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In Reply to: RE: Capacitor Orientation posted by Constrained 1 on May 29, 2007 at 20:49:55
I'm still a bit confused & would appreciate further clarification. This is not a polarized cap. Rather, its color-coding (as I believe you imply) indicates winding orientation in order to obtain proper shield-to-ground connection. The application is two film bypass caps used on V+ & V- powering an op amp: one cap with red lead to V+ power pin and green lead to ground, and the other cap (I'm guessing here) with red lead to V- power pin, and green lead to ground. Thus on V-, a color-coded non-polarized film cap would be in reverse orientation compared to a polarized electrolytic connected to V-. Even though V- is more negative than ground, wouldn't a nonpolar cap still want its shield dumped to ground? Am I correct?
Follow Ups:
"This is not a polarized cap. Rather, its color-coding (as I believe you imply) indicates winding orientation in order to obtain proper shield-to-ground connection."
And apparently the green lead is connected to the outer foil of the cap.
"The application is two film bypass caps used on V+ & V- powering an op amp: one cap with red lead to V+ power pin and green lead to ground, and the other cap (I'm guessing here) with red lead to V- power pin, and green lead to ground."
By attaching the green lead to ground you are in effect using the outer foil of the cap to "shield" the inner part of the cap. In SOME applications this may make a difference by reducing noise pickup.
"Even though V- is more negative than ground, wouldn't a nonpolar cap still want its shield dumped to ground? Am I correct?"
In theory and in this application - yes, you are correct. Whether it will make any difference is to be seen.
Interesting. I wonder about the shielding comment. If nothing else, make sure you orient them the same way.
Bill
"I wonder about the shielding comment."
What is it you wondering about?
I just found it interesting. I wonder if I could try it out on other caps I have but I would have to dissect one to see which lead is which. I also wonder if I could hear a difference if I got that far. I do find that interesting enough to consider trying it.
I typically use Sonicaps if I can as I find them the most benign and they seem to let the data through without masking much of the low level detail information. Out of habit I wire them in the same direction as the writing under the assumption that the writing is in line with the construction. That may be a bad assumption. Maybe I will have to dissect a few and see.
Bill
You can apply a signal to a cap and if you have a scope you can put the probe on the surface of the cap. If you apply the signal to one lead of the cap and then the other the scope will show one lead connection has a stronger signal on the cap surface - that's the one connected to the outer foil or plate (it's right under the surface so the signal is stronger than the other which is further away).
The Sonicap people should be able to tell you which lead is connected to the outer foil, try giving them a shout.
Except at RF frequencies the shielding effect is a non-issue in my experience. But as the old saying goes "a little chicken soup can't hurt", so try it if you want since it costs nothing. It may help if you have strong RF fields in the vicinity of your gear.
Thanks.
I'll be dissecting a 1.5uf Sonicap cap this weekend just to see.
Bill
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