On Wed, 2007-06-06 at 20:38 -0400, Ralph Matheny wrote:
> couple related issues--I don't think it's just the gauge of the wire
> that is a factor. As I remember it, for copper to be a really good
> conductor it must be very pure--I'm thinking 99.9% plus. Beyond that,
> resistance builds up quickly. Thus, the house wire which you buy at the
> home depot or whatever, which was designed to be pulled thru pipe, etc,
> and to carry only a few amps of AC under normal conditions (and blow the
> breaker under abnormal) may not be a good choice for 13.8V DC power
> wiring. A look and feel at home house wire in comparison to good DC cable
> will quickly tell one that the two are not the same. I think (but I don't
> know) that house wire contains some steel to make it have physical
> strength. The steel (or whatever) would reduce the conductivity a bunch.
> The speaker wire the kids use for the high-power audio systems has
> worked well for me. It is flexible, solders very well, and costs a bunch.
UL specs for copper wiring wire demand high conductivity. Its probably
stronger from being hard drawn, or work hardened by stretching. But that
stiffness of the solid wire is death on Molex pins. The speaker wire is
probably Oxygen Free which makes its cost highest and it also has many
strands for great flexibility.
>
> In my opinion--replacing the power connector on the back of a TT radio
> with the same type/size isn't a good idea. There have been too many
> reports here of power connector problems. I'd suggest a neat pigtail with
> an Anderson Powerpole or the like as a big improvement of any TT radio.
> Another solution, on those which have the 4-pin power plug, is to use all
> 4 pins for the DC, 2 for the + and 2 for the minus. Even Yaesu does that
> on their little mobile rigs.
I'm no fan of Powerpole because they depend on plastic for contact
pressure. Look up the definition of PLASTIC... "Flows under pressure"
which relieves that pressure. A rule that was drummed into me at Collins
in the second week I worked there back in 1963.
>
> I have my Omni V on the bench for repairs--and measured the drop from the
> DC line an inch from the power connector to the rig end of the DC fuse.
> Drop, with rig drawing 20 amps, is .35 volts. That's big. Lots of heat
> across the connector, the fuse, and the fuse holder.
I'm preferring the larger blade type modern automotive fuses and think I
have lower voltage drops with them. Some vintages of Yaecomwood radios
have very bad voltage drops in the almost fuse holders they've used. And
the Tentec Scout is sensitive to battery voltage with drops in the cable
and connector causing grief there at times. The last use FT-90 I
acquired has two fuses in the positive wire, enough to drop the power
output 15 watts down to 353 from the rated 50. That will get a new cable
in the car or truck when I install it.
>
> My two cents worth. back to the bench!!
>
>
> Ralph Matheny
> K8RYU
> 207 Gibbons Place
> Marietta Ohio 45750
> mathenyr@marietta.edu
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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