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  #1  
Old 01-22-2022, 10:00 AM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 3,060
Default Strange Alternator + Battery Issue

I guess the best way to tell this, and ask questions about it, is to start from the beginning.

I replaced the Odyssey PC-680 battery about two weeks ago. Was fine for several flights.

I had an avionics shop do a 91.413 transponder check, which involved having the avionics powered up by the battery for, oh, probably 10 minutes.

Just after that, I started the engine with the alternator field switch off, as I always do, it cranked fine and started right up. I did not happen to notice the buss voltage. Then I turned on the field switch and the avionics master, as I always do, and a bunch of strange things happened all at once.
The Dynon EMS-120 display blinked out for a second, then came back showing, just for an instant, a buss voltage of 8.5V, then 15.1V, where it stayed. But the display showed -3 amps, meaning that the battery was discharging to power the avionics. Three amps is about the right load that I normally see, but it should be +3A.

I turned the field switch off, and the buss voltage dropped to 10.9V, and the current remained -3A. I turned the field switch back on, and the voltage again went up to 15.1V, but the current remained -3A.

How can it be that the alternator is putting 15V into the buss, but no current, so that the battery is still discharging? And why was the battery suddenly down to 10.9V?

I have a feeling that two separate failures occurred, perhaps one causing the other.
It seems that the Plane Power voltage regulator has failed and the alternator output is being held at 15.1V by the crowbar? It seems possible that this could be from a high-resistance connection at the field wire plug (that has happened before, although it caused a moderately high output, 14.8V, not 15.1V) or else the regulator just failed.
It also seems like the new PC-680 battery now has a shorted cell. I put it on a charger, and it charges at 13.2V and as soon as the charger is disconnected it drops again to 10.9V.

Did the high voltage cause a failure in the battery? Did a shorted cell in the battery cause the failure of the voltage regulator?

But why and how could the alternator be putting out 15V into the buss and yet not supply any current?

As a final detail because it is necessary to make sense of all this, the ammeter shunt is located between the battery contactor and the power buss, and the alternator output feeds the power buss. So the ammeter indicates current in and out of the battery. + current means battery is charging. - current means battery is discharging.

Looking forward to explanations. Thanks.
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IO-360 A1A
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  #2  
Old 01-22-2022, 10:51 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
 
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Location: Dogwood Airpark (VA42)
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Default

Agree that the battery is dead. Replace it. Do not try to bring it back from the dead. From what you say I do not suspect the alternator to have caused the battery to fail.

The alternator issue may be a reflection of the dead battery. As you turned on the alternator, if the battery was that dead the alternator output breaker or current limiter (if you have either) may have popped. This would explain the continued discharge on the battery, as well as the 15vc measurement IF you sense alternator voltage on the alternator side of the breaker/current limiter.

So replace the battery, check your alternator breaker/current limiter, then see what you have.

Side note - I would not find it unusual for a unloaded Plane Power alternator to show 15vdc at the output terminal. If under normal operations your buss voltage is steady at ~14.1 vdc the alternator internal regulator is working properly.

Side note - if the Plane Power alternator over voltage crowbar protection tripped, your field (sense voltage) breaker or fuse should have popped. As you turned this on and off and the alternator responded I suspect it did not pop.

Side note - I find no practical reason to not have the alternator on line at engine start. I have mine on a breaker, the only time I pull the breaker is for testing (as in does the standby alternator pick up the load).

Let us know what you find.

Carl
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  #3  
Old 01-22-2022, 11:28 AM
RV7A Flyer's Avatar
RV7A Flyer RV7A Flyer is online now
 
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Did you check the fuse or breaker for the alternator field circuit?
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  #4  
Old 01-22-2022, 12:08 PM
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koupster koupster is offline
 
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Location: SLC, UT (KBTF)
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Default Battery

The PC-680 may just have been depleted from the avionics testing.

Charging it at 13.2 volts probably won't help. It likes 14.7 volts and at least 6 amps.
https://www.odysseybattery.com/wp-co...gedODYSSEY.pdf
https://www.odysseybattery.com/wp-co...gedODYSSEY.pdf
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  #5  
Old 01-22-2022, 07:45 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default

Thanks guys.

Neither the 60A breaker for the alternator supply into the buss, nor the field breaker switch, 'popped'. It is encouraging and helpful info that if the crowbar engages, then the field breaker should pop.

I'm not sure my small car battery charger can put out 6A, so it may not be able to put enough out to get the charge voltage up. 13.2 was the best the little charger could muster apparently. I have seen it charge other batteries up to 14V +, but they were not very far discharged.

Batteries Plus says they will charge the battery and test it, and it will either pass, or I will get a warranty replacement.

In the mean time, I have replaced the field wire plug that goes into the Plane Power alternator with a better one, one that has strain-relief o-rings on the wire side of the plug. I've been meaning to do that for a while now anyway.

I do have a replacement regulator/brush holder module that I can install if needed. I'll try with a full battery first.

I usually start with the field switch off because it removes the current drain through that circuit, assuring a higher cranking voltage. If my airplane sits for a month, as it often does unfortunately, the battery isn't usually tip-top, so that is just a habit I got into.

I still don't understand why the battery would not accept charge current. It had enough 'juice' to start the engine, easily, so it couldn't have been too run down. It had enough 'juice' to power the Dynon up prior to start, and subsequently after shutdown (although it reads 10.9V on the Dynon).
If there was a broken wire in the battery-to-buss feed, it wouldn't be able to do that.

I'll report back tomorrow.
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Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
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  #6  
Old 01-23-2022, 02:13 AM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by scsmith View Post
...

I usually start with the field switch off because it removes the current drain through that circuit, assuring a higher cranking voltage. ...
Some say leaving the alternator off is the result of an OWT, but this year at oshkosh the Hartzell/PP guy said something like "I don't know why you would leave your alternator on during all the craziness of the starting cycle - turn it on after the engine is running."
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  #7  
Old 01-23-2022, 05:26 AM
BillL BillL is offline
 
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Location: Central IL
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Quote:
Originally Posted by scsmith View Post
I still don't understand why the battery would not accept charge current. It had enough 'juice' to start the engine, easily, so it couldn't have been too run down. It had enough 'juice' to power the Dynon up prior to start, and subsequently after shutdown (although it reads 10.9V on the Dynon).
If there was a broken wire in the battery-to-buss feed, it wouldn't be able to do that.

I'll report back tomorrow.
Agree Steve, that does not make sense, but getting the battery charged and checked before in-plane diagnostics is the thing to do. When confusing electrical things occur I start over from a known condition and methodically check functionality. I use a 14/15 VDC power supply when at the avionics shop and updating databases, JIC. My PP puts out 14.7 to the buss. A fried-stuck-on regulator could put out 15.1 v at idle but that would not make sense of the amps, unless there is maybe a bad rectifier bridge. You can check AC content of the output in the diagnostics phase.

BTW - 6a is just right per the battery manual. It is worth reading as the AGM seems more particular/different than a lifetime of experience with flooded type.
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Last edited by BillL : 01-23-2022 at 05:31 AM.
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  #8  
Old 01-23-2022, 05:42 AM
sailvi767 sailvi767 is offline
 
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I am betting infant mortality on the battery. With zero load you might see 15.1. Start with the easy thing and get the battery tested.
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  #9  
Old 01-24-2022, 08:23 PM
scsmith scsmith is offline
 
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Default

OK, update, now that I think I have everything sorted out.

I pulled the battery out and took it to Batteries +, where they charged it overnight and load tested it. They said the battery was fine, so I put it back in, and started other troubleshooting.

After re-installing it, voltage at battery terminals was 12.7V. I turned the Master on, and the Dynon EMS showed 11V. So I re-measured at the battery terminals and it was still 12.7V.

Hmmm, starting to look like an instrumentation issue. So I measured the buss voltage directly, and it agreed with the Dynon, 11V.

In the process of doing this, I had cycled the master switch a few times as I moved around, just saving battery. And then, the (I think) smoking-gun event happened. I turned the master on and the contactor did not engage. Nothing. I cycled the master twice more, and I heard the contactor click and everything came back, and now, surprise surprise, the Dynon shows 12.7V !

So I am thinking I have worn contacts on my battery contactor, and cycling it a few times seems to have temporarily rejuvenated it. I buttoned everything up and went flying.

Everything seems normal now. The strange charging behavior was perhaps partly due to the connections on the alternator, which now has a new plug, and seems to be much better than the original. I can't explain the initial battery discharge indication though....

I'll replace the battery contactor as soon as I can and otherwise just keep an eye out, but for now, everything is acting as normal. I suppose it is remotely possible that the master switch itself is failing. It is a standard DPDT toggle switch.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2021
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  #10  
Old 01-25-2022, 04:23 PM
Paul 5r4 Paul 5r4 is offline
 
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Default Battery contactor

I went to a fly in 20 miles away a couple years back. Everything normal. Stayed a couple hours then climbed in to head back. Started the engine, (it was sluggish), and noticed the amps were running +9. Normally I see +1 or 2 down to -1 or 2. I didn't notice the voltage before starting. Otherwise everything was good. I took off and after flying a bit the amps began to come down to normal. I figured the only thing that could have happened was a stuck battery contactor which somehow drained the battery over the two hour period.

Sooo after the above event I ALWAYS listen for that distinctive click when shutting the battery side of the master switch off. It's never happened again.
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Last edited by Paul 5r4 : 01-26-2022 at 07:14 AM.
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