12 to 24 volt conversion, the issue of cost

Michael Tauson wh7hg.hi at GMAIL.COM
Thu Oct 8 18:31:14 EDT 2009

On Thu, Oct 8, 2009 at 5:24 AM, Wilson Lamb <infomet at embarqmail.com> wrote:
> No flames here, but a suggestion to be reasonable.  Some things may be
> beyond your budget, as many are beyond mine!  How much trouble is running
> some old junk radios worth?

Enough that building the converter is an investment for me, as well as
(as stated many times already) an opportunity to gain an education
about toroids.  You know,  a learning experience.  Some people love
them & some hate them.  I'm one of the former.

> You can hook up two batteries and run them for a while...maybe long enough!

Or I can run them via the Jeep's electrical system through the
converter for a lot longer.  The engine has to be running but it
usually is when I'm moving.  (Discounting my most recent approach to
Costco's fuel pumps ... an embarrassing situation wherein I coasted in
with a dry tank ... :-) )

> A very few bucks spent building a modern radio or some time learning a digital
> mode might bring you more rewards.

Oh, you mean like the CW/SSB/AFSK rig on the board that I'm designing
around a DDS VFO?  (Okay, I'm using someone else's VFO design.  Shoot
me for being such a wimp.  I'll have to do some reprogramming so that
should count for something.)  Two different versions are on the board,
one with a 20w PEP solid state PA and an internal antenna matcher -
probably an SGC board - and the other with a 100+w PEP hollow state
one and using an external matcher - probably also SGC.  The former
will be small and light enough to be a pack set if I want.  (It's not
a design requirement, just a neat side benefit.)  The general design
is also part of my learning experience with toroids.

> I struggle to make myself put out the effort to keep up rather than look back.

Is there some reason both can't be done at the same time?  (And why is
it a struggle?)  I happen to like surplus equipment which is handy
since I'm working on a book (my 2nd publication) related to it.  At
the same time, there are areas I managed to miss in keeping up, and
using toroids in any capacity is one of them.  It's my fault as far as
RF goes in that I didn't take some opportunities handed to me but the
aforementioned rigs are handling that part nicely.

> Designing a DC-DC converter to deliver 10-30 amps at 24V is not an exercise
> for non engineers.

It's not?  It seems non-engineer hams and other hobbiests do things
like this all the time.  On the other hand, all I'm looking for is
8-10 amps.  30 amps would be nice if I were powering a PRC-47 which,
thus far, I'm not.  (This may be because I don't have one.  Besides, I
think I would rather go to a 12vdc in & 115vac, 400 cycle out power
supply for that application.)

But let's take the auxiliary battery scenario for a second.  Assuming
I can find somewhere to put them (Jeeps are not known for their
spacious acommodations.), let's put two batteries in series to provide
the required 24 volts.  So why not use the vehicle charging system to
keep them charged via this same 24 volt converter and some extra
circuitry to make it into a battery charger/maintainer?  This way I
probably could operate that selfsame non-existent PRC-47 without a lot
of problems.

> Hefty transistors and cores are needed, as well as sophisticated regulator circuits.

Why would I need a serious regulator if the primary side is operating
in range (12-14 volts) and the output doesn't have to be dead on 24-28
volts?  This is straight brute force, not some dainty little package
that will give .01% or so regulation over some exceedingly wide input
or load range.  It's crude and not very elegant but elegance has no
place in this.  Besides, I'm crude and not a whole lot of elegant so
it fits.

52 years?  I'm right behind you with 48 (Do NOT let my calls fool
you.) and that has been running homebrew and surplus exclusively.
I've only recently gotten into this commercial equipment thing
(serious boatanchors in themselves) and am in the process of
discovering microphones since I've been 100% CW from day one.
Homebrew is also home designed around available parts (often as found
in stripped surplus equipment) using tubes, bipolar transistors, FETs
and ICs for the active components.

On the flip side, I've got some lovely 1920s-1930s neo-antique
transmitters awaiting parts so I can build them to go with an SX-24 as
well as a couple of 1950s transmitters awaiting parts to go with a
BC-312 & 18-30 MCs converter.  All homebrew, of course.

Yeah, I guess I am on the wrong end of the timeline in some things.
On the other hand, you presume too much as to what my knowledge and
experience bases and my interests are.

BEst regards,

Michael, WH7HG
Hiki Nô!

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