Fluctuating voltage, panel lights bright-dim-bright, ammeter needle swinging

[65C_flier]

2 hours ago, Ragsf15e said:

My ammeter has a slight oscillation with the strobes on, but none with them off.

My ammeter oscillates slightly (1/2 needle width or less) even with engine off and all systems (including strobes) off. Needle jumps wildly when systems are turned on (with and without engine running) before quickly settling to the slight oscillation.

5 hours ago, Smiles201 said:

If no voltage drops, suspect vr or master.

I have confirmed no voltage drop up to VR (engine off). I swapped VRs from my old Electrodelta to a Zeftronics and it still does the same slight oscillation with engine off and large jumps when systems are turned on, so I am thinking that it must either be:

1. Internal corrosion of the master (given I have cleaned/ tightened all 4 connectors which seemed to clean up the JPI voltage data. JPI data used to show lots of change from 13.8 to 14.2V before I cleaned switch so hopefully this fixed it, but I dont understand why slight needle oscillation persists)

2. Normal system behaviour.

3. The ammeter itself. I have looked at the connection and it isn't corroded. A bad ammeter also wouldn't cause the alternator to kick off in flight would it?

I am paying close attention as I lost the alternator 2hrs into a 4hr flight recently. After the characteristic full scale ammeter fluctuations that started 1.5hrs into the flight the voltage dropped (alternator quit) and unlike previous times this had happened it didn't come back for most of the 2hr return flight (which was long enough that the Aspen efd1000 ran out of its backup battery...) Fortunately it was day VFR, but I want to be very sure I have fixed the problem before getting back into cross country night IFR. If anyone can confirm whether slight oscillation engine off is normal it would be greatly appreciated 

Edited May 4, 2021 by 65C_flier

[A64Pilot]

1/2 needle width or less could even be the natural harmonic frequency of the needle being excited by engine vibrations.

hook a good multimeter to it and see if voltage is actually fluctuating. put the probes on the cigarette lighter socket any real fluctuation will be in the whole system.

Or simply jumper past the switch, if it’s the switch when jumped the issue will resolve.

 

‘My issue is intermittent, after 10 min or so of flight it seems to stop, I think it’s my switch and it stops when the battery becomes fully charged and the amperage draw lessens, lower amp draw shoud equate to lower field current and the switch can pass a lower current without issue.

‘At least that’s my theory anyway

Edited May 4, 2021 by A64Pilot

[Guest]

What about the connections on the ammeter shunt?

Clarence

[65C_flier]

27 minutes ago, A64Pilot said:

1/2 needle width or less could even be the natural harmonic frequency of the needle being excited by engine vibrations.

hook a good multimeter to it and see if voltage is actually fluctuating. put the probes on the cigarette lighter socket any real fluctuation will be in the whole system.

Or simply jumper past the switch, if it’s the switch when jumped the issue will resolve.

 

‘My issue is intermittent, after 10 min or so of light it seems to stop, I think it’s my switch and it stops when the battery becomes fully charged and the amperage draw lessens, lower amp draw shoud equate to lower field current and the switch can pass a lower current without issue.

‘At least that’s my theory anyway

It could be a natural engine freq, but it does it engine off as well. Very interested in hearing whether your ammeter needle has any slight oscillation before engine start. 

Regarding your issue I wouldn't have thought there would be a lot of current through the master or field wire? Isn't it just passing a voltage drop signal to the alternator to tell it to crank up amps to power the system demand?

Edited May 4, 2021 by 65C_flier

[65C_flier]

5 minutes ago, M20Doc said:

What about the connections on the ammeter shunt?

Clarence

Good idea. I'll go and have a look on the weekend. Now I'm off to the schematics to find where the shunt lives.

Edited May 4, 2021 by 65C_flier

[carusoam]

Shunt usually lives on the firewall...

Has two heavy wires running ship’s power through it...

has two wires with fuses going to the ammeter...

use caution with the shunt... exposed electricity hazard.

PP thoughts only, not a mechanic.

Best regards,

-a-

[FlyBoyM20J]

On 5/3/2021 at 6:42 AM, 65C_flier said:

@FlyBoyM20J
Just wondering if people still see a slight oscillation of the ammeter even when the system is working properly (engine on and off)? 

I have had the intermittent full scale ammeter fluctuation in flight (including some flights where the alternator quits for varying lengths of time - sometimes automatically resets, other times it didnt).

I have cleaned the master switch connectors, tightened the field wire post on the alternator (was a bit loose), checked alt field cb resistance, etc. EDM830 voltage data looks cleaner now and I haven't had the wild random fluctuations in flight, but the ammeter still oscillates very slightly (1/2 needle width) even before engine start. Ammeter also jumps / oscillates a lot when systems are turned on (with and without engine running). I would expect a bit of a response when a load is applied, but the jump and oscillation seems disproportionately large (3/4 scale with some overswings) when low power systems are turned on. Is that normal or a sign that I haven't solved my problem?  78J

Just saw this...I don't have any fluctuations as long as I've manipulated the spade connectors on the back of the master switch recently.  Meaning, every 6 months or so, I start to see the ammeter needle move slightly and so I generally take the spade connectors off the back of the 4 spade lugs, inspect, and put back on...and problem solved until a few months later.

I can only assume some oxide is building up but I can never see anything.

Most recently, I didn't even remove the connectors.  I simply touched them and the needle stopped moving.  That was a couple of months ago, so I expect I'm about due.

Cliff

[A64Pilot]

If the needle moves without the engine running then it’s not the alternator or charging system, or I guess it could be, just unplug one of the spade connectors to the alternator field from the master and see if it makes any difference. I guess maybe the VR could be pulsing the field with the engine off?

Flyboy, take the spade connectors loose and apply some Dow Corning DC4 grease, that will prevent any oxidization, or at least greatly slow it down, AKA silicone or “light bulb” grease.

Edited May 6, 2021 by A64Pilot