R

ron sterba

Well Known Member
My math is a little rusty but I'm thinking I have about 4.80 amps with this 65 watt light. Was wondering what size wire to use from the cockpit to the the tip of the RV9A wing? I thought 18 guage sheilded 2 conductor wire and a 7 amp breaker. I'm thinking 150% 0f the amps used is the breaker size. Is there a site I could go to figure this all out. I have LED nav lights by AVEO and thought 20 guage sheilded and 4 conductor.

All help is appreciated. Ron in Oregon
 
ron sterba said:
My math is a little rusty but I'm thinking I have about 4.80 amps with this 65 watt light. Was wondering what size wire to use from the cockpit to the the tip of the RV9A wing? I thought 18 guage sheilded 2 conductor wire and a 7 amp breaker. I'm thinking 150% 0f the amps used is the breaker size.
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There are several things to consider.

1) The current carrying capacity of the wire must be sufficient for the load current. See AC 43.13-1B table 11-9. On this criteria, 18 AWG is ok. But...

2) The resistance of the wire should not produce an excessive voltage drop. About 0.5V drop is generally considered reasonable in a 12V system. Resistance is a function of wire gauge and length. Again see AC 43.13-1B table 11-9. From instrument panel to wing tip is let's say about a 15-20 ft wire run, so 30-40 ft of wire round trip (assuming you're also running a ground wire of the same gauge). 40 ft of 18 AWG wire will have a total resistance of approx 0.25 ohm, so you'll get a voltage drop of 4.8 A * 0.25 ohm = 1.2 V. That's a bit high, and will mean your landing light would shine a bit dimmer. If you want to keep the voltage drop to about 0.5V, then use 14 AWG wire, which will have about half the resistance and therefore half the voltage drop of 18 AWG wire. (Judgment call here. I'm explaining the general concept so you can decide.)

3) The circuit breaker exists to protect the wire, and its current rating should be less than the current carrying capacity of the wire (that's the idea anyway... some fudge factor in reality). Or just see AC 43.13-1B table 11-3 for generally acceptable breaker values per wire gauge. The breaker's current rating also must obviously be high enough to support the load current with some margin, but it will be anyway if you've sized your wire correctly as described above.

4) There's no reason to use shielded wire for an incandescent lamp.

ron sterba said:
Is there a site I could go to figure this all out.
Click to expand...

The AeroElectric Connection explains these concepts pretty well.

AC 43.13-1B chapter 11 is also a useful reference.
 
It's standard practice to use the airframe for the ground return on things like lights, no need for the extra ground wire in this case.
 
Slightly tangential, but information that may be interesting to some, regarding light output from incandescent bulbs.

The article's focus is the rationale for using relays to drive headlights in automotive applications, but the description of the non-linearity of light output relative to voltage is interesting and applicable to our airplanes, if maximizing light output is considered important.

Note that I'm not submitting this as an argument for using relays in our airplanes! Just providing information. YMMV, etc etc.
 
ron sterba said:
. . .I have LED nav lights by AVEO and thought 20 guage sheilded and 4 conductor.
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The only thing I might add to Roee's information is that these LED lights do not need shielding either. You are only running 12V power out to these lights. In any normal operation no interference will be transmitted through the wire.

I would also concur with Walt's comments about ground. No need to run ground back to the fuselage from the wing tip. Just ground the fixture to the metal wing somewhere near the light fixture.
 
Ron:
If I recall I used 12awg(may have even been #10awg) for my 55watt when I built mine. I did a voltage drop calculation at the time and was suprised at how much voltage drop there was on the smaller wires. Going from memory here and its been 5 years or more so don't hold me to it.

Am doing my annual inspection shortly and will be able to look and see If you are interested.

doug

Ps. snow! in late March! you believe it!:eek:
 
Ron,

For reference, I used 16 gauge power and airframe ground for my 65watt landing lights. I also used this Wig Wag circuit and am very happy with the results.

I don't recall if you were planning to put LED strobes in your wingtips, but here's a good article on how to wire them to reduce noise. I did not find this article until after my wings were already wired and there is a tiny bit of noise coming from my LED strobes, but it goes away when the loud handle is pushed forward. :D
 
Gentlemen. Its a wealth of information that I needed. It was the missing link in my brain.The circuit loss, I see now. Safe on the heavier gauge is what I'll do. Thanks a bunch and I'll use guidence. I Do have one question guys. Do you think there is a potential difference in metals for grounding? Or is it so slight from the copper wire to use aluminum frame. Can I expect corrosion at the grounding clamp near the fixture between the unlike metals at that grounding point? This maybe a non issue with the DC compared with AC grounding in my past years,not sure.
OK, On the lighter side. Snow! Heavy here in Salem Oregon! Expect 3" today. Dafi"s all bent over. I think the USA is in for some strange weather the next 6 months! 80's in Chicago?(>;) James since your close I'll check it out when you are in town.

Tomorrow is Tank access plate install time. Pro Seal here I come! Anybody have pictures of their install ART! I here its can be Messy! Thanks again everyone! Much appreciated.

Ron in Oregon
 
Ron,

Other than the aforementioned snow, I sorta took my panel apart. :rolleyes:

If everything goes smoothly i'll have my airplane back together by the end of the weekend so you might see me next week. It's not a job that can be rushed though. Has to be done right and it takes what it takes...

I remember flying in Dad's Twin Comanche in the snow. It was like Star Wars. :D

Also, I recomend spending the bucks for the 3.5oz proseal tube here. I have the dispenser you can borrow. Makes the job ridiculous easy, almost like cheating. One tube is enough for both access panels.
 
ron sterba said:
Gentlemen. Its a wealth of information that I needed. It was the missing link in my brain.The circuit loss, I see now. Safe on the heavier gauge is what I'll do. Thanks a bunch and I'll use guidence. I Do have one question guys. Do you think there is a potential difference in metals for grounding? Or is it so slight from the copper wire to use aluminum frame. Can I expect corrosion at the grounding clamp near the fixture between the unlike metals at that grounding point?
Click to expand...

Check AC 43-13, it shows the stackup for a ground stud connection to an aluminum airframe.
 
Thanks Walt I'll check that when I get to the hangar tomorrow. Today is HONEY DUE DAY and I NEVER want to miss that DAY! I learned that a HAPPY WIFE IS A HAPPY LIFE! Ok I'am machine sanding a hardwood floor today. Shouldn't be much harder that sanding the epoxy finish on the elevator tips. thanks
Ron in Oregon
 
James I'll call you. Vans convineced me I'll need more proseal around the gear welds at the fuselage opening. I like your idea of the easy part.
Latter today. Ron
 
Thanks Walt. It answered everything and then more. It was interesting about the way the corrosion is limited by stacking the washers of different values in alloy. Much appreciated.
 
We used #14 and airframe ground

For our new 55 watt HID landing lights. I think we could have used #16 but wanted to be conservative. One thing to consider is that lighting is getting much more efficient around power. For example, we replaced the 75watt Halogens in our wingtips with LEDs. Went from 5.5 amps per side to less than 1 amp! Plan to replace the HIDs with LED n the very near future also.

good luck
 
Thanks Bill. I sorta looked at the led landing lights at the Northwest trade show in Washington State last month. By far the NEW LED AVEO landing lights were by the BRIGHTEST I have ever seen! So bright that the Kestrel.com owner gave a demo only when it was safe to do so with so many people at the show. The price was around $950 for two I believe. My Halogen was $12.99 for the lamp. I took the extra money and put it toward a Mode S DYNON transponder for my SKYVIEW. I did buy the LED nav/strobe lights from AVEO or Kestrel the distributor of AVEO west of the Rockies.
 
I think if you use a good tin-plated copper PIDG ring terminal to attach your lighting ground, you won't have to worry about corrision. If you are concerned, after you attach your terminal to the cleaned off rib, spray a little zinc chromate over the top of the junction. You'll never get any corrosion there.
 
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