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  #1  
Old 06-17-2017, 03:52 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Default Need Help Diagnosing Electrical Faultů

I just finishing an uneventful 1.2 hour flight and had a high voltage alarm on the D-180 at 5 miles from final destination. I viewed the EMS screen and saw 14 volts on battery in red arc. I kept manually shutting off the alarm and then landed. All electrical systems were working. High voltage alarm subsided when power was reduced for landing. After landing I reset elevator trim position as I taxied in like normal. Engine shut off was normal followed by the powering down the Master Switch.

I thought the John Deere VR failed now at 245TT. Original Ducati VR failed at 104TT hours but mode of failure then was low voltage and not high voltage.

I have a spare JD VR so I installed by mounting it on the shelf in original location. VR wired correctly and all wiring under cowl looks good.

I turned on the Master Switch and nothing happens. No relay click - nothing.

I detected a strong whiff of electrical smell and quickly disconnected the negative battery terminal. I removed the instrument bay cowling and the smell appears to have emanated from the fuse block/switch cluster. All fuses are good as checked with ohmmeter. I have shined a bright light at the back side of the fuse block and looked down between the circuit boards and don’t see any damaged components. Various capacitors look OK. If I power the D-180 with its backup battery it shows battery voltage at zero with main battery connected. I measure actual battery voltage at 12.9 with a VOM.

I think my next step is to remove the D-180 EFIS and then remove the fuse block/switch cluster for a detailed visual examination. My plane is an early SN so it has the fuse block/switch cluster on the left side.

If anyone has any thoughts I’d appreciate some insight.

Thanks in advance…
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 315
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  #2  
Old 06-17-2017, 07:56 PM
Mich48041 Mich48041 is offline
 
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14 Volts is NOT high voltage. It is normal. If the D-180 alarms at 14 volts, then the alarm set point needs to be raised.
Without the master contactor being energized, the only thing that can emit smoke is the master switch or its wire that connects to firewall D-Sub pin 22.
Or maybe the smoke is coming from the master contactor itself.
Analyze the D-180 datalog to see what the voltage was peaking at. The datalog is csv file that can be opened with MS Excel.
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Old 06-17-2017, 09:43 PM
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After isolating the master relay from power I would check the coil resistance. Battery terminal to front small terminal. I believe it should be about 15 ohms. (guess)
But I suspect it will be ether open or shorted. Bad relay. If it tests bad suspect your master switch may be toasted. (smell) So test the switch contacts for proper operation. P 44 - To ground...open (off)/grounded (on). Check the master relay diode also...


Regards,
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  #4  
Old 06-18-2017, 01:57 AM
trackdom trackdom is offline
 
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Default Diode

A few weeks ago I had some problem when switching on the master switch . One time the switch wire was burning with a lot of smoke, fortunately not flying.
The master relay diode was not working correctly , I replaced it and now all is ok.
I noticed also that I had an overvoltage alarme, reaching 15,8 v , and also a flap runaway alarm. Since I change the diode , no more overvoltage neither flap runaway indication.
Check your diode .
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Old 06-18-2017, 07:07 AM
Mich48041 Mich48041 is offline
 
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In the D-180 electrical system, the small yellow wire that goes to regulator terminal "C" does not have over-current protection. Since the problem occurred after the regulator was replaced, it made me think of that yellow wire. Of course the master contactor would need to be energized before that wire could get into trouble.
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Old 06-18-2017, 08:32 AM
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Piper J3 Piper J3 is offline
 
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Joe

Maybe you're on to something. I forgot to mention that when I changed out the VR and still had no voltage through the Master Switch I tapped the Master Relay with handle of screw driver and that is when whiff of electric happened. I forgot sequence of events - kinda like fake news or alternative facts.

I've been studying D-180 electric schematics for master power flow. I just ordered new Master Relay and Diode from Van's. I'm getting ready to head out to the plane now to remove the AV Control Board 12 (Fuse/Switch Circuit Board).

Thanks for your help. Electrical is not my strong suit...
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 315
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Old 06-18-2017, 09:22 AM
Mich48041 Mich48041 is offline
 
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About a year ago I did an experiment: shut off the master contactor while keeping the voltage regulator turned on. The charging system kept on working even with the battery disconnected. But the voltage was not stable and varied between 13.25 and 14.7 volts. You can read about the experiment in my matronics post HERE 5th post down. Bottom line is that the charging system is unstable without the battery and the voltage will vary. I suspect this is what happened in Jim's (Piper J3) RV-12. The master contactor opened up for some reason while flying. The charging system kept right on working, although the voltage was unstable, causing the D-180 to give a high voltage alarm. So Jim, there is probably nothing wrong with the voltage regulator that you removed. The problem is the master contactor or its circuit.
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Old 06-18-2017, 12:05 PM
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Piper J3 Piper J3 is offline
 
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OK, I just got back from the plane. I removed the AV Control Board 12 and now have it at home for detailed checkout. After studying the electrical schematic I noticed that the original builder of the plane had the Master Relay Diode connected to the battery side instead of the load side of the contactor. I'm thinking perhaps the Master Relay is defective now and may have destroyed itself over time because of improperly wired diode. I have new Master Relay and associated diode on order from Van's. As Joe mentions above, this would explain the over-voltage warning on the D-180 in flight. Thanks Joe...

What I'm still puzzled about is the electrical burning smell when I tapped the Master Relay. Did it back-feed the master switch to ground?

I'll report back on the condition of the AV Control Board 12 when I examine it this afternoon. I will look especially at the master switch and verify that its contacts are "seen" at the pin connector on the backside.
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Jim Stricker
Hinckley, Ohio
PPL - 1970
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC 7/12 Bought Flying 10/2015 with 48TT - Hobbs now 315
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  #9  
Old 06-18-2017, 12:38 PM
Mich48041 Mich48041 is offline
 
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The purpose of the diode is to prevent arcing across the contacts of the master switch. The diode should be connected directly across the contactor coil with the banded end connected to the most positive (battery) terminal. The diode has no affect on the life of the contactor. It sounds like the diode was correctly installed. The diode can be tested to make sure that it conducts one direction but not the other.
A burned copper trace on Van's circuit board could account for the smell and non-working contactor. A shorted diode or contactor coil could burn a copper trace.
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  #10  
Old 06-18-2017, 02:34 PM
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Tommycat Tommycat is offline
 
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Hi Jim,
If your using the schematic downloaded from Van's...somethings not right.

See Van's RV-12 D-180 schematic download HERE.

And don't even think about following the VREG circuit...must have run out of orange ink...

But I think Joe is correct in the diode wiring. To the battery terminal.

Good Reading...on this topic.

Regards,
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