Lighting Circuits - and 12V circuits in general

[splyb]

The spousal unit and I spent WAY too much time at IKEA this past weekend. I, in particular, loitered in lighting much of the day - though I think a lot of their stuff can be adapted to a trailer, and not just lighting.

I'm going 100% LED, interior, exterior, running gear, markers and all. There simply is no reason not to. So, I start looking at the power requirements of the various options - IKEA has some pretty cool wall sconces - but find they are expressed only in watts, while I'm laying out my mental wiring diagram in amps. So, an LED sconce that requires 6 watts (according to the IKEA packaging) uses .5 amps per hour (6 watts / 12 volts = 0.5)? If that's right, couldn't I put just about all the lights, interior and exterior, on a single 12V circuit? What is the max I can put through a single 12V circuit? I know it depends upon the fuse I elect, but what's the upper limit?

If I'm reading the stuff I'm ripping out of her '68 Safari (Land Yacht) correctly, many of the incandescent bulbs used as much as 3 amps. If my math is right, couldn't I replace a single one of those with, like, six 6-watt sconces?

What am I missing/miscalculating?

Jay and Lisa

[idroba]

Yes, W= A x V. So, A = W/V. Thus you are correct, 6 watts/12 volts = 0.5 amps.

Incandescent lights turn 95% of the energy which goes into them to heat, 5% to light. LED's do much much better.

So, yes, you can put a lot of LED lights on the same circuit. I would not load a 15 amp 12 volt circuit up to more than about 12 amps though.

My 2014 20' FC has all LED lights from the factory. If I turn on every one of them at the same time, the total draw is less than 4 amps.

[mimiandrews]

What is the max I can put through a single 12V circuit? I know it depends upon the fuse I elect, but what's the upper limit?

The load limit on a circuit is determined by the size of the wire installed. The fuse is there to protect the wire so that an overloaded, overheated wire does not start a fire. So, putting a big fuse on a small wire just moves the weak point to a place where you really, really don't want it to be.

There are wire size charts available so that you can design a circuit for almost any load. Length of the wire also matters.

If you are changing fixtures on an existing circuit, stay within the limits of the original fuse size. Switching from incandescent lighting to LED's should work, no problem.

[RamblinManGa]

Hi from AZ. . . we swapped all 31 bulbs in our FC28 to LED's (got them from M4), Since the running lights are only on when hooked to the TV, didn't seem as important for battery use/life, taillights were LED. We also added 2 solar panels/charging deal AND a smart charger, since Airstream was too cheap to do so. The solar pre-wire is just barely adequate size wire (I'm told). . . Sounds like you've got it figured out to me, good luck, Craig

[JCWDCW]

Assuming Airstream uses at least 14 Gauge wire on the 12 Volt circuits you can safely load to 80% of 15 amp capacity (12Amps)...standard building code stuff, and hopefully RVA specs as well. You should be able to see the wire size when you pull the original fixtures.
JCW

[Redleger]

One bit of caution, we're the lights at IKEA 12v or 120v? Asked a different way are you sure you were looking at DC lights and not AC lights.

[splyb]

Yes. Most of the products I looked at came with two or more light fixtures and a small converter (the packaging refers to it as a "transformer").My ideas was to simply end-run the converter. Such hacks seem pretty common on YouTube, but I put more stock in this community.

[idroba]

The problem with LED lights from Ikea or any other similar source, which are driven by 12 volts from a wall wart transformer is that you just don't know how close they are run to their design limit with the original setup. As the voltage changes upward, so does the current through the LED's and they are very sensitive to a maximum current limit.

The Airstream "12 volt" system can go up to 14.5 or even 14.7 depending on many things such as the converter/charger setup, solar setup, and tow vehicle charge system. That may or may not be in the limit range of the wall wart driven LED lighting you are buying.

I am not saying you will have a problem, but it is possible. It is also impossible to predict. It very much depends on how the original system is designed and how the maximum current through the LED units is regulated.

[dennis3751]

Check out super bright leds for more info. Most of their "12V" lights will accept a wide range from 11 to 14 volts. I think most nominal 12V led strips or bulbs will accept the variations seen in a trailer.

Dennis

[kb0zke]

One advantage of having different circuits for the lights is that if you blow a fuse you won't be completely in the dark. It sounds like you are doing a pretty complete renovation, so it might pay you to upgrade the electrical system as well. I'm not talking about just replacing the existing lights with LEDs, but also the fuse block. Why not have at least two circuits in the living areas, so that even if one fuse blows you will still have some lights in the area. Better yet, replace the fuses with circuit breakers. That way you won't have to hunt around in the dark for the right fuse.