Steve Costello said:
I don't think this bears going into full panic mode, but I know I would certainly feel better after checking all of the alternator, battery, and bus connections, just to be sure. I'd care a lot less about losing power... it's the fire I'd be concerned with.
Click to expand...

Correct. I got lucky that night, not because I successfully diverted and landed in the dark, but because I didn't have an inflight fire.
 
I would check the wiring connections on the meter and shunt first.
 
Cessna put out a service newsletter (SNL85-24) back in 1985 that dealt with a "flickering or nervous needle". The newsletter cited loose connections in the regulator or field circuits. Other causes cited were high resistance across the alternator contact half of the split master switch, or field circuit breaker.
 
Mine did this, especially under load. There were no issues with connections. Turned out to be a bad voltage regulator.
 
Thanks for all the help, I'll pull the cowl and check all the connections. I haven't looked at the service manual but I'm sure it is all laid out nice and neat in there. Ha.
 
I've seen this with a bad split master switch. A jumper across the alt field portion of the switch will tell if it's the switch.
 
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