Alternator issue?

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Rich
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Re: Alternator issue?

Post by Rich »

astaib wrote: Fri Mar 05, 2021 4:31 pm
Rich wrote: Fri Mar 05, 2021 4:26 pm Also that it's still 100 ohms and hasn't blown/shorted, etc.
Of course, can this make behavior like this ?
That I don't know :scratch:
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Re: Alternator issue?

Post by Rich »

From an Aviation Consumer article:

And yes, there are sensors in the system that might fail, including the output sensor, or alternator-out sensor. It’s usually wired to the AUX terminal lug and triggers a warning light when voltage from the positive diode plate has dropped to a level that prevents the alternator from producing current.


This looks like one of your annunciator lights.
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astaib
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Re: Alternator issue?

Post by astaib »

At this stage, I don’t know is the responsible on that is :
The VR
The alternator
The wiring
A resistor or any other sensor somewhere !
But as I have the strange values on the VM1000 and announciator alarm, I think that there is a real issue.

Also the increasing parasites in the headset...

Arrrg
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Rich
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Re: Alternator issue?

Post by Rich »

Do you still have the "cigarette lighter plug"? Connecting an analog voltmeter (you know, with a needle that jumps around) using this would show voltage fluctuations better than the digital display of the VM1000
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Re: Alternator issue?

Post by astaib »

Do you mean this plug?

I don’t have an analog voltmeter.

What can it shows that the fluctuations are fast, low, constant, by peak etc?
B45B7B54-545B-4C07-B746-5382F6922A25.jpeg
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Re: Alternator issue?

Post by Rich »

astaib wrote: Fri Mar 05, 2021 4:59 pm Do you mean this plug?

I don’t have an analog voltmeter.

What can it shows that the fluctuations are fast, low, constant, by peak etc?
I admit I don't currently have one, either. But they're super-cheap. It would give you more of a sense if the fluctuations are rhythmic or random. Digital gauges are a series of snapshots at regular intervals that don't show you transitory conditions. Ideally some sort of analog oscilloscope would give you a real picture, but those those are hard to come by.

I can't tell if that's the jack I have in mind: the accessory power that's ready access to the battery bus while inside the airplane in flight. The ones I'm familiar with have a placard that says something like "ground operations only" and is always hot, irrespective of the master switch. You'd get a compatible plug and put a couple of leads to connect the voltmeter. Be sure not to cross the leads or you'll blow the fuse inside the engine compartment.

Having reminded myself about that resistor, I would definitely check that and the alternator field lead. I recall hearing of several instances where one or the other broke off over time because of vibration and not enough slack in the wire.
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Re: Alternator issue?

Post by Boatguy »

Some digital meters will show high/low/average. I use a Fluke which does that and will monitor over a period of time. The analog would of course show it in real time.
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Re: Alternator issue?

Post by astaib »

Hi,

I did the test today with the analog voltmeter. It shows values identical as the vm1000 (normal), and the variations are not erratics, I mean that needle is not shaking, but slowly oscillating while the voltage was changing: exactly same behavior as the VM1000.

Again today, when I turned on the engine, I had alternator and low voltage alarm at 1200 rpm. The amp was at zero for a few seconds at the beginning then it starts to show 29.x and the alarms went away and the amp displayed a value.

During the flight I was almost 75% of the time in over
Voltage in the 30.x volts.
And sometimes it blinks.

Each time I changed something (mp or rpm) it most every time make an over voltage from 28.x/29.x to more than 30 or 31v.
There is no moment when the voltage has a steady value in the 28.4 at all.

I also noticed that the parasites in the headset stop when the engine is off.

As there are fluctuations in the voltage, why is it not sure that it is the voltage regulator?

This was my last tests by myself, now I will refer to my mechanic and maybe order a voltage regulator.

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Rick
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Re: Alternator issue?

Post by Rick »

I had a voltage regulator go bad a couple of years ago. I have the G1000, so I had data from all my flights, and could go back and look at what had happened. For nearly a year before it failed, my voltage slowly crept up from 28.4 to 29.6, without me noticing. Then several flights before it failed, it became more erratic in the 29-30 range. Finally one flight (away from home, of course), I took off and all was well until it died in the climb with an "alternator failure" warning on the G1000, so I turned around and went back. But several hours later at the shop, we started it back up and all was well. They tested the alternator and found no problem, so I took off again, but exactly the same result - 'alternator' failure in the climb, so back to the shop.

It was at that point I started looking at the G1000 data and discovered the voltage irregularities, but I also noticed they didn't really start until maybe 10 minutes into each flight. I'm guessing as the engine heated up, it affected the VR's failure mode. Long story short, they replaced the VR and it's been rock solid at 28.4 volts ever since. And I now pay much closer attention to the voltage in flight, not just the current draw!

Based on what you have said so far, I would bet it's the VR. Keep us posted!
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Re: Alternator issue?

Post by Steve »

Rick:

I have always run my bus at 27.9 - 28.0 volts. Concorde has a table of VR settings for different battery temperatures which I have condensed below:

C. Temperature Compensation: Battery service life can be prolonged by compensating the charging voltage based on the battery temperature. For aircraft that have an adjustable voltage regulator, the following table provides recommended settings

Table 1. Recommended Voltage Regulator Settings

Battery Temperature Voltage Regulator Setting (Volts DC)

Below 0°C (32°F) 29.0 – 29.5
0 to 15°C (32 to 59°F) 28.5 – 29.0
16 to 30°C (60 to 86°F) 28.0 – 28.5
31 to 45°C (87 to 113°F) 27.5 – 28.0
Above 45°C (113°F) 27.0 – 27.5

At 60-86°F, charging voltage should be 28-28.5 volts, so you are near the top of that range. The question is, how much of your charging time is spent with your battery at a temperature of 60 to 86°F? Remember this is not OAT, but battery temperature, inside the engine compartment.

Living in S. TX, I would wager that my battery spends most of its time charging at > 100°F. The high temperatures by themselves will shorten battery life, but high charging voltage will compound that issue. If 28.4 volts works for you, stick with it. I'm staying at 27.9 - 28.0...

Just food for thought.

Steve
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