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rv8ch
Joined: 10 Jan 2006
Posts: 250
Location: Switzerland
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 Posted: Sat Sep 19, 2020 12:55 am Post subject: Alternator sawtooth current generation |
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Planepower/Harzell 60Amp, Earthx battery, GRT EIS 4000 w/hall effect sensor on alternator B-lead, running all lights, etc. Steady state getting these kinds of current fluctuations (see attachment).
Got some good suggestions from VAF and tried them all, even replaced the alternator, same behavior.
https://vansairforce.net/community/showthread.php?t=186043
The current shows a consistent pattern, and regular period of a bit over 11 seconds.
I don't know of anything in my aircraft with that period. It's all new, and this has been happening since the start.
Happy for any hints!
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Mickey Coggins
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ceengland7(at)gmail.com
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| Posted: Sat Sep 19, 2020 5:20 am Post subject: Alternator sawtooth current generation |
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On Sat, Sep 19, 2020 at 3:59 AM rv8ch <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)> wrote:
| Quote: | --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch (mick-matronics(at)rv8.ch)>
Planepower/Harzell 60Amp, Earthx battery, GRT EIS 4000 w/hall effect sensor on alternator B-lead, running all lights, etc. Steady state getting these kinds of current fluctuations (see attachment).
Got some good suggestions from VAF and tried them all, even replaced the alternator, same behavior.
https://vansairforce.net/community/showthread.php?t=186043
The current shows a consistent pattern, and regular period of a bit over 11 seconds.
I don't know of anything in my aircraft with that period. It's all new, and this has been happening since the start.
Happy for any hints!
--------
Mickey Coggins
http://www.rv8.ch/
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Hi Mickey,
Questions spawn questions. 
It doesn't look like there's any issue with the voltage.
If you can access a stand-alone high current DC amp meter, that would be my 1st step; wire it in series with the alternator B lead to verify your EIS current readings as vailid.Â
Assuming the current variations are real....
Where's the current sensor installed? On the alt B lead it will show total current. On the Battery 'fat' lead, it will show charge/discharge to/from the battery. On the bus feeder, it will show current consumed by airframe devices.Â
Since it's a Hall sensor, it should be easy to move it around in the electrical system. Move it to the battery's 'fat' pos. lead, to see if the current fluctuates going into the battery. If you see the variations there, repeat the test with an SLA battery....
Try it on the bus feeder. If you didn't see variations on the battery, you should see them going to the airframe's devices.
Start with everything turned on, and one by one, turn off devices, until nothing is left powered in the plane. If it's a device causing the variations, it should be obvious which one is doing it.
Having said that, a 10A 'bump' in current, going to zero current, on an 11 second cycle rate, does not sound like any typical current consuming device in our planes (you don't have anything like electric seat heaters, do you?).
My money is 1st on measurement error, and my hedge is the battery.
Charlie
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nuckolls.bob(at)aeroelect
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| Posted: Sat Sep 19, 2020 6:05 am Post subject: Alternator sawtooth current generation |
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At 03:55 AM 9/19/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "rv8ch" <mick-matronics(at)rv8.ch>
Planepower/Harzell 60Amp, Earthx battery, GRT EIS 4000 w/hall effect sensor on alternator B-lead, running all lights, etc. Steady state getting these kinds of current fluctuations (see attachment).
|
how big are the variations? Is vertical scale
on the plot zero to some max amps?
| Quote: | Got some good suggestions from VAF and tried them all, even replaced the alternator, same behavior.
https://vansairforce.net/community/showthread.php?t=186043
The current shows a consistent pattern, and regular period of a bit over 11 seconds.
I don't know of anything in my aircraft with that period. It's all new, and this has been happening since the start. |
What's the bus voltage doing during this time?
As long as the bus voltage is reasonably constant
and the alternator is not overloaded, I'm not
sure current flow from the alternator has much
significance. The alternator has no
control over current . . . only voltage and
that by way of commands from the regulator.
So it was safe bet that replacing the alternator
wouldn't 'fix' it.
But it's not really clear that anything needs
fixing . . . need to know the scale factors for that
current plot.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sat Sep 19, 2020 6:13 am Post subject: Alternator sawtooth current generation |
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| Quote: | Hi Mickey,
Questions spawn questions.
It doesn't look like there's any issue with the voltage.
If you can access a stand-alone high current DC amp meter, that would be my 1st step; wire it in series with the alternator B lead to verify your EIS current readings as vailid. |
Right on
| Quote: | My money is 1st on measurement error, and my hedge is the battery.
Charlie |
Agreed. I'd conduct some experiments with the sensor
and compared with another instrument and battery
power only. See if that puppy's calibration is good.
The 11-second period is interesting . . . wondering
if this might be a 'beat note' between two regular
features of noise on the bus irritating the a/d
conversion process in the instrumentation.
But if the bus voltage is stable then some sort
of measurement error is high on the list of
probabilities.
Bob . . .
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ceengland7(at)gmail.com
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| Posted: Sat Sep 19, 2020 6:30 am Post subject: Alternator sawtooth current generation |
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On 9/19/2020 9:11 AM, Robert L. Nuckolls, III wrote:
| Quote: | | Quote: | Hi Mickey,
Questions spawn questions.
It doesn't look like there's any issue with the voltage.
If you can access a stand-alone high current DC amp meter, that would be my 1st step; wire it in series with the alternator B lead to verify your EIS current readings as vailid. |
Right on
| Quote: | My money is 1st on measurement error, and my hedge is the battery.
Charlie |
Agreed. I'd conduct some experiments with the sensor
and compared with another instrument and battery
power only. See if that puppy's calibration is good.
The 11-second period is interesting . . . wondering
if this might be a 'beat note' between two regular
features of noise on the bus irritating the a/d
conversion process in the instrumentation.
But if the bus voltage is stable then some sort
of measurement error is high on the list of
probabilities.
Bob . . . |
Bob,
The image in his VAF thread shows V & I ranges; V variation is ~.3V; I is ~0--~10A.
The only 'device' I can think of that might cycle like that, at that wattage level, would be a heater circuit that had a controller capable of ramping power up/down in response to temp changes.
Oh...Pitot heat! Dynon and probably others now have temp controllers for their pitot heat. And the current is about right.
Charlie
 Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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rv8ch
Joined: 10 Jan 2006
Posts: 250
Location: Switzerland
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| Posted: Sat Sep 19, 2020 8:43 am Post subject: Alternator sawtooth current generation |
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Thanks for the hints. The voltage stays very constant. No pitot heat or other big consumers, except lights (landing/wigwag, position, strobes). I did some experiments today without the lights for a longer period, and with the fuel pump, and the current is smooth.
I have the hall effect sensor between the alternator and the main bus on the B lead, so it should only be measuring the output of the alternator.
It really looks like the "culprit" is the lights. I will talk to Paul the Flyleds guy and see if he's seen this. All my lights are Flyleds, but I use Eric's wig-wag controller. It could be totally normal that he grabs a lot of power in a cyclical way which is causing this. Starting to wish I had installed multiple hall sensors, but my system is so simple, I didn't really see a huge advantage.
One other thing I see is that when I remove the consumers, and leave just the EFIS, radio, transponder, and pmags, the current from the alternator drops very low, and then the ALT warning light I have wired in there as shown by PlanePower flickers. It's a 12v LED from Fry's.
I feel kind of bad that PP sent me a new alternator. I described the problem and they were certain it was a faulty alternator. I guess I should have done more investigation on my own. I can only say good things about their quick response to a problem!
Got some rainy days coming up so I might play around with it a bit more before the next flight and report back.
Thanks again for the suggestions!
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Mickey Coggins
http://www.rv8.ch/ |
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