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High Voltage

Champ

Well Known Member
I have a Plane Power AL 12-EI60/V alternator and a 4 year old rear mounted PC680 battery with 200 hrs on it.
Static charge on the battery is 12.8v on its terminals and 12.4v on the buss - both on my Dynon EMS D10 and a multimeter.

In flight buss voltage has gone from 14.3v to 14.8v avg with a saw tooth pattern varying between 14.4v & 15v and a couple spikes to 15.1v. All with constant load. Buss amperage varies as well between -6.6a & +10.5a.

Note: volt/rpm/amp data graph. Dip at 18 min was when I briefly took the alternator off line - here voltage dropped to 11.5v & amperage to -25a.

2022-01-29 Flight Data.png

Amperage variation is very strange with load being constant. Terminals on the shunt are tight.
Should I be saving up for a new alternator or battery or both or is there something else going on?
I've got a ticket in a Savvy looking for their input as well.
 
As long as system voltage is above 13 volts, then the battery is out of the picture and is not a problem.
I question the accuracy of the ammeter, specifically the zero reference line. Aircraft electrical loads will ALWAYS draw current from the source with the highest voltage. Since the voltage is above 14 volts for the most part, then it is impossible for the current to be negative. Loads will NOT draw current from the battery when 14+ volts are available from the alternator.
Can you post a drawing of the electrical system showing the battery and contactor and shunt and alternator B lead connection and diode and bus?
See my post #9 below.
 
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My experience

In my experience this has been caused by corroded connections. I have t figured out why it happens this way but it did.
 
agree on connections. Check connections between battery, alternator, and buss for tightness and corrosion. Corrosion might cause reg/rec to think the battery needs more juice, hence the spike.
 
Master

I had a Cessna style master switch intermittently cause voltage in the mid to high 15v range. Replaced with new and voltage returned to normal mid 14 volts.
 
I had a Cessna style master switch intermittently cause voltage in the mid to high 15v range. Replaced with new and voltage returned to normal mid 14 volts.

A bad alternator field switch or terminals is #1 on the list. On my 9A, I ended up using a relay controlled by my Alt switch to directly connect the Field to the B lead with short wires. External OVP turn the relay off by tripping the field breaker.

Question… are you hearing whining in the headset? This is also a symptom of a poorly regulated alternator or a failing alternator.

VV
 
Static charge on the battery is 12.8v on its terminals and 12.4v on the buss .

That points to your problem. Somewhere between the battery and the buss, you have excess resistance that is producing the voltage drop. Likely a bad connection or corrosion and likely varies with vibration. This can cause numerous issues, including problems with conssistent voltage from the VR. Get your VOM out and start looking for the problem.

Larry
 
I hate to admit it, but I was wrong in my post #2 above. I failed to realize that the battery voltage is at 14 volts for a short period of time after the alternator quits working. Before the battery voltage drops very much, the alternator starts working again when the loose connection remakes contact. The majority of electrical problems are caused by bad connections.
 
Originally Posted by Champ
Static charge on the battery is 12.8v on its terminals and 12.4v on the buss.

That points to your problem. Somewhere between the battery and the buss, you have excess resistance that is producing the voltage drop...

Fair point, but these days, when someone mentions bus voltage, they are typically reading it from an EFIS/EIS, which often has internal diodes in dual 12V+ inputs.
 
Thanks guys. I've got a few things to check.

1. All connections for tightness & corrosion. I did pot the field plug at the alternator with RTV when it was first wired but I'll check it to. Anyone ever used DeoxIT D5 on connections? It worked great on vintage audio equipment I've rehabilitated.

2. Here's a sketch of my system:

C-FDTQ Electrical Sheet 1.jpg

3. I'm still confused by the negative amperage readings. Is positive flowing from the buss/alternator to the battery and negative from the battery to the buss when the alternator isn't working?
 
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Check schematic...

What kind of master solenoid are you using? The typical Cole Hersee/White Rodgers -- 24115 -- has a "Ground-to-Activate" connection.

If the shunt is wired backwards it will indicate (-) AMPS.
 
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Champ, your understanding of current through the shunt is correct.
The EFIS will show negative current when the battery is discharging and positive current when the battery is being charged.
Is the EFIS giving a low voltage alarm? Are there any other symptoms that indicate low voltage or an electrical problem?
-
bjdecker is correct. There is an error with the schematic. When the battery contactor is off, there is no positive voltage
available on the bus to turn on the contactor. Usually the battery contactor is
energized by connecting negative to the small terminal on the battery contactor.
 
Brian & Joe - Thanks

The master solenoid is a Vans ES24115 & yes it is grounded to activate. I revised the sketch to show the master switch better. I've got my low voltage alarm set at 12.5v & haven't had any low voltage alarms or symptoms. I have noticed that the alternator drops off on roll out sometimes when the RPM gets below 600+- but I understand this is normal.
 
I think that you are looking for a problem that does not exist.
The voltage in your RV-8 is steadier than it is in my RV-12, albeit single phase PM alternator.
I would increase the low voltage warning to at least 13, or 13.5 as long as there are no nuisance alarms.
The ammeter in my D-180 has never worked right. I question the accuracy of your ammeter.
The current variation might just be digital noise.
The fact that the battery static voltage is 12.8 means that it has been adequately charged.
When the master switch is turned on, it is expected that the load connected to the battery will drop the voltage.
12.4 volts on the bus is OK with the engine not running.
 
Joe, Sounds reasonable. I’ll bump up the low voltage alarm, monitor volts & amps and keep flying it - soon as the airport is dug out from the big snow. Thanks
 
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