MSFT-1

MSFT-1

Well Known Member
I have the Van's HID landing lights on my RV-10 (one on the leading edge of each wing). They are wired to a single 10amp circuit breaker. Occasionally, when they have been on for several minutes (for a long taxi), the breaker will trip. After a couple minutes it will reset without issue. Most of the time this doesn't happen at all (I can leave the lights on for an hour with out a problem).

I am assuming that the lights are drawing enough current to cause that breaker to heat up and trip.

I asked an experienced builder if it made sense to up the breaker to 15amps. He said that might help but I needed to know the wire guage and length to properly determine the safe breaker size.

Can someone help me with this? What size wire should these lights use? How do I do the calculation?

thanks.
 
I've got no idea but

I got all excited because I wasn't wearing my glasses and I thought you were asking about electrifying your RV's GUNS and I was thinking **** Yeah, Let's see this! Man, I'm disappointed....:p
 
The better idea might be to power them from two breakers not one for a slightly more redundant system.

Is each light switched separately?
 
MSFT-1 said:
I asked an experienced builder if it made sense to up the breaker to 15amps. He said that might help but I needed to know the wire guage and length to properly determine the safe breaker size.
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Absolutely correct.

The breaker is there to protect the wiring.

I suggest going to individual breakers for each light.

You will then need to re-work the switching, a DPST switch will work, or add a second switch.
 
real men don't

If all else fails, try reading the instructions, under "fuses and breakers":

"For each HID use a 10A" - Duckworks
 
Breaker versus wire size

MSFT-1 said:
Can someone help me with this? What size wire should these lights use? How do I do the calculation?

thanks.
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According to my trusty reference, protect 18 gauge wire with a 10 amp breaker, and 16 gauge wire with a 15 amp breaker.

So if you are wired with 16 gauge, feel free to just up the breaker size. You also might consider swapping out the breaker in case it's a "weak" one.

Don
 
As others have pointed out, your choices are kind of limited by your wire size....if you have beefy enough wire then just put in a bigger breaker, if not then add a 2nd breaker or fuse. You're probably in the gray area of current draw being right on the edge of your breaker and environment (how hot things get under the panel, etc..).

My 2 cents as usual!

Cheers,
Stein
 
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I'm a man and I can change, if...

Cruel. - Ron Lee
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Well, I wasn't trying to be cruel. I have spent a many day-job-hours writting technical instructions that too few read. On the other hand; I think if I had been following the Red Green example, instead of spending so much time reading the instructions, I would be finished with my 7.
 
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circuit length

circuit length has nothing to do with the circuit breaker.

The wire is sized to the load (upsized for voltage drop if necessary) and the circuit breaker sized to the wire.

Typically circuit breakers should not be loaded past 80% of the continuous load.

Dave
-9A flying
 
Here is a wire size chart.
From the product documentation, get the current requirements for each light (amps). Find that value in the chart under the 10degree current rise column and the appropriate wire size is found in the left side column.

http://www.matronics.com/aeroelectric/articles/Wire_Chart.pdf

Contrary to an earlier post, the length of the circuit DOES matter, since resistance and voltage loss increase with length. However for the relatively short lengths used in our planes you should be ok. There is a healthy safety margin built in to the chart numbers.

Erich

Ps

The answer to Every electrical question you will ever have for your plane can found somewhere here:
http://www.matronics.com/aeroelectric/articles.html
 
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Thanks for the help

I have one switch and one 10A circuit breaker for the HID landing lights. There really is no logical place to put either an additional switch or circuit breaker so my plan is to use a bigger circuit breaker. I have not confirmed the wire size yet so if I have to use a larger guage wire I will just rerun that wire (which would be a lot easier than trying to add another switch or cb).

My best guess is that the panel builder missed the instruction to use two 10A fuses, but since he is no longer available to comment I can only guess that.

One odd thing is that the taxi lights (the standard ones from Van's) are apparently on a 15A breaker. Do the standard incandescent lights draw more current than the HID lights?
 
For DW 50 Watt HID...

you need 14 ga wire with 10 amp breaker running to each light. I am using 3 switches...one for taxi, landing and wig wag.

All you may have to do is install a dp switch and add another breaker as long as your wires are 14 ga. and you want them both on at the same time.

Another option is to use dp switch, use 20 amp breaker with 10 ga wire running to 6 circuit fuse block, install two 10 amp fuses and run your 14 ga wires from there to switch then out to lights.

DW HID's draw about 4 amps continuously, but more on start up- reason for larger wire size.

75 watt incandescent draws about 5.3 amps.
 
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Contrary to an earlier post, the length of the circuit DOES matter, since resistance and voltage loss increase with length. However for the relatively short lengths used in our planes you should be ok. There is a healthy safety margin built in to the chart numbers.
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True, but I believe that was covered by "(upsized for voltage drop if necessary)"

L.Adamson ---- RV6A
 
bigger is better myth

There really is no logical place to put either an additional switch or circuit breaker so my plan is to use a bigger circuit breaker. - MSFT-1
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There must be some place you can add a fuse holder and a 10 amp fuse? Change the switch for the DP per Wayne....done!

Your alternative of a bigger wire and breaker doesn't fix any small wires in the light itself. The manufacturer was clear on the fuse or breaker needed, have you determined that the circuit in the light can tolerate more current?
 
Lux Wrangler said:
Your alternative of a bigger wire and breaker doesn't fix any small wires in the light itself. The manufacturer was clear on the fuse or breaker needed, have you determined that the circuit in the light can tolerate more current?
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If that was the golden rule.............. we'd be screwed, in regards to a lot of appliances and machinery. I know what you're saying, but it just doesn't happen.

edit: Personally, I'd rather have the two breakers........one to each wing.

L.Adamson ---- RV6A
 
golden rule?

If that was the golden rule.............. we'd be screwed, in regards to a lot of appliances and machinery. I know what you're saying, but it just doesn't happen. - L.Adamson
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You know what I am saying, but you lost me about what you are saying. I am not putting forth any "golden rules". The Duckworks lights have wires, such as those between the ballast and the bulb; or those wires leading to the ballast, from the connection to ship's power. What are the size of those wires? I haven't looked at mine. I would make sure while increasing the breaker size and wire size to the wing tip, that I wasn't ending up with a circuit with the capacity to fry those Duckworks wires which are part of the light assembly, for instance; or, internal circuit within the ballast? In either case a short circuit could be a concern. So, what is it that doesn't "happen"?

We do agree on two, current limiting devices.
 
Lux Wrangler said:
You know what I am saying, but you lost me about what you are saying.
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Jim,

Current is a function of voltage and resistance. The formula is I = E/R, or current equals voltage/divided by resistance.

If a light bulb has one ohm of resistance, then if you supply 14 volts across the lamp, it draws 14 amps. Increasing wire size of breaker size has no effect on this relationship. The only way to increase the current and possibly damage the device would be to increase the voltage.



Bruce,

Another option might be to install a DPST (double pole single throw) switch. Feed one side of the switch and one light from your current 10 amp breaker. Feed the other side of the switch and the other light from another breaker that services an intermittent use device, such as a starter, or cigar lighter outlet. Perhaps you have one that is already 10 amps. I doubt that you would have your landing lights on while you are starting the airplane. Maybe this approach could work for you, depending on what you already have installed.

I might add that the intermittent popping of the breaker could be a) it's a weak breaker, but this is unlikely b) depending on the environment, as the lights get hot their resistance drops a bit and the current increases (pretty likely) or c) your buss voltage could be intermittently going up a bit which would also increase the current (less likely) or d) a, b. and c above.

One way to know is to put an ammeter in line and see what the current draw is. If it's close to 10 amps you would need to make a change as has been discussed before (bigger breaker AND wire or separate circuits).

Don
 
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I think we can conclude that each light draws about 5 amps normally. So under normal use each wire if 18 ga is plenty, remember one wire goes right and one goes left. I would just put in a 15 amp breaker. I look at the breaker protecting you against fire caused by shorts. The length of time it takes to trip a 15 amp breaker if a short occurs is probably a micro second longer than tripping a 10 amp breaker. Both will cause one spark and the breaker is tripped. If you have the unlikely condition where one light draws 10amps steady state, the 18ga wire will handle it. Why only 10 amps? because the other side on the same circuit is drawing 5amps. Any more than 10 on one side and the 15 amp breaker goes.
 
Ohm's law

The only way to increase the current and possibly damage the device would be to increase the voltage. - Don
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I dissagree. At a given voltage, current is inversely proportional to resistance. You can increase current by reducing resistance. Voltage can remain constant while the current rises. I understand Ohm's law just fine, what I don't understand is what L. Adamson is saying.
 
Lux Wrangler said:
what I don't understand is what L. Adamson is saying.
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Simple........

When we get into the devices themselves, many of the wires will be of less size than the main protected lead that services them. In some cases, the device (or sections of) is farther protected with it's own internal or external fuse. But you'll see applications everywhere, in which the breaker/fuse isn't sized to the smallest wire in the electrical path. Just plugging in light cords to a 15 or 20 amp wall outlet is an example. This is a response to where you mentioned protecting the smallest wire in the light setup.

As to my own aircraft............I do have at least three external in-line fuse pacs to protect small wires, that are not in the fuse tray or circuit breaker panel.

L.Adamson
 
the point is that it trips the breaker

Just plugging in light cords to a 15 or 20 amp wall outlet is an example. This is a response to where you mentioned protecting the smallest wire in the light setup. - L.Adamson
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Fair enough. But we don't plug in two devices which are rated for a 20 amp input into that wall outlet. And when the user says: "the breaker keeps tripping", I say read the instruction manual, were it says "use two 20 amp breaker circuits".

In some cases, the device (or sections of) is farther protected with it's (sic) own internal or external fuse. - L.Adamson
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Is this the case with the Duckworks? I doubt it.
 
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WIRE LENGTH VS WIRE SIZE

I think the best reference on this issue is AC43.13-1B

Chapter 11 section 4 is C/B's and Wiring.

Table 11-3 on page 11-15 spells out the rated breaker required for a specific GA of wire as discussed several time above.

But I would hope that everyone is still looking at figures 11-2 and 11-3 on page 11-30/31 to ensure that the GA of the wire is rated for the length of the run and the amps that the unit will draw.

I personally disregard the "Intermittent Flow" chart, and use the "Continuous Flow" chart for a built in level of safety.

Using the CONTINUOUS chart, I find that a 10 amp load on an 18 GA wire should not exceed 7 1/2 ft.

Likewise, a 15 amp load on a 16 GA wire would be good for 7 ft.

ALL ASSUMING A 14V SYSTEM.

Hope that helps!!
 
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To expand on the wire length issue...

Wires have resistance as well. The smaller the wire, the greater the resistance. The wire lengths given in AC43.13 have to do with the allowable voltage drop in the wire at a given amperage. AC43.13 has further charts to choose the wire size given ambient temperature, allowable wire temperature, altitude and weather the wire is by itself or in a bundle. These later charts are really overkill for our applications, but you get the idea that wire current carrying capacity has other variables, one of the important ones being size and length.

Sorry for the long post, but choosing the right size wire is an important safety issue.
 
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