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PP alternator voltage/amps fluctuations

rv8ch

Well Known Member
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PP 60Amp, Earthx, GRT EIS 4000 w/hall effect sensor on alternator B-lead, running all lights, etc. Steady state getting these kinds of fluctuations both voltage and current - is this "normal"? I have not yet tested without the flyleds wigwag lights or strobes or position lights (which are awesome, by the way).

Current fluxuations - Alternator 20200820.png
 
Looks like you have two waveforms with zero cross-correlation. Within each waveform there is strong periodicity.

I would start with the current pulses. If you have no cycling loads, then the Earthx BMS may be cycling. Ask them for more insight into their charging algorithm.

As for the voltage oscillation, any kind of resistance/bad connections in the field circuit can cause this. This is the fundamental problem with internal regulators, and some simple external regulators.

As for being abnormal, what is normal for your aircraft? Is this a new install?

Vern
 
new aircraft

...

As for being abnormal, what is normal for your aircraft? Is this a new install?

Vern
Thanks for the hints Vern. Yes, the aircraft is new, and I see this on all my graphs as saved in my GRT Sport EX EFIS, after it settles down at startup. I assume the startup peak is due to quick charging the battery.
 
0.1 to 0.2 fluctuation in volts does not seem problematic.

You say strobe lights are on as well as wig-wag , and that should explain the amp fluctuations.

Try turning all lights off and see what happens. The battery could also have a unique charging algorithm.
 
You're getting a greater than 10 amp fluctuation which is not normal. The only time I have seen this before it turned out to be a field switch with internal corrosion and the contacts were also corroded. Not sure what the age of your airplane is, but certainly worth a check, easy to swap out your field switch to eliminate that possibility.
 
lights off test

Powered off all the lights and the current shown from the alternator did go down - no surprise.

Current Graph - HB-YMM - Lights Off Test - 20200824.png

Looking at the graphs with everything on (except fuel pump/flaps/trim/AP servos) there seems to be a regular pattern.

Current Graph - HB-YMM - 20200824.png

I will check with earthx and hartzell (plane power) to get their views.

All the connections seem ok but I have not physically disconnected/reconnected them - which I will do. It's all "new", so there could be an installation error.
 
In the olden days (2006) in my 9A, I fixed my externally regulated Vans supplied 35A alternator by rewiring the Alt Field switch to control a relay that connected the Alt B lead directly to the external Voltage Regulator (VR).

This eliminated all of the field wiring, terminals and alt switch from the control loop and gave me rock-solid alternator output and reduced headset noise.

Moral of the story: if your alt field circuit is not perfect, you will have problems. If you have an alternator field switch made by Carling, replace it with a Honeywell and make sure you use the expensive crimp terminals, not the ones from the auto parts store. Digi-Key is your friend.

Hartzell will give you the same advice. My next airplane will use an externally regulated alternator with a sense lead.

V
 
Thank you Mickey for reaching out to us at EarthX with your questions.

The battery has no built-in charger or charging algorithm as suggested that could cause this issue. Based on the supplied graphs of voltage levels, (12-15 volts) it is no different than a lead acid battery.

Based on the supplied trends, the current and voltage are not in sync, so this is not a battery issue and there must be some load on the aircraft.

If it is battery influenced/related issue (any kind of battery) the voltage and current oscillations would be in sync. That is, if the alternator voltage increases, then the current from alternator would also increase because more current would be “pushed” to the battery. As voltage out of alternator decreases, the alternator current would decrease for the battery would supply more current.
 
Not the battery

...
The battery has no built-in charger or charging algorithm as suggested that could cause this issue. Based on the supplied graphs of voltage levels, (12-15 volts) it is no different than a lead acid battery. ...
Thanks Kathy. I am standing by for an answer from PP/Hartzell to see if they have any hints.

BTW, all my switches are honeywell, except my lights.
 
problem continues

Following up on this, Plane Power/Hartzell generously sent me a new RMA alternator and I get the exact same behavior. I hesitate to call it a "problem" since the alternator is charging, just doing it in I believe a strange way.

Here's the waveform from yesterday's flight - peak current is 15 amps, lowest is 4 amps. The period seems to be just over 11 seconds, and is very regular. I'm not aware of anything running in the aircraft with a 11-12 second period.

HB-YMM Alternator Output 20200918.png

Happy to get any ideas.
 
More than likely an indication issue, install a regular shunt.

I am with Walt. Don't see how this can something in your elec system with most things turned off and across two diff alt's.

I have an EIS and find some movement of the current reading, worst when strobes are on. My fluctuations are nothing like yours, but they are also not rock solid like the Garmin and Dynon that I have seen. I wonder if there is an issue with your EIS or the connector plugging into it.

Larry
 
You would definitely see a voltage fluctuation with the current going up and down like that so it's likely an indication error.

Probably a bad hall effect sensor, or voltage induced into the hall effect sensor wiring from other wires running in parallel with it. Use twisted or shielded wires for the sensor and don't bundle it together with wires carrying a lot of current.

Lenny
 
One day, almost 30 years ago, the manager of analog design at our start-up semiconductor company was having trouble with a design.

For those interested, it was an analog front-end for a T1 circuit.

It was behaving strangely, spitting out random bit errors, despite every trick in the book to clean up power and signal circuits.

One day, I walked into the lab to see how it was going, and he was at wits end... it ran all night with zero errors, but during the day it would spit out error bursts every few minutes! The light bulb went on.... I walked over to the Weller soldering iron, removed it from the holder and tapped it on the stand. Every time I tapped it, errors would occur.

He looked at me like I was some kind of magician, but it was just my years of debugging experience at play. By then, I was serving a sentence in Marketing, but I never gave up the chance to spend time in the lab.

Moral of the story: go find an experienced electrical person to help you out. Maybe he or she will spot the problem much faster than some random folks on the interweb. Be prepared to pay in $$ or beer.

Oh, that guy in the lab ended up as CTO of a $billion company.
 
Last edited:
Similar problem... any follow up thoughts?

On 9/30/2020 I replaced an Odyssey 680 battery in my Van's RV 7A aircraft with an EarthX ETX900 battery. During my first flight with the new battery I got an overvoltage indication and my field switch on the alternator [Plane Power 60 amp 12 V] kicked the circuit breaker off and would not reset. In consultation with Plane Power I purchased a new alternator and installed it. I keep getting an alarm/warning of Low Amperage on my Dyson D-120 EMS and the amp readings fluctuate from about 7 amps down to zero amps. every time it gets below 2 amps the warning goes off again. The voltage in the system maintains at 14.2 V. I have a video of the fluctuations I could drop link if needed. I spoke to the engineer at Plane Power [Allen 334-386-5400] and after describing this he indicated that the issue is probably with the Lithium battery BMS. Is this an issue that others have and what can I do to solve it? The gentleman from EarthX seems to indicate it is not a battery problem. Thank you. Dana Stoker (520) 838-0822
 
still the same

I'm still in the same place. I picked up a DC current meter from amazon but have not yet tried it with any of my systems. Won't be that easy to do since I'll need the engine running to test it. Here is a sample from my last flight a couple of days ago. Very clear pattern here.

The EarthX team commented that they can't see how this pattern is related to their battery. As a reminder, PP also recommended a new alternator, which they sent to me and I have the exact same pattern. Struggling to see how this could be an alternator fault. It could be a problem with the hall effect sensor - probably should just order a couple of new ones - they are not that expensive. Please let me know if you discover something!

Paul from flyleds also said he didn't have anything happening with his LEDs that could cause this. Also, it's the same with wigwag on and off.

HB-YMM Current Readings 20201102.png
 
Couldn't you start the airplane, then turn the master switch off and see if it goes away. Turning off the master should open the main contactor and remove the battery from the equation. With the battery disconnected you get a good idea if it's having any impact.
 
If the voltage remains constant at 14.2 volts, then the charging system is
working perfectly. Any fluctuation of current is due to either an indication
problem (likely) or a fluctuating load (unlikely).
 
Interesting test

Couldn't you start the airplane, then turn the master switch off and see if it goes away. Turning off the master should open the main contactor and remove the battery from the equation. With the battery disconnected you get a good idea if it's having any impact.
That would be interesting, but I have a progressive switch where my battery comes on first, then alternator.
 
Couldn't you start the airplane, then turn the master switch off and see if it goes away. Turning off the master should open the main contactor and remove the battery from the equation. With the battery disconnected you get a good idea if it's having any impact.
I did not build this airplane but, I think that the master switch will terminate bus power to the Avionics as well as cut the battery out of the circuit. I will try it but think I will find that the Dynon equipment goes off with the master. Thank you for the thought.
 
voltage stable

If the voltage remains constant at 14.2 volts, then the charging system is
working perfectly. Any fluctuation of current is due to either an indication
problem (likely) or a fluctuating load (unlikely).
Voltage fluctuates slightly, between about 14.2 and 14.5. I see a dip in voltage just after start while the battery tops up. Here's a short extract during "stable" conditions.

HB-YMM Voltage 20201102.png
 
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