AeroLEDs Grounding... Am I over thinking this?

[grayforge]

I too am curious where the shields get grounded. Also where the wire that connects on the other side of the black wire pin in Stephen's setup goes.

[schristo@mac.com]

Originally Posted by grayforge

I too am curious where the shields get grounded. Also where the wire that connects on the other side of the black wire pin in Stephen's setup goes.

Black wire to outboard rib... shield ground at outboard rib and firewall.

[ILikePike]

Do you have a picture of the first rib and other side of the connector? I want to see how much wire is not shielded.

Who knew that there could be so many details about connecting some lights? I think AeroLED's would benefit from further explaining their opinion of "best practices" complete with representative photos. I am not complaining, I really enjoy the research process in order to build things right the first time. I am just saying that it is hard to describe without pictures.

[SvingenB]

Originally Posted by schristo@mac.com

Black wire to outboard rib... shield ground at outboard rib and firewall.

Shield should be grounded at one end only. Else you create two paths for ground and you may have ground loop creating noise.

[aerovin]

Originally Posted by SvingenB

Shield should be grounded at one end only. Else you create two paths for ground and you may have ground loop creating noise.

Not according to AeroLeds' installation instructions. As per their very specific instructions and many VAF topic discussions, the shielding is grounded at both ends.

From a not-knowledgable but know-enough-to-be-dangerous perspective, you ground at both ends of a shielded wire if you want to keep noise inside the shielded cable, and only ground on one end if you want to keep noise from coming inside the shielded cable. Sounds good to me.

[rleffler]

Originally Posted by aerovin

Not according to AeroLeds' installation instructions. As per their very specific instructions and many VAF topic discussions, the shielding is grounded at both ends.

From a not-knowledgable but know-enough-to-be-dangerous perspective, you ground at both ends of a shielded wire if you want to keep noise inside the shielded cable, and only ground on one end if you want to keep noise from coming inside the shielded cable. Sounds good to me.

Bj?rnar is correct. If you use a ground wire and then attach the shield at both ends, you will have a ground loop. We can debate forever what evils may arise from this state.

However, that isn't what AeroLEDS recommends in their instructions. See my earlier post. They state to use the shield as ground, then there is only one path to ground.

If you use a ground and the shield, then the shield should only be connected at one end.

I would personally defer to Dean and AeroLEDS and wire exactly like they recommend.

[Dean_aeroleds]

Originally Posted by ILikePike

Dean what do you do with the shield at both ends? And do you run a ground wire from the light mount back to the first wig rib?

I have tested DO-160 with the shield grounded at both ends, but you alternately can ground the shield at the panel only. I recommend that you use the shield as the return ground path if you do that as that keeps the ground current flowing in the shield adjacent to the power wires. The advantage of this is that the magnetic fields tend to cancel out when the shield carries the ground current. The magnetic field around a wire follows the "right hand rule". If you point the thumb of your right hand in the direction the current is flowing in the wire, the magnetic field that the current creates will circle around the wire in the direction of your curled fingers. Thus if the outbound current is making a magnetic field in one direction, and the return current is making a magnetic field in the opposite direction. With the current flowing in the shield immediately around the power wire, the fields are equal and nearly opposite (roughly forming around the same axis).

Shields on wires will stop electric fields, but they won't stop magnetic fields. This is why it is not a good idea to route power wires that may have dynamic current parellel to and right up against antenna or audio headset coax cables. Such routing can lead to transformer like coupling of magneticly induced noise in the coax cables that winds up being boosted by the downstream amplifier.

I have had people report both kinds of noise problems. If it breaks squelch on the radio, it is RF, but if it shows up in your headset even with the radio off, it is audio frequency. Often, the source of audio frequency noise is cables routed too close to each other (power next to headset coax).

Hope that helps,

Dean Wilkinson
CTO, AeroLEDs LLC

[Dean_aeroleds]

Originally Posted by SvingenB

Shield should be grounded at one end only. Else you create two paths for ground and you may have ground loop creating noise.

That is only true for low frequencies such as audio frequencies. At higher frequencies (above 1Mhz), the ground current prefers to follow the path of least inductance instead of the path of least resistance. The path of least inductance is the path that keeps the ground current as close as possible to the outbound current, which is the shield. Ground loops are a big issue for audio panels and intercoms, but for RFI it is a whole different animal.

Dean Wilkinson
CTO, AeroLEDs LLC

[SMO]

I am installing Pulsars on the wingtips, no strobe at the tail.

Okay, I get terminating the black wire, coming from the light, at the case of the light. Then a wire is run from the case of the light and terminated at the airframe (eg: a rib) at the outboard end of the wing.

I also understand I should terminate one end of the shield at the same place (rib) on the outboard end of the wing, and the other end of the shield at my panel ground forest.

There are three wires inside the shielded cable running from the panel to the wingtip. One of the wires carries power for the strobe, one carries power for the nav lights.

I need confirmation with respect to what I do with the third wire in the shielded cable. I am assuming the "wingtip end" gets terminated at the outboard end (rib) of the wing (the 3rd wire terminated at this location), and the "panel end" goes to the panel ground (in addition to the shield ground).

If my assumption is correct, then I use up 4 tabs on my panel ground forest for my two Pulsar lights. Can someone confirm this?

[grayforge]

The 3rd wire in the cable is the sync wire that you tie to the sync wire to the other lights (other wingtip and tail). This synchronizes the pulses for a more pleasing flash vs the 3 lights flashing out of sync.