4 Sep
2007
4 Sep
'07
2:12 a.m.
IIRC, the 'raw DC' is unregulated, just
rectified and smoothed from the
transformer. As is the 24V line. Both are about 1.7* what they should be.
That's the strange thing to me. The two secondaries from the transformer (one
for the 24V line, and the other for the 10V line [which sources the regulated
5V output]) are 'proper' at 27.8V and 11.2V, respectively. What I don't
understand is how a 24V line can suddenly produce 42V! It's like something
is 'pumping' the circuit, and I admit I have never studied how such things work.
The funny thing is that the 5V regulation is working, even with 17V input
instead of 10V.
It's gettign late, so I'll not find the prints
tonight. But IIRC, the
transformer in this supply is a ferroresonant one, and that's what
stabilises the 'raw' and 24V lines. What happens if the capacitor hung
off that is defective?
Fair point, but can a faulty capacitor 'pump' up the voltage like I'm seeing?
I suspect the last part is very ture. Actually
replacing the faulty part
is the easy bit :-)
Hey, thanks for your confidence! :-) I can use a little outside support! ;-)
Let me add that this RX01 is the second of two RX01 units in this system.
When I went through the first one a week ago, it checked out fine...that is
I saw 25V/10.2v on the outputs, without a load.
And you're not going to like this :-), but for an electronics novice, tonight I
followed my instinct and swapped the regulator PCBs between units.
Yup, the 'good' system's PCB now is putting out 42V and 17V! So, it's
not
the regulation circuit, I guess, or any component on the two system's PCBs.
But after swapping the PS regulator PCBs, all that's left are the transformer (which
appears to be putting out 'expected' voltages), a 660V AC capacitor thingy (which
I obviously don't understand...is it part of the ferrroresonance?) that only connects
back to the transformer itself, and the two smoothing caps (one for the 24V line and one
for the 10V line). Is it possible that one/both
caps are 'pumping' the circuit? <shrug> I'm just too novice to know.
Another suggestion I received privately hints that putting a dummy load
on the PS might bring it into line, and that I will try. I have access to an
oscilloscope, and will put it on the thing, too, to see if I can discover
anything strange.
Thanks,
Jared
3 Sep
3 Sep
7:41 p.m.
IIRC, the 'raw DC' is unregulated, just
rectified and smoothed from the
transformer. As is the 24V line. Both are about 1.7* what they should be.
That's the strange thing to me. The two secondaries from the transformer (one
for the 24V line, and the other for the 10V line [which sources the regulated
5V output]) are 'proper' at 27.8V and 11.2V, respectively. What I
don't understand is how a 24V line can suddenly produce 42V! It's like
something
is 'pumping' the circuit, and I admit I have never studied how such
things work.
The funny thing is that the 5V regulation is working, even with 17V input
instead of 10V.
The whole point of a regulator circuit is that the output voltage is
independant of the input. Of course too high an input voltage will do
damage, and for linear regulator circuits they run hotter as the input
voltage increases. But I could well believe a reasonably designed
regualtor would work correctly on double the input voltage, particularly
on no load.
It's gettign late, so I'll not find the
prints tonight. But IIRC, the
transformer in this supply is a ferroresonant one, and that's what
stabilises the 'raw' and 24V lines. What happens if the capacitor hung
off that is defective?
Fair point, but can a faulty capacitor 'pump' up the voltage like I'm seeing?
And you're not going to like this :-), but for an
electronics novice, tonight I
followed my instinct and swapped the regulator PCBs between units.
Yup, the 'good' system's PCB now is putting out 42V and 17V! So, it's
not
the regulation circuit, I guess, or any component on the two system's PCBs.
But after swapping the PS regulator PCBs, all that's left are the
transformer (which appears to be putting out 'expected' voltages), a
660V AC capacitor thingy (which I obviously don't understand...is it
part of the ferrroresonance?) that only connects
That's the one that I susepct.
back to the transformer itself, and the two smoothing
caps (one for the
24V line and one for the 10V line). Is it possible that one/both
caps are 'pumping' the circuit? <shrug> I'm just too novice to know.
No, the smoothing capacitors could cause low outputs and excessive
ripple, but I don't see how they could cause high outputs.
Another suggestion I received privately hints that putting a dummy load
on the PS might bring it into line, and that I will try. I have access to an
Thing is, you havve an identical PSU that works without a dummy load (as,
BTW, do the ones in my RX01s and RX02s). I don't think you need a load on
this supply/
-tony
4 Sep
4 Sep
4:11 p.m.
Tony Duell wrote:
The whole point of a regulator circuit is that the
output voltage is
independant of the input. Of course too high an input voltage will do
damage, and for linear regulator circuits they run hotter as the input
voltage increases. But I could well believe a reasonably designed
regualtor would work correctly on double the input voltage, particularly
on no load.
Well that may not be practical. Even with household AC you have your
voltage bouncing around -- here 120V to 130V. Playing around with a
high voltage supply @ 300V regulated I have about 475 peak volts.
I don't want to handle twice input that since my 1200 volt diodes will
go bang!
Ben alias Woodelf
12:18 p.m.
On 4 Sep 2007 at 3:12, J Blaser wrote:
That's the strange thing to me. The two
secondaries from the transformer (one
for the 24V line, and the other for the 10V line [which sources the regulated
5V output]) are 'proper' at 27.8V and 11.2V, respectively. What I don't
understand is how a 24V line can suddenly produce 42V! It's like something
is 'pumping' the circuit, and I admit I have never studied how such things work.
Your measurement of the AC output (27.8 volts) is the RMS value of
the voltage. In an unloaded rectifier-capacitor setup, the capacitor
will charge to the *peak* value of the AC voltage. 42 vdc is "close
enough".
Notice that there's no regulator on the +24 PSU line--just a simple
full-wave rectifier formed by D1 and D2 and C1 as a filter cap.
There's a 10K bleeder on the line, but that accounts for only 2 ma of
current draw at 24 volts on a supply that's rated for 1000 times that
current.
Put a load on it, say 12-24 ohms or even two automovtive lamps hooked
in series and watch the voltage drop.
Cheers,
Chuck
7:34 p.m.
On Tuesday 04 September 2007 05:12, J Blaser wrote:
What pops into my head on reading this is that you might possibly be seeing
some sort of an artifact, if you're using a digital meter!
One point about ferroresonant transformers -- that capacitor you mention is
typically "selected" to go with that particular transformer. If you look,
you'll probably find a small dot of the same color paint on both of them.
IIRC, the
'raw DC' is unregulated, just rectified and smoothed from the
transformer. As is the 24V line. Both are about 1.7* what they should be.
That's the strange thing to me. The two secondaries from the transformer
(one for the 24V line, and the other for the 10V line [which sources the
regulated 5V output]) are 'proper' at 27.8V and 11.2V, respectively. What
I don't understand is how a 24V line can suddenly produce 42V! It's like
something is 'pumping' the circuit, and I admit I have never studied how
such things work. The funny thing is that the 5V regulation is working,
even with 17V input
instead of 10V.
A faulty cap can have all sorts of noise, hum, hash, and other nonsense
riding on top of the DC level, and that might (falsely) end up giving you a
higher reading than what you'd expect.
It's gettign late, so I'll not find the
prints tonight. But IIRC, the
transformer in this supply is a ferroresonant one, and that's what
stabilises the 'raw' and 24V lines. What happens if the capacitor hung
off that is defective?
Fair point, but can a faulty capacitor 'pump' up the voltage like I'm
seeing? I suspect the
last part is very ture. Actually replacing the faulty part
is the easy bit :-)
Hey, thanks for your confidence! :-) I can use a little outside support!
;-)
Let me add that this RX01 is the second of two RX01 units in this system.
When I went through the first one a week ago, it checked out fine...that is
I saw 25V/10.2v on the outputs, without a load.
And you're not going to like this :-), but for an electronics novice,
tonight I followed my instinct and swapped the regulator PCBs between
units. Yup, the 'good' system's PCB now is putting out 42V and 17V! So,
it's not the regulation circuit, I guess, or any component on the two
system's PCBs.
But after swapping the PS regulator PCBs, all that's left are the
transformer (which appears to be putting out 'expected' voltages), a 660V
AC capacitor thingy (which I obviously don't understand...is it part of the
ferrroresonance?) that only connects back to the transformer itself, and
the two smoothing caps (one for the 24V line and one for the 10V line). Is
it possible that one/both caps are 'pumping' the circuit? <shrug>
I'm
just too novice to know. Another suggestion I received privately hints that
putting a dummy load
on the PS might bring it into line, and that I will try. I have access to
an oscilloscope, and will put it on the thing, too, to see if I can
discover anything strange.
One more point about ferroresonant transformers -- their output is often NOT
sinewave, but a rather distorted waveform, that would tend to upset some
meters, I'd think. Your scope should show you more of what's actually going
on there.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
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