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Is this capacitor polarized?

M

mm

Jan 1, 1970
0
I have to replace a small capacitor that had a lead ripped out when
the tv was dropped and the pcb broken.

It's a cylinder about a half inch high, a quarter inch in diameter,
with two leads at the bottom, and a narrowing near the bottom, like a
waist line, but it gets back to full diameter at the bottom.

It's black and says on it:

extra info
TL [in an elongated circle]
50v4.7uF --

CD71
40/085/10
N --

There is lead coming out next to the N and next to the 4.7uF.

Does the N mean that that is the negative lead?

If not, does that mean the capacitor is non-polarized?

BTW, what happens if I use a polarized cap where a non-polarized was
intended, or vice versa? Will a reverse voltage puncture the
dielectric? Even if it is less than 50 volts, like the rating here?

Thanks.

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A

Arfa Daily

Jan 1, 1970
0
mm said:
I have to replace a small capacitor that had a lead ripped out when
the tv was dropped and the pcb broken.

It's a cylinder about a half inch high, a quarter inch in diameter,
with two leads at the bottom, and a narrowing near the bottom, like a
waist line, but it gets back to full diameter at the bottom.

It's black and says on it:

extra info
TL [in an elongated circle]
50v4.7uF --

CD71
40/085/10
N --

There is lead coming out next to the N and next to the 4.7uF.

Does the N mean that that is the negative lead?

If not, does that mean the capacitor is non-polarized?

BTW, what happens if I use a polarized cap where a non-polarized was
intended, or vice versa? Will a reverse voltage puncture the
dielectric? Even if it is less than 50 volts, like the rating here?

Thanks.

If you are inclined to email me
for some reason, remove NOPSAM :)

A capacitor of this value and voltage rating could be either polarised, or
not. Usually, a polarised type is quite clearly marked, but an alternative
give-away is the PCB silk screening where it's located. If it is a polarised
type, there is a 99% certainty that one of the legs will be marked.
Sometimes the board will be marked with a " + " sign, and sometimes, there
will be a circle with one side shaded. The shaded side normally indicated
the " - " leg of the cap, and corresponds to a stripe on its body. The ESR
figures for polarised and non-polarised electrolytics are usually quite
different, which could cause a problem if substituting one type for the
other, depending on the cap's circuit function. Also, if the cap is being
subjected to a high level of AC across it, which is why non-polarised types
are usually used, then a polarised type will probably not stand up to it for
very long, although in saying that, standard polarised electrolytics are
often used in the VFD supply multipliers in hifi's and although they do fail
because of the reverse stresses across them, they do last quite a long time.

Arfa
 
F

Franc Zabkar

Jan 1, 1970
0
I have to replace a small capacitor that had a lead ripped out when
the tv was dropped and the pcb broken.

It's a cylinder about a half inch high, a quarter inch in diameter,
with two leads at the bottom, and a narrowing near the bottom, like a
waist line, but it gets back to full diameter at the bottom.

It's black and says on it:

extra info
TL [in an elongated circle]
50v4.7uF --

CD71
40/085/10
N --

All my Googling suggests that "CD71" is a bipolar or non-polarised
aluminium electrolytic. Yours seems to be a standard temperature type,
ie -40C to +85C. The "10" may refer to the tolerance.

- Franc Zabkar
 
M

mm

Jan 1, 1970
0
A capacitor of this value and voltage rating could be either polarised, or
not. Usually, a polarised type is quite clearly marked, but an alternative
give-away is the PCB silk screening where it's located. If it is a polarised
type, there is a 99% certainty that one of the legs will be marked.
Sometimes the board will be marked with a " + " sign, and sometimes, there
will be a circle with one side shaded. The shaded side normally indicated
the " - " leg of the cap, and corresponds to a stripe on its body. The ESR

Thanks. OK, there are no polarity markings on the pcboard, so I
guess it is not.
figures for polarised and non-polarised electrolytics are usually quite
different, which could cause a problem if substituting one type for the
other, depending on the cap's circuit function. Also, if the cap is being
subjected to a high level of AC across it, which is why non-polarised types
are usually used, then a polarised type will probably not stand up to it for
very long, although in saying that, standard polarised electrolytics are
often used in the VFD supply multipliers in hifi's and although they do fail
because of the reverse stresses across them, they do last quite a long time.

The cap is on the other side of a resistor that is near the flyback,
and the other side of the cap goes to the pcb ground. I wish I could
say more than "near the flyback" but it's very hard to see. Later
today, I'll try to unscrew and move the pcb from the plastic frame
it's mounted to.


If you are inclined to email me
for some reason, remove NOPSAM :)
 
M

mm

Jan 1, 1970
0
I have to replace a small capacitor that had a lead ripped out when
the tv was dropped and the pcb broken.

It's a cylinder about a half inch high, a quarter inch in diameter,
with two leads at the bottom, and a narrowing near the bottom, like a
waist line, but it gets back to full diameter at the bottom.

It's black and says on it:

extra info
TL [in an elongated circle]
50v4.7uF --

CD71
40/085/10
N --

All my Googling suggests that "CD71" is a bipolar or non-polarised
aluminium electrolytic. Yours seems to be a standard temperature type,
ie -40C to +85C. The "10" may refer to the tolerance.

Thanks. I didnt' realize CD71 would be the part number.

Since I need 4.7uF, I have two polarised 50v 2.2uF caps of the same
appearance as the one I need to replace, that I was going to connect
in parallel, with the negatives connected together.

If instead I connected them in parallel with each negative connected
to the other's positive, would that give me the equivalent of a
non-polarised cap?
- Franc Zabkar


If you are inclined to email me
for some reason, remove NOPSAM :)
 
A

Arfa Daily

Jan 1, 1970
0
mm said:
Thanks. OK, there are no polarity markings on the pcboard, so I
guess it is not.


The cap is on the other side of a resistor that is near the flyback,
and the other side of the cap goes to the pcb ground. I wish I could
say more than "near the flyback" but it's very hard to see. Later
today, I'll try to unscrew and move the pcb from the plastic frame
it's mounted to.
I guess that the only way that you're ever going to know for sure, is with a
set of schematics and a reference number for the cap. No markings on the
board would suggest a non-polarised type, but the fact that one leg goes to
ground would suggest otherwise. As it's near the flyback, it could be
decoupling for a rail, but its value seems a little small for that, and the
value of the resistor would have to be pretty low if it was a flyback
derived rail. Could be a pulse integrator for use by some other piece of the
circuitry, but that also would not require the cap to be non-polarised. Bit
of a mystery really.

Arfa
 
A

Arfa Daily

Jan 1, 1970
0
mm said:
I have to replace a small capacitor that had a lead ripped out when
the tv was dropped and the pcb broken.

It's a cylinder about a half inch high, a quarter inch in diameter,
with two leads at the bottom, and a narrowing near the bottom, like a
waist line, but it gets back to full diameter at the bottom.

It's black and says on it:

extra info
TL [in an elongated circle]
50v4.7uF --

CD71
40/085/10
N --

All my Googling suggests that "CD71" is a bipolar or non-polarised
aluminium electrolytic. Yours seems to be a standard temperature type,
ie -40C to +85C. The "10" may refer to the tolerance.

Thanks. I didnt' realize CD71 would be the part number.

Since I need 4.7uF, I have two polarised 50v 2.2uF caps of the same
appearance as the one I need to replace, that I was going to connect
in parallel, with the negatives connected together.

If instead I connected them in parallel with each negative connected
to the other's positive, would that give me the equivalent of a
non-polarised cap?

To "make" a non polarised electrolytic, you have to connect two
electrolytics of twice the required value - in your case that would be 10uF
each - in inverse series. Usually, you connect the two ' - ' legs together
leaving the two ' + ' legs to go to the outside world. Each cap need only be
half the working voltage of the original non-polarised in theory, but it's
not a bad idea to make each one the same as the original as, depending on
what exactly is across the cap, you can't guarantee that the voltage will
divide equally between them. However, all that said, non-polarised caps are
readily available, so unless you are really stuck for obtaining one, it's
better to fit what was originally there.

Arfa
 
P

PeterD

Jan 1, 1970
0
Since I need 4.7uF, I have two polarised 50v 2.2uF caps of the same
appearance as the one I need to replace, that I was going to connect
in parallel, with the negatives connected together.

If instead I connected them in parallel with each negative connected
to the other's positive, would that give me the equivalent of a
non-polarised cap?

In series, either positive to positive or negative to negative (back
to back.) You need to compute the value that results (formulas and
calculators abound on the web...) but with just two, you'd end up with
half the capacitance so you need a couple of 10 uF caps (each rated at
50 volts).

However, series back to back capacitors are not (IMHO) a good
solution--better to go out and get the right part instead.
 
M

mm

Jan 1, 1970
0
To "make" a non polarised electrolytic, you have to connect two
electrolytics of twice the required value - in your case that would be 10uF

I remember that now from 10 or 20 years ago, although I never knew the
details you give below.

Thanks to you and Peter.

One more question for now. Like I said, the tv must have been droped,
even though there is no damage on that part of the case. I'm
soldering jumpers across all the broken traces.

But my supply of spare caps is small, I guess because I only inherited
a few and there are so many possible kinds to have.

So it will take me a while to get this one little cap. Can I apply
power to the tv without damaging anything if I have nothing where the
capacitor under discussion should go?

Or a bigger or smaller non-polarised one temporarily?


each - in inverse series. Usually, you connect the two ' - ' legs together
leaving the two ' + ' legs to go to the outside world. Each cap need only be
half the working voltage of the original non-polarised in theory, but it's
not a bad idea to make each one the same as the original as, depending on
what exactly is across the cap, you can't guarantee that the voltage will
divide equally between them. However, all that said, non-polarised caps are
readily available, so unless you are really stuck for obtaining one, it's
better to fit what was originally there.

Arfa


If you are inclined to email me
for some reason, remove NOPSAM :)
 
B

bz

Jan 1, 1970
0
In series, either positive to positive or negative to negative (back
to back.) You need to compute the value that results (formulas and
calculators abound on the web...) but with just two, you'd end up with
half the capacitance so you need a couple of 10 uF caps (each rated at
50 volts).

However, series back to back capacitors are not (IMHO) a good
solution--better to go out and get the right part instead.

Should there not also be a couple of diodes, one across each capacitor, to
prevent applying reverse voltage to either?

I seem to remember that electolytic do NOT like reverse voltage applied. It
removed the 'insulating layer' that has been electroplated on one of the
plates (that also serves as the dielectric). This tends to lead to high
current flow and breakdown. Since there is another capacitor in series, the
current will be limited, and the dielectric may reform when polarity is
right again, but I would not expect it to be very reliable.

http://yarchive.net/electr/electrolytic_caps.html
has some interesting information.







--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap
 
A

Arfa Daily

Jan 1, 1970
0
mm said:
I remember that now from 10 or 20 years ago, although I never knew the
details you give below.

Thanks to you and Peter.

One more question for now. Like I said, the tv must have been droped,
even though there is no damage on that part of the case. I'm
soldering jumpers across all the broken traces.

But my supply of spare caps is small, I guess because I only inherited
a few and there are so many possible kinds to have.

So it will take me a while to get this one little cap. Can I apply
power to the tv without damaging anything if I have nothing where the
capacitor under discussion should go?

Or a bigger or smaller non-polarised one temporarily?

Personally, without knowing the purpose of the cap, I wouldn't go ahead and
apply power. If it was in some kind of snubber circuit for instance, the
effect of it not being there might prove catastrophic to some following
semiconductor

Arfa
 
M

mm

Jan 1, 1970
0
Personally, without knowing the purpose of the cap, I wouldn't go ahead and
apply power. If it was in some kind of snubber circuit for instance, the
effect of it not being there might prove catastrophic to some following
semiconductor

Arfa
OK. Thanks.

If you are inclined to email me
for some reason, remove NOPSAM :)
 
A

Arfa Daily

Jan 1, 1970
0
bz said:
@4ax.com:


Should there not also be a couple of diodes, one across each capacitor, to
prevent applying reverse voltage to either?


In theory I guess, that works, but in practice, I don't think that it would
prove to be an issue

I seem to remember that electolytic do NOT like reverse voltage applied.
It
removed the 'insulating layer' that has been electroplated on one of the
plates (that also serves as the dielectric). This tends to lead to high
current flow and breakdown. Since there is another capacitor in series,
the
current will be limited, and the dielectric may reform when polarity is
right again, but I would not expect it to be very reliable.

http://yarchive.net/electr/electrolytic_caps.html
has some interesting information.

You are right that again, in theory, electrolytics do not like reverse
polarity, but I think that the trick to this is the duration / duty factor
of the reverse polarity. Electrolytics are subjected to AC across them in
many circuit locations, and sometimes, in output stages for instance, the
level of reverse voltage that they are subjected to can be quite
substantial, but it does not seem to cause any long term problems, except
when a cap with a poor ESR or insufficient basic voltage rating is used. One
particular hifi that I used to repair a lot of, springs to mind in this
regard. Both of it's output coupling caps used to fail open circuit, quite
regularly. Once they had been replaced with low ESR 105 degree types with
twice the voltage rating, there was never any further trouble. However, even
though caps in this sort of position do suffer reverse voltage across them,
the average duty factor is 50%, and the durations of the reverse excursions
are relatively short, all of which, I think, contributes to the scheme
working by and large, reliably.

As I said elsewhere, another area where electrolytics are subjected to a
severe reverse pounding, is in the voltage multipliers for VFD supplies. In
these circuits, they have transformer derived line-power frequency AC of
high levels across the multiplier input cap. Sometimes, ultimately, these do
fail - it's very common in Aiwa's for instance - leading to a dark display.
There also used to be a very popular Sony tape deck that was part of a
stacking system, where two normal polarised electrolytics were in the VFD
filament supply lines. These used to fail and wreck the display tube. Sony
supplied a revised type that was brown with gold writing, but it was still a
normal polarised type. However, the revised ones did not re-fail, so there
doesn't seem to be any hard and fast rule that designers stick rigidly to in
this regard.

Arfa
 
M

mm

Jan 1, 1970
0
Personally, without knowing the purpose of the cap, I wouldn't go ahead and
apply power. If it was in some kind of snubber circuit for instance, the
effect of it not being there might prove catastrophic to some following
semiconductor

Well, lucky me. This is one of 46 capacitors that Radio Shack sells,
and it's even one that they normally keep in the store, AND according
to the webpage, it is in 3 different stores near me.

That's a good thing, because I was having a lot of trouble keeping
myself from turning the tv on.

There is a store I know has every such part, but it's 6 times as far
away.


If you are inclined to email me
for some reason, remove NOPSAM :)
 
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