For discussion of radio power supplies.

32 responses total.

I have some "wall warts" I'd like to use as power supplies for
transceivers. Prior to making a study of them - what kind of variety of
regulation and filtering (if any) might I find? Ones I've had apart used
for charging batteries in HTs are just an xformer and diode, giving
half-wave rectification and no filtering. One I have is nominally
12V@1.5A, but gives 15.5V open and pulls down to 14V at 0.3A (and only
maybe 12V at 1.5A? - I haven't scoped it yet so I don't know what
filtering it has). Another is mutli-voltage - 7 voltages from 1.5 to 12 at
1.0 A. The board has 4 diodes, 2 caps and a couple of resistors, but no
chip for regulation (and on 12V setting gives 22.4V open and 16.8V at
0.75A): how does this one work to give multiple voltages (board is
heat-sealed in case so I can't see its underside).

Considering these things as just xformers with essentially no regulation
or filtering, I'd have to use them with a separate regulation/filtering
circuit. I'm thinking of just an LM317 and big cap. So, does anyone have
any experience in doing this, or other obscure facts about the variety of
wall-warts? 

Wall warts tend to be low-current, and with minimal filtering and no
regulation.  Though not all of them, of course.  Generally the regulation is
done inside the device being powered.  For a transciever you may have
trouble getting enough current for transmitting, unless we're talking very
low power levels.

The largest wall wart I've seen is the one my Zip drive uses.  It's rated at
5 volts, 1 amp, and judging from the heat it throws off may very well have an
internal regulator.  Oddly, the wall wart for my scanner has a *three* prong
plug -- maybe for an internal spike supressor?

A LM317 regulator and cap should take care of voltage pulldown and ripple.
The transceiver powers I'd use them for are less than 7 watts. I think
I'll have a set up a 'production line' and do load and ripple tests on
all the wall-warts I have, and get a better idea of what different kinds
there are. 

I like using switching wall warts for HT's and the like.  Keep an eye
out for them at surplus computer and electronic places for cheap.  New
they cost too much.  For 7 watts of output you will need at least 14 watts
of input.  Regulators also require 2 to 3 volts below the ripple to
regulate.  I've never seen a wall wart with more than a full wave rectifier
and capacitor.  Any required regulation is usually done inside the device
that the wall wart powers. i.e. A modem.

How do you identify a switching wall-wart? I have a Dell unit that was
advertised as switching, but it doesn't say so on it, and and an Atari
unit that was advertised as regulated, but also with nothing noting
that on it. (These two really aren't wall-warts, as they have power cords,
but they are still both little black boxes... :) )

Hmm...well, a switching one won't have a power transformer inside, not of
the normal sort anyway.  If you can hear a faint (or not so faint) hum with
your ear against the case, it's not a switcher.  The presence of lots of RF
noise on nearby AM radios is a sign of a switcher in operation, too. ;)

Oh oh - I want to use it with sensitive radio transceivers...I'll listen in.

The switchers are usually little boxes with a line cord that plugs into
the wall.  They usually power lap tops.  They are usually very light for
their power output and run cooler.  I have a small one I use with my HT
that I found at a computer swap and a 120 watt switcher I use with my
packet radio.  I don't have problems with RF noise on either radio and
both are quite sensitive.  (I use to worry about the RF noise too but
tried it and found it not to be an issue.)

It's not as much of an issue for FM, and at VHF frequencies.  The switching
circuits in these tend to run in the ultrasonic range, say 50 kHz, so the
harmonics from the square wave they generate die out by the time you get up
into the VHF range, generally.

hmm...I got a power supply question :)

ok I have a 2mtr linear amp given to me for free
It takes 1-4 W in and spits out 80-120 W 
the label says it uses 13.8 V (nothin unusual about that)

So I finally got ahold of a Astron SL-15R power supply, it puts out 12 Amp
contuinuous and is rated at 15 Amp peak. 

Well I know a linear running a full 120 out would not work with my Astron
but I figured 80 W might..

got every thing hooked up...turned all the gizmo's on..then said:

"This is KC8BYL......KC*B"....

then I saw a blue flash out of the power supply, my fuse had blow. :(
(the schematics say use a 5AMP fuse, but I found only a 3AMP'er)

anywho...im not suprised it blew....just wondering what size power supply
do I need to run this monster?

That's FM, so the power is continuous when transmitting. Should be OK
with 80 watts, as that's only ca. 7 amps at 100% efficiency. Let's say
10 amps at 12V, so should be <2 amps at 120 V. So, what power did you
use to drive it? 

So this 5A fuse that blew was on the 115 vac line side?  That's 575 watts!
I usually figure that I need twice the power going into an FM amp as what's
going out to the antenna.  So, your 80 watt output amp needs 160 watts input.
That works out to almost 14 amps, which your supply should be able to handle.
Something is / was out of wack.  It should not take 575 + watts for 80
watts out.  Perhaps that's why the amp was free ;-)

exactly 1 Watt according to my watt meter.

actually it only had a 3amp fuse in there....the fuse was in series
with the primary windings of the transformer.

Get a stack of fuses and do some testing. For starters, what current
does the amp draw when it is not excited? 

At 3 amps its 345 watts in.  If it's a chinchy linear supply design, however,
it could possibly be drawing that kind of power from the line to get you 160
watts of output.

umm...I only have a cheap $35 Wavetek multimeter, looks like the highest
current setting is 200mA..

re#16 Its an Astron....I've always thought they were top-of-the-line.

The Astron that I blew the fuse on was borrowed, but im thinking of buying
one to keep...probilly a 35Amper, so i'll never have to buy another one.

Anyone know of any other power supply manufactures?

You know, if you can find a high-current 1 ohm resistor you can pass the
supply power through it, then measure the voltage difference between the ends
and use Ohm's Law to figure out the current...

With ca. 7 amps, that would sap most of the voltage. Use an ammeter -
or perhaps 10 1-ohm resistors in parallel (they don't have to be high
current each, then). 

I called the company and they sent me a fax of the tuning instructions and
schemetics...which were clear as mud.

After performing a close visual inspections, to determine which capacitor 
was which. (the parts layout diagram was wrong and the PCB was not labeled).  
I noticed that one of the ground wires was charred and melted in half...this 
is not a good sign.

So now my options are:

1)      try to fix it, myself..easy to do..but there could be other things
wrong. 2)      send it to the manufacture to be fixed ($60/hr) 3)      buy a
new one (I really don't need 80-120 W) 4)      label it as "broken" and sell it
for $5 at a hamfest. 5)      let it sit im my closet for a few more years as a
future "project".

im leaning towards #5 :)

  You should know, as a condition of being licensed that you MUST have at
least 1 unfinished project in your closet for a duration not to exceed 10
years. 
  Or, a junque box that has at least 75% non-working, or parts that will never
work or be used.

Why only up to 10 years? What happens then? 

In about ten years I'll have my basement back under control so you bring it
over than and I'll help you fix it.  That way you won't have to see what
happens if you wait longer that five years ;-)

The cheapest 12 volt, 200 amp, or more, power supply I know of is a car
battery with an alternator supplying power to it.  It will even turn a piece
of 12 gage wire into a fuse.

I have a 100 watt switching power supply that I use to run a 50 watt radio.
It works very well.  I picked it up at a swap for $25 several years ago.  The
ARROW's 2 M repeater puts out 100 watts and its power supply also supplies
power to the 440 and 220 machines.  It's a Motorola repeater and it uses a
crude switching power supply, since it was built back in the mid 60's, and
also works very well.  When you get into those kinds current, switch mode
power supplies make a lot of sense because they don't waste so much power in
the regulation stage.  Yes, Astron makes a good foot warmer.  However, an
electric motor turning a car alternator, charging a car battery would probably
be more efficient.

 The Arrow repeater is a good example of the old statement "Flying on a wing
and a prayer." Someone up there must be really crazy about it.

No, stuff was built to last back than resulting in it being built like a
tank and still being functional.  Now they have perfected engineering to
the point where things can be designed to last so long and then die.

Yup.  Witness RCA TVs, which demonstrate an amazing ability to die just
after the warranty expires.  Or motherboards with non-replacable lithium
batteries housed in sealed clock modules.

#25 is not really true.  There was junk built back than just as there is now
and there is good stuff built now just like there was than.

Manufacturers have indeed gotten better at being able to design parts to a
specific amount of life.  This saves money both for them and for the
consumers, although you could argue that having stuff last longer would be
better in the long run.

Re #27: Right, and only the good stuff from 40 years ago is what we bother
to keep, which is why it *seems* like ``they don't build stuff like they
used to''.

Some of the Radio Shacks in the area are changing their focus from a hobbiest
oriented store to more computers type stuff. Anywho, they are expanding some
stores and closing others. 

The store in Kzoo was going out of business and was selling stuff for 50 -
70% off.

I picked up a 15 amp 13.8 DC power supply for $32. The regular prices was $80.

It does feel a little light for a 15amp supply. Judging from the size, it
looks like it has a tiny transformer. I always assummed there was a
correlation between the transformer size and the current capacity. My old DC
power supply (also from rat shack) weighs alot more, but is only rated as a
3amp supply.

Is it a switching supply?  They're a lot lighter for the same current 
capacity than a linear supply, and they've gotten cheap enough that I'm 
even seeing them in high-current wall warts.

They've been closing a few stores in the Detroit region too, including
store on Washtenaw, in Ypsi.  I've gotten to know the manager there, and
he's not too happy with some things.  But that's life in the big corp.

Reminds me, I haven't been there in a couple weeks, I should stop back
in, assuming they're not gone.

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