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  #1  
Old 02-26-2021, 09:30 AM
Mdragon Mdragon is offline
 
Join Date: Nov 2020
Location: Jacksonville Florida
Posts: 19
Default Gauges all go bad when landing lights, nav lights on

I have a new to me RV9a. Went up for a night flight today, first time flying it at night.
And after my first landing: oil pressure pegged high, alternator voltage low, fuel pressure read zero. Turn off landing lights, slowly come back to normal.

Iím guessing I have a bad ground. Took the engine cowl off, and have been tracing wires. Nothing obvious.

Anyone run into this?

Frustrated.

Seems it is related to excessive current draw of landing lights, Strobe, radio, etc.
Lights werenít dim so think the alternator output is fine.

Any help greatly appreciated.
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  #2  
Old 02-26-2021, 09:52 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by Mdragon View Post
I have a new to me RV9a. Went up for a night flight today, first time flying it at night.
And after my first landing: oil pressure pegged high, alternator voltage low, fuel pressure read zero. Turn off landing lights, slowly come back to normal.

I’m guessing I have a bad ground. Took the engine cowl off, and have been tracing wires. Nothing obvious.

Anyone run into this?

Frustrated.

Seems it is related to excessive current draw of landing lights, Strobe, radio, etc.
Lights weren’t dim so think the alternator output is fine.

Any help greatly appreciated.
Doubtfull it is due to excessive draw in the alternator; That should result in a voltage sag, not these kinds of issues. Not sure that simple noise from the lights would cause this kind of problem with all of your gauges. It would seem that the lights are throwing something nasty on to the buss or ground plane. I would avoid turning on those lights again until you find the source. Don't want to trash a bunch of sensitive electronics.

Larry
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Last edited by lr172 : 02-26-2021 at 09:54 AM.
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  #3  
Old 02-26-2021, 10:08 AM
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wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 4,377
Default Ground

I would start with the ground for the lights.
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Donated 01/01/2021, plus a little extra.
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I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #4  
Old 02-26-2021, 10:16 AM
OKAV8r OKAV8r is offline
 
Join Date: Feb 2007
Location: Seattle
Posts: 153
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Quote:
Originally Posted by Mdragon View Post
Iím guessing I have a bad ground. .
I think you're right. Try running a 14 ga jumper from the landing light ground direct to battery negative. If the problem goes away, then it would indicate the existing ground path is overloaded or resistive. Also, check ground points back to battery ground for resistance. Anything over 5 milliohm should be suspect.
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  #5  
Old 02-26-2021, 10:20 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
Posts: 2,943
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Not enough data to draw a conclusion, so I will speculate.

Electrical noise is one reason why you have these symptoms. Electrical noise associated with landing or NAV/Strobes could be with an old school strobe power supplies or new school LED lights. Another source could be high resistance contacts ďarching and sparkingĒ (power or ground).

I first suggest further isolation of the issue. Is this problem what just landing lights, just strobes or just nav lights? If so, that dictates the next step. If the problem is common across the lights, look for the common component - like everything powered via one breaker.

One other potential issue, do you ground these lights locally to the airframe? For an older plane this can be is a source of issues.

Carl
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  #6  
Old 02-26-2021, 11:15 AM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 626
Default Grounding...

Based on prior posts, I think you have a set of round gauges in your panel. Start by locating the ground for each gauge, and ensure the terminations are solid, corrosion free, and low resistance -- in the sub Milliohm (<.001) range.

From there, look at the grounding of the Landing, NAV, etc. lights. In all likelihood, they are using the aluminum structure as the ground path. Same routine -- verify the grounding is solid, corrosion free, and low resistance.

Local or Airframe grounding is common practice and not a problem as long as the path back to the current source is low resistance. Remember that the return (ground) wire of a circuit should be the same size as the supply, and the airframe represents a HUGE gauge of wire (000 AWG) if connections are done correctly. Are there jumpers installed between major airframe assemblies? Across Anodized Pieces? Corrosion free between panels? etc.

The gauges in the Mooney I had would "sag" when the landing light was turned on -- The point contact ground that the cluster gauge used had vibrated itself into a little puddle of AlO2 dust. The solution was to run a real wire from the gauge case to airframe.

As an aside: "Noise", which is AC riding on top of DC (imagine little ripples on the top of a pond -- the surface of the pond is DC, the ripples are AC), is caused by e-fields being induced in or coupled in a circuit; power supplies for LED lights, Alternator, Ignitions, Magnetos, etc. are the typical sources in an airplane. You will hear this in your headphones if the frequency of the AC is between 20 - 20KHz, and your hearing is that good.

Expanding out a bit more, RFI > 20KHz won't be audible in headset, but can still cause problems with other systems in the aircraft -- errant temperature readings in OAT/CHT/EGT, GPS losing lock, Data errors in RS-232,485, CANBus, ARINC 429, etc. ad nauseum...
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2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #7  
Old 02-26-2021, 11:37 AM
pilot2512 pilot2512 is offline
 
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Location: Spring, TX
Posts: 485
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I guess I am going to be the contrarian here. If those are conventional landing lights (not LED) and they are drawing quite a bit of current then if they are bundled to closely to those wires for the guages, then you may be inducing current in the adjacent wires. You might need to move the landing lights wires away from the others.

Jay
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  #8  
Old 02-26-2021, 01:56 PM
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bjdecker bjdecker is offline
 
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Location: Georgetown, TX
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Quote:
Originally Posted by pilot2512 View Post
I guess I am going to be the contrarian here. If those are conventional landing lights (not LED) and they are drawing quite a bit of current then if they are bundled to closely to those wires for the guages, then you may be inducing current in the adjacent wires. You might need to move the landing lights wires away from the others.

Jay
...Only if the gauge wires run parallel to the high current wire for a non-insignificant distance ( Depends upon field strength, distance betwixt wires, etc.)

https://www.khanacademy.org/science/.../v/magnetism-7
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Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #9  
Old 02-26-2021, 02:52 PM
74-07 74-07 is offline
 
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Location: Greenville, SC
Posts: 562
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Do you have separate gages or perhaps a Rocky Mountain Monitor?
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  #10  
Old 02-26-2021, 03:33 PM
Mdragon Mdragon is offline
 
Join Date: Nov 2020
Location: Jacksonville Florida
Posts: 19
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Wow,

Great responses! Thanks guys.

I went back out this AM before work and took a look with better light.
I was unable to find a firewall to engine or firewall to motor ground strap. I found a 2 gauge wire running from negative battery terminal to a bolt on back of the engine, which was properly scuffed down to bare metal.

All of the negative wires go to a negative bus bar on the subframe just behind my panel. This panel has a large post for a wire, but it is not attached to anything.

It seems that with everything running, i.e. nav lights, strobes, ahrs, garmin, radio, landing lights, that the fuel and oil temp don't work, and the voltage meter reads low. Yet the alternator idiot light doesn't come on. Both the oil pressure sender and the fuel pressure sender have a single wire in the sender, and are grounded through the manifold attached to the firewall.

From how I describe this do you think the subpanel is adequately grounded?

I may just run a strap from the subpanel to to a through bolt on firewall, and make a strap from that bolt to the engine.
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