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Old 08-06-2017, 07:30 PM   #1
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Default Electrical gremlins

Greetings all,

Toward the end of last flyin' season I had an intermittent issue where the volt gauge would show ~12 volts in flight, rather than the typical (and marked) 14. If I cycled the master switch, that would fix it temporarily. On a hunch, I took the alternator to a specialist who said the regulator was dead and replaced that. That worked great for 20-30 flight hours. During the same downtime, I installed an LED fuel gauge.

Well, fast forward to about 2 weeks ago. Not only is the volt meter showing the same symptoms again, but the new fuel gauge went kaput. Ordered a new fuel gauge, and that one lasted a whole flight hour before blowing up too - this time in flight.

Can't help but think there is some root cause that's making the regulator fall over, and maybe taking the fuel gauge with it. Probably a high voltage spike of some kind. But what might that be/what steps could I take to eliminate that possibility? Replacing a $75 fuel gauge every flight hour could get expensive and labor intensive, even by airplane standards!

Cheers,

jpr


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Old 08-06-2017, 07:51 PM   #2
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What kind of alternator? As for LED, some, not all, want exact voltage. if it says 12 v that does not mean 12.1, 13.5 or whatever. If the circuit does not have a built in regulator add your own to keep spikes down.


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Old 08-06-2017, 11:44 PM   #3
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"I had an intermittent issue where the volt gauge would show ~12"

Questions:

1) Does the regulator include an overvoltage circuit that shuts the alternator down?
2) Is there a filter capacitor on the output of the alternator?
3) What kind of battery is in the airplane?
4) What brand alternator-regulator and fuel gauge?

If the regulator shuts down the alternator when the voltage spikes, that could explain your volt meter showing battery voltage, 12V, and the spikes could be killing your fuel gauge.
A filter cap on the output side of the alternator might smooth out the spikes. Historically the ship's battery has also absorbed alternator "ripple".

Best of luck,

Wes

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Old 08-07-2017, 11:57 AM   #4
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If you killed the regulator again I'd suspect the alternator?

(Edit, yes it could be heat or something else?)
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Old 08-08-2017, 02:01 AM   #5
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Is the regulator in the engine compartment, or nice and cool a bit behind.

Some of them dont like hight temps and just prior to dying they could i suppose allow the voltage to wander or spike a bit.
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Old 08-08-2017, 03:55 AM   #6
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TFF1,

The alternator installation was logged as a "12 volt 50 amp ND AL12D4 alternator kit". The label on it says "AIR-TEC, Inc."

Wes,

1) Does the regulator include an overvoltage circuit that shuts the alternator down?
- I wasn't able to determine whether it has one.
2) Is there a filter capacitor on the output of the alternator?
- There doesn't appear to be one. Ordered one this morning.
3) What kind of battery is in the airplane?
- A Concorde sealed lead acid battery.
4) What brand alternator-regulator and fuel gauge?
- It looks like the alternator is the top kit from this page: http://www.airtecinc.us/aircraft.html This is the fuel gauge: https://www.aircraftspruce.com/catal...ugeadapter.php

Peter,

The regulator is installed right on the alternator, which is mounted on the front right of the engine right up by the nose bowl. Can't imagine it's cool there...

Come to think of it, the alternator kit was installed about 25 hours before the first failure. So I'm going on one regulator every 30 +/- 5 hours. A remote regulator is probably a good idea here...
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Old 08-08-2017, 01:15 PM   #7
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ND stands for Nippon Denso. The alternator-regulator is common on cars imported from Japan. My understanding is that the B&C folks offer the opinion that they are spun way over their rated RPM when installed on a Lyco. You may have one that is more out of balance than average, creating enough vibration to make the regulator electronics unhappy. But lots of folks have used them successfully. Your local auto electric shop should be able to test and rebuild as needed.

Your local auto electric shop should also be able to answer questions about whether the regulator includes over-voltage protection. And they may be able to sell you replacement parts for a lot less than your original source. The internet may be able to answer the question about features with the model number.

The filter capacitor is likely to help with the fuel gauge failures. But a call to the manufacturer might yield some info on how tolerant the unit is to electrical problems.

Best of luck,

Wes
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Old 08-09-2017, 11:33 AM   #8
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Don't discount a faulty battery. Test it somehow.
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Old 08-09-2017, 12:18 PM   #9
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Hm - what failure mode would cause that kind of problem? It holds a charge and spins the prop exactly like it did the day I first flew the plane.


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