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Gauges all go bad when landing lights, nav lights on

Mdragon

Active Member
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.
 
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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I’m 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.
 
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 “arching and sparking” (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
 
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...
 
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
 
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...tic-field-current-carrying-wire/v/magnetism-7
 
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.
 
Have you checked the voltage with a meter? The problem could be failure of the charging system.
Voltage should be around 14. If less than 13 at cruise RPM, the charging system is definitely not working.
 
Have you checked the voltage with a meter? The problem could be failure of the charging system.
Voltage should be around 14. If less than 13 at cruise RPM, the charging system is definitely not working.

I thought about that. Would think that the landing lights would be dim, but they weren't. Also, did the same thing when in the hangar, engine off.
 
If its easy to add a strap from that negative bus to the battery, then do it and see if it makes a difference!

Paul
 
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.

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.

It appears from your post that the negative bus bar and the airframe have no dedicated ground path to the negative terminal of the battery. In this case, the airframe mounted electrical devices resort to finding a ground through things such as fuel system braided lines and engine control cables (throttle, mixture, and prop).

For a quick check, connect a battery jumper cable between the large post on the negative bus bar and the negative battery terminal and see if that temporarily resolves the problem.

The negative bus bar should have a wire or strap of sufficient gauge to handle the return current of all the airframe mounted electrical devices that leads to the negative battery terminal directly or through the grounding bolt on the engine. Also, make sure that the negative bus bar is grounded to the subpanel that it's mounted to.
 
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It appears from your post that the negative bus bar and the airframe have no dedicated ground path to the negative terminal of the battery. In this case, the airframe mounted electrical devices resort to finding a ground through things such as fuel system braided lines and engine control cables (throttle, mixture, and prop).

For a quick check, connect a battery jumper cable between the large post on the negative bus bar and the negative battery terminal and see if that temporarily resolves the problem.

The negative bus bar should have a wire or strap of sufficient gauge to handle the return current of all the airframe mounted electrical devices that leads to the negative battery terminal directly or through the grounding bolt on the engine. Also,make sure that the negative bus bar is grounded to the subpanel that it's mounted to.

The bus bar is flat and against the metal subpanel, screwed into it. I assume this would ground it. Are you saying putting a wire from the bus bar to the subpanel, and another wire from the bus bar to the negative battery terminal?

Going to make a 2 gauge negative tomorrow and ground the bus to the negative battery terminal, see how it goes. Hope it is that simple.
 
If the problem is caused by the lack of a direct connection between the battery negative terminal and the firewall mounted ground bus, then that may imply that the problem has always been there, from when the plane was first built. Can you check with the previous owner to see if he/she encountered the problem? And if there is a wiring diagram?

Otherwise, you mentioned that the system recovers slowly after the lights are turned off. That could indicate a bad battery that is on its way out. Do you know the age and condition of the battery?

Assuming that the fuel and oil pressure senders on the firewall manifold are the VDO resistive type, I think it is less likely that interference is causing the problem. My guess is that it's a bad ground, or a short somewhere, or the battery.

Attached is a sample wiring diagram to show the connections between battery, engine, firewall ground.
 

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The bus bar is flat and against the metal subpanel, screwed into it. I assume this would ground it. Are you saying putting a wire from the bus bar to the subpanel, and another wire from bus bar to the negative battery terminal?

Going to make a 2 gauge negative tomorrow and ground the bus to the negative battery terminal, see how it goes. Hope it is that simple.

The heavy wire should lead from the large post on the negative bus bar to the negative battery terminal. Sounds like the negative bus bar is adequately grounded to the subpanel.

2 gauge wire may be overkill since it doesn't have to carry the return current from the starter, just the airframe mounted electrical devices.
 
If the problem is caused by the lack of a direct connection between the battery negative terminal and the firewall mounted ground bus, then that may imply that the problem has always been there, from when the plane was first built. Can you check with the previous owner to see if he/she encountered the problem? And if there is a wiring diagram?

Otherwise, you mentioned that the system recovers slowly after the lights are turned off. That could indicate a bad battery that is on its way out. Do you know the age and condition of the battery?

Assuming that the fuel and oil pressure senders on the firewall manifold are the VDO resistive type, I think it is less likely that interference is causing the problem. My guess is that it's a bad ground, or a short somewhere, or the battery.

Attached is a sample wiring diagram to show the connections between battery, engine, firewall ground.

Yes I have VDO type senders for fuel and oil temp. Battery is 2016, cranks the starter well and fast. I'm going to start with negative bus to the negative battery terminal and test, as that is relatively simple and quick.

The builder hasn't been very helpful and has gone ghost since I bought it. A bit of a weird dude. Overall happy with the plane. The panel and wiring were not the strongest part of the build.

What gauge wire for ground would you think appropriate to handle all the panel electronics, strobes, and lights?
 
What gauge wire for ground would you think appropriate to handle all the panel electronics, strobes, and lights?



You could total up all the airframe mounted electrical device loads and consult a wiring chart that takes into consideration the length of the wire involved, or you could match the wire that feeds the main bus from the master relay. If you think the builder may have skimped here, just go two wire gauges heavier.
 
Marc,
To answer your second question, I don’t think your ground bus is adequately grounded. Typically, what many of us have used is similar to this:

https://www.steinair.com/product/20tab-grounding-buss/

This is typically mounted on the stainless steel firewall with instrument panel grounds connected to the tabs, and the negative terminal of the battery, AND the engine ground strap both connected to the large brass bolt on the forward side of the firewall. The easiest solution for you might be to get yourself a brass bolt (5/16”), drill a hole in your firewall for it (close to a structural angle), and attach a ground ground wire - 10-12 awg - from your ground buss/block to that brass bolt on the cockpit side. On the forward side, get a braided ground strap (2 awg) at NAPA or some other suitable place, and connect it from the brass bolt on the engine side to the same engine bolt where your battery negative terminal is connected. The only gotcha is that you need to isolate that ground bus from the metal sub panel it is currently mounted to. This can be done with creative use of nylon blocks, or by using something like this:

https://www.steinair.com/product/8-position-terminal-block/

These can use either screws and ring terminals as shown, or faston tabs that attach under the screws. This would eliminate the need to splice ground wires to reach the firewall where the ground buss should have been mounted in the first place. Of course you will need to tie all these points together electrically. There are jumpers made for this purpose, available on this Stein site, Aircraft Spruce, Mouser, etc. Grounding to the firewall (best) and to the sub panel both, invites possible ground loop issues. You don’t want that.
 
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6 Gauge

That wiring diagram that Paul vS sent shows 6 AWG feeding the main bus and also handling the alternator output. I think that would be appropriate for your ground wire.
 
Marc,
To answer your second question, I don’t think your ground bus is adequately grounded. Typically, what many of us have used is similar to this:

https://www.steinair.com/product/20tab-grounding-buss/

This is typically mounted on the stainless steel firewall with instrument panel grounds connected to the tabs, and the negative terminal of the battery, AND the engine ground strap both connected to the large brass bolt on the forward side of the firewall. The easiest solution for you might be to get yourself a brass bolt (5/16”), drill a hole in your firewall for it (close to a structural angle), and attach a ground ground wire - 10-12 awg - from your ground buss/block to that brass bolt on the cockpit side. On the forward side, get a braided ground strap (2 awg) at NAPA or some other suitable place, and connect it from the brass bolt on the engine side to the same engine bolt where your battery negative terminal is connected. The only gotcha is that you need to isolate that ground bus from the metal sub panel it is currently mounted to. This can be done with creative use of nylon blocks, or by using something like this:

https://www.steinair.com/product/8-position-terminal-block/

These can use either screws and ring terminals as shown, or faston tabs that attach under the screws. This would eliminate the need to splice ground wires to reach the firewall where the ground buss should have been mounted in the first place. Of course you will need to tie all these points together electrically. There are jumpers made for this purpose, available on this Stein site, Aircraft Spruce, Mouser, etc. Grounding to the firewall (best) and to the sub panel both, invites possible ground loop issues. You don’t want that.

For sake of understanding, why must the bus block be isolated from the subframe?
 
I have found on several aircraft that turning on the boost pump seems to put out some RF, and along with the lights, can make the gauges erratic. Play with the boost pump switch and see if it makes a difference.

DAR Gary
 
I have found on several aircraft that turning on the boost pump seems to put out some RF, and along with the lights, can make the gauges erratic. Play with the boost pump switch and see if it makes a difference.

DAR Gary

Fly with the fuel boost pump on all the time, never an issue. Thanks for the thought though.

Planning on connecting a jumper wire from bus bar to negative battery terminal to see if this fixes the issue, then will do a more permanent fix if it does. Have some ground straps coming as well for firewall to engine.

Original builder did it weird, and obviously didn't test it at night with everything on.
 
For sake of understanding, why must the bus block be isolated from the subframe?

Only if you decide to install an additional ground wire from your ground bus to the firewall/engine ground/battery ground point (preferred). If that ground bus is also grounded to the sub panel - that likely has a more than zero resistance pathway to your main battery ground plane, you are likely to have ground loop issues on the more sensitive avionics in your plane, which include the indications you said you are seeing. This is much more pronounced when your battery voltage is low, like with a weak battery, or during engine start on cold days. If it was mine, I would be asking myself the question, why is that large brass bolt on the ground bus not connected to anything? Your battery is the center of your electrical system. You need a very low, or zero resistance pathway to the negative terminal of your battery. Current doesn’t flow from positive to negative. It flows in the opposite direction. Grounds are probably the most important pathway in your airplane, electrically. Resistance in this pathway will create problems that might be hard to track down.
 
Only if you decide to install an additional ground wire from your ground bus to the firewall/engine ground/battery ground point (preferred). If that ground bus is also grounded to the sub panel - that likely has a more than zero resistance pathway to your main battery ground plane, you are likely to have ground loop issues on the more sensitive avionics in your plane, which include the indications you said you are seeing. This is much more pronounced when your battery voltage is low, like with a weak battery, or during engine start on cold days. If it was mine, I would be asking myself the question, why is that large brass bolt on the ground bus not connected to anything? Your battery is the center of your electrical system. You need a very low, or zero resistance pathway to the negative terminal of your battery. Current doesn’t flow from positive to negative. It flows in the opposite direction. Grounds are probably the most important pathway in your airplane, electrically. Resistance in this pathway will create problems that might be hard to track down.

Do you think the builder left the large brass bolt on the bus vacant because of other problems, or are you saying he screwed up by not connecting it? When I crawled under my panel, that was the first thing that stood out, I asked " Why the **** is there a giant brass bolt here, and not wire attached?"
 
I would not ever say that a builder “screwed up”, especially without looking at the installation, but the evidence indicates that you could have some grounding issues, which might be causing erroneous indications. From what you describe, your current ground bus might be causing some, or all, of these problems, and it’s easy to check. Isolate that ground bus from the airframe (SECURELY), and connect it to the negative terminal of the battery via a robust wire connection. It needs to carry all the current loads of everything connected to it. If you have a 60 amp alternator, that wire should be capable of handling 60 amps. That’s why connecting that bus to the firewall is so good. If you still have those erroneous indications, you have some other problem. If your problems go away, you will need to come up with a permanent solution to your grounding issue as I mentioned earlier. The good thing is, this is something that you can figure out. It’s probably the most logical science we encounter in our airplane builds or ownership. With all the help you get on this forum, I’m sure you will get it straightened out soon.
 
It sounds like you have a ground from the battery to the engine, but the only path for electrons to flow from the ground tabs to the engine is through the engine mount. The rubber engine mounts insulate the electrical connection between the engine and the firewall forward. You need an electrical jumper between the engine and the FWF via the engine mount, engine to forest of tabs or the negative terminal on the battery and the forest of tabs. Any one of those options would accomplish the job.
 
So I drilled a 5/16 hole through the firewall, put in a big brass bolt, and the used 6 cable from negative bus to bolt, And 6 cable from the firewall forward part of the bolt to the negative battery terminal. Just messing with the plane in the hangar, seems like everything works better. Flaps faster, fuel pump faster, etc. Turned on everything, landing lights, radios, txponder, strobes, etc, and Volts were over 14 with engine running, and no wonky gauges.

Knock on wood, still have to test out flying, but seems to have fixed issue.

Also threw in the Uavionics tailbeacon today, which went pretty smooth. Took me longer to put in a single screw on the baffling today than to Install the adsb. The price on that think is more per ounce than gold though. ****.

Funny how that works.

Thanks for help,

Will post once I put a test flight on it.
 
Ground Loops

Ground Loops https://en.wikipedia.org/wiki/Ground_loop_(electricity) occur when airframe mounted electrical devices don't have a common ground point. Sounds like these devices are all connected to the negative bus bar. That's a common ground point.

I don't see a problem with the negative bus bar being grounded to the subpanel. It's as if you didn't have any 6AWG wire, and used an 8AWG and a 12AWG in parallel to carry the ground current to the new brass bolt.

I stand ready to listen to arguments to the contrary.

Enjoy flying your 9,and rejoice in the fact that the stainless braid on your firewall forward fuel hoses is no longer carrying the ground current.
 
Marc,

I sent you a PM.

Are you telling us the builder ONLY connected the (-) terminal of the battery to a bolt lug on the engine? Please confirm...

Cheers!
 
Braided 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...

Marc, while you're at it, you may want to consider using a braided strap for the existing ground connection between the engine and the battery negative (or firewall ground bolt). Braided strap will be better for handling engine movement than the 2 gauge wire.
 
Marc,

I sent you a PM.

Are you telling us the builder ONLY connected the (-) terminal of the battery to a bolt lug on the engine? Please confirm...



Yes

He only did the negative battery to the engine, and that was it. Didn't work that well. Don't think the guy probably ever flew it at night with all the lights on.

On the positive note, I'm getting to learn a lot about the plane.
 
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