My Astron VS-35M power supply (http://www.astroncorp.com/linear.shtml)
isn't working right. Unable to get support from Astron I'm hoping
someone here can help me fix it. I'd really hate to ship it to
California, this thing must weigh 30 lbs..

Here is a symptom of the problem:
When the power supply is set at 13V and the current knob at zero, on
connecting it to a 3-ohm power resistor the current goes to 2 amps and
the voltage drops to 6V. When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

Here's voltages I measured on the LM723 voltage regulator:
[No load voltages]
Pin Voltage
2 13.69
3 13.26
4 6.38
5 6.38
6 7.18
7 0
10 14.25
11 29.33
12 29.31
13 15.51

Here's the schematic for the power supply:
http://www.didah.com/astron/circuit.gif
And here's the data sheet on the voltage regulator:
http://www.didah.com/astron/LM723.pdf

I'm no electronics expert (or I probably could have fixed it). But I am
good with a soldering iron and have lots of test equipment. Any
suggestions on what to look at?

Thanks for your help.

On Thu, 20 Nov 2003 11:36:39 -0500, "Bruce W...1"
put finger to keyboard and composed:

My Astron VS-35M power supply (http://www.astroncorp.com/linear.shtml)
isn't working right. Unable to get support from Astron I'm hoping
someone here can help me fix it. I'd really hate to ship it to
California, this thing must weigh 30 lbs..

Here is a symptom of the problem:
When the power supply is set at 13V and the current knob at zero, ...

When you say "zero", do you mean "minimum"?

... on connecting it to a 3-ohm power resistor the current goes to
2 amps and the voltage drops to 6V.

Sounds like the PSU is working as designed, ie you have set the max
current limit to 2A and the PSU is obliging with foldback current
limiting. You will probably find that a 4 ohm load will produce a Vout
of 8V, a 5 ohm load a Vout of 10V, etc.

When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

No, it should be 13V / 3 ohms = 4.3A.

Here's voltages I measured on the LM723 voltage regulator:
[No load voltages]
Pin Voltage
2 13.69
3 13.26
4 6.38
5 6.38

Pins 4 and 5 are the inputs to the error amp. It looks like the PSU is
regulating properly.

6 7.18
7 0
10 14.25
11 29.33
12 29.31
13 15.51

Here's the schematic for the power supply:
http://www.didah.com/astron/circuit.gif
And here's the data sheet on the voltage regulator:
http://www.didah.com/astron/LM723.pdf

I'm no electronics expert (or I probably could have fixed it). But I am
good with a soldering iron and have lots of test equipment. Any
suggestions on what to look at?

Thanks for your help.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

I concur. At the minimum current setting, it won't take much current to
cause the supply to go into current-limit mode, at which time it will lower
the output voltage to cut back. Turning the current knob back up a bit will
raise the threshold and the supply will be allowed to put out more current,
so the voltage will rise in an attempt to reach the set voltage. Once the
set voltage is reached, it should stay at that point until you exceed the
current setting. This is how a fold-back current-limited power supply is
supposed to work.

Sounds like the supply is working just as it should. If you can find a load
that will run the current up to 35 amps at 14 volts, you should see it start
limiting there even with the current knob turned all the way up. That kind
of load will get hot, so take the appropriate precautions. The 35 amp
supplies are rated for about 25 amps continuous and 35 amps peak. If a
sudden current surge causes the 35 amp limit to be exceeded, the supply
could shut down completely, giving you one volt or less on the output
terminals. Cycling the power should bring it back to life.

Bob M.
======
"Franc Zabkar" wrote in message
...
On Thu, 20 Nov 2003 11:36:39 -0500, "Bruce W...1"
put finger to keyboard and composed:

My Astron VS-35M power supply (http://www.astroncorp.com/linear.shtml)
isn't working right. Unable to get support from Astron I'm hoping
someone here can help me fix it. I'd really hate to ship it to
California, this thing must weigh 30 lbs..

Here is a symptom of the problem:
When the power supply is set at 13V and the current knob at zero, ...

When you say "zero", do you mean "minimum"?

... on connecting it to a 3-ohm power resistor the current goes to
2 amps and the voltage drops to 6V.

Sounds like the PSU is working as designed, ie you have set the max
current limit to 2A and the PSU is obliging with foldback current
limiting. You will probably find that a 4 ohm load will produce a Vout
of 8V, a 5 ohm load a Vout of 10V, etc.

When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

No, it should be 13V / 3 ohms = 4.3A.

Here's voltages I measured on the LM723 voltage regulator:
[No load voltages]
Pin Voltage
2 13.69
3 13.26
4 6.38
5 6.38

Pins 4 and 5 are the inputs to the error amp. It looks like the PSU is
regulating properly.

6 7.18
7 0
10 14.25
11 29.33
12 29.31
13 15.51

Here's the schematic for the power supply:
http://www.didah.com/astron/circuit.gif
And here's the data sheet on the voltage regulator:
http://www.didah.com/astron/LM723.pdf

I'm no electronics expert (or I probably could have fixed it). But I am
good with a soldering iron and have lots of test equipment. Any
suggestions on what to look at?

Thanks for your help.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

If the above scenarios are not correct, I would try replacing the 723. I've
worked on the Asrons before. Another problem on these (common) is the SCR in
the foldback goes bad.Remove it and that fixes the problem. As a matter of fact
you should just remove it and see if that fixes it. Lastly check the output
transistors (odds are unless it got nailed big time like Lightning or power
surge) they are probably still good.
DagW00d
"Tigers Older brother DAG"

When the current knob is then set to full, the
voltage returns to 13V and the current goes to 4 amps (should be 35A).

No, it should be 13V / 3 ohms = 4.3A.

Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman

It's broken. I'll give you $5.00 for it.

Alan Harriman wrote:


Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman
================================================== ===========

No it's not working properly. When set at 13V and the current knob all
the way counterclockwise (no current), when connected to a power
resistor it should maintain 13V and put out no current. Instead, it
puts out 2 amps and the voltage drops to 6V.

I noticed this problem first when it was connected to a radio
transmitter. It was set at 13V with no current limiting. On transmit
the current would jump to 20 amps as it should then quickly fall back to
just a couple of amps. The radio was unable to transmit at that point.

Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman
================================================= ============

No it's not working properly. When set at 13V and the current knob all
the way counterclockwise (no current), when connected to a power
resistor it should maintain 13V and put out no current. Instead, it
puts out 2 amps and the voltage drops to 6V.

According to the Astron web site, the current limit is adjustable from 1.5A to
full load. See http://www.astroncorp.com/linear.shtml


I noticed this problem first when it was connected to a radio
transmitter. It was set at 13V with no current limiting. On transmit
the current would jump to 20 amps as it should then quickly fall back to
just a couple of amps. The radio was unable to transmit at that point.

I'm curious, is this an amateur radio transmitter? Have you tried a different
P.S.? I have an Astron P.S. myself, but it's an RS-20M for my Ten-Tec HF Omni-D.
Nice power supply.

Alan Harriman
kb8wcq

On Fri, 21 Nov 2003 09:12:18 -0500, "Bruce W...1"
put finger to keyboard and composed:

Alan Harriman wrote:


Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman
================================================= ============

No it's not working properly. When set at 13V and the current knob all
the way counterclockwise (no current), when connected to a power
resistor it should maintain 13V and put out no current. Instead, it
puts out 2 amps and the voltage drops to 6V.

How can any PSU disobey Ohm's Law?

V = I * R
13 = 0 * 3 ???????????


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

"Bruce W...1" wrote in message
...
Alan Harriman wrote:


Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V.
Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman
================================================== ===========

No it's not working properly. When set at 13V and the current knob all
the way counterclockwise (no current), when connected to a power
resistor it should maintain 13V and put out no current. Instead, it
puts out 2 amps and the voltage drops to 6V.

I noticed this problem first when it was connected to a radio
transmitter. It was set at 13V with no current limiting. On transmit
the current would jump to 20 amps as it should then quickly fall back to
just a couple of amps. The radio was unable to transmit at that point.

I have to agree with the others who have answered your question. The PS
appears to be working correctly. The current control is a current LIMIT
control. That is, it sets the maximum current that the PS will allow to be
drawn from the supply. It does not allow the PS to disobey Ohm's law.
This, and any other PS, will output whatever current is demanded by the
load, up to the set point of the current limit control. At this point, the
voltage will start to fall, in keeping with Ohm's law. For instance, if the
current limit is set to 2A, the voltage control is set to 12 volts, and you
connect a 12 ohm resistor across the terminals, the PS will only output 1A
into the resistor. Why? OHM'S LAW! 12V/12ohms = 1A
Replace the 12 ohm resistor with a 6 ohm resistor. Don't change any
settings on the PS. What happens? The PS will output 2A into the resistor.
Why? OHM'S LAW!! 12V/6ohms = 2A
Replace the 6 ohm resistor with a 3 ohm resistor. What happens? The PS
will not output more than 2A. Why? Because you set the current limit
control to 2A. What happens to the voltage? It falls to 6V. Why? OHM'S
LAW!! 3ohms * 2A = 6V
If you leave the 3 ohm resistor attached, and start turning the current
limit control up, you will see the current increasing on the meter. You
will also see the voltage increasing. Why? OHM'S LAW!!! If R is
constant, and I increases, V has to increase.
If you keep increasing the current limit control, you will come to a point
at which the voltage will stop increasing. At this point, the current will
also stop increasing. This is the point at which the current limit control
setting is above the current that ohm's law says you can draw from the
supply. The voltage at this point will be 12V, and the current reading will
be 4A. Why? OHM'S LAW!!! 12V/3ohms = 4A

Now, to what you said in your last paragraph here... "It was set at 13V
with no current limiting." What do you mean by "no current limiting"? If
you have the current limit control set to minimum, then the supply is
operating normally. According to the specs on that supply, the minimum
current limit is 1.5A, which is approximately what you are seeing. If,
however, you mean that the current limit control is set to maximum, then
your transmitter may be overloading the supply, and causing it to go into
foldback. Fix the transmitter, not the power supply. (You have checked the
transmitter with another power source, haven't you?)
If you find that the transmitter is operating properly, you may indeed have
a bad power supply, but from your previous posts, all symptoms point to a
properly operating power supply.

Find a 1ohm/250W resistor (not normally a junquebox item) and try the above
tests. The supply should perform exactly the same as above, up to a current
output of 12A, at which point the voltage will be 12V. Just redo the Ohm's
law calculations with 1 ohm rather than 3 ohms to get the voltages and
currents.
Cheers!
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

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

On Fri, 21 Nov 2003 09:12:18 -0500, "Bruce W...1"
wrote:

Alan Harriman wrote:


Sounds like he needs a 0.37 ohm resistor to allow a 35A current at 13V. Better
make it a 500w resistor or better to handle that kind of current.

I agree, it sounds like the P.S. is working properly.

Alan Harriman
================================================= ============

No it's not working properly. When set at 13V and the current knob all
the way counterclockwise (no current), when connected to a power
resistor it should maintain 13V and put out no current. Instead, it
puts out 2 amps and the voltage drops to 6V.

I noticed this problem first when it was connected to a radio
transmitter. It was set at 13V with no current limiting. On transmit
the current would jump to 20 amps as it should then quickly fall back to
just a couple of amps. The radio was unable to transmit at that point.

I agree totally. I'll give you $7.50 for this broken piece of junk

Franc Zabkar wrote:


How can any PSU disobey Ohm's Law?

V = I * R
13 = 0 * 3 ???????????

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
================================================== ========

I must apologize to all of you. I have been an idiot. I did not notice
that the current limiter only went down to 1.5 amps until Alan pointed
it out. And to say I neglected Ohm's law would be an understatement.

On further testing at 20 amps I found no problem.

They should revoke my Amateur Radio License on grounds of stupidity.

Thanks all.

On Fri, 21 Nov 2003 22:44:07 -0500, Bruce W...1 hath writ:

snip

They should revoke my Amateur Radio License on grounds of stupidity.

Well, if they did it according to "deserve-abilty",
your name would appear far down the list. HI!HI!

73
Jonesy
--
| Marvin L Jones | jonz | W3DHJ | OS/2
| Gunnison, Colorado | @ | Jonesy | linux __
| 7,703' -- 2,345m | config.com | DM68mn SK