DC Wireing

unjonharley · Post by **unjonharley** » Mon Jul 12, 2004 3:25 pm

Any one know why most or all DC is wired with strand-wire a oposed to soide-wire????

dman · Post by **dman** » Mon Jul 12, 2004 4:31 pm

something about surface area, multiple strands having more, electrons travelling along the surface, less resistance...ah...um...sorry, any more than that has leaked back out......my, isn't the sky lovely today?

gilmore · Post by **gilmore** » Mon Jul 12, 2004 4:41 pm

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Stranded is less likely to break or crack under stresses of movement and vibration in auto applications.

Solid wire, like the wire used in your home, is put it in and (hopefully) forgetten. Never to move or be moved.

Then again, I don't know a volt from a watt......

safetythird · Post by **safetythird** » Mon Jul 12, 2004 8:24 pm

I think gilmore might be on to something. I know that cat5 cable (your basic networking/ethernet cable) comes in stranded and solid. I use solid for permanent (in wall / across ladder/ etc) purposes and stranded for making patch cables.

dman also has a point. I seem to remember learning why cable has so much more bandwidth the telco lines. The wire is bigger, more surface area = more electrons able to pass over it. .... or something.

Perhaps some electro engineer will pipe up and set us straight.

Safety Third!

BAS · Post by **BAS** » Mon Jul 12, 2004 9:15 pm

IIRC, electricity flows on the outside surface of a wire, and multiple strands means more surface area (or more surfaces, which amounts to the same thing pretty much). It would also be more flexible, I think. Also, one strand could break and not have the connection broken.

I used to know more about this stuff, but I have been working too many brain dead jobs for too long.

Spokes · Post by **Spokes** » Mon Jul 12, 2004 9:17 pm

Gilmore is mostly correct I believe.

The issue of current travelling on the outside partion of the wire is called skin effect and has more to do with AC or switched circuits than dc power wiring.

http://whatis.techtarget.com/definition ... 69,00.html

BAS · Post by **BAS** » Mon Jul 12, 2004 9:30 pm

Okay, I defer (sp?) to someone who has read up on electricity more recently than me.

Dustdevil · Post by **Dustdevil** » Mon Jul 12, 2004 11:19 pm

DC loses more current over a given distance than AC. The loss is due to resistance which becomes heat. The current is carried (as correctly stated in the above posts) on the outside of the strands. More strands are needed to minimize the loss. This was demonstrated clearly during the early period of electricity in this country. Gearge Westinghouse and Nickola Tesla proposed alternating current generators while Edison wanted direct current units. Edison told everyone who would listen that AC current was far too dangerous for homes, in fact, that is what Sing-Sing used in "old sparky" the first electric chair. As we know, Westinghouse and Tesla won the battle. The true reason that Edison wanted DC current was that he held the patent on DC generators of that time. Westinghouse held the patent on AC generators. One AC generator could power a small city. It took one DC generator for every 10 square miles as the current would degrade over any greater distance. Do the math.

sgrunspa · Post by **sgrunspa** » Mon Jul 12, 2004 11:23 pm

you are all mostly correct. in the absence of an external electric field all charge will move to the surface of a conductor. so this means if you charge up something and then take away battery it is all on the surface.

however, a DC current will produce a steady flow through the conductor (wire). while the electrons do not travel the surface, it is true that stranded and solid wire differ in their resistivity.

Skin effect is purely an AC phenomanum and only comes into play around 100MHz.

robotland · Post by **robotland** » Tue Jul 13, 2004 6:04 am

I'm glad I read this thread in the morning......now I don't need to learn anything else ALL DAY!

Thanks, everyone!

brain powering down now........mmmmmmbuh. ready for day at work.

unjonharley · Post by **unjonharley** » Tue Jul 13, 2004 7:52 am

Thanks guys, I had forgotten and to lazy to look it up.

unjonharley · Post by **unjonharley** » Tue Jul 13, 2004 8:31 am

What I had frgotten was: Dc loses it's punch over a very short distance. If I were to start out with #14 wire. I would have increase the wire size every few distances. Ending up with #8 wire quickly. Easy rule to have but my head hurts to think of it.

Tiahaar · Post by **Tiahaar** » Tue Jul 13, 2004 11:01 am

As applies to the playa and large +1000watt power inverters, it follows that though you can happily plug your 110VAC 10 amps of whatever into the inverter with 50' of 14 gauge extension cord, you'll want 0 or 00 gauge in as short a run (a few feet) as possible for the 12VDC run from the inverter to the battery bank. Speaking of which...in jumper cables, bigger really is better, get the 6 or 4 gauge (or bigger) at least. Have you seen some of the things passing as "jumper cables" in cheapie car tool kits??? My kitchen toaster has bigger wires!! My bus laughs at the weenee toy jumper cables and promptly fries them. (OK so if you leave them hooked up long enough you can revive a battery sometimes...just unhook before trying to pull starting load)

unjonharley · Post by **unjonharley** » Tue Jul 13, 2004 11:13 am

Tiahaar wrote:As applies to the playa and large +1000watt power inverters, it follows that though you can happily plug your 110VAC 10 amps of whatever into the inverter with 50' of 14 gauge extension cord, you'll want 0 or 00 gauge in as short a run (a few feet) as possible for the 12VDC run from the inverter to the battery bank. Speaking of which...in jumper cables, bigger really is better, get the 6 or 4 gauge (or bigger) at least. Have you seen some of the things passing as "jumper cables" in cheapie car tool kits??? My kitchen toaster has bigger wires!! My bus laughs at the weenee toy jumper cables and promptly fries them. (OK so if you leave them hooked up long enough you can revive a battery sometimes...just unhook before trying to pull starting load)

/\
I was sitting here looking at my battery set up. I came up with jumper cables for wire. Then read your post. I'm going to have the whole set up on a little cart. It will include the generator. That way I can wheel it in and out of the shade structure and lock it down. It's a damn shame we have to start locking things up.

Dork · Post by **Dork** » Tue Jul 13, 2004 1:02 pm

Here's a wire size chart for y'all:

http://www.powerstream.com/Wire_Size.htm

You could probably run lower gauge wire for short runs.

Stranded wire is necessary for anything other than a fixed installation. If the wire is going to flex at all, solid wire will eventually fail. The more you need something to flex, the more highly standed (higher number of smaller strands) it should have.

It's all about the amps.. I don't think AC or DC makes a huge difference for the short lengths we're dealing with. The only difference is the old power=volts x amps rule. For the same power, 12v of DC will have 10x the amount of amps as 120v of AC. So, much bigger wire is required. If you're going through an inverter, keep the inverter as close to the DC source as you can then run cheap AC extension cables.

Welding shops carry #0 and bigger wire with nice, flexible, high temperature covering. Good stuff. The lower the number, the bigger the wire. After 0 comes 00, then 000, etc. 00 is pronounced 2-ought (I've also seen 2-naught) and also listed as 2/0.

If your wire will be near anything hot or you're running a smaller gauge than you probably should, make sure the wire has a high temperature sheath such as silicone rubber or PTFE. The cheap "speaker wire" sheaths will melt and short out without much prompting.

unjonharley · Post by **unjonharley** » Tue Jul 13, 2004 1:18 pm

Dork wrote:Here's a wire size chart for y'all:

If your wire will be near anything hot or you're running a smaller gauge than you probably should, make sure the wire has a high temperature sheath such as silicone rubber or PTFE. The cheap "speaker wire" sheaths will melt and short out without much prompting.

/\
Also figure in the playa heat,generator heat and sound bafal holding heat. if you have then

sgrunspa · Post by **sgrunspa** » Tue Jul 13, 2004 2:05 pm

now that we are taling about wire sizes and and their lengths, I would like to suggest that people over-engineer the size of their wires.

unless the wire is made for high temp applications, in which case it will say high-temp on it, it is assumed to be used under normal conditions.

when the wire is used, it heats up, and the resistance increases with heat. The increase in resistance cause the wire to heat up more and so on. this isn't a problem if the wire is in some conduit in your house. but on the playa it may heat up so much that you will start to smell the insulation meltiing (don't ask how I know this). so if you are going to run 15 amps, get 30 amp wire. it is a little more expensive, but cheaper than a fire.

unjonharley · Post by **unjonharley** » Thu Jul 15, 2004 7:57 am

I cut into a old set of jumper cables. The wires were all black and green. also for all the rubber around the wire. It turned out to be #10. So I am going with all new #9 wire. I know the joints should be tined. But looking at the inverters wires they have glue-stick. Much easyer. And no sparks down the leg. This is a cheap way to go and wont feel bad if I have to build new again.

unjonharley · Post by **unjonharley** » Sun Jul 18, 2004 7:26 pm

Some thing strange. I have two batteries set up to charge my scooter. It works fine. Them I put a lighter socket on and ran a small 12v. drop light. First evenig was fine. The next evening I plug in the light an the bulb blows. So I fliped it to the flasher light. One flash and poof¿¿¿¿¿¿

DC Wireing

DC Wireing

Solid vs Stranded

mostly correct

come to think of it