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Bi-polar electrolytic capacitors vs. polarized
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lucid



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PostPosted: Thu Jan 03, 2013 2:29 am    Post subject:  Bi-polar electrolytic capacitors vs. polarized Reply with quote  Mark this post and the followings unread

Hello
My name is Milan
I am quite new here and started with DIY just few weeks ago. Studying everything from scratch and also from this great forum.

I made one wrong purchase when buying parts for my Klees - bought bi-polar electrolytic 10microF/25V caps instead of polarized ones, it is used for decoupling I think (C19 and C20 analogue board).
Tried to search for such topic or basic info but failed.

Can someone help and explain if bi-polar capacitor can be used instead of polarized, especially here?
[Well it will help to explain also where else it can be used, or to give some good direction where to find such answers.]

If cannot be used as replacement in my case, what can I use from alternatives I have:
polarized 10microF/50V
polarized 22microF/25V
???
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JovianPyx



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PostPosted: Thu Jan 03, 2013 5:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Welcome to electro-music.com and enjoy your new addiction! Cool

nonpolar electrolytic capacitors can be used instead of polar ones. The only things that are important are the value in uF and the voltage rating.

And where you need nonpolar and you don't have them, you can use 2 polar ones and connect them in series with + to +. In that case, you need to double the capacitance needed for each capacitor because they are in series and the capacitance halves when in series. The voltage for both can be the same as what is needed. That is, if you need 5 uF at 50 volts, you can use two 10 uF at 50 volts in series (connecting + to +) and the aggregate capacitance will be 5 uF with a voltage rating of 50.

EDIT: Argh... I wrote this post way before coffee... I had used the word "bipolar" which wasn't right, so I edited the post. I should also state that this information is rather general. Regarding bypass capacitors in particular, in my own opinion, they are (at least) usually not electrolytic as these are rather large in capacitance and too much capacitance can cause inrush current problems for the PSU. However, there may be circumstances under which electrolytics are beneficial, it's just not common. Bypass caps are there to reduce noise generated by (especially) digital ICs and also to form a sort of mini local power supply for individual ICs since they are connected very close usually to each IC). This means that the PCB trace resistance is very low due to the short distance between the bypass cap and the IC and therefore pulse current will be easier to supply to an IC from them "easier" than from the longer rail traces. This becomes more important when the width of the rail traces is small. As Jan points out below, nonpolar electrolytics are more expensive and usually physically larger than polar ones. Internally, I believe that nonpolar electrolytics are actually two series connected polar electrolytics.

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Last edited by JovianPyx on Thu Jan 03, 2013 12:25 pm; edited 2 times in total
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analog_backlash



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PostPosted: Thu Jan 03, 2013 5:44 am    Post subject: Re: Bi-polar electrolytic capacitors vs. polarized Reply with quote  Mark this post and the followings unread

Hi Milan and welcome Here's my thoughts on the subject.

lucid wrote:
I made one wrong purchase when buying parts for my Klees - bought bi-polar electrolytic 10microF/25V caps instead of polarized ones, it is used for decoupling I think (C19 and C20 analogue board).
Tried to search for such topic or basic info but failed.

Can someone help and explain if bi-polar capacitor can be used instead of polarized, especially here?
[Well it will help to explain also where else it can be used, or to give some good direction where to find such answers.]

If cannot be used as replacement in my case, what can I use from alternatives I have:
polarized 10microF/50V
polarized 22microF/25V
???


C19 and C20 are power supply decoupling capacitors which always use polarized electrolytics. They are there to reduce any non-DC content from the power supply reaching the circuit. This may be residual ripple from the AC supply, or that picked up from another circuit running on the same power supply. A non-polarised capacitor will allow both the positive and negative-going portion of an AC signal to be transmitted, so will not be effective here. One of the major uses of non-polarised electrolytics is in loudspeaker crossover units, where a large value capacitor is required, but it must be able to transmit an AC signal.

Depending on which version of the circuit that I look at, I see that C19 and C20 are specified as 10uF/25V or 10uF/35V. If your version states 35V, then I'd probably use the 10uF/50V. The only problem I've heard of when using a higher working voltage capacitor, is that once used, they may not work at their original specified working voltage again. This is purely academic, since you are unlikely to be removing and reusing them! If your version states 25V, then I would not see a problem in using the 22uF/25V capacitors.

Gary
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analog_backlash



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PostPosted: Thu Jan 03, 2013 6:13 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
Welcome to electro-music.com and enjoy your new addiction! Cool

Bipolar electrolytic capacitors can be used instead of polar ones. The only things that are important are the value in uF and the voltage rating.

And where you need polar and you don't have them, you can use 2 polar and connect them in series with + to +. In that case, you need to double the capacitance needed for each capacitor because they are in series and the capacitance halves when in series. The voltage for both can be the same as what is needed. That is, if you need 5 uF at 50 volts, you can use two 10 uF at 50 volts in series (connecting + to +) and the aggregate capacitance will be 5 uF with a voltage rating of 50.


OK JovianPyx beat me to it and disagrees! I have never seen non-polarized capacitors used in this kind of application and I always thought that there was a good reason for this. Perhaps it's just that you need a reasonably large value capacitor and the polarized types are easier to come by. I did also look at this document:

http://electro-music.com/forum/phpbb-files/em_klee_build_issue4_123.pdf

Here, the word Polarized has been underlined for C19 and C20, so the author also thought that this was important.

If I am wrong about this, I apologise, but could you explain why either type is OK?

Gary
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Blue Hell
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PostPosted: Thu Jan 03, 2013 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:
[...]I always thought that there was a good reason for this. Perhaps it's just that you need a reasonably large value capacitor and the polarized types are easier to come by.


Yup, and price of course, but no principal reason ... the polarized ones are the compromise really as a trick to make large valued capacitors.

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analog_backlash



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PostPosted: Thu Jan 03, 2013 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Jan. One of these days, I'll get something right Laughing

Still, it's all part of the learning process...

Gary
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lucid



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PostPosted: Thu Jan 03, 2013 9:09 am    Post subject: Reply with quote  Mark this post and the followings unread

If I understood it correctly, with polarized caps you need to be pretty sure how you place them in circuit. Otherwise could happen that only two legs will remain there...
from wiki:
"Most electrolytic capacitors are polarized and require one of the electrodes to be positive relative to the other; they may catastrophically fail if voltage is reversed. This is because a reverse-bias voltage above 1 to 1.5 V will destroy the center layer of dielectric material via electrochemical reduction. Following the loss of the dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst, often in a spectacularly dramatic fashion.

To minimize the likelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity is very clearly indicated on the case.
...
Special capacitors designed for AC operation are available, usually referred to as "non-polarized" or "NP" types. In these, full-thickness oxide layers are formed on both the aluminum foil strips prior to assembly. On the alternate halves of the AC cycles, one of the foil strips acts as a blocking diode, preventing reverse current from damaging the electrolyte of the other one."


Does it means that bi-polar (or non-polarized) could be used, just it is more expensive and bigger with the same capacitance?

Is there any other reason to use polarized for decoupling?

another interesting reading:
decoupling - http://en.wikipedia.org/wiki/Decoupling_capacitor

edit:
Also asked Scott, here is the answer:
"You know - I honestly don't know if bi-polar caps are appropriate as bypass caps or not! I've never thought about it; Googling didn't seem to give any good answers, either. You might pose this question on the forum - someone like Ian Fritz would probably know definitely one way or the other. I'd hate to say that it was OK, then have your Klee go >poof< one day."
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JovianPyx



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PostPosted: Thu Jan 03, 2013 4:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bottom line here for me (as in this is my opinion and your milage may vary) is that the there can be a fair amount of variance in what will work and what will not. That said, it's probably best to use the exact specified components for a published circuit. Especially if the circuit is popular and known to be well designed by the fact that if the exact specified components are used, then the circuit works well and does so for a good long span of time.

In the long run, substitutions should be made only when the exact specified components cannot be obtained and either you yourself posess the knowledge and experience to get the substitutes to work well enough or you have a source of reliable alternative knowledge. Yes, I do understand that there are times when we as DIYers kinda blow it and order the wrong stuff. And yes, I understand that components cost money. I, myself, have quite a collection of stuff that I wish I hadn't purchased. heh - there's always Ebay... OR the "save-it" bin where you toss stuff that didn't make it to a project. Surely, I would agree that it's economically best not to do that, but hey, this is Earth and we are just naked apes... Cool Again - all that said - perhaps the best way to deal with that is to re-buy the correct parts when we've made such errors, take a deep breath, have a beer and get on with life... well, that's what I do anyway... And I can tell you that there are times when I've been saved by having that "save-it" bin... But then I've been doing this for more than 30 years... (oh yeah, you should see my "save-it" bin)

BTW, I have a couple of SPI SRAMs (128 Kbytes) that are 2.2 volt that I can't use because my needs are 3.3 volt... Confused

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analog_backlash



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PostPosted: Thu Jan 03, 2013 5:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like a good philosophy for approaching a project JovianPyx.

I don't have so much of a "save-it" bin, more a "hoard-it" heap, which contains not only things I bought by accident, but also components that I thought might come in useful one day (especially if they were being sold off at ridiculously low prices - end-of-line stuff etc). I also have lots of scavenged components (I never throw away anything with a circuit board in it). I just go to the dump with anything left over that I can't see a use for, usually rattling around in a sack.

BTW, unlike some I could mention (you know who they are) I don't get pissed off when I'm proved wrong - life's too short for having stupid arguments. I either accept them as something new I've learned, or if I still really don't agree, I leave it as it is. I started posting on this web site to try to learn as much as possible and to enjoy the exchange of ideas, not to start rows with people that I don't even know.

So, if have posted a load of crap on here, don't hesitate to correct me - I don't bite back...

Gary
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Blue Hell
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PostPosted: Thu Jan 03, 2013 6:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
BTW, I have a couple of SPI SRAMs (128 Kbytes) that are 2.2 volt that I can't use because my needs are 3.3 volt... Confused


The wonder world of modern electronics ... these days there are more power supplies and level shifters on my PCBs than stuff that actually does something Shocked (component wise).

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JovianPyx



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PostPosted: Thu Jan 03, 2013 6:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Damn it, Jan, that's funny because today while I was in the shower I was actually thinking if I could make some funky diode weirdness to use those 2.2v RAMs in a 3.3 volt circuit Shocked

And Gary, you're doing just fine. heh, if I could give the correct answer 100% of the time, they'd call me God - which I am most certainly not. I welcome being corrected, because if I'm following a misconception and making crappy designs, I'd rather be informed of that than keep doing it wrong. That's why I love this community, I've learned more than plenty here and know that I've still got plenty more to learn from all of you.

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Last edited by JovianPyx on Thu Jan 03, 2013 7:09 pm; edited 1 time in total
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PostPosted: Thu Jan 03, 2013 7:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah! DDIHLL [1] Cool




[1] Diode Diode Integrated High Level Logic

Laughing

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JovianPyx



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PostPosted: Thu Jan 03, 2013 7:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Got a schematic? Cool
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PostPosted: Thu Jan 03, 2013 7:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

I scribbled it somewhere .. oh wait I'm not Fermat Shocked
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PostPosted: Thu Jan 03, 2013 7:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Uh, making a bipolar out of two polarized is done by connecting + to +? I thought it was - to - .... and I have at least one wired up that way right now. Am I in trouble and need to go fix that?
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PostPosted: Thu Jan 03, 2013 7:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

as far as I know it doesn't really matter, but I connect - to - too.
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PostPosted: Thu Jan 03, 2013 7:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

+ / + or - / - whats the difference .. it's a symmetric situation .. half of the time of an AC sine one of the caps is polarized backwards.

So why do they survive at all Shocked

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PostPosted: Thu Jan 03, 2013 7:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

heh, yeah, I've just always seen it + to + in schematics, but there's no electrical reason that you couldn't do - to -. And yeah, Jan, I have the same question, for half the cycle of AC, one cap is backwards... why does that work?... but it does, so I just accept...
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PostPosted: Thu Jan 03, 2013 8:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

maybe because it's AC and not reversed DC dunno , something tells me you should not try it with tantalum caps.
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elmegil



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PostPosted: Thu Jan 03, 2013 8:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'll pay $5 to the first person who tries to make purple smoke with tantys Smile
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PostPosted: Thu Jan 03, 2013 10:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
I scribbled it somewhere .. oh wait I'm not Fermat Shocked


And I'm not Andrew Wiles...

Thomas Henry
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PostPosted: Fri Jan 04, 2013 3:32 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
Uh, making a bipolar out of two polarized is done by connecting + to +? I thought it was - to - .... and I have at least one wired up that way right now. Am I in trouble and need to go fix that?

etc. etc.

Just looked at the LFO circuit diagram for the Transcendent 2000 synth I built several hundred years ago (well it feels like that) and that uses two 1uF capacitors - to - and it still works fine (well apart from the fact that the keyboard contacts need replacing).

JovianPyx wrote:
And Gary, you're doing just fine. heh, if I could give the correct answer 100% of the time, they'd call me God - which I am most certainly not. I welcome being corrected, because if I'm following a misconception and making crappy designs, I'd rather be informed of that than keep doing it wrong. That's why I love this community, I've learned more than plenty here and know that I've still got plenty more to learn from all of you.

Thanks for that - don't feel so Embarassed now.

Gary
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PostPosted: Fri Jan 04, 2013 5:03 am    Post subject: Re: Bi-polar electrolytic capacitors vs. polarized Reply with quote  Mark this post and the followings unread

ow, where are my manners,

lucid wrote:
Hello
My name is Milan
I am quite new here and started with DIY just few weeks ago. Studying everything from scratch and also from this great forum.


welcome party!

as scott allready mentioned, it can be quite addictive, so you are warned Cool

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frijitz



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PostPosted: Fri Jan 04, 2013 9:45 am    Post subject: Reply with quote  Mark this post and the followings unread

lucid wrote:
Does it means that bi-polar (or non-polarized) could be used, just it is more expensive and bigger with the same capacitance?

The Klee schematic is not public, and I don't know if Scott specified a particular type of electrolytic, so there is no way to tell if there is some special situation here. But in general, your statement above is correct. At any rate it's not going to blow anything up, so go ahead and use the bipolars if you like.

Ian
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lucid



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PostPosted: Fri Jan 04, 2013 10:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks to all, and specially to Ian, as he was recommended by Scott Stites as reliable source of wisdom. study
I will go ahead...
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