AeroLEDs Grounding... Am I over thinking this?

[ILikePike]

As far as grounding at the wing tip rib. I am planning to use sunrays and pulsars. Is there any issue with splicing the 2 case grounds, 2 black wires, and 2 shields to a single conductor then bundling that with the a shielded 3 conductor wire for the pulsars and a shielded single conductor for the sunrays back to the first rib or should 6 single ground conductors be run from the light location to the first rib?

I am very intested in Aeroleds opinion.

[rleffler]

I just read the following off AeroLEDs support site. It appears that this may be a presentation that they did at Oshkosh this past year.

http://www.aeroleds.com/LinkClick.as...;3d&tabid=8593

[rleffler]

I've included the whole text of this appendix, since not everyone has a VP-X, but the instructions seem reasonable for other installations as well.

bob

From the Vertical Power VP-X Pro Installation Manual

Appendix F - AeroLED Wiring Tips

Here is some information that should be helpful to builders installing AeroLEDs wingtip lights:

LED strobes operate differently than legacy Xenon strobes. Legacy Xenon strobes use a flash capacitor that charges up continuously between flashes, pulling a steady amount of current (current is continuously pulsating at the frequency of the charge pump, typically 10’s of kilohertz), then dump the charge to the Xenon tube in a single burst.

LED strobes pull their current while the strobes are lit, and pull nearly zero current between flashes.

As a result, the way that the LED strobes are wired will make a huge difference in whether or not audio frequency noise gets into your intercom. Because the current pulses to LED strobes flow in a loop with the outgoing current flowing in the outbound power wire, and the return current flowing in the ground path, there is the potential for the wiring to create time varying magnetic fields that can couple into adjacent wires such as headset jack cables, or even your antenna coax cable.

To prevent this, it is highly recommended that you follow the following wiring recommendations:

1. Use shielded wire, AeroLEDs has 3 conductor 20 gauge shielded wire available for this purpose.
2. Use the shield as the ground return. When the ground current flows immediately adjacent to the power wire, the magnetic field produced by the power wire current is canceled out by the current flowing in the shield. The ground current prefers to stay in the shield rather than flow through structure because generating a magnetic field takes energy, and the current wants to follow the path that takes the least effort because the fields cancel out (called the path of least inductance).
3. Bring the shielded wire run all the way to the panel, where the power wire can go to the switch, and the shield ground can be run to the behind the panel grounding block. If you need to break the wire run at the wing root with a connector or terminal block, that is OK as long as you resume the shielded wire in the fuselage and connect the shield grounds through the interconnect.
4. As much as possible, keep some separation between the strobe wires and sensitive cables such as intercom audio cables, headset jack cables, or antenna coax for the radios.

Note that the above recommendations are primarily intended to prevent audio frequency signals from getting into your intercom. For preventing RFI, you should also follow these recommendations:

1. If you have a mounting bracket that is anodized (silver colored brackets), then you must remove the anodization coating from the screw wells so that the counter-sunk screw heads will make good electrical contact for making the chassis ground connection. You can test the grounding of the wingtip lights by measuring the resistance from the rear set screw head to aircraft structure ground. If your brackets are gold colored then they have a conductive alodine coating and this step is not needed.
2. You must ground at least one of the mounting screws to aircraft struture either directly or via a ground wire.
3. Tie the black ground wire, and the shield braid ground to aircraft structure ground (or wing spar ground in a composite or tube and fabric wing) at or near the spot where the chassis ground for the light is grounded. It is important that the loop formed by the black wire ground from the light, and the chassis ground from the light be kept short. Keeping this loop short is very important as it reduces radio emissions from the wingtip lights by 30db in the communications band wavelengths, both for the position lights and the strobes.

If you have wired your plane, and didn’t follow all of the above recommendations and think you have an audio noise problem, we can provide in-line filters that you can put in each wingtip that will help to reduce the edge rate on the current pulses, but ultimately the best way to handle it is to prevent it from occurring in the first place.

Dean Wilkinson

CTO, AeroLEDs LLC

[rleffler]

Originally Posted by schristo@mac.com

Firewall and outboard rib.

Since that creates a ground loop with two points of airframe ground, I would suspect it may introduce noise issues.

Wouldn't it be best just to terminate the shield just at the firewall?

bob

[Richard Connell]

Originally Posted by schristo@mac.com

The most critical issue with these lights in reducing emitted noise into the radios and intercom is returning the ground to the case with a short run... this makes a BIG difference. I used a handheld radio to evaluate the noise from the strobes and position lights and the difference is quite remarkable.

Here is a shot of the wingtip connection for reference.

Tie the black ground wire, and the shield braid ground to aircraft structure ground (or wing spar ground in a composite or tube and fabric wing) at or near the spot where the chassis ground for the light is grounded. It is important that the loop formed by the black wire ground from the light, and the chassis ground from the light be kept short. Keeping this loop short is very important as it reduces radio emissions from the wingtip lights by 30db in the communications band wavelengths, both for the position lights and the strobes.

I think this is most likely where I will get my improvement. I have no issues in the ICM at all, just RFI at a specific frequency. My chassis ground to ground loop is short, but not that short. I guess it would be useful to quantify "short". All the rest of the requirements as set out by Aeroleds have been complied with. Ill try this next and let everyone know the results.

Question for Stephen: any reason why you didn't co-locate the 2 grounds on a common stud? I assume its just a lack of thread real-estate.

DB, have left a message for you.

[grayforge]

Stephen,

What's your wiring look like on the other side of that connector? Shield and airframe ground to the black wire pin or just to the shield that gets grounded at the panel?

Thanks,
Russ

Originally Posted by schristo@mac.com

The most critical issue with these lights in reducing emitted noise into the radios and intercom is returning the ground to the case with a short run... this makes a BIG difference. I used a handheld radio to evaluate the noise from the strobes and position lights and the difference is quite remarkable.

Here is a shot of the wingtip connection for reference.

[Richard Connell]

I removed my "short" separate chassis ground and co-located the chassis ground with the light ground at the mounting stud (Similar to Stephens) and all of my noise problems appear to have been solved.
I wonder how many others have followed the schematic and have a similar install to mine with varying degrees of RFI?
Also, it seems a little convoluted and not so intuitive. Im intrigued as to why the lights aren't manufactured with this in place. would seem simpler and less prone to installer error.
Cheers

[Dean_aeroleds]

Originally Posted by schristo@mac.com

The most critical issue with these lights in reducing emitted noise into the radios and intercom is returning the ground to the case with a short run... this makes a BIG difference. I used a handheld radio to evaluate the noise from the strobes and position lights and the difference is quite remarkable.

Here is a shot of the wingtip connection for reference.

This is exactly how I recommend that the grounding be done. We are making a design change that will connect the chassis and power grounds internal to the lights in future units, but the photo shown is the way I recommend that grounding be done on the current generation of lights.

Best Regards,

Dean Wilkinson
AeroLEDs LLC

[Canadian_JOY]

Dean - thanks for chiming in here. When are you expecting the "new" grounding design to be in production? I'm hoping to use your product in our aircraft, but not at the risk of decreased COMM and NAV performance as a result of RFI. I'd like to know when this product improvement will hit the store shelves so I can avoid this pitfall.

Having been in the avionics business for a lot of years it boggles my mind that power and chassis grounds would not have been tied together internally. That's been the "magic" of DO160 compliance for decades now.

[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?