Modify Astron Power Supply
 

I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!

Modify Astron Power Supply
 

On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:


"Toby" wrote in message news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

Cheers,
__
Gregg

Modify Astron Power Supply
 

"Toby" wrote in message news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

Modify Astron Power Supply
 

On May 4, 10:27*pm, "Toby" wrote:
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!

If you will install a 2500 ohm pot between pin 5 and 6 on the
regulator chip ,that will give you variable output.. I agree with the
use of the crowbar circuit, saves damaging your equipment and damaging
the power supply too.. GL W4PQW

Modify Astron Power Supply
 

On Mon, 05 May 2008 03:27:10 GMT, "Toby" wrote:

I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


While the output voltage of practically any regulated linear power
supply can be varied by changing one or two resistors, one should
remember that the power dissipation in the series pass transistors
will increase significantly, if voltages much below the nominal
voltage is required, thus you may have to increase the number of
series pass transistors or at least increase the heatsink surface 2-4
times the original.

Also you may have to use some foldback current limitation system to
keep the series pass transistor dissipation at a reasonable level e.g.
when driving car head lights or other nearly short circuit loads.

When fully understanding these issues, the commercially available
devices can be quite interesting building blocks, when creating power
supplies for your own needs.

Paul OH3LWR

Modify Astron Power Supply
 

OK Thanks everyone for your input. Might post when I have it done.....Toby
"Toby" wrote in message news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!

Modify Astron Power Supply
 

On May 5, 2:51*am, geek wrote:
On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:

"Toby" wrote in messagenews:i8vTj.791$b%1.295@trndny04....
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!

Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

Cheers,
__
Gregg

Ive modified a couple of these(similar) power supplies by doubling the
the number of pass transisors. In the process I also double the value
of the emitter
resistors. If they were .05 I make them .1. Seemed like a reasonable
thing to do. Any opinions?

Geez, I never thought about the SCR but you are right. While I have
added crowbar circuits and placed them before the pass transistors I
hadnt noticed that this connection on these power supplies needed to
be relocated.

Jimmie

Modify Astron Power Supply
 

On Tue, 06 May 2008 16:25:50 -0700, jimmie68 wrote:

On May 5, 2:51*am, geek wrote:
On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:

"Toby" wrote in messagenews:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!

Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

Cheers,
__
Gregg

Ive modified a couple of these(similar) power supplies by doubling the
the number of pass transisors. In the process I also double the value
of the emitter
resistors. If they were .05 I make them .1. Seemed like a reasonable
thing to do. Any opinions?

Yeah, go 0.1 ohms. The 0.05 ohm resistors are useless for practical
purposes.


Geez, I never thought about the SCR but you are right. While I have
added crowbar circuits and placed them before the pass transistors I
hadnt noticed that this connection on these power supplies needed to
be relocated.

Jimmie

And there should be a fuse in there to blow between the filter cap and
crowbar.

The supply was actually 3rd world designed and made I swear.

Cheers,
__
Gregg

Modify Astron Power Supply
 

On Sun, 04 May 2008 23:51:08 -0700, geek
wrote:

On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:


"Toby" wrote in message news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

The diagram looks strange to me, with a direct connection from the
higher voltage driver supply (e.g. pin 12 of the 723 or collector of
Q2) to the base of the series pass transistors.

With a higher separate driver power supply the driver current should
flow through the Q2 driver transistor, through the small resistors
into the base connection of the series pass transistor. Thus in the
diagram the direct connection from the driver supply to the series
pass transistor base should be removed.

I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

When using crowbars, there should be a some kind of fuse on the
feeding side, preferably immediately after the filter capacitor.

If the crowbar is before the series pass transistors, it is a good
idea to put a large reverse biased diode across the series transistors
(CR7 in the diagram), which would discharge any large capacitors on
the regulated side through the crowbar. Without the diode, the
collector side would be at 0 V after the crowbar tripped, but the
emitters could still be at +12 V due to any large capacitors on the
regulated side.

Paul OH3LWR

Modify Astron Power Supply
 

After reading all these posts, the modification is likely over my head. I
think I'll sell it and find a nice used variable supply. Thanks for all in
the input.
"Paul Keinanen" wrote in message
...
On Sun, 04 May 2008 23:51:08 -0700, geek
wrote:

On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:


"Toby" wrote in message
news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that
people
have modified this model to become a variable voltage supply but have
not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


Here is the schematic for a 35, it should ve similar to the 20 except
for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

The diagram looks strange to me, with a direct connection from the
higher voltage driver supply (e.g. pin 12 of the 723 or collector of
Q2) to the base of the series pass transistors.

With a higher separate driver power supply the driver current should
flow through the Q2 driver transistor, through the small resistors
into the base connection of the series pass transistor. Thus in the
diagram the direct connection from the driver supply to the series
pass transistor base should be removed.

I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

When using crowbars, there should be a some kind of fuse on the
feeding side, preferably immediately after the filter capacitor.

If the crowbar is before the series pass transistors, it is a good
idea to put a large reverse biased diode across the series transistors
(CR7 in the diagram), which would discharge any large capacitors on
the regulated side through the crowbar. Without the diode, the
collector side would be at 0 V after the crowbar tripped, but the
emitters could still be at +12 V due to any large capacitors on the
regulated side.

Paul OH3LWR

Modify Astron Power Supply
 

In article ain,
geek wrote:

And there should be a fuse in there to blow between the filter cap and
crowbar.

The supply was actually 3rd world designed and made I swear.

Cheers,
__
Gregg

Better yet, put in a Resettable Circuit Breaker, as you can never find
the right fuse, and they ALWAYS blow at the worst possible moment.....

--
Bruce in alaska
add path after fast to reply

Astron power supplies...
 

We had a thread recently on Astron power supplies and I thought I'd
mention that I have an RS-35A (35 amps intermittent) for VHF brick
amplifiers (main use) and I've had it for some 20 years. Recently, the PS
has started to "crowbar" off on me (voltage goes to zero) and not even
with high currents (maybe around 15 amps or so) and have to shut it off,
wait a few seconds, and turn it back on.

I also had another different regulated fairly high current DC PS go bad
long ago, in a similar way.

I'm wondering how many others of you have seen defective operation,
sooner or later, or other deterioration in your high current regulated DC
supplies?

And, if the overvoltage crowbar craps out, it blows up your rig? I'm
thinking of going exclusively back to deep cycle marine batteries, again.

Astron power supplies...
 

"A" wrote in message
x.com...

We had a thread recently on Astron power supplies and I thought I'd
mention that I have an RS-35A (35 amps intermittent) for VHF brick
amplifiers (main use) and I've had it for some 20 years. Recently, the PS
has started to "crowbar" off on me (voltage goes to zero) and not even
with high currents (maybe around 15 amps or so) and have to shut it off,
wait a few seconds, and turn it back on.

I also had another different regulated fairly high current DC PS go bad
long ago, in a similar way.

I'm wondering how many others of you have seen defective operation, sooner
or later, or other deterioration in your high current regulated DC
supplies?

And, if the overvoltage crowbar craps out, it blows up your rig? I'm
thinking of going exclusively back to deep cycle marine batteries, again.


Sometimes adding a .1 or .22 uF cap on the gate of the SCR to ground
will stop nuisance crowbars. Some Astrons are more sensitive than others
in this regard. We had a similar problem with a few 50 amp Astrons in
repeater service.

Pete

Astron power supplies...
 

I'm wondering how many others of you have seen defective operation,
sooner or later, or other deterioration in your high current regulated
DC supplies?

And, if the overvoltage crowbar craps out, it blows up your rig? I'm
thinking of going exclusively back to deep cycle marine batteries, again.
====================================
The crowbar is there to NOT blow up your equipment.

However operation of a crowbar should blow a fuse fitted 'upstream' of
the pass transistors. As already explained earlier in this thread ,the
crowbar should also be fitted 'upstream the pass transistors (but
'downstream' the fuse , while sensing the output voltage .

If the Astron voltage regulator would be suspect I would recommend a
very simple circuit with a 7812 voltage regulator and a PNP transistor
,its output 'steering' the pass transistors .

Ref : Experimental Methods in RF Design , by W7ZOI-KK7B- W7PUA
page 1.15


Instead of the 3 legged 7812 you can also use the similar LM317 enabling
output voltage adjustment
After all this is a homebrew NG

Frank GM0CSZ / KN6WH

Astron power supplies...
 

In article ,
Highland Ham wrote:

The crowbar is there to NOT blow up your equipment.

However operation of a crowbar should blow a fuse fitted 'upstream' of
the pass transistors. As already explained earlier in this thread ,the
crowbar should also be fitted 'upstream the pass transistors (but
'downstream' the fuse , while sensing the output voltage .

If the Astron voltage regulator would be suspect I would recommend a
very simple circuit with a 7812 voltage regulator and a PNP transistor
,its output 'steering' the pass transistors .

Ref : Experimental Methods in RF Design , by W7ZOI-KK7B- W7PUA
page 1.15


Instead of the 3 legged 7812 you can also use the similar LM317 enabling
output voltage adjustment
After all this is a homebrew NG

and if your really smart, you will dump the fuse, and replace it with
a Resettable Circuit Breaker, because Murphy's Law states the Crowbar
will do it's thing, ALWAYS at the worst possible moment, and the
appropriate replacement fuse will be a 5 miles drive away, at the
closest. You mileage may vary.....

Astron power supplies...
 

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete

Astron power supplies...
 

On Fri, 16 May 2008, You wrote:

In article ,
Highland Ham wrote:

The crowbar is there to NOT blow up your equipment.

However operation of a crowbar should blow a fuse fitted 'upstream' of
the pass transistors. As already explained earlier in this thread ,the
crowbar should also be fitted 'upstream the pass transistors (but
'downstream' the fuse , while sensing the output voltage .

If the Astron voltage regulator would be suspect I would recommend a
very simple circuit with a 7812 voltage regulator and a PNP transistor
,its output 'steering' the pass transistors .

Ref : Experimental Methods in RF Design , by W7ZOI-KK7B- W7PUA
page 1.15


Instead of the 3 legged 7812 you can also use the similar LM317 enabling
output voltage adjustment
After all this is a homebrew NG

and if your really smart, you will dump the fuse, and replace it with
a Resettable Circuit Breaker, because Murphy's Law states the Crowbar
will do it's thing, ALWAYS at the worst possible moment, and the
appropriate replacement fuse will be a 5 miles drive away, at the
closest. You mileage may vary.....


Just to add, I've had a lot of problems with high amperage fuses, too, in
brick amplifiers and power supplies and VHF rigs with those "sexy" in-line
fuse holders. Seems like the connections become corroded, resistance goes
up enough that the current induces drop voltage high enough to do
significant heating...etc... Sometimes I've removed those fuses
completely, even in one brick amplifier (25-30 amps for a 3AG fuse!!) just
soldered a jumper wire across the &%$& fuse holder. Yeah, I know, bad
idea. But, all my problems went away.

Also, I had circuit breakers go bad, too. Brand new ones. Expensive ones.

KIS = keep it simple.

Astron power supplies...
 

On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

Astron power supplies...
 

On Fri, 16 May 2008 20:48:17 -0400, A wrote:
Just to add, I've had a lot of problems with high amperage fuses, too, in
brick amplifiers and power supplies and VHF rigs with those "sexy" in-line
fuse holders. Seems like the connections become corroded, resistance goes
up enough that the current induces drop voltage high enough to do
significant heating...etc... Sometimes I've removed those fuses
completely, even in one brick amplifier (25-30 amps for a 3AG fuse!!) just
soldered a jumper wire across the &%$& fuse holder. Yeah, I know, bad
idea. But, all my problems went away.

If you are referring to those cheap, butt-contact, twist-and-lock
cylindrical fuse holders, I'll agree! They are problematic in many
instances, but especially so in high current situations.

I had no end of problems with the from-the-factory in-line fuse holder
with my IC-706. The IC-706 is a poor enough performer at voltages under
about 12.599999VDC, and the voltage drop across the fuse holder was
often enough to drop the volts into the rig even lower than that.

(Don't even get me started about the use of a butt-contact cigarette
lighter "power plug".)

I now replace that style of fuse/fuse holder with the automotive,
"horse-shoe" shaped style. (I'm sure there must be a more 'formal' name
for them.) You can even get them with weather proof caps for under-the-
hood applications.

And, for mobile operations, you can find replacement fuses up and down
the hiways and byways A WHOLE LOT EASIER than you can find the old
cylindrical fuses.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

Astron power supplies...
 

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
commuters or a bad ground connection.

Astron power supplies...
 

"K4ERG" wrote in message
.. .

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at
current well below current ratings and the output voltage goes to 0.5 or
less and had to off-on cycle the main switch. Makes me mad. Gotta get
back to that deep cycle 12 v battery.... They always go bad very very
very slowly. Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
connectors or a bad ground connection.

Stupid spell checker!

Astron power supplies...
 

On Sat, 17 May 2008, K4ERG wrote:


"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack.

Not likely if you've been running the gear for years and didn't touch
anything. see my response to your second post.

Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
commuters or a bad ground connection.

Astron power supplies...
 

On Sat, 17 May 2008, K4ERG wrote:


"K4ERG" wrote in message
.. .

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at
current well below current ratings and the output voltage goes to 0.5 or
less and had to off-on cycle the main switch. Makes me mad. Gotta get
back to that deep cycle 12 v battery.... They always go bad very very
very slowly. Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
connectors or a bad ground connection.

Stupid spell checker!


Not my idea but it sounded good when I heard it: "Life's too short for
spell checkers"

Ham radio advertisement many years ago: "Life's too short for QRP" and it
was for a big amplifier.

;-)

Modify Astron Power Supply
 

Hello everyone,

Regarding Astron Power Supplies, repair, retrofit, information and
modifications of the supply hardware and replacement Regulator Boards.

There are/were a number of different Astron Power Supply Regulator Board
versions made and configured. What is placed on the specific board is
related to it's capacity and type of operation. Depending on the year of
production, the size and the series the boards can and do change a bit.
Here's the url for the Repeater Builder web page,which has a lot of good
information:

http://www.repeater-builder.com/astr...ron-index.html

In some of the online yahoo groups I've mentioned some of the short
falls of the original Astron Circuit design and how I dealt with them.
Since that time I started selling replacment regulator boards with
updates and related information.

I offer a complete updated Astron Regulator board package, which is the
populated board and instruction sheet. The package also contains my
notes, information and various circuit diagrams. The price is $45 plus
the cost or US Priority Mail (about $4.35)

When your original Astron Board becomes problematic... my drop in
replacement is an updated clone of the original board with modern
improvements. Indeed Astron has included some of the mentioned
improvements onto some of their current regulator boards (but not all).
I've also addressed the fairly problematic crow-bar circuit layout and
part values to make the retrofit regulator board more stable. I've never
had one fail...

The variable supply is the same type board with part modifications to
allow adjustment of the output voltage within a practical range. The
ability to convert your specific supply to variable control is probably
more dependent on the date of mfgr of your regulator and the version of
your board. I have a list of each original Astron Regulator Board part
value based on size and the values on my replacement boards. If you've
charcoaled a part value I can supply the value information.

By Email and telephone I'm happy to help you trouble shoot your supply,
regardless of the mfgr. But my time is limited and I might not get back to
you right away so please be patient.

cheers,
skipp

skipp025 at yahoo.com
www.radiowrench.com

: Toby wrote:
: I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
: have modified this model to become a variable voltage supply but have not
: found any schematics etc for this mod. Can anyone point me in the right
: direction? Thanks!

Modify Astron Power Supply
 

: Here is the schematic for a 35, it should ve similar to the 20 except for
: an extra pass transistor or two.
: http://www.repeater-builder.com/astr...tron-vs35m.jpg

No, it's different... and also dependent on the age of the supply. The
other size supply diagrams should be used as a guide only.

cheers,
skipp

Modify Astron Power Supply
 

The crowbar circuit operation should never damage the meter movements or
related sense resistors.

cheers,
s.

: geek wrote:

: I modded one of those significantly. Too long ago to remember the exact
: thing I did, but DO put that crowbar SCR anode on the collector of the
: pass transistors. If it trips as is, you kiss the current meter and
: expensive current sense resistor goodbye.

: Cheers,
: __
: Gregg

Modify Astron Power Supply
 

: And there should be a fuse in there to blow between the
: filter cap and crowbar.

No, a really bad practice... don't do it.

: The supply was actually 3rd world designed and made I swear.

Many parts/portions are done in Mexico...

: Better yet, put in a Resettable Circuit Breaker, as you can never find
: the right fuse, and they ALWAYS blow at the worst possible moment.....

No... you're asking for a serious problem and it's just a question of
when and not if.

cheers,
skipp

Astron power supplies...
 

A number of gremlins cause the crow-bar to mis-fire. Just depends on
your specific regulator board version and part values used. One of the
reasons I came up with my replacment regulator board option.

http://www.repeater-builder.com/astr...ron-index.html

I've not seen a newer generation crow-bar circuit fail causing
equipment damage.. but as always your results might vary.

cheers,
s.

: A wrote:

: We had a thread recently on Astron power supplies and I thought I'd
: mention that I have an RS-35A (35 amps intermittent) for VHF brick
: amplifiers (main use) and I've had it for some 20 years. Recently, the PS
: has started to "crowbar" off on me (voltage goes to zero) and not even
: with high currents (maybe around 15 amps or so) and have to shut it off,
: wait a few seconds, and turn it back on.

: I also had another different regulated fairly high current DC PS go bad
: long ago, in a similar way.

: I'm wondering how many others of you have seen defective operation,
: sooner or later, or other deterioration in your high current regulated DC
: supplies?

: And, if the overvoltage crowbar craps out, it blows up your rig? I'm
: thinking of going exclusively back to deep cycle marine batteries, again.

Astron power supplies...
 

Astron Power Supply Crow-bar Circuit Operation

: I'm wondering how many others of you have seen defective operation,
: sooner or later, or other deterioration in your high current regulated
: DC supplies?

Happens more with the older supplies... part values change with time.

: However operation of a crowbar should blow a fuse fitted 'upstream' of
: the pass transistors. As already explained earlier in this thread ,the
: crowbar should also be fitted 'upstream the pass transistors (but
: 'downstream' the fuse , while sensing the output voltage .

I don't agree...

: If the Astron voltage regulator would be suspect I would recommend a
: very simple circuit with a 7812 voltage regulator and a PNP transistor
: ,its output 'steering' the pass transistors .
: Ref : Experimental Methods in RF Design , by W7ZOI-KK7B- W7PUA
: page 1.15

Not a good idea... regulation really suffers bad.

: Instead of the 3 legged 7812 you can also use the similar LM317
: enabling output voltage adjustment
: After all this is a homebrew NG

No good... if you're only trying to get in the ball park maybe... if
you plan to use and trust the supply with expensive equipment you should
stick with an LM-723 or similar circuit properly designed using the mfgrs
data sheet information.

cheers,
skipp

Astron power supplies...
 

: and if your really smart, you will dump the fuse, and replace it with
: a Resettable Circuit Breaker, because Murphy's Law states the Crowbar
: will do it's thing, ALWAYS at the worst possible moment, and the
: appropriate replacement fuse will be a 5 miles drive away, at the
: closest. You mileage may vary.....

The auto reset circuit breaker helps to start the fire, which takes out
the site/building. Not a good idea...

cheers,
s.

Modify Astron Power Supply
 

: The diagram looks strange to me, with a direct connection from the
: higher voltage driver supply (e.g. pin 12 of the 723 or collector of
: Q2) to the base of the series pass transistors.

The pass transistor pre-drive transistor is a simple current amplifier.

: With a higher separate driver power supply the driver current should
: flow through the Q2 driver transistor, through the small resistors
: into the base connection of the series pass transistor. Thus in the
: diagram the direct connection from the driver supply to the series
: pass transistor base should be removed.

Some of the available circuit diagrams have mistakes...

:I modded one of those significantly. Too long ago to remember the exact
:thing I did, but DO put that crowbar SCR anode on the collector of the
:pass transistors. If it trips as is, you kiss the current meter and
:expensive current sense resistor goodbye.

: When using crowbars, there should be a some kind of fuse on the
: feeding side, preferably immediately after the filter capacitor.

No, you want the entire supply to remove itself from operation if
the crow-bar circuit fires.

: If the crowbar is before the series pass transistors, it is a good
: idea to put a large reverse biased diode across the series transistors
: (CR7 in the diagram), which would discharge any large capacitors on
: the regulated side through the crowbar. Without the diode, the
: collector side would be at 0 V after the crowbar tripped, but the
: emitters could still be at +12 V due to any large capacitors on the
: regulated side.

An expensive part... the crow-bar is best left at the tail end of the
supply (where it is now).

cheers,
s.

Modify Astron Power Supply
 

Amen Paul,

The Astron 25 amp variable supply is pretty much the parts for the higher
rated supply in the same case. The no free lunch rule applies. If you
modify your specific supply for varilable control... it will quickly
become to hot at lower voltage - higher current values.

cheers,
s.

: Paul Keinanen wrote:

:I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
:have modified this model to become a variable voltage supply but have not
:found any schematics etc for this mod. Can anyone point me in the right
:direction? Thanks!


: While the output voltage of practically any regulated linear power
: supply can be varied by changing one or two resistors, one should
: remember that the power dissipation in the series pass transistors
: will increase significantly, if voltages much below the nominal
: voltage is required, thus you may have to increase the number of
: series pass transistors or at least increase the heatsink surface 2-4
: times the original.

: Also you may have to use some foldback current limitation system to
: keep the series pass transistor dissipation at a reasonable level e.g.
: when driving car head lights or other nearly short circuit loads.

: When fully understanding these issues, the commercially available
: devices can be quite interesting building blocks, when creating power
: supplies for your own needs.

: Paul OH3LWR

Modify Astron Power Supply
 

On Wed, 07 May 2008 08:08:44 +0300, Paul Keinanen wrote:

On Sun, 04 May 2008 23:51:08 -0700, geek
wrote:

On Mon, 05 May 2008 02:04:09 -0500, Ralph Mowery wrote:


"Toby" wrote in message news:i8vTj.791$b%1.295@trndny04...
I have an Astron RS-20A, 20amp 12v fixed DC supply. I've heard that people
have modified this model to become a variable voltage supply but have not
found any schematics etc for this mod. Can anyone point me in the right
direction? Thanks!


Here is the schematic for a 35, it should ve similar to the 20 except for
an extra pass transistor or two.

http://www.repeater-builder.com/astr...tron-vs35m.jpg

The diagram looks strange to me, with a direct connection from the
higher voltage driver supply (e.g. pin 12 of the 723 or collector of
Q2) to the base of the series pass transistors.

With a higher separate driver power supply the driver current should
flow through the Q2 driver transistor, through the small resistors
into the base connection of the series pass transistor. Thus in the
diagram the direct connection from the driver supply to the series
pass transistor base should be removed.



You're right about the schematic in the link above. There is an error in the
drawing. The wire between the collector of Q2 and the bases of the pass
transistors Q101 and Q102 should not be there. That connection would put full
rectifier output on the bases of the pass transistors, turning them fully on,
resulting in the PS output going way high with no regulation. Maybe even
destroying the pass transistors.

However, the link is to a schematic for a RS-35, not an RS-20. The OP has an
RS-20, and the proper schematic link should be
http://www.repeater-builder.com/astr...1988-09-23.gif.


I modded one of those significantly. Too long ago to remember the exact
thing I did, but DO put that crowbar SCR anode on the collector of the
pass transistors. If it trips as is, you kiss the current meter and
expensive current sense resistor goodbye.

Remember that the purpose of the crowbar is to protect the load from power
supply overvoltage, not to protect the power supply. The crowbar should be
connected to the regulator output, not the input. If connected to the input,
the reservoir capacitor(s) on the output are still charged when the crowbar
fires, and the overvoltage condition is applied to the load until the capacitors
drain. The load is unprotected.

Remember also that most of the Astron supplies have current foldback limiting.
That means that on a shorted output condition, the regulator should reduce the
available current into the short to a significantly lower level, protecting the
pass elements and regulator.

When using crowbars, there should be a some kind of fuse on the
feeding side, preferably immediately after the filter capacitor.

If the crowbar is before the series pass transistors, it is a good
idea to put a large reverse biased diode across the series transistors
(CR7 in the diagram), which would discharge any large capacitors on
the regulated side through the crowbar. Without the diode, the
collector side would be at 0 V after the crowbar tripped, but the
emitters could still be at +12 V due to any large capacitors on the
regulated side.

Paul OH3LWR

==============

Dave M

Never take a laxative and a sleeping pill at the same time!!

Modify Astron Power Supply
 

On Thu, 29 May 2008 18:57:47 -0400, Dave M
wrote:

Remember that the purpose of the crowbar is to protect the load from power
supply overvoltage, not to protect the power supply. The crowbar should be
connected to the regulator output, not the input. If connected to the input,
the reservoir capacitor(s) on the output are still charged when the crowbar
fires, and the overvoltage condition is applied to the load until the capacitors
drain. The load is unprotected.

Just put a reverse biased diode across the series pass transistors.
When the crowbar at the main capacitor fires, the output capacitor
will be discharged through that diode and crowbar, protecting the
load.


Remember also that most of the Astron supplies have current foldback limiting.
That means that on a shorted output condition, the regulator should reduce the
available current into the short to a significantly lower level, protecting the
pass elements and regulator.

Foldback limiting requires that the differential amplifier (in the
723), driver and series pass transistors are working properly, thus,
the crowbar+foldback limiting works properly only if the 723 reference
voltage is erratic. In all other failure modes, such as dead 723,
shorts in driver or series pass transistors, it is quite unlikely that
the foldback would work as expected, if the crowbar fires due to
output overvoltage.

Paul OH3LWR

Astron power supplies...
 

In article ,
Skipp Isaham wrote:

: and if your really smart, you will dump the fuse, and replace it with
: a Resettable Circuit Breaker, because Murphy's Law states the Crowbar
: will do it's thing, ALWAYS at the worst possible moment, and the
: appropriate replacement fuse will be a 5 miles drive away, at the
: closest. You mileage may vary.....

The auto reset circuit breaker helps to start the fire, which takes out
the site/building. Not a good idea...

cheers,
s.

Nobody said ANYTHING about an "auto reset" circuit breaker, or anything
else "auto reset". Don't be reading in your own prejudices.....