> Dave VanHorn <[EMAIL PROTECTED]> wrote:
> At 11:54 AM 6/8/2005, skipp025 wrote:
> >Most Astron Supplies will easily operate at 15 volts
> >output if you mod the crow-bar circuit for the higher
> >fire/trigger voltage. If fact, they actually work
> >better at the higher output voltage.
> Well, they end up with a bit less dissipation, due
> to the input-output differential going lower.
> Another good reason to use switchers.
During ~20 amp dc current demands, the reduction in
heat can easily be over 25 watts. That's a small light
bulb worth of heat I'd rather do without anyway.
Most common 12 volt radio equipment works betta'
at 13.8 to 14.6 volts.
I don't like most low cost 13.8 volt dc switching
power supplies... I've not found a consumer switcher
that doesn't hose up some portion of the spectrum
I'm interested in. Sure, might be fine at VHF or
UHF, but I have receivers down in the low hf and vlf
range that go away when the MFJ and Astron and a few
other brand units (I've tried) operate.
Hard to listen to AM talk radio from the other end
of the shop when the switcher supplies turn everything
into hybrid white noise generators.
> >I WOULD NEVER DISABLE THE CROWBAR CIRCUIT IN ANY
> >ASTRON SUPPLY UNLESS YOU WANT BBQ RADIO. (get my
> >hint with the cap letters?) It's not a question
> >of if, only when it will be required (unless you have
> >one of the new generation regulator boards). I
> >would not trust this type linear regulated high
> >current supply to operate without a crowbar
> >protection circuit.
>
> If you have a large (relative to the power supply's output current)
> battery across the terminals, the voltage won't get high enough to
> trigger the crowbar (if the crowbar is properly set) until the
> battery is damaged. A crowbar isn't really useful here, and just
> adds potential problems.
You've never had a battery dry out or go high-Z? In
my humble opinion... it's nuts not to protect expensive
equipment from both low and excessive high voltages.
The first user question is should really be latching or
auto-reset low & high voltage disconnect circuits.
I've seem way too many boiled battery banks... not
pretty. Not fun to clean up (unless your the boss... hey
is that my phone ringing? I'll be right back...)
> Fuse the input of the supply appropriately, so that
> it will blow if the output is held to maximum for 10
> seconds or so. See the buss guide called "Fuseology"
> on selecting fuses.
I'm not a fan of the above fuseology methods. I would
hope to reduce any glitch events to a much smaller
amount of time.
> Even a full short on the regulator isn't going to
> bring up the battery voltage much, and you won't
> see "BBQ RADIO" at that point.
Don't know what world you're living in... My ganged
set of high current supplies at full unregulated tilt
will take out an 8D size battery faster than I
can drive to the site to shut the supplies off.
I don't care to admit why I know the above...
After the battery boils out, the terminal voltage rises
pretty fast. About 16 to 18 volts the common emitter
balasted pa transistor starts to complain before going
on vacation. .... a very expensive fix.
Heat, cold, mechanical failure and bullets throught
the buildings can easily cause a battery to leak.
Best to assume it will happen some day and hope it
never does.
> Anything that is designed to live in a vehicle will
> tolerate 15-16V on the input.
The unregulated side of an Astron Supply is easily
(greater than) >16 volts. 18 & higher volts comes
to mind from memory.
> >Voltage (battery) back-feed to the supply terminals
> >will kill many supply regulator circuits unless you
> >know how to inspect the circuit design and retrofit
> >the circuit to pass the reverse voltage source
> >back to the filter caps (and any other low z sources
> >on the input side of the regulator circuit)
>
> This is a known fault of 78XX series regulators and similarly
> constructed discrete linear regulators, but it's only an
> issue if the battery is connected to a supply that is not
> turned on, and has discharged it's input caps.
Sort of, but... first off the Astron Regulator is a
723 layout. Momentary AC Mains failures (a "glitch")
and some poor circuit designs are sources of regulator
board trouble and failures. Early Astron regulator
boards are horible and the SCR crow-bar circuit is
well known to be problematic. More than one of the
group readers here has complained about the Astron
Crowbar Circuit.
My powerline monitor says the our wonderous California
Utility Company (PG&E) (grid) switches our regular mains
supply around 8am nearly every week day.
Sometimes the power goes away for fractional second times...
often it's off for a few seconds. More than enough time
to have been a trouble source for early Astron Regulator
boards* and many other common pass regulator designs.
*(Early Astron Regulator board designs are crap)
> A 3A diode across the regulator fixes it nicely.
Depends on the layout of the supply and the circuit
operation. Many really high current supplies (station
systems) with larger ganged filter cap values will
smoke a reverse connected 3A diode no problama. I
had to go with a much larger 40A diode with a much
faster switching time.
> If you don't know the circuit, you can simply connect
> the banded end to the input filter caps (16-35V
> ratings, 10,000uF or thereabouts) and the other
> end to the output of the supply.
If the filter caps are that small in value. Larger
larger filter caps require different controls as
should the typical 723 regulator circuit, which is
most often fed from a higher secondary dc supply.
Astron uses a second dc supply for the regulator
board, which would not be fed using the single
diode method/trick.
The reverse connected diode method/trick can protect
the pass transistors, but the typical 723 regulator
second supply sourced circuit doesn't see the
diode back-fed voltage. I found the above to be a
source of problems with the early Astron regulator
circuit. Many people get away with only the diode...
some of us have not been so lucky.
You can often get away the reverse connected diode
in/with smaller analog dc power supplies. When you
step up to a large high current supplies the game
changes. It's about how to play the game in the
larger ball park. Hot dog anyone..?
> Yet another good reason to use a switcher. The
> only thing you'd be "backfeeding" into would be
> the output filter caps.
Switcher vs analog is another debate. I might be
there already if I could find one that didn't hose
up my nearby receivers. Still analog supplies are
cheap as heck and for the most part still quite
user fixable. Used DOA Astron Supplies pop at the
flea markets pretty regular. DOA supplies are actually
a lot of fun to fix.
Your results will probably vary...
cheers,
skipp
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