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

Smitty Two wrote in message
news
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

Bit before the days of little inverter, Selenium rectifier package , like my
pics
http://home.graffiti.net/diverse:graffiti.net/Se_R.jpg
pic to right is half wave one
Siemens is a common make.

Difficult to test as so much droppage, usually replace with some Si diodes
and sag resistors if appropriate.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"Smitty Two" wrote in message
news
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

On Thu, 26 Mar 2009 08:01:17 -0700, Smitty Two
wrote:

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

Simple selenium bridge rectifier. Terminal marking shows what the
function is (AC in, DC out) and the design is familiar to any
old-timer... (Oh, crap, gave that one away, didn't I?)

On Thu, 26 Mar 2009 08:01:17 -0700, Smitty Two
put finger to keyboard and composed:

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

https://www.wellgainelectronics.com/...ROD&ProdID=453

ITT B30C400
BRIDGE RECTIFIER DIODE

VINTAGE ... 30V 400MA full wave selenium rectifier

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

Smitty Two wrote:

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

Good old Selenium rectifier ! Not seen one of those in years.

--
Best Regards:
Baron.

On 3/26/2009 7:01 AM Smitty Two spake thus:

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

So this far down in the thread we know by now that it's a selenium
bridge rectifier.

Question is, why can't he just replace it with a silicon bridge
rectifier? Someone pointed out that Si has less voltage drop, but would
that really be an issue? (Of course, it might help to know *something*
about the equipment surrounding this component ...)


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

In article ,
Franc Zabkar wrote:

On Thu, 26 Mar 2009 08:01:17 -0700, Smitty Two
put finger to keyboard and composed:

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

https://www.wellgainelectronics.com/...ROD&ProdID=453

ITT B30C400
BRIDGE RECTIFIER DIODE

VINTAGE ... 30V 400MA full wave selenium rectifier

- Franc Zabkar

Thanks. Figured them damn numbers must be specs of a sort!

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but there's
a secondary winding in there putting out about 17, and he's getting
about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is it
an R & R job? (remove and replace)

Smitty Two wrote in message
news
In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but there's
a secondary winding in there putting out about 17, and he's getting
about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is it
an R & R job? (remove and replace)


Combined motor and "transformer" very common for "Dansette" type record
players of the Selenium rectifier era. When higher power amps came in then
they had to split apart.



--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Smitty Two Inscribed thus:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but
there's a secondary winding in there putting out about 17, and he's
getting about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is
it an R & R job? (remove and replace)

That is an AC shaded pole motor with a tapped winding feeding the
rectifier. It also means that one side of the circuit is directly
connected to the mains.

These commonly get glued up bearings. The cure is to strip it clean and
lubricate the shaft on both sides. Use only a very fine oil ! Sewing
machine oil is ideal. Reassemble. Job done.

The shaft should rotate freely without any binding. The only other
possible problem would be shorted turns on the coil ! But if that was
the case I would expect smoke !

--
Best Reagrds:
Baron.

"Smitty Two" wrote in message
news
In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but there's
a secondary winding in there putting out about 17, and he's getting
about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is it
an R & R job? (remove and replace)

This used to be very common practice back in the day. Record players often
used a motor constructed in that way. FWIW, I can't remember ever having one
of those motors, which were used in all sorts of things from tape recorders
to fan heaters, that had any kind of electrical problem. It used to be very
common for the oilite type bearings to completely dry out leaving a gummy
residue, which then made the motor run slowly. Usually, when the motor runs,
the rotor moves forward a couple of mm in its bearings. If it is not able to
do this, that can cause it to drag on the 'brake' pad that's sometimes
fitted in there. They don't have a lot of power even when working correctly.
Also, the bearings are usually 'self-centering' as in they are fixed in a
sort of ball mount. If the motor has been knocked or jarred, the bearing
balls can be knocked out of line, and don't re-centre if it has gone gummy
in there. The motor in the picture looks as though it may have simple fixed
bearings, though.

Usually, these motors are very easy to service, being held together by two
long screws which pass through one bearing plate, through the stator core,
and into the other bearing plate, where the holes are threaded. In the case
of this one, the rivets that they have used would have to be drilled out
first, and then long screws with nuts substituted to hold it back together.
Servicing usually involves cleaning the shaft and bearings with a solvent
such as IPA, and soaking the bearings in a light machine oil for a while,
before poking the rotor shaft through each in turn, and giving it a 'swing
around' - a bit like working a joystick if you will - to make sure that the
ball mounts are free to move. They should be tight enough to stay put
wherever you leave them, but free enough to move fairly easily. The rotor
and bearings are then assembled back onto the stator core, 'working' the
ball mounts on the bearings as needed, until the rotor runs totally smoothly
with the bearing plates refixed to the core by the screws. You should be
able to easily spin the rotor with your fingers, and it should spin on for
quite a while - several seconds at least.

When it's all back together, it doesn't hurt to add a little more machine
oil to the bearings, particularly if there are felt 'resevoir' pads in them
or by them. On some motors of this type that I have seen, there is actually
a little oil hole in the bearing housing. Good luck to your friend. Hope he
succeeds in rescuing it !

Arfa

Baron wrote in message
...
Smitty Two Inscribed thus:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but
there's a secondary winding in there putting out about 17, and he's
getting about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is
it an R & R job? (remove and replace)

That is an AC shaded pole motor with a tapped winding feeding the
rectifier. It also means that one side of the circuit is directly
connected to the mains.

These commonly get glued up bearings. The cure is to strip it clean and
lubricate the shaft on both sides. Use only a very fine oil ! Sewing
machine oil is ideal. Reassemble. Job done.

The shaft should rotate freely without any binding. The only other
possible problem would be shorted turns on the coil ! But if that was
the case I would expect smoke !

--
Best Reagrds:
Baron.


Are shaded pole motors synchronous to the mains frequency unless overloaded
?
I was always surprised how much axial movement there was of the rotor
between the bearings, is this a necessary part of the design ? maybe to
assist startup as relatively low torque even when rotating.

In the present case could low revs be a consequence of a fault in the
electronics, via back emf? is the motor speed the same when the Se
rectifiers are disconnected , not just the electronics disabled?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N_Cook Inscribed thus:

Baron wrote in message
...
Smitty Two Inscribed thus:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but
there's a secondary winding in there putting out about 17, and he's
getting about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or
is it an R & R job? (remove and replace)

That is an AC shaded pole motor with a tapped winding feeding the
rectifier. It also means that one side of the circuit is directly
connected to the mains.

These commonly get glued up bearings. The cure is to strip it clean
and
lubricate the shaft on both sides. Use only a very fine oil !
Sewing
machine oil is ideal. Reassemble. Job done.

The shaft should rotate freely without any binding. The only other
possible problem would be shorted turns on the coil ! But if that
was the case I would expect smoke !

--
Best Reagrds:
Baron.


Are shaded pole motors synchronous to the mains frequency unless
overloaded ?

Yes !

I was always surprised how much axial movement there was of the rotor
between the bearings, is this a necessary part of the design ? maybe
to assist startup as relatively low torque even when rotating.

Generally it allows the rotor to align itself in the magnetic field.

In the present case could low revs be a consequence of a fault in the
electronics, via back emf? is the motor speed the same when the Se
rectifiers are disconnected , not just the electronics disabled?

Very unlikely ! Even if you reduce the voltage the speed tries to stay
constant. Smoke is more likely particularly if stalled or shorted
turns.

--
Best Reagrds:
Baron.

In article ,
Baron wrote:

Smitty Two Inscribed thus:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but
there's a secondary winding in there putting out about 17, and he's
getting about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is
it an R & R job? (remove and replace)

That is an AC shaded pole motor with a tapped winding feeding the
rectifier. It also means that one side of the circuit is directly
connected to the mains.

These commonly get glued up bearings. The cure is to strip it clean and
lubricate the shaft on both sides. Use only a very fine oil ! Sewing
machine oil is ideal. Reassemble. Job done.

The shaft should rotate freely without any binding. The only other
possible problem would be shorted turns on the coil ! But if that was
the case I would expect smoke !

Thanks. My friend says the motor spins freely by hand, and since the
secondary voltage seems correct, giving 12 VDC on the other side of the
rectifier, I'm doubtful about shorted windings. But, he now says that
the mechanism jammed for a few seconds (not longer) just prior to
failure. That seems like it ought to be a good clue, but I haven't been
able to fathom it yet.

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but there's
a secondary winding in there putting out about 17, and he's getting
about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or is it
an R & R job? (remove and replace)

This used to be very common practice back in the day. Record players often
used a motor constructed in that way. FWIW, I can't remember ever having one
of those motors, which were used in all sorts of things from tape recorders
to fan heaters, that had any kind of electrical problem. It used to be very
common for the oilite type bearings to completely dry out leaving a gummy
residue, which then made the motor run slowly. Usually, when the motor runs,
the rotor moves forward a couple of mm in its bearings. If it is not able to
do this, that can cause it to drag on the 'brake' pad that's sometimes
fitted in there. They don't have a lot of power even when working correctly.
Also, the bearings are usually 'self-centering' as in they are fixed in a
sort of ball mount. If the motor has been knocked or jarred, the bearing
balls can be knocked out of line, and don't re-centre if it has gone gummy
in there. The motor in the picture looks as though it may have simple fixed
bearings, though.

Usually, these motors are very easy to service, being held together by two
long screws which pass through one bearing plate, through the stator core,
and into the other bearing plate, where the holes are threaded. In the case
of this one, the rivets that they have used would have to be drilled out
first, and then long screws with nuts substituted to hold it back together.
Servicing usually involves cleaning the shaft and bearings with a solvent
such as IPA, and soaking the bearings in a light machine oil for a while,
before poking the rotor shaft through each in turn, and giving it a 'swing
around' - a bit like working a joystick if you will - to make sure that the
ball mounts are free to move. They should be tight enough to stay put
wherever you leave them, but free enough to move fairly easily. The rotor
and bearings are then assembled back onto the stator core, 'working' the
ball mounts on the bearings as needed, until the rotor runs totally smoothly
with the bearing plates refixed to the core by the screws. You should be
able to easily spin the rotor with your fingers, and it should spin on for
quite a while - several seconds at least.

When it's all back together, it doesn't hurt to add a little more machine
oil to the bearings, particularly if there are felt 'resevoir' pads in them
or by them. On some motors of this type that I have seen, there is actually
a little oil hole in the bearing housing. Good luck to your friend. Hope he
succeeds in rescuing it !

Arfa

Thanks for your usual comprehensive treatise! I forwarded your comments
to my friend. I'm off for a weekend of work and play at "her" house in
another city, so he's on his own for a bit now, and maybe by the time I
get back he'll have it sorted out. The machine is critical to his
business, not just a hobby, so he's anxious to have it operational.

Smitty Two wrote:

In article ,
Baron wrote:

Smitty Two Inscribed thus:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but
there's a secondary winding in there putting out about 17, and he's
getting about 12 VDC out of the bridge, so that part seems OK now.

Is there anything on that type (shaded pole?) of motor to fix, or
is it an R & R job? (remove and replace)

That is an AC shaded pole motor with a tapped winding feeding the
rectifier. It also means that one side of the circuit is directly
connected to the mains.

These commonly get glued up bearings. The cure is to strip it clean
and
lubricate the shaft on both sides. Use only a very fine oil !
Sewing
machine oil is ideal. Reassemble. Job done.

The shaft should rotate freely without any binding. The only other
possible problem would be shorted turns on the coil ! But if that
was the case I would expect smoke !

Thanks. My friend says the motor spins freely by hand, and since the
secondary voltage seems correct, giving 12 VDC on the other side of
the rectifier, I'm doubtful about shorted windings. But, he now says
that the mechanism jammed for a few seconds (not longer) just prior to
failure. That seems like it ought to be a good clue, but I haven't
been able to fathom it yet.

In that case it is possible that there is some sizing in some other part
of the mechanism.

It looks like a belt drive. If the motor still runs slow without the
belt it could be that the bearings have worn oval allowing the rotor to
catch the frame ! For that matter there could be debris in the gap
that could cause the problem.

--
Best Regards:
Baron.

"PeterD" wrote in message
...
On Thu, 26 Mar 2009 08:01:17 -0700, Smitty Two
wrote:

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

Simple selenium bridge rectifier. Terminal marking shows what the
function is (AC in, DC out) and the design is familiar to any
old-timer... (Oh, crap, gave that one away, didn't I?)

Pete I knew you were an OF because of all the knowledge you have to share.
WW

In article ,
Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
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?

"Smitty Two" wrote in message
news
In article ,
Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
In article ,
Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
In article ,
Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.

Arfa is spot on ! 24v as near as makes no difference.

--
Best Regards:
Baron.

"Smitty Two" wrote in message
news
In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news
In article ,
Smitty Two wrote:

In article ,
"Arfa Daily" wrote:

"Smitty Two" wrote in message
news 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.


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 wrote:

:In article ,
: Smitty Two wrote:
:
: In article ,
: "Arfa Daily" wrote:
:
: "Smitty Two" wrote in message
: news : 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
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 wrote in message
...

"Smitty Two" wrote in message
news
In article ,
"Arfa Daily" wrote:

"Smitty Two" 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



probably just for a solenoid for PTO activation off the motor , for slide
carriage/carousel movement.

In article ,
"Arfa Daily" 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

"Smitty Two" wrote in message
news
In article ,
"Arfa Daily" 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

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 ,
"Arfa Daily" wrote:

but
then marvel at other 'useless' information and facts that seem to have
stayed with me taking up space for ever.

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.