Pulsing lights/voltage indicator

[Seth]

I have an issue that is less sporatic and more consistent.  The voltate indicator is pulsing from negative to positive and back almost non stop now on most flights.  Every now and then, when I turn off the landing light, the needle centers, but then starts its propensity to start wiggling in ever greater moments.  When night flying, the panel lights become brighter then dimmer as it pulses. 

 

There is also sometimes a beeping noise as it pulses, but that may just been a high wine with the power fluctuations.  I'm not sure if this is a short, an alternator issue, a draw on the system, etc . . .

 

The JPI 830 shows the charges jumping up and down as well 13.9 to 14.1 to 14.6 to 14.2 every few seconds or so.  If the JPI gets the feed from direclty from the voltage gauge with the needle, then it's just showing that data.  If it has an indpendent source, then I've got more than just a faulty gauge.  Something I'll expalin has become a permanent issue since annual, but that was an inconsistent issue beforehand.

 

It has started and stopped in the past, but it's a consistent problem now. 

 

Has anyone else had a similar issue/problem? 

 

-Seth

[Smiles201]

I had this in my previous plane. Turned out to be bad master switch. My understanding is that what happens is as the plane ages wiring and switches fail and develop more resistance, alternator increases output, then gets triggered down, then up, hence the back and forth on your gauge. You have to check the voltage drop between every wire, switch and connection from the battery to the alternator. With master on, engine off, should be no more than 0.1 volt drop at every juncture, can be hard to trace, could also be loose or bad connection, or other Mooney gremlin. IMHO. Good luck!

[Smiles201]

Of course, most mechanics do not understand electrical systems and will replace voltage regulator and other components before actually testing the system. Don't ask how I know.

[carusoam]

Master solenoids have a tendency to increase resistance with age. As do starter solenoids. They may be cleanable or easily replaced, I believe... Now, how to measure their resistance could be key... Jose' probably could add valuable experience to this challenge. Miles, welcome to MooneySpace... -a-

[carusoam]

Where'd my carriage returns go??? -a-

[M016576]

The 830 measures voltage across its own power input; it doesn't try to read voltage from some other source (would be overly complicated to do that when you already need power for the unit, and since most Single engine GA aircraft only have one bus, makes the most sense).

[Smiles201]

Thinking about this some more, forget if 0.1 volt is the correct number, but the point is that their should be a minimal drop in voltage, and you have too much of a drop somewhere. Also, I had bad master and bad connection on my field wire at the alternator.

[N601RX]

I think some of the aftermarket regulators have a self resetting overvoltage feature built into them.  It it's not a loose wire or corroded busbar something may be going on with the regulator/ overvoltage.

[Seth]

_{Thank you everyone for your suggestions.  I have a lot of knowledge in some areas, and not in others.  This information and speculation is very helpful.}

 

_{What long term damage may I be causing by not immediately correcting the issue and living with it?  I plan to have it dealth with soon, but soon may be a month or two with some flights in between.}

 

_{I just replaced the batteries as well - concords instead of gils after one fell the preload test at annual.}

 

_-Seth

[sreid]

_{Thank you everyone for your suggestions.  I have a lot of knowledge in some areas, and not in others.  This information and speculation is very helpful.}

 

_{What long term damage may I be causing by not immediately correcting the issue and living with it?  I plan to have it dealth with soon, but soon may be a month or two with some flights in between.}

 

_{I just replaced the batteries as well - concords instead of gils after one fell the preload test at annual.}

 

_-Seth

I used to fly a 201 that had these same symptoms. I wrote it up after a night flight with pulsing cabin lights and ammeter. The mechanic found that the alternator brushes were very worn. New brushes and it was back to normal. In that case, with the wear to the brushes that I saw, I would guess that airplane didn't have a lot of time left before the alternator would have died.

[FBCK]

I would think its the master switch.  I have been running my for 3 years with the same issue and it hasn't caused any damage but it will be fixed this year. I went though a couple of shops and asked them to fix it, none did and the third shop told me its the master, we will fix it next time around.

[Randy_B]

About a year ago I had a low level feed back in the head sets that oscillated about once every second. It matched up with a slight movement in the volt meter needle and very faint dimming of the panel lights. It wound up being a bad voltage regulator. Replace at annual and the symptoms went away.
Good luck locating the issue and let us know what you find.

[SheryLoewen]

Paul Says: Most commonly it's a simple fix at the master switch-- the alternator field side of the switch. all that is necessary is to clean the spade connectors contacts on the back of the switch. You can usually see results by touching the connectors with your fingers while the engine is running..

[Swissmooney]

Hi there everybody I had this problem also during our flight from switzerland to the USA...during a 100hr inspection by Don Maxwell in Longview he confirmed that the Masterswitch is the culprit...cleaned all connections and the problem was done...however 6 months later the problem reappears...so there is a new masterswitch in my future... See Don's publication @ http://www.donmaxwell.com/publications/MAPA_TEXT/Fluctuating%20Ammeters/Fluctuating%20Ammeters.htm Kind regards from swissmooney in Fort Myers Beach (unfortunately without the Mooney...!!) Heinz

[Piloto]

Paul Says: Most commonly it's a simple fix at the master switch-- the alternator field side of the switch. all that is necessary is to clean the spade connectors contacts on the back of the switch. You can usually see results by touching the connectors with your fingers while the engine is running..

The above was my case and got it fix. Also spray contact cleaner while at it.

José

[Seth]

I touched the master from behind (hoping not to shock myself out) and it seemed to fix the issue.  I'll go ahead and try to clean the connection up.

 

Thanks for the advice.

 

-Seth

[FLYFST]

The master switch contacts was my problem too -- fixed now. 

 

My ammeter, oil gauge and sometimes the RT fuel indicator would dance at a steady frequency of around 2 cycles/sec, at night the cabin and instruments lights would slightly dim and brighten at the same frequency, and I would periodically note a high pitch, low volume tone in my headsets at the same frequency; very annoying. Pulling the ALT FLD circuit breaker steadiied the needles and showed a slow battery discharge.

 

I used this posting trail and some of the references provided to give my MSC a priority list of what to look for first, to save me some troubleshooting dollars and they solved it after step one.  The article posted by Don Maxwell was the most helpful.

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

 

Here's the summary list I provided, hoping that it helps someone else too.

1. Master Switch.  Check for corrosion and clean the spade connector contacts of the master switch, particularly the alternator field side, as the most probable cause of fluctuating ammeter and oil temperature gauges. 
2. Defective Diode.  Check for possible defective diode in the rectifier. 
3. Voltage Regulator. Data from the EDM-700 shows battery voltage cyclically varying during flight between 13.9V and 15.0V. but according to the Mooney Service Manual (section 24-31-02) the maximum voltage for a 14V system is 14.2V +0.2/-0.0. 
4. Alternator Brushes. Check for possibly worn or defective alternator brushes.

Post Repair Update: after cleaning the master switch, the large variances in the EDM-700 voltage display also returned to within range od the Mooney Service Manual.

 

all the best - Hank

[Seth]

Long time to follow up, but prior to my Mad Missile Dash, with the contacts cleaned - boom - problem solved.

 

Same master switch, just had to clean the contacts, no more pulsing.

 

-Seth

[Marauder]

Long time to follow up, but prior to my Mad Missile Dash, with the contacts cleaned - boom - problem solved.

 

Same master switch, just had to clean the contacts, no more pulsing.

 

-Seth

 

Thanks for bringing this back up! Mine just started doing this!

[Bill_Carter]

So I have nothing to add other than a question or two. I am glad the problem was found, but I was sitting here thinking about the ramifications of the switch not making proper connections. So I was wondering two things.

First, what type of corrosion is happening and why (just normal oxidation?)?

Second, due to the lack of a good contact, is it affecting the charge in the battery(s)?