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Turning master off makes volts go up? http://t18.net/thorpforum/viewtopic.php?f=16&t=7153	Page 1 of 2

Author:	Ryan Allen [ Fri Nov 09, 2012 7:08 pm ]
Post subject:	Turning master off makes volts go up?
I was flying today and noticed my amps were pretty low at about -5 amps. Voltage was good at 14 volts. Then my amps went way low to -10amps. My voltage was still good at 14volts. I reached up and turned my alternator and master off. When I turned the alternator off my amps stayed at -10 or -11. Then I switched the master off, and none of my electrical stuff turned off and my volts shot up to 15 or 15.5. After about 10 seconds I turned my master and alternator back on. The voltage went back to a normal 14volts and my amps went back to -5 amps (still lower than normal). I landed and shut down like normal. When I turned the master switch off this time, everything turned off as it should. What concerns me the most is that the master didnt turn off my stuff while in flight. I am trying to think why the master didnt turn off my electrical stuff while in flight. Could it be a faulty master switch (ie poor connection) or a stuck master solenoid? Anyone have any thoughts or suggestions?

Author:	bfinney [ Fri Nov 09, 2012 7:13 pm ]
Post subject:	Re: Turning master off makes volts go up?
Your alternator did not shut down when you removed the field voltage and kept the main bus powered. All the master does is disconnect the battery from the main bus.

Author:	Ryan Allen [ Fri Nov 09, 2012 7:45 pm ]
Post subject:	Re: Turning master off makes volts go up?
I dont guess I had thought of that. In this scenario, I would have to guess the alternator switch was a fault in this case, because it didnt turn the alternator off in the air, but upon landing and normal shutdown, the master turned everything off like it should (the alternator switch was turned off just prior to turning master off).

Author:	James Grahn [ Sat Nov 10, 2012 12:47 am ]
Post subject:	Re: Turning master off makes volts go up?
Ryan, I've been through a lot of these type issues. Can't really help much until we know how your airplane is wired. My thoughts; your alternator is definitely fried. It is not putting out any juice, obviously. As far as why things reacted the way they did, my first question would be, does the alternator have an internal voltage regulator? They can fry to the on position very easily. Test your alternator switch at the alternator field. It should have 14 volts with a healthy battery, and both the master and alternator switches on. Then test it again with the master on and alternator off. It should be zero. Cubes

Author:

Ryan Allen [ Sat Nov 10, 2012 6:44 am ]

Post subject:

Re: Turning master off makes volts go up?

its externally regulated. Right or wrong, I havent explored the wiring to know it as well as I should. I've traced the wiring visually and its adaquate, but I dont know much more detail than that.

im getting the b&c alternator (externlly regulated) to replace it. I have no breaker on my "Alt Field", if i had a breaker on my alt field wire, i think it would have tripped in this scenario. Maybe my voltage regulator should be replaced while I'm at it.

This is good timing. I have a new panel to install, with new voltage regulator, OV protection, new solenoids, etc. All wired per one of Bob Knuckolls drawings. This way, I'll know my wiring and be able to troubleshoot a little better.

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Author:	218KR [ Sat Nov 10, 2012 9:32 am ]
Post subject:	Re: Turning master off makes volts go up?
Nice looking panel. Clean, simple, and I likey. Some alternator/gen switches double as a breaker right? If you already have your breaker panel set and didn't want to add one, but wanted the "breaker", then maybe one of those would work? Dunno, just a thought.

Author:	Ryan Allen [ Sat Nov 10, 2012 12:27 pm ]
Post subject:	Re: Turning master off makes volts go up?
i dont have any of the breaker/switches installed. This panel has the alternator field breaker placed on the right side with all the other breakers. Now I just have to go out and get it installed. Already, I'm thinking of replacing the glove box with a 2.25"ASI and 2.25"ALT. When this incident occured and I tried to shut my master off (if the master would have shut everything down like its supposed to), I felt good knowing I have the old school round dial ASI and ALT in my panel as back ups. The D100 does have the back-up battery and it would have worked if the master had shut all else down like it should have, but it still made me feel good to have the round guages.

Author:	James Grahn [ Sat Nov 10, 2012 3:57 pm ]
Post subject:	Re: Turning master off makes volts go up?
Normally the alternator field does not have a breaker. It's just 12v to excite the alternator. The alternator supply line MUST have a breaker. Ryan, realize that an alternator can self excite. With changing over to your new set up that is externally regulated, you are starting over. I think that is a good thing. The master just disconnects the battery from the airplane, as was previously pointed out. If you find that the master only works intermittently, you can test the switch easy enough. It is either the switch, or the battery solenoid.

Author:	Ryan Allen [ Sat Nov 10, 2012 7:17 pm ]
Post subject:	Re: Turning master off makes volts go up?
I readily admit wiring the airplane is a big job for me, so I just followed the diagram to a T. i put a breaker on the alt field line and the supply line because the wiring diagram said to do it that way. I figure it cant hurt anything. I read over on the vans site that the alt field breaker trips in case of an over volt situation. Check my logic here, after talking to you guys: the alt field line didnt turn off my alternator because the alternator was failing and exciting itself, thus keeping everything powered up. Also, the voltage spike I was seeing can sometimes be a symptom of a failing (or failed) alternator. Is that possibly what happened?

Author:	dan [ Sat Nov 10, 2012 9:16 pm ]
Post subject:	Re: Turning master off makes volts go up?
I just replaced my Alternator, diode failure in the built in regulator let the thing run away, pegged out the Voltmeter. I jut killed the alt at the master switch( Double switch) and flew home.It had been acting a little weird until finally just turned loose. I had a very faint whine in my head set could just barley hear it, went to lookin at everything and the voltmeter was pegged all the way over. new 55amp alt fixed er right up....Dan

Author:	Rich Brazell [ Sat Nov 10, 2012 10:18 pm ]
Post subject:	Re: Turning master off makes volts go up?
My Plane Power alternator has a field CB on my Master control panel. RB

Author:	fytrplt [ Sun Nov 11, 2012 7:40 am ]
Post subject:	Re: Turning master off makes volts go up?
Circuit breakers/fuses protect wiring. My system, from Tony Bingalis, calls for a 2 amp breaker on the field wire. Note: breakers and fuses are rated in amps, not volts. They break the circuit when too much power surges through the wire, keeping the wire from overheating and causing a fire. A runaway alternator is an emergency. It can overcharge the battery making for a rather large bang. You need to have a way to turn it off in flight. Noise in the headset from the alternator is mostly indicating bad bearings.

Author:	dickwolff [ Sun Nov 11, 2012 8:56 am ]
Post subject:	Re: Turning master off makes volts go up?
Just to muddy the waters, Vans folks have been using ANL fusible links on the firewall for years to protect the system from a runaway alternator. The beauty of this set-up is that the B wire (B means Big) from the alternator is protected from the outside of the cockpit, not at the bus. The down side is that it is not re-settable in flight; but really, who in their right mind is doing to reset a 60A breaker in flight anyway? Not me!

Author:	Ryan Allen [ Sun Nov 11, 2012 10:20 am ]
Post subject:	Re: Turning master off makes volts go up?
I am still confused about how I could have turned off my alternator during this scenario. Both the alt switch and alt field breaker (if I had one) are on the field line. The switch did nothing so an alt field breaker would have had the same result if Ihad pulled it. I have a 60A alt breaker, but it did not trip. At this point, was I solely relying on the 60A breaker to trip if things got too far out of whack? How could I have turned off the alternator since the alt switch didnt turn it off? Signed, confused in LA PS Dick, in my new wiring, i have gone overboard and have an ANL60 fuse on the engine side of the firewall on the B line of the alt and an ANL60 fuse on the engine side of the firewall on the wire that powers my buss just before it enters through the firewall and I have a 60A breaker on my panel...

Author:	James Grahn [ Sun Nov 11, 2012 10:41 am ]
Post subject:	Re: Turning master off makes volts go up?
You are right. You could not have turned it off with the exception of pulling the 60A breaker. The alternator switch controls power to the field wire. Turning it off, eliminates the 12V power to the field that excites the alternator. Most of the time, when an alternator self excites, it is due to failed circuitry in the internal regulator. That's why I asked which kind you had. And externally regulated alternator would require several failures to self excite. Without testing your current alternator, there is no way of knowing what failed. BTW, I have taken an alternator to Auto Zone to be tested. It tested fine. After I reinstalled it and it failed again, I took it apart. There were no brushes in it. So don't trust the cheap auto supply stores to test anything. Go to an alternator shop. Cubes

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