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royalmp2001
Guest
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 Posted:
Tue Feb 22, 2005 2:05 am Post subject:
Need help with Tantalum polarity |
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This is my first project using tantulum capacitors.
I cannot tell from the markings what the polarity is.
I see a "+" that is halfway between the leads (maybe slightly nearer
the left lead) and there is a bold upside down "L" to the right of that
which is still between the leads but now slightly nearer the right
lead.
Which is lead is which please?
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Larry Brasfield
Guest
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Tue Feb 22, 2005 4:21 am Post subject:
Re: Need help with Tantalum polarity |
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"royalmp2001" <royalmp2001@hotpop.com> wrote in message
news:1109015399.913618.222160@c13g2000cwb.googlegroups.com...
| Quote: | This is my first project using tantulum capacitors.
I cannot tell from the markings what the polarity is.
I see a "+" that is halfway between the leads (maybe slightly nearer
the left lead) and there is a bold upside down "L" to the right of that
which is still between the leads but now slightly nearer the right
lead.
Which is lead is which please?
|
I cannot tell from this distance. The devices must
be misprinted if the polarity indicator is ambiguous.
I would look at the collection you have, (of the same
make and type) and see whether some of them have
a less ambiguous indication. Then use that polarity
for all of the similar set.
Be sure to stand back or wear goggles when you
first apply power. Backwards tantalum caps can
spew molten blobs of tantalum in a random direction.
You don't want to rely on the blink reflex to limit the
damage to merely superficial scars.
You could measure leakage with a cap in series with
a large resistor, biasing the string at the rated voltage.
If the cap is backwards, it will probably leak a lot
more than when properly biased. This can be done
without the danger of red hot streamers mentioned
above, if the resistor is at least a few K Ohms.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me. |
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royalmp2001
Guest
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| Posted:
Tue Feb 22, 2005 5:28 am Post subject:
Re: Need help with Tantalum polarity |
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I have 19 of these tantalums and some are the same and the rest have
the "+" smack bang in the middle and the inverted "L" above the right
leg.
What does the inverted L mean? Is it "-ve" or is it meant to point to
where the "+" lead is?
I cannot test these at the rated voltage as I do not have a 35V supply.
Any ideas anyone?
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Matt J. McCullar
Guest
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| Posted:
Tue Feb 22, 2005 6:08 am Post subject:
Re: Need help with Tantalum polarity |
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Sad so say that sometimes tantalum capacitors get printed with the text
off-center, and therefore you get this ambiguous marking occasionally.
Tantalums do NOT like being connected backward, so I recommend trying to
attach it to a DC power supply at its rated voltage. Mark which way you've
connected it; and if it blows up, then you know that's the wrong way to do
it. Yes, one must be sacrificed for the good of the rest. |
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Bob
Guest
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| Posted:
Tue Feb 22, 2005 6:09 am Post subject:
Re: Need help with Tantalum polarity |
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Try this (at your own risk):
Connect two to a power supply. Connect them in parallel, but one must be
reversed from the other). Note their hookup (i.e., their polarity with
respect to the polarity of the applied voltage). Anything up to the rated
voltage is okay.
Put the two caps in a protective enclosure (like a strong box). Wear eye and
ear protection.
Turn on the supply. The one that either blows up, or gets hot (check after
you've turned off the power) is the one that was hooked up incorrectly.
Throw out the one that got hot (or blew up).
Bob
"royalmp2001" <royalmp2001@hotpop.com> wrote in message
news:1109028509.859298.253960@g14g2000cwa.googlegroups.com...
| Quote: | I have 19 of these tantalums and some are the same and the rest have
the "+" smack bang in the middle and the inverted "L" above the right
leg.
What does the inverted L mean? Is it "-ve" or is it meant to point to
where the "+" lead is?
I cannot test these at the rated voltage as I do not have a 35V supply.
Any ideas anyone?
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Rich Grise
Guest
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| Posted:
Tue Feb 22, 2005 6:10 am Post subject:
Re: Need help with Tantalum polarity |
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On Mon, 21 Feb 2005 15:28:29 -0800, royalmp2001 wrote:
| Quote: | I have 19 of these tantalums and some are the same and the rest have
the "+" smack bang in the middle and the inverted "L" above the right
leg.
What does the inverted L mean? Is it "-ve" or is it meant to point to
where the "+" lead is?
I cannot test these at the rated voltage as I do not have a 35V supply.
Any ideas anyone?
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A reasonable guess would be that, if they're all from the same batch,
they're probably the same, polarity-wise. Look at one that is clearly
marked, and then look at the rest with the same orientation - if the
marking is merely displaced, that won't change the polarity of the part.
Good Luck!
Rich |
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royalmp2001
Guest
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| Posted:
Wed Feb 23, 2005 2:51 am Post subject:
Re: Need help with Tantalum polarity |
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Thank you everyone for your input. I went with gut instinct and
connected one of these critters to 20VDC and stood far back. I had the
positive going to the right leg under the inverted "L" or bar sign, and
it didn't explode or get hot. |
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