Looking for a replacement for a blown Mallory electrolytic capacitor for a
power supply. The capacitor has three terminals, 2 red and one black. The
capacitor label has the following notation:

Mallory
5000 MFD 20 VDC RED
5000 MFD 20 VDC RED
25002 235-7244A

I did a Google search and could not find anything similar. I am wondering
if anyone has any idea where I could find a suitable replacement.

The capacitor is part of an EICO Battery ELiminator and Charger, Model
1064S.

Any assistance would be greatly appreciated.

- D. Boucher

On Sun, 5 Mar 2006 17:11:37 -0600, "DB" wrote:



Looking for a replacement for a blown Mallory electrolytic capacitor for a
power supply. The capacitor has three terminals, 2 red and one black. The
capacitor label has the following notation:

Mallory
5000 MFD 20 VDC RED
5000 MFD 20 VDC RED
25002 235-7244A

I did a Google search and could not find anything similar. I am wondering
if anyone has any idea where I could find a suitable replacement.

The capacitor is part of an EICO Battery ELiminator and Charger, Model
1064S.

Any assistance would be greatly appreciated.

---
Unless you need an exact replacement for esthetic reasons, any
modern aluminum electrolytic capacitor rated for 20V or more should
work.

If the capacitors are used singly you'll need to get something like
two, 5100µF 20V caps or of they're wired in parallel, a single
10000µF 20V cap should work. Check Digi-Key or Mouser, they're sure
to have something you can use.

Do you have a schematic you can post?

--
John Fields
Professional Circuit Designer

Unfortunately I don't have a schematic. There is only one capacitor, but it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

- D. Boucher

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 17:11:37 -0600, "DB" wrote:



Looking for a replacement for a blown Mallory electrolytic capacitor for a
power supply. The capacitor has three terminals, 2 red and one black.
The
capacitor label has the following notation:

Mallory
5000 MFD 20 VDC RED
5000 MFD 20 VDC RED
25002 235-7244A

I did a Google search and could not find anything similar. I am wondering
if anyone has any idea where I could find a suitable replacement.

The capacitor is part of an EICO Battery ELiminator and Charger, Model
1064S.

Any assistance would be greatly appreciated.

---
Unless you need an exact replacement for esthetic reasons, any
modern aluminum electrolytic capacitor rated for 20V or more should
work.

If the capacitors are used singly you'll need to get something like
two, 5100µF 20V caps or of they're wired in parallel, a single
10000µF 20V cap should work. Check Digi-Key or Mouser, they're sure
to have something you can use.

Do you have a schematic you can post?

--
John Fields
Professional Circuit Designer

DB wrote:
Unfortunately I don't have a schematic. There is only one capacitor, but it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

- D. Boucher

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 17:11:37 -0600, "DB" wrote:


Looking for a replacement for a blown Mallory electrolytic capacitor for a
power supply. The capacitor has three terminals, 2 red and one black.
The
capacitor label has the following notation:

Mallory
5000 MFD 20 VDC RED
5000 MFD 20 VDC RED
25002 235-7244A

I did a Google search and could not find anything similar. I am wondering
if anyone has any idea where I could find a suitable replacement.

The capacitor is part of an EICO Battery ELiminator and Charger, Model
1064S.

Any assistance would be greatly appreciated.
---
Unless you need an exact replacement for esthetic reasons, any
modern aluminum electrolytic capacitor rated for 20V or more should
work.

If the capacitors are used singly you'll need to get something like
two, 5100µF 20V caps or of they're wired in parallel, a single
10000µF 20V cap should work. Check Digi-Key or Mouser, they're sure
to have something you can use.

Do you have a schematic you can post?

--
John Fields
Professional Circuit Designer



Two capacitors, that share a single negative terminal, in the one
package. Cannot say I've seen it before but sounds reasonable.

Failing a schematic, can you try following the actual circuit to give us
an idea?

Is it possible that the wires off the capacitor red leads go to the
cathodes of two diodes who's anode then connect to windings on a
transformer with the capacitors negative terminal going to another
transformer terminal?

Daniel
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In article ,
Daniel wrote:

DB wrote:
Unfortunately I don't have a schematic. There is only one capacitor, but it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

- D. Boucher

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 17:11:37 -0600, "DB" wrote:


Looking for a replacement for a blown Mallory electrolytic capacitor for
a
power supply. The capacitor has three terminals, 2 red and one black.
The
capacitor label has the following notation:

Mallory
5000 MFD 20 VDC RED
5000 MFD 20 VDC RED
25002 235-7244A

I did a Google search and could not find anything similar. I am
wondering
if anyone has any idea where I could find a suitable replacement.

The capacitor is part of an EICO Battery ELiminator and Charger, Model
1064S.

Any assistance would be greatly appreciated.
---
Unless you need an exact replacement for esthetic reasons, any
modern aluminum electrolytic capacitor rated for 20V or more should
work.

If the capacitors are used singly you'll need to get something like
two, 5100µF 20V caps or of they're wired in parallel, a single
10000µF 20V cap should work. Check Digi-Key or Mouser, they're sure
to have something you can use.

Do you have a schematic you can post?

--
John Fields
Professional Circuit Designer



Two capacitors, that share a single negative terminal, in the one
package. Cannot say I've seen it before but sounds reasonable.

Failing a schematic, can you try following the actual circuit to give us
an idea?

Is it possible that the wires off the capacitor red leads go to the
cathodes of two diodes who's anode then connect to windings on a
transformer with the capacitors negative terminal going to another
transformer terminal?

Daniel
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http://www.SecureIX.com ***

I guess you guys never worked with toob circutis. Multiple capacitors in
one can with one negative are quite common. But not in the values you
show. I'm looking at one right now:

22-3457 F
10 Mfd 400V
4 Mfd 350V
4 Mfd 150V
20 Mfd 50V

Date Code, ta dah, 6149

I know this doesn't help your problem, but don't be misled. I've taken
cans apart carefully and replaced the internal capacitors. You would
never know from the outside.

Al

On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

---
Please bottom post.

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

The reason I ask is because there are lots of people selling Mallory
capacitors on the web, and if you know the type number you should be
able to use Goggle to find a source.

Failing that, If you took the thing apart to find out what's
_really_ in the can, as Al suggested, you could substitute what's in
there with new caps or, if you wanted to get really fancy, put the
new caps in the old can for a tidy repair. Caps today are so much
smaller than they were back then they'd prob'ly fit right in there.

--
John Fields
Professional Circuit Designer

"John Fields" schreef in bericht
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor,
but it
has three terminals. That and the notation on the side makes me
think it
may be some kind of a dual capacitor in one big can. I had never
heard of
such a thing before, but could that be what it is?

---
Please bottom post.

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

The reason I ask is because there are lots of people selling Mallory
capacitors on the web, and if you know the type number you should be
able to use Goggle to find a source.

Failing that, If you took the thing apart to find out what's
_really_ in the can, as Al suggested, you could substitute what's in
there with new caps or, if you wanted to get really fancy, put the
new caps in the old can for a tidy repair. Caps today are so much
smaller than they were back then they'd prob'ly fit right in there.

--
John Fields
Professional Circuit Designer

I remember a VCR I disposed of 'bout a year ago.
This one had a nice cap with 4 terminals in it this part and other
parts were defect.
btw. the VCR was a Video 2000 (one of the first of them).
I never fancied opening Capacitors, even those descriped, because
sometimes you immediatly get the electrolyt out of the case.
Sometimes the opening happens by accident

Alexander

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

---
Please bottom post.

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

The reason I ask is because there are lots of people selling Mallory
capacitors on the web, and if you know the type number you should be
able to use Goggle to find a source.

Failing that, If you took the thing apart to find out what's
_really_ in the can, as Al suggested, you could substitute what's in
there with new caps or, if you wanted to get really fancy, put the
new caps in the old can for a tidy repair. Caps today are so much
smaller than they were back then they'd prob'ly fit right in there.

--
John Fields
Professional Circuit Designer

I opened the power supply up and traced the wires. The black terminal is
connected directly to the negative output terminal. One of the red
terminals is connected directly to the positive output terminal. The other
red terminal is also connected to the positive output, but through a large
coil with an iron core. The second red terminal is also connected to a DPDT
switch that selects the output range and through that to a diode array and a
variable transformer.

There are no markings on the capacitor other than what I indicated in my
first post.

I'll try the thing of putting new caps in the old can -- it would certainly
make it easier to mount them.

- DB

In article , "DB"
wrote:

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

---
Please bottom post.

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

The reason I ask is because there are lots of people selling Mallory
capacitors on the web, and if you know the type number you should be
able to use Goggle to find a source.

Failing that, If you took the thing apart to find out what's
_really_ in the can, as Al suggested, you could substitute what's in
there with new caps or, if you wanted to get really fancy, put the
new caps in the old can for a tidy repair. Caps today are so much
smaller than they were back then they'd prob'ly fit right in there.

--
John Fields
Professional Circuit Designer

I opened the power supply up and traced the wires. The black terminal is
connected directly to the negative output terminal. One of the red
terminals is connected directly to the positive output terminal. The other
red terminal is also connected to the positive output, but through a large
coil with an iron core. The second red terminal is also connected to a DPDT
switch that selects the output range and through that to a diode array and a
variable transformer.

There are no markings on the capacitor other than what I indicated in my
first post.

I'll try the thing of putting new caps in the old can -- it would certainly
make it easier to mount them.

- DB



Looks like what you have is a pi filter. Leading cap., choke, trailing
cap. Values of the caps are important in this schema.

Al

Looks like what you have is a pi filter. Leading cap., choke, trailing
cap. Values of the caps are important in this schema.

Al

db, are you for sure that the caps are bad?
What was the problem that lead you to diagnose the caps?

leaking or exploded? I have changed caps before , but its not that often
a main power supply filter dies. Tell us what the unit was doing...

"James Thompson" wrote in message
...
Looks like what you have is a pi filter. Leading cap., choke, trailing
cap. Values of the caps are important in this schema.

Al

db, are you for sure that the caps are bad?
What was the problem that lead you to diagnose the caps?

leaking or exploded? I have changed caps before , but its not that
often a main power supply filter dies. Tell us what the unit was doing...


One minute the Power supply was working fine, then it vibrated for a split
second and then the fuse blew. I replaced the fuse, and the same thing
happened again when I turned it on. I opened the power supply up and I saw
that there was some dried yellow crusty material that appeared to have oozed
out of the capacitor near one of the terminals. It looked like it had been
that way for a while, but I had just recently started using this power
supply after it had been sitting on a shelf for about 12 years.

I checked the resistance between the capacitor terminals (without removing
the capacitor from the circuit), and found that there was no resistance. I
don't know if that is normal.

- D. Boucher

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?


More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping that
they might be suitable replacements. The new capacitors are marked "Type
PFP." The old 5000 MFD 20VDC dual capacitor didn't have any markings to
indicate the type. The old capacitor case looks like it is made of
bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum case,
and a fourth terminal slightly off-center from the base. The fourth
terminal has a little square marking next to it. There does not appear to
be any measureable resistance between any of the terminals, including the
central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should be
connected to the positive output of the power supply, and which to the
negative. Any assistance would be greatly appreciated.

- D. Boucher

On Sat, 11 Mar 2006 14:36:05 -0600, "DB" wrote:

"John Fields" wrote in message
.. .
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?


More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?

I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping that
they might be suitable replacements. The new capacitors are marked "Type
PFP." The old 5000 MFD 20VDC dual capacitor didn't have any markings to
indicate the type. The old capacitor case looks like it is made of
bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum case,
and a fourth terminal slightly off-center from the base. The fourth
terminal has a little square marking next to it. There does not appear to
be any measureable resistance between any of the terminals, including the
central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should be
connected to the positive output of the power supply, and which to the
negative. Any assistance would be greatly appreciated.

---
The capacitor you have is one of the Mallory PFP types which is a
twist-lock capacitor for PCB mounting. Twist-lock because usually
the tabs on the case were slipped through slots in the PCB (type
PFP) or through the chassis (type FP), and then the tabs were
twisted with a pair of pliers to lock the capacitor down.

The case is almost certainly negative, leaving the center pin
positive.

The reason you're measuring zero resistance between the center pin
and the case is because they're pretty good size capacitors and
it'll take a good while for them to charge up with the current from
your ohmmeter. Also, if they haven't been used in some time the
oxide on the plates might not be in the best condition, so what you
might want to do is put an ammeter in series with the cap and
measure the current going into it while it's charging from a low
voltage. When you first connect it the ammmeter will show a _LOT_
of current, but as time goes by you should see the current drop and
eventually settle on a very low value. When it gets stable,
increase the voltage and watch the current until it gets stable
again. Do that until the voltage across the capacitor is at 25V,
and then just let it sit there with power on it for a few hours. If
everything is OK the ammeter should read only a few milliamperes
after a few hours.

BTW, what kind of test equipment do you have access to?

--
John Fields
Professional Circuit Designer

DB wrote:
"James Thompson" wrote in message
...
Looks like what you have is a pi filter. Leading cap., choke, trailing
cap. Values of the caps are important in this schema.

Al
db, are you for sure that the caps are bad?
What was the problem that lead you to diagnose the caps?

leaking or exploded? I have changed caps before , but its not that
often a main power supply filter dies. Tell us what the unit was doing...


One minute the Power supply was working fine, then it vibrated for a split
second and then the fuse blew. I replaced the fuse, and the same thing
happened again when I turned it on. I opened the power supply up and I saw
that there was some dried yellow crusty material that appeared to have oozed
out of the capacitor near one of the terminals. It looked like it had been
that way for a while, but I had just recently started using this power
supply after it had been sitting on a shelf for about 12 years.

I checked the resistance between the capacitor terminals (without removing
the capacitor from the circuit), and found that there was no resistance. I
don't know if that is normal.

- D. Boucher



Just to be clear, do you mean that you ohm-meter showed there was zero
ohms between the terminals or did it show there was no connection (i.e.
an open circuit) between the terminals?

Daniel
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John Fields wrote:
On Sat, 11 Mar 2006 14:36:05 -0600, "DB" wrote:

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?
I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping that
they might be suitable replacements. The new capacitors are marked "Type
PFP." The old 5000 MFD 20VDC dual capacitor didn't have any markings to
indicate the type. The old capacitor case looks like it is made of
bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum case,
and a fourth terminal slightly off-center from the base. The fourth
terminal has a little square marking next to it. There does not appear to
be any measureable resistance between any of the terminals, including the
central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should be
connected to the positive output of the power supply, and which to the
negative. Any assistance would be greatly appreciated.

---
The capacitor you have is one of the Mallory PFP types which is a
twist-lock capacitor for PCB mounting. Twist-lock because usually
the tabs on the case were slipped through slots in the PCB (type
PFP) or through the chassis (type FP), and then the tabs were
twisted with a pair of pliers to lock the capacitor down.

The case is almost certainly negative, leaving the center pin
positive.

The reason you're measuring zero resistance between the center pin
and the case is because they're pretty good size capacitors and
it'll take a good while for them to charge up with the current from
your ohmmeter.

If the capacitors are discharged at the start, when connecting the
ohm-meter there should be maximum current flow, indicating zero ohms,
for an instant, then, as the capacitor charges, the amount of current
will decrease until, in the end, the capacitor is charged to the same
voltage as the ohm-meter is providing, so indicates zero current flow,
or as an open circuit, i.e. infinite resistance.

Depending on the internal resistance of the ohm-meter, this could take
almost zero time or substantial time

Daniel

Also, if they haven't been used in some time the
oxide on the plates might not be in the best condition, so what you
might want to do is put an ammeter in series with the cap and
measure the current going into it while it's charging from a low
voltage. When you first connect it the ammmeter will show a _LOT_
of current, but as time goes by you should see the current drop and
eventually settle on a very low value. When it gets stable,
increase the voltage and watch the current until it gets stable
again. Do that until the voltage across the capacitor is at 25V,
and then just let it sit there with power on it for a few hours. If
everything is OK the ammeter should read only a few milliamperes
after a few hours.

BTW, what kind of test equipment do you have access to?

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On Sun, 12 Mar 2006 09:35:33 +1100, Daniel
wrote:

John Fields wrote:
On Sat, 11 Mar 2006 14:36:05 -0600, "DB" wrote:

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?
I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping that
they might be suitable replacements. The new capacitors are marked "Type
PFP." The old 5000 MFD 20VDC dual capacitor didn't have any markings to
indicate the type. The old capacitor case looks like it is made of
bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum case,
and a fourth terminal slightly off-center from the base. The fourth
terminal has a little square marking next to it. There does not appear to
be any measureable resistance between any of the terminals, including the
central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should be
connected to the positive output of the power supply, and which to the
negative. Any assistance would be greatly appreciated.

---
The capacitor you have is one of the Mallory PFP types which is a
twist-lock capacitor for PCB mounting. Twist-lock because usually
the tabs on the case were slipped through slots in the PCB (type
PFP) or through the chassis (type FP), and then the tabs were
twisted with a pair of pliers to lock the capacitor down.

The case is almost certainly negative, leaving the center pin
positive.

The reason you're measuring zero resistance between the center pin
and the case is because they're pretty good size capacitors and
it'll take a good while for them to charge up with the current from
your ohmmeter.

If the capacitors are discharged at the start, when connecting the
ohm-meter there should be maximum current flow, indicating zero ohms,
for an instant, then, as the capacitor charges, the amount of current
will decrease until, in the end, the capacitor is charged to the same
voltage as the ohm-meter is providing, so indicates zero current flow,
or as an open circuit, i.e. infinite resistance.

Depending on the internal resistance of the ohm-meter, this could take
almost zero time or substantial time

---
Most of my multimeters, on the 200 ohm full scale range, supply
about 1A into a short, so if we consider the ohmmeter a constant
current source it'll take:

dv C 1V * 5E-3F
t = ------ = ------------ = 5 seconds
I 1e-3A

to charge the cap up to a volt through the ohmmeter. Not exactly
what I'd call "almost zero time"

But, to be fair, I put a Fluke 8060A on the 200 ohm range across a
4700µF 35V cap and it only had time to give me one reading before it
went "OL". OTOH, on the megohm range it took it 10s to get to
0.0020, so if the OP's using a cheap 3-1/2 digit meter on the high
resistance range, he may have seen 0.000 and not given it a chance
to rise any higher before disconnecting.


--
John Fields
Professional Circuit Designer

"Daniel" wrote in message
om...
John Fields wrote:
On Sat, 11 Mar 2006 14:36:05 -0600, "DB" wrote:

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor,
but
it
has three terminals. That and the notation on the side makes me think
it
may be some kind of a dual capacitor in one big can. I had never
heard of
such a thing before, but could that be what it is?

More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?
I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping
that they might be suitable replacements. The new capacitors are marked
"Type PFP." The old 5000 MFD 20VDC dual capacitor didn't have any
markings to indicate the type. The old capacitor case looks like it is
made of bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum
case, and a fourth terminal slightly off-center from the base. The
fourth terminal has a little square marking next to it. There does not
appear to be any measureable resistance between any of the terminals,
including the central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should
be connected to the positive output of the power supply, and which to
the negative. Any assistance would be greatly appreciated.

---
The capacitor you have is one of the Mallory PFP types which is a
twist-lock capacitor for PCB mounting. Twist-lock because usually
the tabs on the case were slipped through slots in the PCB (type
PFP) or through the chassis (type FP), and then the tabs were
twisted with a pair of pliers to lock the capacitor down.

The case is almost certainly negative, leaving the center pin
positive.

The reason you're measuring zero resistance between the center pin
and the case is because they're pretty good size capacitors and
it'll take a good while for them to charge up with the current from
your ohmmeter.

If the capacitors are discharged at the start, when connecting the
ohm-meter there should be maximum current flow, indicating zero ohms, for
an instant, then, as the capacitor charges, the amount of current will
decrease until, in the end, the capacitor is charged to the same voltage
as the ohm-meter is providing, so indicates zero current flow, or as an
open circuit, i.e. infinite resistance.

Depending on the internal resistance of the ohm-meter, this could take
almost zero time or substantial time

Daniel

Also, if they haven't been used in some time the
oxide on the plates might not be in the best condition, so what you
might want to do is put an ammeter in series with the cap and
measure the current going into it while it's charging from a low
voltage. When you first connect it the ammmeter will show a _LOT_
of current, but as time goes by you should see the current drop and
eventually settle on a very low value. When it gets stable,
increase the voltage and watch the current until it gets stable
again. Do that until the voltage across the capacitor is at 25V,
and then just let it sit there with power on it for a few hours. If
everything is OK the ammeter should read only a few milliamperes
after a few hours.

BTW, what kind of test equipment do you have access to?


The only test equipment I have is a $9.99 multi-meter from Harbor Freight.
The PFP capacitors have never been used, and appear to be brand new. The
ohmmeter reading is zero ohms across all terminals, for both the new and old
capacitors.

I tried connecting one of the new caps in series with a flashlight battery
and measuring the current. The current slowly but steadily declined. I did
the same thing with each side of the old dual capacitor, and in each case
there was a quick spike in current, followed by a steady current of approx.
0.9 mA.

- D. Boucher

On Sat, 11 Mar 2006 17:46:42 -0600, "DB" wrote:


The only test equipment I have is a $9.99 multi-meter from Harbor Freight.
The PFP capacitors have never been used, and appear to be brand new. The
ohmmeter reading is zero ohms across all terminals, for both the new and old
capacitors.

---


I tried connecting one of the new caps in series with a flashlight battery
and measuring the current. The current slowly but steadily declined. I did
the same thing with each side of the old dual capacitor, and in each case
there was a quick spike in current, followed by a steady current of approx.
0.9 mA.

---
With a 1.5V flashlight battery supplying a steady 0.9mA into the
capS, that indicates that their internal resistances we

E 1.5V
R = --- = ------ ~ 1.67K ohms,
I 09mA

so those caps are definitely bad

Why don't you cut them out of there, wire the new ones in where the
old ones were, just to test them, and see what happens as you crank
the voltage up _slowly_ from zero? If you put your meter in series
with the output filter:


RAW +DC---[+METER-]--+--[CHOKE]--+----+DC OUT
|+ |+
[5000µF] [5000µF]
| |
RAW -DC--------------+-----------+-----DC OUT

You'll be able to see what the total leakage current into the caps
is. With no load, I'd expect something substantially less than 5mA
with the full 25V across the caps.

--
John Fields
Professional Circuit Designer

John Fields wrote:
On Sun, 12 Mar 2006 09:35:33 +1100, Daniel
wrote:

John Fields wrote:
On Sat, 11 Mar 2006 14:36:05 -0600, "DB" wrote:

"John Fields" wrote in message
...
On Sun, 5 Mar 2006 22:49:35 -0600, "DB" wrote:

Unfortunately I don't have a schematic. There is only one capacitor, but
it
has three terminals. That and the notation on the side makes me think it
may be some kind of a dual capacitor in one big can. I had never heard of
such a thing before, but could that be what it is?
More than likely, that's precisely what it is. Back in the stony
ages it was quite common to have two or three electrolytics in the
same can. The way you describe yours though, makes it sound like
there's a separate terminal coming out of the base for the common
connection, when usually a tab which was part of the case was used
for the common connection. Is thare any other marking on the case?
Like "TYPE FP" or anything like that?
I picked up a couple of 5000 MFD 25VDC capacitors for $1 each, hoping that
they might be suitable replacements. The new capacitors are marked "Type
PFP." The old 5000 MFD 20VDC dual capacitor didn't have any markings to
indicate the type. The old capacitor case looks like it is made of
bakelite, by the way.

The new capacitors have three terminals that are part of the aluminum case,
and a fourth terminal slightly off-center from the base. The fourth
terminal has a little square marking next to it. There does not appear to
be any measureable resistance between any of the terminals, including the
central one.

I am wondering how I can determine if these capacitors are suitable
replacements. I'm also not sure how to figure out which terminal should be
connected to the positive output of the power supply, and which to the
negative. Any assistance would be greatly appreciated.
---
The capacitor you have is one of the Mallory PFP types which is a
twist-lock capacitor for PCB mounting. Twist-lock because usually
the tabs on the case were slipped through slots in the PCB (type
PFP) or through the chassis (type FP), and then the tabs were
twisted with a pair of pliers to lock the capacitor down.

The case is almost certainly negative, leaving the center pin
positive.

The reason you're measuring zero resistance between the center pin
and the case is because they're pretty good size capacitors and
it'll take a good while for them to charge up with the current from
your ohmmeter.
If the capacitors are discharged at the start, when connecting the
ohm-meter there should be maximum current flow, indicating zero ohms,
for an instant, then, as the capacitor charges, the amount of current
will decrease until, in the end, the capacitor is charged to the same
voltage as the ohm-meter is providing, so indicates zero current flow,
or as an open circuit, i.e. infinite resistance.

Depending on the internal resistance of the ohm-meter, this could take
almost zero time or substantial time

---
Most of my multimeters, on the 200 ohm full scale range, supply
about 1A into a short, so if we consider the ohmmeter a constant
current source it'll take:

dv C 1V * 5E-3F
t = ------ = ------------ = 5 seconds
I 1e-3A

to charge the cap up to a volt through the ohmmeter. Not exactly
what I'd call "almost zero time"

All fine and dandy if the Ohm-meter were a constant current source and
the capacitor could just keep absorbing those electrons, but neither is
the case so your logic fails.

(As a side note, I'll give you 5E-3F is the same as 5000 microfarads,
but 1e-3A is not the one amp you say your multimeter can supply into a
short. If you fix this in the workings, t = 5 milli-seconds, which I
would call "almost zero time" when talking about digital multi-meter
response time.)


But, to be fair, I put a Fluke 8060A on the 200 ohm range across a
4700µF 35V cap and it only had time to give me one reading before it
went "OL". OTOH, on the megohm range it took it 10s to get to
0.0020, so if the OP's using a cheap 3-1/2 digit meter on the high
resistance range, he may have seen 0.000 and not given it a chance
to rise any higher before disconnecting.



Daniel
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On Sun, 12 Mar 2006 20:50:41 +1100, Daniel
wrote:

John Fields wrote:

---
Most of my multimeters, on the 200 ohm full scale range, supply
about 1A into a short, so if we consider the ohmmeter a constant
current source it'll take:

dv C 1V * 5E-3F
t = ------ = ------------ = 5 seconds
I 1e-3A

to charge the cap up to a volt through the ohmmeter. Not exactly
what I'd call "almost zero time"

All fine and dandy if the Ohm-meter were a constant current source and
the capacitor could just keep absorbing those electrons, but neither is
the case so your logic fails.

---
Not at all. On the higher resistance ranges the ohmmeter _does_
approximate a constant current source; at least for the purpose of
this discussion.
---

(As a side note, I'll give you 5E-3F is the same as 5000 microfarads,
but 1e-3A is not the one amp you say your multimeter can supply into a
short.

---
Yes, but that one amp '1A', earlier, was a trypo. It should have
read: "1mA", so the math is correct as it stands. I'm surprised you
didn't catch that, since it's not likely _any_ common ohmmeter is
going to push 1 amp through the resistance it's measuring.

Even my trusty old Simpson 260 on the 'R times 1' range only puts
about 100mA through a 100mA d'Arsonval movement with an internal
resistance of 1.08 ohms.
---

If you fix this in the workings, t = 5 milli-seconds, which I
would call "almost zero time" when talking about digital multi-meter
response time.)

---
It doesn't need to be fixed, though. All that needed to happen was
for the typo to be corrected, so the 5 seconds stands at 5 seconds,
which even for a relatively slow digital multimeter with an update
rate of 2 readings per second isn't "almost zero time".

--
John Fields
Professional Circuit Designer