T

tdk

Active Member
I understand best practice is to ground all the avionics to a common point on the firewall to avoid ground loops.

My avionics vendor provided ground wires that only reach the sub-panel, so I need to put my forest of tabs there. I guess I have three options:

1) Insulate the forest of tabs, and run a cable to a common grounding point on the firewall.

2) Bond the forest of tabs on the sub panel, and let the current flow through the airframe.

3) Bond the forest of tabs at the sub panel AND run a cable to the common ground on the firewall.

Problems with any of these options? Which is best?
 
Last edited:
Tom,
I had almost the same questions. My vendor made the grounds long enough to reach the firewall, but in front of the pilot, not above the battery on the 9A I am building. I have the tabs that mount on each side of the firewall. I will just run the grounding wire from the battery to the bolt on the tabs.

I had a scary experience hooking all the grounding tabs up. I have been installing my panel and components but hadn't hooked up the grounds. I crimped all the ends on and hooked them to the tabs. I went into dinner, came out and my panel was turned on! I freaked out. I looked at the empty battery tray and couldn't figure out what was going on. Then I remembered the backup battery system and realized it wasn't working until I hooked up the grounds. It scared the **** out of me for a few seconds wondering what was going on!
 
Grounding lights and non-avionics

Can LED lights be grounded locally to airframe or should their ground wires come all the way back to common ground buss?
 
sglynn said:
Can LED lights be grounded locally to airframe or should their ground wires come all the way back to common ground buss?
Click to expand...

That's a great question. Here is my discovery....learned the hard, long way.
I grounded my AeroLed Wingtip nav/strobes to the wing rib per AeroLeds wiring diagram. My 100W bulb (non LED) landing light is less than 2 foot away. Whenever I had the nav lights on I would get interference static and when the strobes were on, tic tic tic over the headset. Well in the process of trying this and that to determine the cause I concluded that the RFI emitted from the LED's was being picked up in the filament of the landing light (the landing light is also grounded to the alum wing). This RF pickup in the filament was happening with the landing light off. Once I disconnected the landing light ground wire the static/interference all went away. On my to do list is to run a separate ground wire from the landing light to the common firewall ground block. If I had an LED landing light the RF may not be picked up and cause static but really don't know for sure-maybe someone else can comment on that.

And by the way, I first tried everything that AeroLEds had suggested to eliminate the RFI from the nav/strobe light installation.....namely, installing an aluminum back plate, shortening up the ground wire to light case, installing ferrules (all not on the original LED light installation instructions) and all to no avail. I quess that's why they call this "experimental"

Jim
RV9a
 
Why not crimp on extensions and still ground them at the firewall?

Yes, you can ground the lights locally. I added platenuts where I needed them eith no noise issues.
 
sglynn said:
Can LED lights be grounded locally to airframe or should their ground wires come all the way back to common ground buss?
Click to expand...

Lights and other stuff are usually fine with local grounds, however, led power supplies are notorious for generating noise with some lights being worse than others, it all depends on the design. So you "should" be able to ground them locally but depending on the particular light, local grounding may cause issues.
 
tdk said:
I understand best practice is to ground all the avionics to a common point on the firewall to avoid ground loops.

My avionics vendor provide ground wires that only reach the sub-panel, so I need to put my forest of tabs there. I guess I have three options:

1) Insulate the forest of tabs, and run a cable to a common grounding point on the firewall.

2) Bond the forest of tabs on the sub panel, and let the current flow through the airframe.

3) Bond the forest of tabs at the sub panel AND run a cable to the common ground on the firewall.

Problems with any of these options? Which is best?
Click to expand...

Option one is in line with the information in the aero electric connection. Grounding the forest of tabs through two feeds is no different than grounding the devive in the same manner. You run the risk of ground loops with two separate ground paths.
 
jimbo said:
That's a great question. Here is my discovery....learned the hard, long way.
I grounded my AeroLed Wingtip nav/strobes to the wing rib per AeroLeds wiring diagram. My 100W bulb (non LED) landing light is less than 2 foot away. Whenever I had the nav lights on I would get interference static and when the strobes were on, tic tic tic over the headset. Well in the process of trying this and that to determine the cause I concluded that the RFI emitted from the LED's was being picked up in the filament of the landing light (the landing light is also grounded to the alum wing). This RF pickup in the filament was happening with the landing light off. Once I disconnected the landing light ground wire the static/interference all went away. On my to do list is to run a separate ground wire from the landing light to the common firewall ground block. If I had an LED landing light the RF may not be picked up and cause static but really don't know for sure-maybe someone else can comment on that.

And by the way, I first tried everything that AeroLEds had suggested to eliminate the RFI from the nav/strobe light installation.....namely, installing an aluminum back plate, shortening up the ground wire to light case, installing ferrules (all not on the original LED light installation instructions) and all to no avail. I quess that's why they call this "experimental"

Jim
RV9a
Click to expand...

I understand how the filament could pick up the RF interference and put it on the ground plane. That was a good catch, by the way. I don't understand why it would matter where the filament is grounded though. It would seem to me that once the filament picked up the interference, it would radiate about it's circuit and it doesn't seem that it should matter whether it is grounded on the frame in wing or the frame on firewall. Clearly the interference is strong enough to travel to your avionics that are grounded at the firewall. I am interested to learn if moving the ground connection point fixes the issue. I am guessing that it won't.

Larry
 
1) Insulate the forest of tabs, and run a cable to a common grounding point on the firewall.

2) Bond the forest of tabs on the sub panel, and let the current flow through the airframe.

3) Bond the forest of tabs at the sub panel AND run a cable to the common ground on the firewall.

-----------------------------

There is also a #4 option.

4) Bond the forest of tabs to the aft side of the firewall and use its mounting bolts to connect the main battery ground to the forward side of the firewall.

The extra length of the ground wires is not that much in our RVs.
 
You must log in or register to reply here.