component identification

In article <pnmCl.208764$IC4.40255@newsfe13.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-4E9729.18065405042009@news.west.cox.net...
In article <prestwhich-FA8B06.23132726032009@news.west.cox.net>,
Smitty Two <prestwhich@earthlink.net> wrote:

In article <pPPyl.55669$aR3.25479@newsfe17.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-D121DC.08011726032009@news.west.cox.net...
Please tell me whether this is an inverter or a bridge rectifier, if
you
recognize it out of circuit context.

http://members.cox.net/prestwich/51.jpg

Selenium stack bridge, by the looks of it. Equipment it's in ?

Arfa

Ancient European slide projector with rotary carousel. Trying to help a
friend get the thing going again, via email since he lives in another
city.

Problem with it is that this motor:

http://members.cox.net/prestwich/52.jpg

turns very slowly.



All right then, here's what happened with this. (Recall that the motor
is 240VAC and has a secondary winding to power some simple DC stuff
through the bridge) My friend disconnected the AC supply to the
rectifier, and presto, the motor returned to normal speed.

Thinking something downstream could be drawing too much current, he
reconnected the rectifier supply wires and then disconnected the DC side
of the rectifier. Motor slowed down. So he replaced the rectifier, and
all is well.

But I'm still puzzled, and since I was never on-site I didn't do any of
the tests myself. If the rectifier had some fault that was drawing too
much current and it pulled the voltage down, how could he have measured
240 on the slow-turning motor, and 17VAC / 12VDC on the rectifier?

As it was a selenium stack, I would suspect that one arm was leaky. Enough
to make it draw excess current, but not enough to represent a 'serious'
failure that would load up the supply really hard - such as happens when one
arm of a silicon bridge fails short circuit. With the other three arms
functioning normally, the result may well have been a DC output sufficient
for the rest of the circuitry to work.

Out of interest, did your friend replace with a silicon bridge, and
re-measure the AC in / DC out voltages ? Looking again, assuming that a
resevoir cap follows the rectifier, with 17v AC in, you would expect to see
around 24v DC at the output, rather than the 12v that was apparently
measured with the defective bridge in place.

Arfa
Click to expand...
Arfa, are you sure about that? I thought you were supposed to divide by
the square root of 2, not multiply by it. Oddly, my friend says there is
no smoothing cap in the circuit. I did not ask him whether he checked
voltages again, but I will.
 
Smitty Two wrote:

In article <pnmCl.208764$IC4.40255@newsfe13.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-4E9729.18065405042009@news.west.cox.net...
In article <prestwhich-FA8B06.23132726032009@news.west.cox.net>,
Smitty Two <prestwhich@earthlink.net> wrote:

In article <pPPyl.55669$aR3.25479@newsfe17.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-D121DC.08011726032009@news.west.cox.net...
Please tell me whether this is an inverter or a bridge
rectifier, if you
recognize it out of circuit context.

http://members.cox.net/prestwich/51.jpg

Selenium stack bridge, by the looks of it. Equipment it's in ?

Arfa

Ancient European slide projector with rotary carousel. Trying to
help a friend get the thing going again, via email since he lives
in another city.

Problem with it is that this motor:

http://members.cox.net/prestwich/52.jpg

turns very slowly.



All right then, here's what happened with this. (Recall that the
motor is 240VAC and has a secondary winding to power some simple DC
stuff through the bridge) My friend disconnected the AC supply to
the rectifier, and presto, the motor returned to normal speed.

Thinking something downstream could be drawing too much current, he
reconnected the rectifier supply wires and then disconnected the DC
side of the rectifier. Motor slowed down. So he replaced the
rectifier, and all is well.

But I'm still puzzled, and since I was never on-site I didn't do
any of the tests myself. If the rectifier had some fault that was
drawing too much current and it pulled the voltage down, how could
he have measured 240 on the slow-turning motor, and 17VAC / 12VDC
on the rectifier?

As it was a selenium stack, I would suspect that one arm was leaky.
Enough to make it draw excess current, but not enough to represent a
'serious' failure that would load up the supply really hard - such as
happens when one arm of a silicon bridge fails short circuit. With
the other three arms functioning normally, the result may well have
been a DC output sufficient for the rest of the circuitry to work.

Out of interest, did your friend replace with a silicon bridge, and
re-measure the AC in / DC out voltages ? Looking again, assuming that
a resevoir cap follows the rectifier, with 17v AC in, you would
expect to see around 24v DC at the output, rather than the 12v that
was apparently measured with the defective bridge in place.

Arfa

Arfa, are you sure about that? I thought you were supposed to divide
by the square root of 2, not multiply by it. Oddly, my friend says
there is no smoothing cap in the circuit. I did not ask him whether he
checked voltages again, but I will.
Click to expand...
Arfa is spot on ! 24v as near as makes no difference.

--
Best Regards:
Baron.
 
"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-42172D.06390906042009@news.west.cox.net...
In article <pnmCl.208764$IC4.40255@newsfe13.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-4E9729.18065405042009@news.west.cox.net...
In article <prestwhich-FA8B06.23132726032009@news.west.cox.net>,
Smitty Two <prestwhich@earthlink.net> wrote:

In article <pPPyl.55669$aR3.25479@newsfe17.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-D121DC.08011726032009@news.west.cox.net...
Please tell me whether this is an inverter or a bridge rectifier,
if
you
recognize it out of circuit context.

http://members.cox.net/prestwich/51.jpg

Selenium stack bridge, by the looks of it. Equipment it's in ?

Arfa

Ancient European slide projector with rotary carousel. Trying to help
a
friend get the thing going again, via email since he lives in another
city.

Problem with it is that this motor:

http://members.cox.net/prestwich/52.jpg

turns very slowly.



All right then, here's what happened with this. (Recall that the motor
is 240VAC and has a secondary winding to power some simple DC stuff
through the bridge) My friend disconnected the AC supply to the
rectifier, and presto, the motor returned to normal speed.

Thinking something downstream could be drawing too much current, he
reconnected the rectifier supply wires and then disconnected the DC
side
of the rectifier. Motor slowed down. So he replaced the rectifier, and
all is well.

But I'm still puzzled, and since I was never on-site I didn't do any of
the tests myself. If the rectifier had some fault that was drawing too
much current and it pulled the voltage down, how could he have measured
240 on the slow-turning motor, and 17VAC / 12VDC on the rectifier?

As it was a selenium stack, I would suspect that one arm was leaky.
Enough
to make it draw excess current, but not enough to represent a 'serious'
failure that would load up the supply really hard - such as happens when
one
arm of a silicon bridge fails short circuit. With the other three arms
functioning normally, the result may well have been a DC output
sufficient
for the rest of the circuitry to work.

Out of interest, did your friend replace with a silicon bridge, and
re-measure the AC in / DC out voltages ? Looking again, assuming that a
resevoir cap follows the rectifier, with 17v AC in, you would expect to
see
around 24v DC at the output, rather than the 12v that was apparently
measured with the defective bridge in place.

Arfa

Arfa, are you sure about that? I thought you were supposed to divide by
the square root of 2, not multiply by it. Oddly, my friend says there is
no smoothing cap in the circuit. I did not ask him whether he checked
voltages again, but I will.
Click to expand...

Hi Smitty
Peak DC out is root 2 (1.414) *times* the RMS AC in, so with a resevoir
cap of sufficient size, and not too much loading and source impedance,
that's about the level of DC that you would measure on a normal multimeter.
You are thinking of calculating the AC RMS figure from the DC where you
*divide* the DC level by root 2 (or multiply by 0.707).

The fact that there is no resevoir cap, throws a bit of a spanner in the
works when it comes to measuring the 'DC' out from the bridge because,
whilst by strict definition it *is* DC, what you will actually have is a
train of unipolar pulses, which the meter will make some attempt to
integrate into a DC level that it can display. Obviously, this will be a
misleading figure, and may even differ between an analogue, and a digital
meter. The meter reading of "12" might well have been 'correct' in this
case - if you see what I mean !

I wonder what additional circuitry this supply is powering ? It can't be
anything 'electronic', as such a raggedy-arsed rail would play havoc ...

Arfa
 
On Sun, 05 Apr 2009 18:06:54 -0700, Smitty Two <prestwhich@earthlink.net> wrote:

:In article <prestwhich-FA8B06.23132726032009@news.west.cox.net>,
: Smitty Two <prestwhich@earthlink.net> wrote:
:
:> In article <pPPyl.55669$aR3.25479@newsfe17.ams2>,
:> "Arfa Daily" <arfa.daily@ntlworld.com> wrote:
:>
:> > "Smitty Two" <prestwhich@earthlink.net> wrote in message
:> > news:prestwhich-D121DC.08011726032009@news.west.cox.net...
:> > > Please tell me whether this is an inverter or a bridge rectifier, if you
:> > > recognize it out of circuit context.
:> > >
:> > > http://members.cox.net/prestwich/51.jpg
:> >
:> > Selenium stack bridge, by the looks of it. Equipment it's in ?
:> >
:> > Arfa
:>
:> Ancient European slide projector with rotary carousel. Trying to help a
:> friend get the thing going again, via email since he lives in another
:> city.
:>
:> Problem with it is that this motor:
:>
:> http://members.cox.net/prestwich/52.jpg
:>
:> turns very slowly.
:>
:
:
:All right then, here's what happened with this. (Recall that the motor
:is 240VAC and has a secondary winding to power some simple DC stuff
:through the bridge) My friend disconnected the AC supply to the
:rectifier, and presto, the motor returned to normal speed.
:
:Thinking something downstream could be drawing too much current, he
:reconnected the rectifier supply wires and then disconnected the DC side
:eek:f the rectifier. Motor slowed down. So he replaced the rectifier, and
:all is well.
:
:But I'm still puzzled, and since I was never on-site I didn't do any of
:the tests myself. If the rectifier had some fault that was drawing too
:much current and it pulled the voltage down, how could he have measured
:240 on the slow-turning motor, and 17VAC / 12VDC on the rectifier?


Now that it is fixed measure at the same points again and see what voltages you
get. That should give an indication as to whether the original readings were as
they should have been.
 
Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:ViECl.173639$q45.121209@newsfe07.ams2...
"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-42172D.06390906042009@news.west.cox.net...
In article <pnmCl.208764$IC4.40255@newsfe13.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

"Smitty Two" <prestwhich@earthlink.net> wrote in message



Hi Smitty
Peak DC out is root 2 (1.414) *times* the RMS AC in, so with a resevoir
cap of sufficient size, and not too much loading and source impedance,
that's about the level of DC that you would measure on a normal
multimeter.
You are thinking of calculating the AC RMS figure from the DC where you
*divide* the DC level by root 2 (or multiply by 0.707).

The fact that there is no resevoir cap, throws a bit of a spanner in the
works when it comes to measuring the 'DC' out from the bridge because,
whilst by strict definition it *is* DC, what you will actually have is a
train of unipolar pulses, which the meter will make some attempt to
integrate into a DC level that it can display. Obviously, this will be a
misleading figure, and may even differ between an analogue, and a digital
meter. The meter reading of "12" might well have been 'correct' in this
case - if you see what I mean !

I wonder what additional circuitry this supply is powering ? It can't be
anything 'electronic', as such a raggedy-arsed rail would play havoc ...

Arfa
Click to expand...
probably just for a solenoid for PTO activation off the motor , for slide
carriage/carousel movement.
 
In article <ViECl.173639$q45.121209@newsfe07.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

Hi Smitty
Peak DC out is root 2 (1.414) *times* the RMS AC in, so with a resevoir
cap of sufficient size, and not too much loading and source impedance,
that's about the level of DC that you would measure on a normal multimeter.
You are thinking of calculating the AC RMS figure from the DC where you
*divide* the DC level by root 2 (or multiply by 0.707).

The fact that there is no resevoir cap, throws a bit of a spanner in the
works when it comes to measuring the 'DC' out from the bridge because,
whilst by strict definition it *is* DC, what you will actually have is a
train of unipolar pulses, which the meter will make some attempt to
integrate into a DC level that it can display. Obviously, this will be a
misleading figure, and may even differ between an analogue, and a digital
meter. The meter reading of "12" might well have been 'correct' in this
case - if you see what I mean !

I wonder what additional circuitry this supply is powering ? It can't be
anything 'electronic', as such a raggedy-arsed rail would play havoc ...

Arfa
Click to expand...
Thanks Arfa, and others. School was over many years ago, and never
having made the subject into an occupation, as I had planned, the theory
quietly slipped away ...

Friend obliged my request for another reading, and now shows 28 VDC out
of the unfiltered bridge, with his Fluke handheld meter. Would have
saved us all a lot of bother if I'd recognized that 12 VDC as faulty
right off, rather than thinking it was spot on.

N. Cook is correct, the DC only drives a relay to operate the carousel
on command.

Smitty
 
"Smitty Two" <prestwhich@earthlink.net> wrote in message
news:prestwhich-5FBFAB.19004907042009@news.west.cox.net...
In article <ViECl.173639$q45.121209@newsfe07.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:



Hi Smitty
Peak DC out is root 2 (1.414) *times* the RMS AC in, so with a resevoir
cap of sufficient size, and not too much loading and source impedance,
that's about the level of DC that you would measure on a normal
multimeter.
You are thinking of calculating the AC RMS figure from the DC where you
*divide* the DC level by root 2 (or multiply by 0.707).

The fact that there is no resevoir cap, throws a bit of a spanner in the
works when it comes to measuring the 'DC' out from the bridge because,
whilst by strict definition it *is* DC, what you will actually have is a
train of unipolar pulses, which the meter will make some attempt to
integrate into a DC level that it can display. Obviously, this will be a
misleading figure, and may even differ between an analogue, and a digital
meter. The meter reading of "12" might well have been 'correct' in this
case - if you see what I mean !

I wonder what additional circuitry this supply is powering ? It can't be
anything 'electronic', as such a raggedy-arsed rail would play havoc ...

Arfa

Thanks Arfa, and others. School was over many years ago, and never
having made the subject into an occupation, as I had planned, the theory
quietly slipped away ...

Friend obliged my request for another reading, and now shows 28 VDC out
of the unfiltered bridge, with his Fluke handheld meter. Would have
saved us all a lot of bother if I'd recognized that 12 VDC as faulty
right off, rather than thinking it was spot on.

N. Cook is correct, the DC only drives a relay to operate the carousel
on command.

Smitty
Click to expand...
Ah yes ... ! Hindsight is a wonderful thing ! Still, at least if it ever
goes wrong again in any of our lifetimes, we'll have a better idea where to
start looking ! You say about theory quietly slipping away. Sometimes I
despair at the things I've forgotton - often from just 5 seconds ago - but
then marvel at other 'useless' information and facts that seem to have
stayed with me taking up space for ever. And even with all the stuff I've
forgotten, and the very 'normal' upbringing and education I had, allbeit at
a decent school, my three grown children think that I am a 'genius', just
because I know something like the fact that New York is north of the equator
....

Makes you wonder just where we're headed over the next couple of
generations, and whether the current world crisis is anything to do with the
general standards of education and morals that our current and previous
generations enjoy ... :-\

Arfa
 
In article <DbZCl.9902$Le.6587@newsfe12.ams2>,
"Arfa Daily" <arfa.daily@ntlworld.com> wrote:

but
then marvel at other 'useless' information and facts that seem to have
stayed with me taking up space for ever.
Click to expand...
A few years ago, on "Who Wants to Be a Millionaire," some fellow made it
to the million dollar question. Now, once they get above 25,000, I'm
hopelessly lost most of the time.

So I was absolutely shocked when they trotted out a factoid that I've
known in my sleep since I was seven: the distance from the earth to the
sun. "Doesn't every single person in the entire world know that?" I ask
aloud incredulously. And now it's a *million dollar* (multiple-choice no
less) question. Unbelievable.

We know what we know.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top