[Bglug] DC Current and Wire Size

William Park opengeometry at yahoo.ca
Sat Dec 5 12:04:07 EST 2015


On Sat, Dec 05, 2015 at 11:32:42AM -0500, Peter wrote:
> There was a brief talk about running DC 12V LED lamps and the required wire
> size.
> 1) Remember that for DC, the wire length is from source to device AND BACK
> TO SOURCE.

Hmm, so DC current is bi-directional on the wire, also?  I thought only
AC current does that. :-)

> 2) There will be many sources on the Internet on this. From my copy of Nigel
> Calder's Boat Owner's Mechanical and Electrical Manual, pages 90 and 91
> for a 10% voltage drop on a 5 ampere load
> Wire size    Length in feet from source to device and back to source
> 18                10
> 16                40
> 14                60
> 12                90
> 10                140

Long ago, I was curious (and still am) how much current USB cables can
carry.  USB wires are 26, 28, or 30 AWG.  Ethernet is 24AWG wires.  Rule
of thumb to remember:
    - 24AWG is rated for 500mA, and 
    - USB specs says 500mA max.
So, I don't know how 5V/2A USB chargers passed certification, when USB
cables can't do 2A.

Anyways, here are my bookmarks:
    - http://www.engineeringtoolbox.com/wire-gauges-d_419.html
    - http://www.powerstream.com/Wire_Size.htm

If you guys have other URLs, I'd appreciate it.
-- 
William


> 3) From my limited experience with wiring, I take my estimated wire length
> required to run the wire and then double it to allow for all those bends and
> up walls and down walls. And for DC, possibly double it again for the return
> leg.
> YMMV,
> Peter Richards
> 
> Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe. -  Albert Einstein
> 
> On 12/04/2015 12:00 PM, group-request at bglug.ca wrote:
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> >Today's Topics:
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> >    1. Using Raspberry Pi to emulate USB keyboard? (William Park)
> >
> >
> >----------------------------------------------------------------------
> >
> >Message: 1
> >Date: Thu, 3 Dec 2015 19:31:36 +0000 (UTC)
> >From: William Park <opengeometry at yahoo.ca>
> >To: Bruce-Grey Linux Users Group <group at bglug.ca>
> >Subject: [Bglug] Using Raspberry Pi to emulate USB keyboard?
> >Message-ID:
> >	<493813006.11990419.1449171096811.JavaMail.yahoo at mail.yahoo.com>
> >Content-Type: text/plain; charset="utf-8"
> >
> >Following on the recent discussion of $5 Raspberry Pi...
> >Do you guys know if it's possible to use Raspberry Pi to emulate USB keyboard?? As far as PC is concerned, it's receiving keypresses from some keyboard, which happens to be RPi faking as keyboard.
> >If so, where do I start my reading?
> 
> 
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