12v lighting advice needed!

[HoFFdOg]

Hey everyone.

Have a question as regards rigging up electric in my truck as i know not a thing about it.

At the moment im cladding the roof and want to fit the lights and wiring while im cladding so i dont have to take down the roof again.

-What type of cabling should i use, T&E or 3-core flex cable. What thickness? i was told by someone to use 4mm-6mm as 12v systems can get hot or does this just apply for cable between solar panels and the battery!?

- Halogen or LED lighting??! I know obviously LED runs on much less power but all the LED lights i see come with a transformer/ junction box, how can i integrate this into my circuit or can i scrap it completely and just wire up as normal with T&E or flex core.

- Once ive wired up all my lights do i take other ends of the cabling into a fuse box linked to the battery?

Any advice for lighting in a housetruck wud be much appreciated.

Thanks.

[Sharkey]

I'm going to be at a bit of a disadvantage here, as I am not familiar with the terminology over in the UK, but I'll give it a shot. Perhaps if AccordGuy sees this, he will respond, he's over on your side of the Atlantic and explains things very well.

If I'm reading the wire gauge conversion table on Wikipedia correctly, 6mm wire is about #2 in American Wire Gauge. Good lord no! You don't need anything nearly that large for lighting circuits! All of the lighting circuits in my Housetruck are wired with #12 (2mm), and that is quite adequate for old-fashioned incandescent lamps up to 50 watts or so. The feeder bus from the batteries for the lighting circuit is only #6 (4mm), and it carries all of the loads fine.

The idea is to use oversized wire to minimise voltage drop between the batteries and the lights. A percent or two at mains voltage is insignificant, but at 12 volts, it can mean the difference between dull, dim lighting and proper brilliance.

Halogen lamps over here are commonly 25 to 50 watts, which corresponds to 2 and 4 amperes at 12 volts, respectively. If several of these lamps were installed on a single feeder circuit, you might want to bump up to #10 (2.5mm) or even #8 (3mm). If you are using LED lighting, then the wire requirements are even less demanding.

As for shucking the transformer on LED lighting, yes, it's quite possible, but might require some reverse-engineering to determine the operating current required on the individual LED arrays. LED's are constant-voltage devices, so they can run from a variety of voltage sources, but they are absolutely dependent upon proper current, which is determined by the current limiting resistor used in the circuit. If you want help figuring this out, I can help, but it will require having the LED lamps you intend to use, and some small amount of skill and nerve to rip into them and figure out that they will need.

In case you haven't yet seen it, I have a few pages dedicated to similar subjects:

http://www.mrsharkey.com/busbarn/electrics/chapt4.htm
http://www.mrsharkey.com/busbarn/electrics/chapt10.htm

There's an index page for more info.

Also, Rob Gray just went thought a similar fit-out on Wothahellisat:
http://www.robgray.com/wothahellizat/wo ... /index.php
Scroll down to June 22nd and August 21st.

I am guessing that 3-core flex is similar to "Non-metallic cable" over here? Two insulated and one bare grounding conductor inside of a plastic sheathing? It would work for lighting circuits, and if installed properly, could be used safely for mains power if you ever converted over to that for lighting power. My Housetruck (and the Crown, when it's finished) use single-conductor wires inside the ceiling and walls. I knew that I would always use battery power for lighting, although my desk lamp is a 120 volt Compact Florescent powered by the 12-to-120 volt inverter.

Fuses. More fuses is usually better. If each lighting circuit has it's own fuse, then problems are easier to isolate, protection from overheating due to short circuits is better, and circuits can be reconfigured when necessary to power other loads. All of my lighting circuits are powered on individual wires all run to a central location (cabinet over the entry door). Some of the circuits are combined (for instance, the three ceiling lights are all on one fuse), while others are fed by individual fuses.

One tip: I know that your framing is timber, so it's probably not an issue, but I always have thought that running individual negative wires to each fixture was superior to using the frame of a vehicle as "ground" and commoning one leg to the frame or sheet metal. I've also heard that using the frame as a current conductor is more likely to cause galvanic problems in the framing and sheathing, resulting in oxidation, rust, and erosion of the metals.

[AccordGuy]

Wot Sharkey said... plus...

I wouldn't use Twin and Earth (T&E) as it's solid core stuff for use in houses. Being a mobile application you'd be better off with actual auto cable or 3 core mains flex (also stranded). Solid core will fracture (eventually) with flexing and vibration. But 3 core is going to be a bit of a waste if you're never going to run mains and only 12V. You'd be better off with 1mm or 1.5mm twin core.

If you aren't going to use negative return wiring but the chassis then automotive red cable is probably best. If you want out and return wire then Maplin does automotive red/black figure 8 up to 50A capacity. You could use 35/50A as a ring bus and tap it for each light. You'd have to have a 50A fuse on the ring and 2/4A fuses in line with each lamp but that would keep the spaghetti down at the battery end. For short runs to one or two bulbs you can use 78 strand speaker wire that you can get at B&Q. It's white figure 8 but has a black stripe for polarity. You can use it for any 12V system but not mains. I also bought a cheap 50m box of Ring 12V outdoor lighting wire at B&Q. It's #16 gauge (about 1.4mm) and is very flexible. It's only drawback is that it's black figure 8 with texturing for polarisation so you have to be a bit careful when using it.

Dunno how far the battery is going to be from the lights or how many you want to run but the longer you go the thicker the wire needs to be... So you can use 1.0mm for a short run (like <5m) with a 50W bulb but if you need 10m then you have to go to 2mm.

Ikea does some nice 12V halogen downlights called "Non". I bought some for lighting up my display case in the living room. They come with a 12V mains adapter but the lights themselves have spade plugs that connect to the transformer wire and the transformer wire also plugs into the transformer with a DIN speaker plug! So you can easily bin the transformer and just plug 12V DC into the wire supplied. The lamps take commonly available 12V 10W halogen capsules. You can surface mount them or recess them in a ceiling (allow some space above them if recessing to allow the heat from the bulb to escape through the vents in the plastic shell.)

In my theatre I'm running a pair of 2W LED lamps I got from these solar kits I've been buying from Maplins. The kit came with these 12V LED bulbs in the shape of standard E27 screw in bulbs with some plain holders. I had a tough time finding mains fittings that would take the bulbs as they are quite long sticks with the plastic diffusers. Eventually, I found some E27 angle spot lights with switches at a car boot sale and cut off the mains plugs and put in the LED bulbs. They run off the solar batteries directly and I screwed the fittings to the wall. They aren't very bright but are perfect for ambient light when watching TV or the projector.

Caravan shops do loads of 12V fluorescent strip lights but for some reason they are always a sickly blue-white light - probably because they use the high efficiency phosphors that are blueish (like old mono TVs).

I'd probably not go 12V at all though as mains inverters are quite cheap (but see my thread on cheap inverters!) and mains lights and appliances are often much better made and cheaper than 12V "specials". Plus if you're at a camp site with mains feeds you can plug into the mains and use all your kit. If you go 12V then you have to use the battery (or get an expensive high power 240V to 12V transformer) when you're at a camp site with mains feeds.

[Robert]

I am in a similar situation as my large Camper has both 12 VDC and 120VAC. The 12V is seconded by a deep cycle marine battery so when the main 120VAC fails, I still have lights. There are two of every system on here and it makes repairs a real pain. What I find useful is the propane refrigerator and stove, the separate lights and plumping are useless, actually worse than useless. If I were you I would use no 12VDC and just use line voltage 240VAC in your case. 1/20th the electrical current thus smaller wires for a given wattage.

Definitely use stranded wire over solid core for vibration reasons.