Ammeter fluctuating

[PTK]

I noticed on yesterday's flights my ammeter needle was dancing back and forth around the "zero" top position. Very small amplitudes on either side of the zero top center.

Also the digital voltage indications on the Davtron 655 was jumping back and forth 13.8 and 13.7 V. I didn't think much of it as I was setting up for an approach. Didn't check the EDM800.

I had the master switch replaced last annual and I still have to check the connectors in the back to be sure they're nice and tight.

Any other ideas from the pros?

[tony]

Turn everything on you can, do you see a bigger fluctuation with a high current demand?

[PTK]

I cycled the landing light. I did see the usual larger amplitude but settled around zero.

This is normal in flight.

So to answer your question I'd say no not bigger amplitude dancing back and forth with landing light on. Just one initial jump which I consider normal.

[mike_elliott]

I noticed on yesterday's flights my ammeter needle was dancing back and forth around the "zero" top position. Very small amplitudes on either side of the zero top center.

Also the digital voltage indications on the Davtron 655 was jumping back and forth 13.8 and 13.7 V. I didn't think much of it as I was setting up for an approach. Didn't check the EDM800.

I had the master switch replaced last annual and I still have to check the connectors in the back to be sure they're nice and tight.

Any other ideas from the pros?

Peter, take the 4 spade ends off the master switch and clean the lugs and spade ends, and reattach. While myself not a "pro", this fix comes from a pro, Dmax. Some of that non existent NJ corrosion is setting up a resistance here causing the VR to fluxuate between charge, no charge. Simple fix.  

[PTK]

Peter, take the 4 spade ends off the master switch and clean the lugs and spade ends, and reattach. While myself not a "pro", this fix comes from a pro, Dmax. Some of that non existent NJ corrosion is setting up a resistance here causing the VR to fluxuate between charge, no charge. Simple fix.

Thank you Mike. I did have the master replaced a few months ago though. Although it may not be corrosion that fast could it be jumpy connector?

I never had this fluctuation before. I think it's related to master somehow.

[aviatoreb]

Mine was behaving like that when I got this new to me airplane 5 years ago - in the end it was the voltage regulator.

[Marauder]

Thank you Mike. I did have the master replaced a few months ago though. Although it may not be corrosion that fast could it be jumpy connector?

I never had this fluctuation before. I think it's related to master somehow.

The screws may have loosened a bit. It would give the same indication as corrosion resistance (poor connection). Worthwhile checking to make sure they are secure.

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[CWM20f]

Had similar flucuation on a one year old alternator. The brush holder failed causing non-repairable damage. Sucky part is only a 6 month warranty.

[N201MKTurbo]

Almost certainly an intermittent connection somewhere.

My first choice would be the diode assembly in the alternator.

See if there is any correlation to engine RPM/vibration.

With a constant field current, when a diode disconnects there will be drop in output current and a proportional drop in output voltage. The regulator will compensate by increasing the field current to restore the output voltage. When the diode reconnects there will be a momentary increase in output current until the regulator compensates.

If you are a CB with good hangar elves (it seems this term is more PC) disassemble the alternator and re-solder the six flying leads from the diodes.

To get to the diode assembly, remove the alternator, remove the screws holding the case halves together and the nuts on the output terminal. Pull the back half off. To re-solder you will need a high power soldering iron like a 250W Weller gun. To re-install the back half, push the brushes in and poke a small wire or drill bit through the small hole by the brushes. Slide the back half back on and remove the wire allowing the brushes to extend. Replace and lock wire the screws.

[N201MKTurbo]

A broken brush holder can cause the same indications with much bigger current current spikes.

[Oldguy]

Had the same problem on my J last year. Ordered a Master Switch, but it was back ordered. Ended up cleaning all four terminal connections like Mike noted in his response and have not had a problem since.

I will say when I downloaded the EDM 800 data it was obvious it was having some constant problems. Hope yours is as easily remedied as mine was.

John

[mike_elliott]

Thank you Mike. I did have the master replaced a few months ago though. Although it may not be corrosion that fast could it be jumpy connector?

I never had this fluctuation before. I think it's related to master somehow.

One of the connectors might not be making as secure of a connection as it should vs corroded. It would pay to remove, take some electrical cleaner to them and put them back together. Cost? about 15-20 minutes of time, plus a little electrical cleaner. Check for tightness of the connectors also. If this isn't it, start chasing other connection possibilities mentioned here. You will know right off if you fixed it typically.  

[flyboy0681]

I had what sounds to be a similar situation last year. While it wouldn't always occur, I'd look at the ammeter and noticed it was pulsating back and forth and if I had the panel light on at the same time, they would pulsate dim to bright as well. This went on for a couple of months. Fast forward to when I needed something checked and the cowl was removed for something unrelated. On the flight after the cowl was removed I noticed the ammeter was no longer pulsating and the lights glowed normally. The only thing I could assume is that the A&P secured a ground wire when replacing the cowl or doing his inspection.

[PaulB]

I've got the same problem but my oil temp also wiggles. I've tried cleaning the master switch with no change. I get a buzzing in the headsets that changed with electrical load and RMP. Occasionally on the ground under a high electrical load the alternator drops offline putting the buss voltage at 12 and will suddenly pop back up to 14 after 30 seconds or so. I checked the field wire with then engine off and it shows 10v while everything else in the system is 12v. I suspect either the field wire or voltage regulator is the culprit.

[Piloto]

I've got the same problem but my oil temp also wiggles. I've tried cleaning the master switch with no change. I get a buzzing in the headsets that changed with electrical load and RMP. Occasionally on the ground under a high electrical load the alternator drops offline putting the buss voltage at 12 and will suddenly pop back up to 14 after 30 seconds or so. I checked the field wire with then engine off and it shows 10v while everything else in the system is 12v. I suspect either the field wire or voltage regulator is the culprit.

You have a bad diode in the alternator. Typical for low RPM voltage and buzzing sound.

[Piloto]

Peter try pulling and pushing the alternator and field CB several time to clean the CB contacts.

 

José

[PTK]

Thank you José. I didn't even think of that. I will.

I paid closer attention to it on today's flights.

I noticed that it fluctuates with much greater amplitude in cruise. On the ground idling or taxiing it is a very very faint fluctuation. Barely even visible. You have to stare at the needle to maybe even notice it.

The voltage never drops below 13.6 or .7 on the Davtron. It was 13.9 on the EDM.

I noticed something else that may or may not be related. I keep a battery minder plugged in all the time. Usually when I go to the airplane the day after a flight, it shows that it's in trickle charge mode. Flashing trickle mode. Today I noticed it was not flashing! It was steady on. This means that it's charging which is unusual a whole day after.

Can it be a small drain somewhere?

Master connectors seem secure. I did not have time to clean them but plan to.

[ArtVandelay]

PTK, your battery may be on its last legs, do a capacity test.

[tony]

_{Do you hear anything different in your headset when someone keys the mic?   Do you have a separate circuit breaker for the alternator field that you can toggle?}

[PTK]

Do you feel battery going would cause the fluctuations more noticeable at higher RPM teejay? A battery is better fix than an alternator I suppose!

No headset symptoms or any other. Just what I've described Tony.

When I cycle the landing lite in cruise the needle goes crazy! Its amplitude increases momentarily it seems.

[ArtVandelay]

Do you feel battery going would cause the fluctuations more noticeable at higher RPM teejay?

No headset symptoms or any other. Just what I've described Tony.

When I cycle the landing lite in cruise the needle goes crazy! Its amplitude increases momentarily it seems.

The battery minder problem, what's common to all of the above...

The battery

It's both a simple test and simple to fix, I'd rule it out first.

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[tony]

Without putting an O-scope on the system, I would guess  you lost a diode in your alternator.  You have three diodes in your alternator.  When you increase the load on the alternator (when you turn on the landing light)  your getting higher ripple because the time when one of the diodes is supposed to be conducting, its not and your sourcing from the battery. 

 

If you have a good battery, under a lite load, you should hardly see anything on the amp meter.

 

Problem is no shop will have an O-scope to know for sure. 

[PTK]

Thank you Teejay.

I see what you mean and you're right. I'll check the battery next. I've pretty much ruled out the master.

Thank you Tony.

Does losing a diode also mean that battery is constantly being taxed in flight with lower than landing lite loads as well? And not charging?

Why does it appear to be still charging the day after on battery minder?

I'll investigate the alternator next after battery.

[carusoam]

Diodes in an array have the effect of turning AC to DC....

Each diode acts like a one-way valve for electrons, allowing the electrons to flow only in one direction.

Losing a diode is a (somewhat) common problem. Having 2/3 of the AC waves entering the system probably doesn't give 2/3 of the DC power output that may be expected.

If you can visually inspect the diodes(?), you can usually tell if one is burned out.

Next question:

Since they all have the same age and number of cycles....

What would it take to replace them all?

I am only a PP, not a mechanic, but I burned the diode out of my lawn tractor/tug project...

[mike_elliott]

Thank you Teejay.

I see what you mean and you're right. I'll check the battery next. I've pretty much ruled out the master.

Thank you Tony.

Does losing a diode also mean that battery is constantly being taxed in flight with lower than landing lite loads as well? And not charging?

Why does it appear to be still charging the day after on battery minder?

I'll investigate the alternator next after battery.

So cleaning the terminals didn't work?