Ammeter fluctuating

[N201MKTurbo]

Actually you have 6 diodes in a three phase bridge. Three for the positive half cycles and three for the negative half cycles. So, losing 1 diode will remove 1/6 of the power from the alternator output.

[PTK]

So cleaning the terminals didn't work?

Ad I said Mike, I didn't get to it yet. I have ruled out the master pretty much though.

[mike_elliott]

Ad I said Mike, I didn't get to it yet. I have ruled out the master pretty much though.

Ok, I thought by ruling out the Master switch, you had tried this already. my bad. 

[PTK]

Update.

Battery in great shape and trickle charging on battery minder fine.

Here's a plot of a flight with fluctuating ammeter. The voltage dips are the cycling of landing light.

I don't see anything abnormal but I'm not an expert. If diode was bad wouldn't it show up?

Does anyone have any plots of bad diode to compare?

[ArtVandelay]

So it looks like the voltage is constant, except short dips when turning on the landing light, did you leave the light on for an extended period, or you just cycled on-off?

Do you have mechanical voltage regulator?

[PTK]

I only cycled it on and off a few times.

Not sure about voltage regulator. Which should I have Teejay? We have same J!

Are you thinking field wire resistance due to a poor connection?

I haven't cleaned master connectors yet but plan to. They appear tight but may not be. Even though it was replaced a few months ago at annual.

[ArtVandelay]

I'm thinking it seems to be holding the voltage, so the voltage regulator is working.

If you turn on the landing light, a voltage drop is normal, especially for a mechanical voltage regulator that would be a little slow in reacting to the increased load.

But if it stays low, then that means the alternator is not producing enough amperage. Which is normal if at idle, but not at cruise RPM.

I assume the ammeter doesn't fluctuate when the engine isn't running, if just powered on while on the ground. Then you back to a diode problem.

[PTK]

I'll check what it's doing when leaving landing light on longer in cruise RPM.

Also I'll see what it's doing without engine running to confirm it doesn't fluctuate. I'd assume it'll dip a little and stay there because it'd be pulling from battery. Right?

I'll be back!!

Edit:

Iirc I had left landing lite on longer in cruise from previous flight. Here's plot:

[1964-M20E]

What type of strobe light to you have?

 

Have you turned it off while flying to see if the fluctuations go away?

[PTK]

Update:

Went over to the hangar today. Checked on the ground without engine running.

Battery charged well and ammeter centered on "zero."

Master on. Ammeter moved very little towards discharge direction. This I consider a normal response to small load on battery. (Avionics cooling fans come on with master.)

Landing lite on, ammeter dips noticeably to about -30 or so and stays there until landing lite off. It then returns to almost center depending on how long things stay on and pulling from battery.

Are all roads leading to alternator?? It certainly seems that way to me!

I'll still clean master contacts and pull field and alt cb's to be sure they're clean.

[mike_elliott]

I'll still clean master contacts and pull field and alt cb's to be sure they're clean.

Good, let us know how that turns out. Like I said, I had that issue with a 1984 J, Don Maxwell told me to do this, problem solved. (It re-appeared a year later, and once again I cleaned the four terminals, and once again, it solved this very issue). I hope it is that simple for you also, Peter.

[ArtVandelay]

Are all roads leading to alternator?? It certainly seems that way to me!

I'll still clean master contacts and pull field and alt cb's to be sure they're clean.

I don't think you can rule out the voltage regulator yet. Unfortunately unless you can recreate on the ground it's tough diagnosing which is the culprit.

[mooniac15u]

Here's Don's write-up on the subject:

http://donmaxwell.com/publications/MAPA_TEXT/Fluctuating%20Ammeters/Fluctuating%20Ammeters.htm

[N201MKTurbo]

Probably not the voltage regulator. Your graph shows the regulator is doing its job. Whatever is causing the current to fluctuate, bad connection on the master switch or alternator. The regulator is doing its best to keep the voltage constant.

 

P.S. you can't check much with the engine off.

[quik flite]

Had the same problem , the alternator had an oily film all over inside it. As usual a trip to Webers took care of it. Call Dorn at Webers  if you have not done so ,he will be glad to help.

[wishboneash]

Could be the field wiring of the alternator. My ammeter used to fluctuate and suddenly dip when the wiring got frayed. When I checked it, it was down to 1 or 2 strands. That could explain the spikes in voltage whenever there is any sudden draw of current.

[ArtVandelay]

Probably not the voltage regulator. Your graph shows the regulator is doing its job. Whatever is causing the current to fluctuate, bad connection on the master switch or alternator. The regulator is doing its best to keep the voltage constant.

P.S. you can't check much with the engine off.

The graph of voltage in post 33 was not constant, if it was a bad connection on the master I would think there would be other symptoms like having problems with the avionics.

[PTK]

Well, I haven't done anything about this. Its been kind of hot and sticky to work in the hangar anyway. Plus I'd rather fly.

Much to my pleasant surprise the fluctuation disappeared! Not there on today's flights. Gone!

I'll have to see if it returns. 

 

 

Edited September 5, 2015 by PTK

[mike_elliott]

Well, I haven't done anything about this. Its been kind of hot and sticky to work in the hangar anyway. Plus I'd rather fly.

Much to my pleasant surprise the fluctuation disappeared! Not there on today's flights. Gone!

I'll have to see if it returns. 

 

 

Yep, sure sounds like resistance .. It will return.

[capthaak]

We just had this problem too. New alternator solved the issue

Sent from my iPad using Tapatalk

[PTK]

My A&P seems to feel it's the ammeter itself! He says it'll fluctuate until it just stops working one day.

Gas anyone ever seen one fail?

Edited September 16, 2015 by PTK

[Oldguy]

I have seen one fail on a car before, but never with the needle movement mimicking the graph fluctuations the way your picture from Savvy shows. But then again, I am not an A&P.

I'm still pulling for it being a cleaning of the master that resolves it once and for all like Mike talked about.

 

John

[mike_elliott]

Had one pop in a 1969 Datsun 2000 once, but never heard of one go bad in a J. I'm sure they can, but I would think it would be a total failure, not fluxuating reading.

[romair]

I am also having the same problem of the amps fluctuating. I checked the terminals on the Master switch and they are clean, absolutely no corrosion. The volts stay steady, which makes me think it is not the voltage regulator. The amp fluctuation goes away if I take the alternator off line. Popping every CB with the alternator on does not result in the fluctuations disappearing. Interestingly though, when I pop the announciator panel CB, it automatically takes the alternator off-line, and I have to reset the alternator CB in order to get it back on.

The alternator and the battery are about 1 year old. What do you guys think...it seems that there is an alternator connection to all this - diodes?  I have the PlanePower Alternator installed. Also, why does popping the Announciator panel CB result in the alternator going off-line?

Thanks

Stefan

[carusoam]

That is a sign of the wire that controls the voltage at the alternator is being supplied by the 24V reference coming from, in this case, your Annuciator panel..?

chase that wire to see if that is what is really going on.  Check your wiring diagram in your POH to see if that is proper.  It may be.  The Annuciator is a required info supplier and probably is a proper place to get the reference from... 

I am a PP, i am not a mechanic.

best regard,

-a-

Edited September 26, 2015 by carusoam