[Elecraft] Local Noise Problem

[Edward R. Cole]

It would seem 120/240 to 12v converters will be the logical solution 
for low-voltage lighting.

Regarding high-current dc distribution:  I ran into that issue lots 
of years ago when I wanted to run some ham gear outside my travel 
trailer and use the 12v system as power source.  I quickly found that 
30-feet of #14 or #12 wire would not do.  I finally used a 12v 
battery and floated it from the trailer power.  And I was only 
running 150w on 2m.

At one time I was considering solar power for a two-story log-cabin 
in the bush, but the wiring gets expensive (so do the panels).  The 
cabin now has 120vac utility service so its a moot issue (and I sold 
it in 2003).

My present shack has 13.8v provided by  50A Astron which is connected 
via a 12-foot run of #6 welding wire to the main 30A buss fuse.  This 
connected to a heavy barrier terminal strip to provide power to all 
the amplifiers and high-current equipment.  I see about 13.5v at the 
main fuse when running loads; unloaded it shows 13.75v.

Two power leads run from there to two more barrier strips:  one is 
#12 solid house wire and the other #8.  Both about 3-foot long.  My 
new 144-28 50w transverter runs off the strip fed by #8 wire and 
voltage runs at 13.2 under load.  My K3/10 is fed from the #12 wired 
strip.  There are only two other items connected there: panel lights 
for my manual antenna tuner and the main station controller (fused at 5A).

Many of my new amps require 28vdc.  I have a 8A and two 50A supplies 
for 28vdc.  One 50A PS runs the 16-foot dish rotator-motors and will 
run 432-100w and 1296-300w PA's at the dish.  I run #12 romex out 
there for 120vac power (remotely switched).  The other 50A PS may go 
to the base of one tower where I may install some big amps for 900 
and 1296 MHz.  To place the amps at 50-feet will require #6 wiring up 
the tower.  Installing a switching PS at tower-top becomes attractive 
(not the 90-lb. 50A PS).

Ohms law rules dc-wiring!
Ed

------------------------------

Message: 5
Date: Sun, 03 Apr 2011 11:05:02 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
Subject: Re: [Elecraft] Local Noise Problem
To: elecraft at mailman.qth.net
Message-ID: <4D98B6CE.8060303 at audiosystemsgroup.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 4/3/2011 10:12 AM, AB8XA wrote:
 > The sub-panel will also have a 30 amp circuit to my "shack," 
feeding a 24 VDC to 13.8 VDC converter for full nominal voltage to 
our 100 watt rig. There are many advantages to 24 VDC over 12 VDC in 
residential use.

Yes, BUT -- that 24VDC to 12VDC converter is almost certainly some sort
of switching power supply, and you will need to carefully search to find
one that is not a source of RF noise..  AND the conductors are going to
need to be pretty large, because they're carrying a 10A load (at 24V)
just to run your 100W rig.  Multiply that current (and copper) by about
9X if you also want to run a 500W amp. And the only one I know of that
runs on 13.8V is the Ten Tec Hercules II, a very nice amp that's been
out of production for about 20 years.

73, Jim K9YC





73, Ed - KL7UW, WD2XSH/45
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