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Topic: 12v Wiring: Supplies and Technique (Read 13 times) previous topic - next topic
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12v Wiring: Supplies and Technique
Yahoo Message Number: 148607
Hi All, I'm looking to do some 12v wiring in our LD to add some (high-quality) fixed USB charging ports above the dinette in our 26MB. I have a background in small electronics, but have been struggling more than I'd like to admit with the "house wiring" style. I know that I should fuse the positive wire, but beyond that, I'm seeking some practical advice.

1) Supplies: I started by trying to use solid core 14AWG wire and crimping butts to split the wire off into the part I wanted to work on. Well, they were a pain in the butt! Wire was too stiff, and kept falling out of the crimps (maybe because I was not using the right AWG stepdown on the crimps.

a) I'm thinking I'd like to use a stranded wire instead. What AWG should it be? (Some of this will be for short runs to splice back into the 12V "trunk" that is run for the cig. lighter socket above the dinette, some will be to my "circuit," which will draw only 5A.
b) and use the "twisty cap" method of splicing. Does any sort of black "twisty cap" work that I would get from HD or Lowe's?

2) Technique: Any specific techniques that might help? As I said I will fuse positive leads and I will use shrink tape where appropriate. Anything else I should think of? I'd rather not solder as some of the spaces are tight.

Thanks very much.

Best, Chris
Re: 12v Wiring: Supplies and Technique
Reply #1 –
Yahoo Message Number: 148610
First, don't use solid conductor wire for 12-volt circuits.  You need stranded wire.  You didn't say how long the run would be, but 16-guage will probably be OK.  Use 14-guage if more than a few feet.
 If you don't want to solder, you can use one of these: http://tinyurl.com/o7e2j7h , http://tinyurl.com/ljy77q9 or http://tinyurl.com/p42sr22 .

Dick
Re: 12v Wiring: Supplies and Technique
Reply #2 –
Yahoo Message Number: 148613
Thanks for that. Just curious, why is stranded better? I tried to use the butt splice, but to no avail (they fell off). (Maybe I just answered my own question?)

The first link was broken, but I'm wondering also if I could use something like this: http://www.homedepot.com/p/Ideal-74B-Yellow-Wire-Nut-Wire-Connector-250-Pack-30-1074J/202894290

I wish I had known about the tap splice earlier! Those seem great.
-- C
Re: 12v Wiring: Supplies and Technique
Reply #3 –
Yahoo Message Number: 148614
Something happened to the first link. Just go to the Home Depot website and search for wire splice. You will find all of them.
 Actually every wire in a moving vehicle should be stranded. The possible exception would be the A/C wiring in the walls. Note that you will never find a solid conductor wire in an automobile. At least nothing the manufacturer puts in. Stranded handles the vibration better. When I worked in aerospace all of our wiring was stranded. Solid works in homes because they don't move.
 Personally, I would not use wire nuts in a motorhome. My preference would be to twist the wires together in-line, solder them, then apply shrink sleeving over the connection. I like very permanent splices.

Dick

Re: 12v Wiring: Supplies and Technique
Reply #4 –
Yahoo Message Number: 148615
That makes sense re: stranded. Thanks a lot for your input.
 I love solder as well, my only reservation is that there's not a lot of "slack" in the existing wiring. Maybe I'm approaching something wrong.

Also, I think I noticed that all the LD wiring used wire nuts with a lot of electrical tape?

Thanks again, Chris
Re: 12v Wiring: Supplies and Technique
Reply #5 –
Yahoo Message Number: 148616
If there's "no slack" in a wire that you want to tap into, here's one way to do so:

Using a sharp utility knife, slice a thin short length, 1/2" long or so, of insulation from one side of the wire - just like peeling a potato. Repeat, slicing until you can just see the copper wire. It is important to use care and avoid nicking or cutting into the copper.

Once you have exposed a short length of copper, grasp the insulation on the opposite side of the wire and pull it free from the conductor. The insulation, being elastic, will pull away far enough for you to use a scissors or dikes (wire cutters) to snip the insulation at each end of the exposed bare copper.

Strip 3/4" of insulation from the end of wire you will be splicing. wrap it tightly around the bare copper and solder.

Use self vulcanizing rubber insulation tape to insulate the splice. 3M Rubber Splicing Tape

Note that I would only recommend using this method when there is no slack or "service loop" in a wire to allow any other more convenient method of splicing - though this does work well. If you need to use this method to splice into two adjacent wires, then offset the two splices if possible so they are not alongside each other so as to minimize the bulk of the cable etc.

I'm also in the "solder and heat shrink is usually best" crowd.

bumper
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bumper
"Yonder" '05 MB
"WLDBLU" glider trailer
Re: 12v Wiring: Supplies and Technique
Reply #6 –
Yahoo Message Number: 148618
Excellent advice. One caution when soldering things like this, be careful you don't hold the iron on too long so you allow the solder to wick up under the insulation. Wicked stranded wire becomes weak. Not much of a problem here as the wire probably isn't going to be moved much. Just something to be aware of.
 Many years ago when I ran the wiring harness department at General Dynamics Pomona, I couldn't believe wicking was a problem until a Navy inspector showed me how easily the wire would break off with very little bending. I could then see why the inspectors always rejected wicked wires. Not good in a guided missile. Never forgot that lesson.

Dick
Re: 12v Wiring: Supplies and Technique
Reply #7 –
Yahoo Message Number: 148622
Dick,

Agree on all counts.

Solder wicking up stranded wire causes any wire flexing to rapidly fatigue stress the bare copper wire strands right at the copper to solder interface, as the soldered wire is rigid. This is one reason that soldered wiring is a no-no in aviation.

Most insulated crimp type connectors, when installed correctly, provide a gas-tight connection between the wire and connector as well as a more gentle crimped support for the wire insulation, thus avoiding potential stress risers.

Stranded, soldered wire also presents a problem in compression type connections when high current is involved. The solder malleable and tends to flow under pressure, this creates a loose connection with surfaces that can oxidize (not gas-tight). The oxidation causes resistance to increase and this in turn builds heat as power is dissipated, often causing the solder to melt - bad things happen. Essentially the same thing happens on the LD 12 VDC fuse board - i.e. the stranded soft copper wire tends to flow in the screw clamp connections, so they loosen over time. If not tightened, high resistance and burned wire result. A good fix is this type of wire end termination before sticking the wire into the screw clamp:

800 Wire Copper Crimp Connector Insulated Cord Pin End Terminal AWG 22 to 10

bumper
bumper
"Yonder" '05 MB
"WLDBLU" glider trailer
 
Re: 12v Wiring: Supplies and Technique
Reply #8 –
Yahoo Message Number: 148623
I'm not sure how many charging ports you need, but I use a dual USB charging port built into a cigarette lighter plug that fits nearly flush with the front of the socket. If you need more than two ports, you could mount a 1X2 or 1X4 socket array. This would be much easier to wire up than USB port, and the adapters have built-in efficient dc-dc converters for 5V.

Steve
2004 FL
2013 Honda Fit