Question about capacitor

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southsider
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Question about capacitor

Post by southsider » Fri Sep 11, 2015 8:45 am

Hey everyone, I had a question.

I'm recapping some of my input modules on my console, and ran across a a few caps that don't seem to have a positive or negative.

Most all of them have the negative side labeled, and the spot on the PCB where they go looks like this -) |-

However, these other ones, although they look just like all the radial caps on the module, don't have a negative side labeled. They have similar ratings, such as 25V 47uf or 16v 100uF or whatever, but once again, dont' appear to have a positive or negative side. They mount the same way as the others (two leads coming from the same side, wrapped in a black casing)

Could these be "non polarized capacitors"?

Anyone know what these things are called so I can order the proper ones?

Thanks in advance,

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Post by Snarl 12/8 » Fri Sep 11, 2015 9:56 am

What does the symbol on the schematic look like for these possibly non-polarized capacitors look like? I believe it should be || or similar. And for the polarized it should be +)|- (or maybe, -)|+ ) IIRC.
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Post by Drone » Fri Sep 11, 2015 10:08 am

They could be, but it's more likely that the -ve is just labelled in some other fashion.

I imagine they do make radial non-polarized electrolytics, but all the ones I've seen have been axial, for use in crossovers and the like.

The schematic, hopefully also has a comprehensive parts list?

Do you have any pictures of them? Worth a 1000 words and all that :D
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Post by southsider » Fri Sep 11, 2015 12:05 pm

I don't have the manual with me at the moment, but I do have it, and I'll check. If I remember correctly, the PCB was labeled -| |- , but I need to double check.

I'll work on getting a picture as well. (but i still use a flip phone and cant quickly upload a photo)

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Post by Drone » Fri Sep 11, 2015 12:17 pm

What's the module from?
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Post by Scodiddly » Fri Sep 11, 2015 5:57 pm

Not all caps have a positive/negative. If the values are fairly low then they're most like ceramic or film caps, and there's no polarity for those. It's only when you have electrolytic or tantalum caps that you have to worry about polarity.

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Re: Question about capacitor

Post by Drone » Fri Sep 11, 2015 6:20 pm

Well he did say
southsider wrote:However, these other ones, although they look just like all the radial caps on the module, don't have a negative side labeled. They have similar ratings, such as 25V 47uf or 16v 100uF or whatever, but once again, dont' appear to have a positive or negative side. They mount the same way as the others (two leads coming from the same side, wrapped in a black casing),
So figure those values are likely electrolytics.
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Post by dfuruta » Fri Sep 11, 2015 6:29 pm

Most of the nonpolarized electrolytics I've used are marked with "BP" for bipolar.

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Re: Question about capacitor

Post by Scodiddly » Fri Sep 11, 2015 7:14 pm

Drone wrote:Well he did say
southsider wrote:However, these other ones, although they look just like all the radial caps on the module, don't have a negative side labeled. They have similar ratings, such as 25V 47uf or 16v 100uF or whatever, but once again, dont' appear to have a positive or negative side. They mount the same way as the others (two leads coming from the same side, wrapped in a black casing),
So figure those values are likely electrolytics.
Good point.

A photograph would be remarkably useful.

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Post by Drone » Sat Sep 12, 2015 6:09 am

Or even the make/name of the module :mrgreen:

But hey, it's half the fun round here.
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Post by Jim Williams » Sat Sep 12, 2015 8:03 am

Bipolar EL caps will not have the black stripe down one side with a - sign on it. Otherwise, the markings for them can be anything.

Best to use a DVM and check the DC offsets facing each cap first, most manufacturers don't do that so many cases the cap is wired in the wrong way and doesn't get the proper bias for a low THD reproduction.

Use high quality, low impedance caps like Panasonic FR series, enlarge the values to extend the low end and reduce phase shift. Wire in the + lead towards the positive DC offset, - towards the negative DC offset.

Bipoar caps are really two polarized caps connected internally, double the losses. If you find DC offsets below about 5 mv, usually you can remove that cap and use a wire in it's place. The best cap I ever heard was a piece of wire.
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Post by ashcat_lt » Sat Sep 12, 2015 8:51 am

Jim Williams wrote:Bipoar caps are really two polarized caps connected internally, double the losses. If you find DC offsets below about 5 mv, usually you can remove that cap and use a wire in it's place. The best cap I ever heard was a piece of wire.
Schematics help immensely, but measuring voltage will probably answer the question too.

I personally can't imagine a reason for a cap that large except as a bypass for a power supply node somewhere along the line. Straight wire there would usually cause malfunction if not destruction. Course, you would be seeing a significant voltage at that point...

It's worth mentioning that you can make your own bipolar cap from two appropriately sized polars exactly by connecting the negative legs together. Probably won't fit in the original hole unless maybe you use axial caps.

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Post by Jim Williams » Sat Sep 12, 2015 10:25 am

I've never seen a bipolar el cap used for psu decoupling, they are polarized with a black stripe showing polarity. Knowing what you are doing is first before anything else.

Don't let the smoke out.
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Post by ashcat_lt » Sat Sep 12, 2015 2:01 pm

Jim Williams wrote:I've never seen a bipolar el cap used for psu decoupling, they are polarized with a black stripe showing polarity. Knowing what you are doing is first before anything else.

Don't let the smoke out.
No, I agree. I just can't think of any place that a cap that big would do any good AND need to be bipolar. Course, it's all speculation for us out here without a schematic...

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Post by dfuruta » Sun Sep 13, 2015 1:14 pm

Bipolar caps show lower distortion than polarized electrolytics (Douglas Self, among others, has written about this) of the same size. The phantom blocking cap on a mic preamp will often be 47uF or bigger; the voltage would be higher, though.

Bipolar caps are easy to source (from digikey, mouser, or wherever) and not terribly expensive. It's probably there for a reason...

"NP" is another relatively common marking on those.

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