Baja design landing light wire size

I am using the Baja squadron landing lights. I believe the AMP draw is only 3.5 amps per light. What I need to know is what size and type of wire to use. @0 would probably work but not sure.

1. Shielded or not shielded (have Aero LED nav/strobes and they have to be shielded. So should these LED's be shielded. They will be on a Wig Wag circuit also.

2. My attempt for this RV8 is to have no local grounding so I will need to have a two conductor wire.

any help or comments are appreciated.

laz said:

I am using the Baja squadron landing lights. I believe the AMP draw is only 3.5 amps per light. What I need to know is what size and type of wire to use. @0 would probably work but not sure.

1. Shielded or not shielded (have Aero LED nav/strobes and they have to be shielded. So should these LED's be shielded. They will be on a Wig Wag circuit also.

2. My attempt for this RV8 is to have no local grounding so I will need to have a two conductor wire.

any help or comments are appreciated.

Click to expand...

If you mean 0 AWG, then yeah, I think it would handle it. The wing might not, but no problem with the current.

No local grounding means roughly double the wire size (aluminum airframe can be considered essentially zero resistance).

Lots of calculators, online & off, to tell you what size wire is adequate. I like
http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=14&phase=dc&noofconductor=1&distance=6&distanceunit=feet&amperes=50&x=38&y=15

which assumes out&back (2 conductor) wire; enter 1-way distance. Try to keep voltage drop under 5% for continuous loads. Landing lights could probably stand a bit higher % drop, unless you intend to run them continuously.

Note that 'victims' (intercom, radios, etc) are much more likely to be adversely affected by local grounding than lights, motors, etc. LED's can be 'iffy' due to the switch mode power supplies used in most. But if they work without radio interference in cars using local ground (almost universally the case for cars), then if you have problems in the plane it's likely due to wiring issues on the 'victim' side.

In a plastic a/c, you don't have a choice, but in an aluminum airframe, you're almost doubling your wire weight (and money). Your call, but...

Charlie

Sorry for the typo I meant to say 28AWG.

I figured you were joking about the '0'; I was, too.

But 28 awg is way too small, from both a voltage drop perspective (assuming the lights go in the wings), and from a physical strength/durability standpoint. 24awg is just about as low as you can reasonably go when running wire through the airframe, and 22awg is better for durability and typically easier to get with tefzel insulation.

Charlie

Man am I getting old or what . Second typo 18AWG . The only28 AWG wire in the plane that small are the darn Ray allen trim wires.

laz said:

Man am I getting old or what . Second typo 18AWG . The only28 AWG wire in the plane that small are the darn Ray allen trim wires.

Click to expand...

I would check a chart due to length, but I would think that is more than adequate for 4 amps @ 20. Feet

18AWG should be fine, and I have not had any noise from the Baja Designs lights with unshielded wire.

Impact of local vs firewall ground on wire size

Hi All,

Along similar lines of this thread, what does the impact of local grounding v's grounding back at the firewall have on wire size. I imagine that the resistance grounding locally in an aluminium is much lower than running back through a wire the same size as the positive lead you ran to the device, thus you think this would then impact the size of wire you need to keep the voltage drop below 0.5V for a 14V system. I've crawled through AC43.13-1B and I can't find anything that specifically calls this out. I guess in summary, does the continuous current chart below (from page 11-30) account for a local grounding or a ground return line back to the firewall?
Cheers,
Tom.

You guys really should subscribe to the Aeroelectric list. I asked this specific question on that list several months ago.

Answer: If grounding locally, ignore the return path length. As you suspected, the aluminum airframe 'ground wire' is so massive in cross section, its resistance can be ignored. If using a 'home run' ground wire, include the entire round trip length of wire to compute voltage drop.

Charlie

edit: If you use Google to find a wire size calculator, read the instructions on the web page carefully. Many online wire calculators are written for industrial applications, and some build the return length into the calculator. In those cases, if you're lucky, the instructions will tell you to enter the one-way length.

I use local grounding for everything out in the wing, including the strobe PS and Baja lights. I have no noise issues.

Larry

Thanks Charlie. You absolutely crush me, as this really impacts wire size. Do you or does anyone know where in chapter 11 this is spelt out? I read through the entire chapter last night and couldn't find reference to it, or maybe it's just one of those things that's just so blindingly obvious it is assumed and not written.
Larry, per your local grounding point, my problem is I am planning on a magnetometer in the wing tip, and it is a requirement to have a twisted pair with a return ground from any current drawing device near the said magnetometer.
Cheers,
Tom.

I don't recall it being spelled out in the book either; that's why I actually asked Bob via the Aeroelectric email list. His answer was basically what I gave you earlier. As to why it's not mentioned in the book, in another thread I mentioned one of my guiding principles, which I call the 'center of the universe principle'. If the speaker knows about something, he assumes everyone else does, too. I suspect that when Bob wrote that chapter, the incredibly low resistance of the airframe was so obvious to him that he didn't think to mention it for the benefit of those who need everything explained. I can tell you that I've had two or three different careers that dealt with electricity & electronics, and I still asked the question, just to be sure.

[edit: Just realized you were talking about AC43; not the 'Connection book. The 'Principle' still applies...]

Having said all that... Depending on the device in question, you could probably get away with significantly more voltage drop than .5 volts, and if the load is intermittent, you wouldn't have to worry too much about heating, either. Bob does talk about those issues in the 'Connection. He mentions that tefzel insulated wire can be loaded waaay past what the charts say, if you're willing to accept significant voltage drop (which is fine, in some cases).

Charlie

Hi Larry. I'm not so worried about headset noise, but influence on my magnetometer. Garmin recommends running twisted pair (i.e. a return ground) anywhere near it's magnetometers. For the RV-7 this adds approximately 1/2 a pound in additional wire per light, assuming it forces you to jump from 18AWG to 14AWG to keep the voltage loss below 0.5V, because you now have double the conductor length that you have to account for. I have read back through AC 43.13-1B again and the only part I can find that is applicable as to whether you need to account for the return line or not is as follows:
Section 11-66, Subpart B
"...The tabulation shown in table 11-6 defines the maximum acceptable voltage drop in the load circuits between the bus and the utilization equipment ground..."
Indicating to me that the 0.5V allowable drop must include the return wire if you are grounding back at the firewall forest of tabs, and forcing you to increase the wire diameter to account for the longer run. Between the landing lights and the pitot heat, this is another 1.5lbs I didn't account for. It's just one crushing blow after the next.
Tom.

As I said before, don't get too wrapped up in that .5V drop spec, until you know it matters. Ask the device mfgr what their device does if it's powered by a straight 12 volts (basically without the engine running). In the case of those lights, it wouldn't be surprising if there's no degradation in output.

Another thing to ask yourself is where the light is, in relation to the magnetometer. If the light is a couple of feet inboard of the magnetometer, then the magnetic field induced by a 1-wire/local ground setup to the light might well have no effect on compass readings, since the wire wouldn't pass anywhere near the magnetometer.

Umm... this is an area where the guidelines set out in AC 43.13 are there for a reason. Sure, the guidelines were drafted when we had more truly analog devices in aircraft, and light bulbs are about as analog as they come.

In the case of running wires out to the wingtips, if using a twisted shielded pair, 18ga is sufficient for the Baja Squadron Pro lights, or at least the 4300 lumen incarnation of these lights. In the aircraft we're building, our wings are longer than most of the RVs and our total wire run is certainly several feet longer than a two-place RV. The lights work just fine under these conditions. Truth of the matter is they do not draw 3.5 amps each. My testing puts them at less than 2.2 amps at 13.75 VDC, our normal system operating voltage.

If you are sticking a magnetometer out in the wingtip near the lights I would suggest using twisted shielded pair wire with the shield grounded at your primary grounding point. I know, normally we ground the shield at the device that's making the noise, but in this case that's not practical as we can induce a ground loop by grounding the shield out at the wingtip, potentially making noise worse instead of better.

You bring up a good point regarding the light not giving a hoot if it swallows volts or amps. I will run one tonight at both 12 and 14V, see if there is a perceptible difference in output and at the same time monitor the current draw.
Tom.

To quote Dan H, "in God we trust, all others must bring data".
Well here's your data.
I ran one of the lights (4,900 lumen Squadron Pro) with the vehicle off then running, and the results were as follows:
Engine Off: 12.2V, 3.65A giving a draw of 44.5W
Engine Running: 14.1V, 3.00A giving a draw of 42.3W

With the engine off or on there was absolutely no difference in the light intensity.
Thus it appears there are some fancy electronics doing their thing and ensuring that the light output remains constant regardless of the voltage. The only thing is that as the voltage drops, so does the efficiency of the light, but without sacrifice its lumen output value.
I also noted the AWG of the cables, and it appears that when running both lights through one cable, Baja Designs uses 18 AWG, then when they split the lights into two cables after the switch they use 20 AWG. I forgot to measure the cable length, but I'm guessing a run of about 10 ft (or 20 ft if you include the return ground) or about half what we are working with.
Thus, if you were happy with only a 1 volt voltage drop, which is half what I was dealing with in my test this evening, then the light would be drawing approximately 3.3A. For a 1A voltage drop you use chart 11.3 on page 11.31 of AC 43.13-1B, which results in a wire size of 18 AWG, which seems to reflect everyones previous experience with the lights!
The only thing I did note that was a bit of a downside, is that with the lights now installed in the tips, there seems to be a lot more diffusion of the lights because of the slightly recessed positioning, resulting in a reduction in ultimate range, but giving better taxiing lighting. For sure only get the spot version, as the diffusers are not necessary if using them in this recessed tip configuration. I think in hindsight I may have made cutouts in the leading edges and placed them in there if I was to do things again, or even use the larger XL 80 version if I can make them fit, which would about double my light output. I may still place an additional one on in the cowl (I need some nose weight anyway).
Thanks for helping me save 0.32lbs by stopping me go down the 14AWG path.
Tom.

Good data.

Now, install your magnetometer and light in their planned locations. Power up the EFIS, and with the light locally grounded, switch it on/off & see if you get compass errors. If you don't, then another wire (and a batch of electrons) is saved.

Hmmm interesting to see the newer lights (4900lm) are drawing a fair bit more current than the older 4300lm units. Seems like the newer ones might be closer to making rated light output than the older ones. No matter, even the older ones make a LOT of light!