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bbcmicro
October 27th, 2006, 03:20 AM
What (If there any) Is the difference between say, a ceramic capacitor and an electrolytic capacitor? Are they interchangable/interchangable for certain purposes?
There's loads of ciruit diagrams out there that never specify which type to use, so I'm a tad confused as to what the difference is. This includes all the other types too.

ziloo
October 27th, 2006, 07:08 AM
Electrolytic capacitors are used for low frequency, high capacity
applications and they are "polar" meaning that one leg (that is noted
on the capacitor) must be connected to negative, and the other must be
connected to positive supply. One of their use is as low frequency filter in
power supplies :idea:.

Ceramic capacitors are typically used in high frequency, low capacity
applications. One of their use in computers is for filtering high frequency
noise from the system :idea:.

Because electrolytic caps (capacitors) are polar, they cann't be interchanged
by ceramic caps and vice versa :wow:!

bbcmicro
October 27th, 2006, 07:33 AM
hmm...So what is accepted as low frequency? Hz, kHz?

Is there a way to tell which type of cap is meant by looking at the circuit diagram, and not its actual use?

carlsson
October 27th, 2006, 08:17 AM
I thought the symbols on the circuit diagram are different, or at least supposed to be different. A ceramic capacitor is two filled vertical bars, while the electrolytic one has one filled and one unfilled bar and a plus sign? Or maybe my memory suffers from bit rot after being many years since I tried to read a such diagram. In any case, a bit of Google help should get you on track until someone with the proper skills answers here.

ziloo
October 27th, 2006, 09:14 AM
Non-polar caps are represented by two (filled) parallel bars, or two
parallel lines. The polar electrolytic caps are represented by two
parallel bars, one filled and another which is the positive side is
bordered and not-filled. IIRC, in older referencs, they used a different
representation for electrolytic caps :confused:.

If you get yourself an introductory book in electronics, it shows you
the standard notations for representing various electronic parts.
Googling is nice and there are zillion electronic sites with loads of
material, but it is better to have a "hard copy" reference book to
begin with :wink:. There is also circuit simulator that is a software you
setup on your computer, and then you draw the circuit diagram using
its CAD utility, and then it simulates what the circuit is supposed to
do. It alows you to measure the voltage, and current at any location
you want, and it also has an oscilloscope feature that lets you see the
instantaneous behavior of the circuit :sly:. This sort of software is
usually referred to as a SPICE variety.

Best wishes

carlsson
October 27th, 2006, 09:58 AM
But are there non-polar electrolytic caps? I admit I'm a noob in these matters, but I thought there is a 100% correlance between polar = electrolyte and non-polar = other (ceramic).

ziloo
October 27th, 2006, 10:41 AM
polar = electrolyte and non-polar = other (ceramic).

It was a matter of semantics; I wanted to emphasize that electrolytic caps
are polar!

DimensionDude
October 27th, 2006, 11:39 AM
But are there non-polar electrolytic caps? I admit I'm a noob in these matters, but I thought there is a 100% correlance between polar = electrolyte and non-polar = other (ceramic).

Yes, there are non-polarized electrolytic capacitors. If I remember correctly, non-polarized caps are typically used in the output coupling of low-powered audio amps.

A rule of thumb for determining whether a capacitor in a schematic should be ceramic or electrolytic is by the value. Usually, ceramics have very small values, nano or picofarads. Electrolytics have higher values, from 1 to several thousand microfarads.

Kent

ziloo
October 27th, 2006, 11:48 AM
Yes, there are non-polarized electrolytic capacitors....
Kent

That, I didn't know!! Go figure...

ziloo
October 27th, 2006, 12:30 PM
That, I didn't know!! Go figure...

Well folks, I did go figure:

http://news.elektroda.net/polar-vs-nonpolar-capacitors-vt66669.html

It seems that we are all right (isn't that a beautiful world?!! :sigh:)

bbcmicro
October 27th, 2006, 01:49 PM
thanks all, that celared that up!
another question; When looking at caps online, I find one with the right capacitance, say 1 microfarad, but it says operating voltage is 63v. Does this mean I cant use it on a say, 3v power supply on a PCB?

chuckcmagee
October 27th, 2006, 05:00 PM
I believe those are MAXIMUM voltage figures, above the voltage they start breaking down. Soooo, will work fine for 3v (or 10v or 20v).

DimensionDude
October 27th, 2006, 05:56 PM
Yep, what chuckcmagee said. That voltage rating is the maximum sustained voltage that should be applied. Running the cap at a lower voltage is perfectly acceptable with 2 caveats. The higher the voltage rating, the larger the capacitor will be physically (for the same capacitance rating). Also, electrolytics that are driven well below their voltage rating may lose their capacitance value over time. It's a chemistry thing, I think, as an electrolytic works more like a rechargeable battery than the classic two plates separated by a dielectric.

Kent

bbcmicro
October 28th, 2006, 04:10 AM
Thanks all, I can carry on tinkering now!

Matty.

bbcmicro
December 10th, 2006, 09:32 AM
Anuzzer question:

Is this an electrolytic capacitor symbol?

---|(---

There's a little plus sign next to the right of the pipe

I'm guessing it's a varient of

---||---

nige the hippy
December 10th, 2006, 10:25 AM

DON'T GET IT WRONG! applying the wrong polarity to an electrolytic (whether by putting it in the wrong way round, or as I did, putting a rectifier diode in the wrong way round) can cause "non-passive failure" as a small hole in my bedroom ceilling, and a room full of noxious wadding snow bore witness to!

electrineer
April 16th, 2011, 05:41 AM
Anuzzer question:

Is this an electrolytic capacitor symbol?

---|(---

There's a little plus sign next to the right of the pipe

I'm guessing it's a varient of

---||---

I have always seen symbols for nonpolar capacitors representing the negative side with the curved line, with the positive side represented as a straight line. Reference this link:

http://en.wikipedia.org/wiki/Electrolytic_capacitor#Polarity

Double check your schematic. I'm not sure where you read that the curved line represents positive, but that doesn't seem right to me.

electrineer
April 16th, 2011, 05:44 AM

DON'T GET IT WRONG! applying the wrong polarity to an electrolytic (whether by putting it in the wrong way round, or as I did, putting a rectifier diode in the wrong way round) can cause "non-passive failure" as a small hole in my bedroom ceilling, and a room full of noxious wadding snow bore witness to!

I have always seen symbols for nonpolar capacitors representing the negative side with the curved line, with the positive side represented as a straight line. Reference this link:

http://en.wikipedia.org/wiki/Electrolytic_capacitor#Polarity

Double check your schematic. I'm not sure where you read that the curved line represents positive, but that doesn't seem right to me.

eeguru
April 16th, 2011, 06:42 AM
Some misinformation here.

- The use of capacitor symbol varies from country to country - region to region. The only required mark that need to be present for a polarized cap is which end is + (and conversely which end is -).
- Capacitors are capacitors. They can be interchanged. Ceramic caps are the cheapest to make but generally have a low threshold on when their max capacitance and voltage make the size impractical for electronics. Though Murata did just came out with a 150uF layered SMD ceramic!
- Electrolytic are generally more expensive, but have a much practical physical size ratio vs high capacitance/voltage. So they are more commonly seen as voltage buffer caps on power supply lines to prevent sag when current draw changes.
- Tantalums are a middle ground but at a cost premium. They have the similar physical appearances to ceramic but are polarized so they always have a polarity indicator. And generally marry the density of electrolytic values with sizes comparable to ceramic - for a price.
- Electrolytics are sealed with a wet dielectric so they will eventually dry-out and short. A tell-tell sign is bulging top. Tantalums are good replacements but react very badly but spectacularly to over-voltage.

Chuck(G)
April 16th, 2011, 09:00 AM
Wow, nothing like posting on a 5-year old thread! :)

eeguru
April 16th, 2011, 09:44 AM
Wow, nothing like posting on a 5-year old thread! :)

Well this is a vintage forum!

MikeS
April 16th, 2011, 09:55 AM
Wow, nothing like posting on a 5-year old thread! :)And adding more misinformation to the misinformation ;-)
- Capacitors are capacitors. They can be interchanged.Sometimes true, but quite often not.

- Electrolytic are generally more expensive, but have a much practical physical size ratio vs high capacitance/voltageHigher capacitance than most other types, but generally a much lower voltage rating.

- Electrolytics are sealed with a wet dielectric so they will eventually dry-out and short. A tell-tell sign is bulging top.Two different problems; an aging electrolytic can dry out, but will generally lose capacitance (i.e. open, not short). The bulging top problem was mainly the result of bad manufacturing; those did sometimes short out.

Gerry_MAN
June 5th, 2011, 12:41 PM
Hey Folks,

I thought I would jump in here on this discussion and share some of the info that I've been taught in College and see what perspectives you Gurus have regarding it.

I'd love to get feedback regarding this Capacitor topic to solidify my understanding and make sure that it is correct.

So my understanding is that as far as swapping capacitors goes, between Ceramic and Electrolytic... the answer is No! Each type of capacitor serves a specific purpose.

In Digital circuits the small ceramic capacitors are present in the circuits to remove High frequency noise from the DATA lines on your Data Bus. The noise that manifests here is referred to as "Crosstalk noise".

This Crosstalk noise occurs due to a small capacitance that forms between the PCB Traces by being so close together. The gaps between the traces act like the Gap between the plates in a capacitor. So sometimes when one trace has a higher voltage than the adjacent trace (Logic 1 or 0) the pulse can sometimes cause the adjacent line to pop high for a nanosecond. This high "Pop" or voltage spike is the Crosstalk noise. So these ceramic caps are connected to remove this high frequency noise. Also, this is the reason that Circuit boards will have "Ground planes" present. ( Large area of the PCB covered with copper.) The ground Planes provide a more attractive and direct route to Ground for the noise.

Now, Electrolytic capacitors are there for filtering the noise present on the Power supply voltage lines which is a Lower frequency noise. As an example, when someone decides to use a Wall power adapter to run their electronic device or allot of the time, there is a transformer and voltage rectifier internally installed in the unit like in a stereo Amplifier.

The noise on the power supply wires comes from the voltage rectification process which entails converting the AC voltages generated by the Hydro Power plant Generators (Sinewave oscillations) to DC.

When this AC is converted to DC with a Voltage rectifier circuit... by those little Black boxes we all plug into the wall sockets to power our favorite electronic devices; there is a slight popping "noise" that occurs when the negative half of the AC voltage Sinewave is forced to go positive by the diodes in the Voltage rectifier circuit
(again this is within your little Black box adapters). So my question for you GUrus is this: Technically, isn't the noise on the Power supply lines actually generated by the Diodes within the Voltage rectifier circuit? I've had some people tell me that it is present on the Hydro Pole AC power lines.

Regardless, this noise has to be filtered out and is the reason for the Electrolytic Caps.

Now when you use Batteries, there is no AC to DC rectification happening, so there is no power supply noise at all. Batteries are the cleanest and Noise free source am I right?

I've heard that some Military systems will use Batteries as a Power supply noise filter. Essentially swapping between Battery banks while the other is being charged and these circuits are both isolated from each other.

That's about it as far as I've learned regarding Caps and noise.

Any feedback regarding my understanding on this would be appreciated.
Again, I just want to make sure I have the proper understanding regarding Capacitors and circuit noise.

Thanks Folks!
-Gerry

eeguru
June 5th, 2011, 02:07 PM
Caps are caps. They maintain an electric field between two conductors separated by a dielectric. Electrolytic, layered ceramic, and tantalum are just different physical constructions of the same thing. Those physical construction properties may require voltage to always be maintained in one direction - hence polarized caps (electrolytic, tantalum and others). In general you can replace any cap with any other so long as the rated operating levels are not exceeded and if the replacement is a polarized cap, voltage is always maintained in the proper direction.

You generally see a voltage supply trace feeding to an AC coupled capacitor pad and then to the supply pin on an IC to prop up switch sag. When transistor junctions turn on and off in a digital IC the corresponding power draw changes with it. No power supply is ideal. There is always a steady state power constant. Whenever the instantaneous current draw changes, the power stays constant and the voltage sags for an instant. This creates noise on the power supply voltage. This switch noise feeds back on the power supply rails and can affect other components in the system. The AC coupled cap is there to prop up the power rail locally so the voltage sag cause by digital switching is minimized. Same is true in a battery supplied system.

Ground pours on PCB are generally done to create as low of an impedance path back to ground as possible. The wider the copper trace, the lower the impedance. And in some systems they help dissipate heat.

rebeltaz
June 5th, 2011, 10:46 PM
I work on televisions everyday and quite often come across bipolar (BP) electrolytic caps. When I don't have a bipolar electrolytic, it's a simple matter to make one using two standard electrolytic caps tied in series with either the two positives or the two negatives tied together (doesn't matter which) using caps with twice the required microfarad rating and at least the same voltage rating. Just in case anyone ever needs that knowledge....