Why is it?

Guest
Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead? Just askin'
Eric

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com
 
On Tue, 18 Mar 2014 12:58:51 -0700, etpm wrote:

Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the positive
lead? Just askin'
Click to expand...

To confuse the hell out of us all?

I dunno -- but if you change the nomenclature on your circuit board to
make it more clear, expect to get it back from the assembly house with a
bunch of reversed caps.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
On Tue, 18 Mar 2014, Tim Wescott wrote:

On Tue, 18 Mar 2014 12:58:51 -0700, etpm wrote:

Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the positive
lead? Just askin'

To confuse the hell out of us all?

I dunno -- but if you change the nomenclature on your circuit board to
make it more clear, expect to get it back from the assembly house with a
bunch of reversed caps.

So it's a consistent standard in a reverse kind of way.
Click to expand...

Michael
 
etpm@whidbey.com wrote:
Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead?
Click to expand...

My guess is that just a - on the circuit board might get interpreted as
a "pin 1" mark, mechanical alignment mark, or just a mistake, whereas a
+ is less ambiguous. On PC motherboards, I often see a circle around
both capacitor leads, with the half-circle around the negative lead
filled in.

Sometimes you see the - or the + mark enclosed in a circle, especially
around batteries. This might be another attempt to make - less
ambiguous.

The next question is why the caps don't have a + mark instead. I have
heard that back in tube days, on wound capacitors that weren't even
polarized, it was common to mark the lead that went to the outer foil
layer. This might have been so you could use it for shielding; it may
or may not have gone to a more negative voltage than the other lead.
Maybe this is where the idea of "mark the negative" came from.

Matt Roberds
 
On 3/18/2014 10:55 PM, mroberds@att.net wrote:
etpm@whidbey.com wrote:
Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead?

My guess is that just a - on the circuit board might get interpreted as
a "pin 1" mark, mechanical alignment mark, or just a mistake, whereas a
+ is less ambiguous. On PC motherboards, I often see a circle around
both capacitor leads, with the half-circle around the negative lead
filled in.

Sometimes you see the - or the + mark enclosed in a circle, especially
around batteries. This might be another attempt to make - less
ambiguous.

The next question is why the caps don't have a + mark instead. I have
heard that back in tube days, on wound capacitors that weren't even
polarized, it was common to mark the lead that went to the outer foil
layer.
Click to expand...

Yup. Outside-foil-to-ground made a big difference.

This might have been so you could use it for shielding; it may
> or may not have gone to a more negative voltage than the other lead.

I haven't seen many positive-ground tube circuits.

> Maybe this is where the idea of "mark the negative" came from.

Could well be. Early metal-can electros were pretty much all intended
for positive supplies, being wired with the can as the common negative
terminal, but that might explain the marking of axials.

And I've recently come across radial lead electros with the _positive_
side marked with a bar. As the old saying go, "once you've seen one
tiger, the woods are full of them."

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Wed, 19 Mar 2014 11:36:01 -0400, Phil Hobbs
<hobbs@electrooptical.net> wrote:

On 3/18/2014 10:55 PM, mroberds@att.net wrote:
etpm@whidbey.com wrote:
Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead?

My guess is that just a - on the circuit board might get interpreted as
a "pin 1" mark, mechanical alignment mark, or just a mistake, whereas a
+ is less ambiguous. On PC motherboards, I often see a circle around
both capacitor leads, with the half-circle around the negative lead
filled in.

Sometimes you see the - or the + mark enclosed in a circle, especially
around batteries. This might be another attempt to make - less
ambiguous.

The next question is why the caps don't have a + mark instead. I have
heard that back in tube days, on wound capacitors that weren't even
polarized, it was common to mark the lead that went to the outer foil
layer.

Yup. Outside-foil-to-ground made a big difference.

This might have been so you could use it for shielding; it may
or may not have gone to a more negative voltage than the other lead.

I haven't seen many positive-ground tube circuits.

Maybe this is where the idea of "mark the negative" came from.

Could well be. Early metal-can electros were pretty much all intended
for positive supplies, being wired with the can as the common negative
terminal, but that might explain the marking of axials.

And I've recently come across radial lead electros with the _positive_
side marked with a bar. As the old saying go, "once you've seen one
tiger, the woods are full of them."

Cheers

Phil Hobbs
Click to expand...

Tantalums generally mark the + side.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On 03/20/2014 04:47 PM, John Larkin wrote:
On Wed, 19 Mar 2014 11:36:01 -0400, Phil Hobbs
hobbs@electrooptical.net> wrote:

On 3/18/2014 10:55 PM, mroberds@att.net wrote:
etpm@whidbey.com wrote:
Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead?

My guess is that just a - on the circuit board might get interpreted as
a "pin 1" mark, mechanical alignment mark, or just a mistake, whereas a
+ is less ambiguous. On PC motherboards, I often see a circle around
both capacitor leads, with the half-circle around the negative lead
filled in.

Sometimes you see the - or the + mark enclosed in a circle, especially
around batteries. This might be another attempt to make - less
ambiguous.

The next question is why the caps don't have a + mark instead. I have
heard that back in tube days, on wound capacitors that weren't even
polarized, it was common to mark the lead that went to the outer foil
layer.

Yup. Outside-foil-to-ground made a big difference.

This might have been so you could use it for shielding; it may
or may not have gone to a more negative voltage than the other lead.

I haven't seen many positive-ground tube circuits.

Maybe this is where the idea of "mark the negative" came from.

Could well be. Early metal-can electros were pretty much all intended
for positive supplies, being wired with the can as the common negative
terminal, but that might explain the marking of axials.

And I've recently come across radial lead electros with the _positive_
side marked with a bar. As the old saying go, "once you've seen one
tiger, the woods are full of them."

Cheers

Phil Hobbs

Tantalums generally mark the + side.


These were wet aluminums, though.
Click to expand...

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Tue, 18 Mar 2014 12:58:51 -0700, etpm@whidbey.com wrote:

Why is it that electrolytic caps have a line marking the negative lead
but the circuit board they get soldered into has a mark for the
positive lead? Just askin'
Click to expand...

That's the case (heh) with canned aluminum electrolytics but tantalums
are marked on the positive electrode. Obviously, therefore, boards
that are marked thusly are really intended for tantalum caps.

Just kidding! Damn, it's been a slow day...
 
On Tuesday, March 18, 2014 12:58:51 PM UTC-7, et...@whidbey.com wrote:
Why is it that electrolytic caps have a line marking the negative lead

but the circuit board they get soldered into has a mark for the

positive lead? Just askin'
Click to expand...

The line (and it isn't just on electrolytic capacitors, it appears on
nonpolarized caps too) indicates the OUTER CASE of the gizmo.
For signal-pickup reasons, it sometimes matters. If that outer
case can be grounded, signal pickup due to proximity to the
component is small.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top