[Boatanchors] Boatanchors Digest, Vol 69, Issue 24

[Stanley Adams]

Hey Drew, why not just buy a 24 volt switching supply that is on the surplus
market, there are many many of them that are being junked that come from
communications equipment.  If you want a simple 12 to 24 volt converter,
just build a voltage doubler circuit such as is found the ARRL handbook.  A
few caps, diodes and you got it. The regulation will come from the 12 volt
unit.  Just a thought to try out.

Stan Adams
Memphis
W4SBA


Message: 1
Date: Sun, 11 Oct 2009 09:30:07 -0700 (PDT)
From: "Drew P." <drewrailleur807 at yahoo.com>
Subject: Re: [Boatanchors] 12 to 24 volt conversion, the issue of cost
To: boatanchors at mailman.qth.net
Message-ID: <347228.86679.qm at web38508.mail.mud.yahoo.com>
Content-Type: text/plain; charset=us-ascii

On 12V to 24V converters, Michael Tauson wrote:

<snipped for brevity>

"Only a few actually caught on to what I want to do - build (yes,
build.  You know, individual components and winding transformers and
soldering and all like that there stuff.) an inexpensive 12-to 24 volt
converter and learn about toroids at the same time.  How that got to
buying trucks is way beyond my comprehension but it tells me the
thread has gotten out of hand.  Go back to my original post to see
what I'm looking for ... and, as a hint, it has nothing to do with
adding batteries, adding alternators, or buying vehicles."

I share much the same mindset as you do.  I enjoy designing and tinkering
with electronics, but I cannot, and probably never will be able to allocate
funding for construction of big bucks things like high power RF amplifiers.
In short, I am a product of an era when a career in engineering in the U.S.
has become all but obsolete; I have little in funding to spare and a big
desire to experiment.  And besides, I revel in using salvaged components
obtained for little to no cost - a sort of getting something for nothing.
This mindset is reflected in my recent post regarding use of motor
capacitors as DC power supply filters.

How about an intermediate plan?  There is much modifiable computer junk to
be had for free.  I have had, for example, good luck converting computer
switch mode power supplies for other uses.  A starting point for magnetics
in a 12V to 24V converter might be disassembly of the ferrite E-I
transformer taken from a desktop computer power supply and counting turns
with an eye to rewinding to your own specs.  The salvaged toroidal energy
storage inductor could be treated similarly.  These magnetics could be good
for power levels same as in the original application. If you don't care to
build the driver circuitry, the PWM control circuit from that salvaged power
unit could likely be modified to that end.

Another intermediate plan might be modification of a computer UPS unit.
These usually use a 12V internal gelled electrolyte lead acid battery, and
the units frequently find their way to the dumpster because no one cared to
replace the failed battery.  One could yank the battery and install
connections for providing 12V. The 115V output would then be available
without further modifications.  Further modification could consist of
rewinding the unit's transformer for the desired output, or just plug a
transformer having the correct output voltage into the UPS's 115 V output.
Then, recify and filter to taste.  Many of these UPS units use a laminated
iron core transformer operating at 60 Hz, and some others use a high
frequency ferrite transformer scheme. These would call for a different plan.


So, start attending those seemingly otherwise useless computer swap meets,
cruise the curbsides on trash day, dive those dumpsters and even inquire at
computer repair shops, proprietors of which often have large amounts of junk
hanging around.  Or, post a want ad on your local freecycle.org forum -
you'll likely be overwhelmed with responses.  Then, base your
plan/scheme/design around that which you will have acquired. 

Detractors of this type of plan might do well to remember that many of us
are not financially well off, and though our reduced-cost solutions might
not always be technically optimal, they can represent workable solutions
when ALL variables - cost included - are considered.

Drew