electrolytic capacitor and polarity of AC

Discussion in 'General Electronics Chat' started by PG1995, Jul 31, 2011.

  1. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    Hi

    Please help me to understand how an electrolytic capacitor work.

    1: Please have a look here; you would find my question there. Thank you.

    2: Can we use electrolytic capacitor with DC?

    Regards
    PG
  2. Kermit2

    Kermit2 Well-Known Member

    Joined:
    Feb 5, 2010
    Messages:
    2,494
    electrolytic capacitors are very similar to batteries as concerns how they react to the polarity of voltages. They should NOT be used with AC voltages.

    Google can provide you many examples of the construction and chemistry of these capacitors. You simply give some key words and then look through the hundreds of thousands of results; click on one to read what it has to say.

    ;)
  3. Kermit2

    Kermit2 Well-Known Member

    Joined:
    Feb 5, 2010
    Messages:
    2,494
  4. PeeSeeBee

    PeeSeeBee Member

    Joined:
    Jun 17, 2011
    Messages:
    43
    Location:
    London. UK
    You can use electrolytics in ac circuits (audio amplifiers are full of them), but not in the way you have shown in that diagram. Don't build that circuit. A capacitor appears as a low resistance to ac (depending on value & frequency). The capacitor will get hot very quickly & may explode.

    For electrolytics to work properly they have to have a voltage across the terminals for the chemical reaction to take place. This voltage must be correctly polarised (i.e. the +ve terminal must always be more +ve than the -ve terminal). So as a coupling capacitor in an amplifier, for example, you can use an electrolytic to couple the ac (audio) to the next stage, as long as the circuit is arranged such that a dc voltage is across the capacitors terminals.

    As for using them with dc circuits. Look at most circuit diagrams & you will see them across the dc power supply connections.
  5. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    Thank you, everyone.

    Actually I was wrong in a way. Because electrolytic capacitor is in fact used with DC. For AC, there are special kind of electrolytic capacitors.

    I have read that 'regular' capacitor can store very little amount of charge in comparison to a electrolytic capacitor and that's the reason they are preferred over 'regular' or 'normal' capacitors. Is this really so? Please let me know. Thank you.
  6. SgtWookie

    SgtWookie Expert

    Joined:
    Jul 17, 2007
    Messages:
    22,093
    Location:
    In the vast midwest of the USA; CST
    Just to make sure you're understanding it; there are "polarized electrolytic capacitors" and "non-polarized electrolytic capacitors".

    The polarized type are by far the most common. When we mention electrolytic caps on here, we're talking about the polarized type, unless we specifically state non-polarized or "NP".
  7. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    Thank you for the clarification, Sgt.

    Regards
    PG
  8. Adjuster

    Adjuster Well-Known Member

    Joined:
    Dec 26, 2010
    Messages:
    2,147
    Location:
    London UK (GMT)
    In typical DC applications at moderate voltages, electrolytic capacitors generally can store more energy than other types. They are very popular for many uses, and may be the only practical choice in certain applications, such as some power supplies and compact photographic flash equipment.

    On the other hand, they have a number of limitations which can make alternative types more appropriate. Here is my list - I expect I will have missed some things out.

    1. The commonest types of electrolytics are polarised, as already mentioned.
    2. They have relatively wide value tolerances, perhaps tens of percent.
    3. They have larger leakage currents than almost any other capacitor type.
    4. They have relatively low Q-values (aka large loss angles, or high esr). The above limitations restrict their use in filtering applications, apart from smoothing filters in power supplies. You would not expect to tune a radio with an electrolytic.
    5. They can be more prone to generating distortion products than some other types. There is a degree of controversy here, but some designers of high-fidelity audio systems do not recommend their use in sound equipment, at least within the signal path.
    6. They can be made for use up to several hundred volts, but are unavailable above about 1kV (unsure of the exact limit).
    7. NP or AC rated electrolytics often cannot be used continuously at their maximum ratings, and may be more suitable for short-term work such as motor starting.
    8. Their life expectancy and reliability is not as good as some other types. This has been improving over the years, but recently some very poor devices have come on to the market.
    9. If left un-powered for long periods of time, some electrolytics may fail if powered up again abruptly without a re-forming process - but this applies mainly to old equipment.
    10. Their operating temperature range is limited, often with a steep trade-off of lifespan versus temperature.
    11. They are sealed devices containing fluid, often not truly hermetic. This can lead to pressure limitations, and can pose a contamination hazard.
    Electric capacitors may therefore not be permitted under the design rules for certain very high reliability products.

    http://electrochem.cwru.edu/encycl/art-c04-electr-cap.htm

    http://en.wikipedia.org/wiki/Capacitor_plague
  9. Bill_Marsden

    Bill_Marsden Moderator Staff Member

    Joined:
    Mar 24, 2008
    Messages:
    19,233
    Location:
    Dallas, TX (GMT-5 w/ DST)
    There is an exception to these rules, a way to use two polarized caps with AC. It works, though I can't really explain the mechanism. I think it is how they make non polarized electrolytics.

    [​IMG]

    One of the explanations I've heard (and I don't claim it is true) is the correctly polarized cap takes up all the strain, while the other basically conducts slightly.
  10. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    I genuinely appreciate your help, Adjuster, Bill. I understand it takes much times and effort to help others. Thanks a lot.

    1: I think in the linked image, the caps on the left side of the red 'line' are electrolytics, and on the right regular/normal ones, please correct me if I'm wrong:
    http://img641.imageshack.us/img641/7758/capshn.jpg

    2: In the linked image on the left side of ICs you have transistors:
    http://img818.imageshack.us/img818/3044/semiconductors.jpg

    Are ICs (integrated circuits) pre-fabricated circuits which work as a unit in a circuit in which they are used?

    Thank you for your time and help.

    Regards
    PG
  11. Bill_Marsden

    Bill_Marsden Moderator Staff Member

    Joined:
    Mar 24, 2008
    Messages:
    19,233
    Location:
    Dallas, TX (GMT-5 w/ DST)
    The bottom two of the electrolytics may or may not be electrolytics. They could be foil/paper types. I think I see a value of 4.7nf, which would mean they're not.

    When it comes to ICs, the datasheet is everything. Pretty close for the transistors too, come to think of it.
  12. Adjuster

    Adjuster Well-Known Member

    Joined:
    Dec 26, 2010
    Messages:
    2,147
    Location:
    London UK (GMT)
    The lowest two silvery-looking capacitors with axial leads look more like polystyrene or some other plastic film capacitors.

    Integrated circuits are pre-fabricated circuits, most commonly made on a piece of silicon. (Did you seriously have to ask that?). Some are made to perform a specific and pretty much complete task, like providing all the electronics for a wristwatch.
    Others are meant to be used as sub-units in a bigger system
  13. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    I was watching this video on UTube and thought it might be useful to someone like me who stumble onto this thread:

    http://www.youtube.com/watch?v=z47Gv2cdFtA

    I didn't know that ICs also contain resistors and capacitors; I thought they contains in themselves only semiconductor components - i.e. diodes and transistors.
  14. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    Thank you for your replies, Bill, Adjuster. You guys are very helpful without any attitude. :)


    1: Do ICs ever contain inductors?


    2: Computer processors are also ICs. In the video in my previous post the presenter compares the size of an IC and its equilant circuit in 'normal' form. How large would an equivalent circuit of a modern day processor (IC), let's say Intel P4, be?


    3: Almost every computer processor has its Hz rating. Nowadays processors come in GHz ratings. Wht does this frequency rating mean? A computer works in digital mode, i.e. on and off state. So, does this Hz rating tell how many times an invidual transistor can turn on and off without damaging itself? I don't want to get into technical details of this. So, please it involves some very technical details then you can skip this query. Thanks.


    Many thanks for all your help.


    Regards
    PG
  15. bertus

    bertus Administrator Staff Member

    Joined:
    Apr 5, 2008
    Messages:
    12,609
    Location:
    Amsterdam,Holland (GMT + 1)
    Hello,

    When making a non-polarized capacitor out of two electrolitic capacitors, one capacitor will act as a wet rectifier.
    See this quote from the wiki for more info:

    This comes from this wiki page:
    http://en.wikipedia.org/wiki/Rectifier

    Bertus
  16. Bill_Marsden

    Bill_Marsden Moderator Staff Member

    Joined:
    Mar 24, 2008
    Messages:
    19,233
    Location:
    Dallas, TX (GMT-5 w/ DST)
    1. Almost never. There is a fairly simple circuit (simple to build that is, the math is horrendous) called a gyrator, which takes the properties of a capacitor and flips them around where it simulates an inductor. This is only useful for filter and what not, real inductors store power and have properties that make them uniquely useful for things like switching mode power supply regulators (either voltage or constant current). It makes SMPS extremely efficient, much more so than linear versions.

    2. Consider this, a 4Gig memory chip has a minimum of 4 billion transistors. It can be multiples of that (12 billion say). A modern CPU is every bit as complex. Each transistor only uses a few pico watts, but when you multiply that extremely low power by the billions you can see why heat sinks and fans are needed. Modern fabrication techniques add some redundancy to these chips, so if a section doesn't work they can switch in the spare section and get their $250 for the part, you will never notice.

    3. Unfortunately, marketing has dug its grubby little hands in Mhz and Ghz rating, where it is now a joke. If you read the fine print concerning these numbers they will tell you it "act like" 2.5Ghz, where the actual clock speed of the chip is 1.3Ghz.

    Clock speed is pretty simple. Think of the various counters you may have encountered, the square wave that drives them is the clock speed. By making function parallel in CPUs they have figured out various ways of speeding up the internal operations. This is how marketing gets by with lying to the consumer. Back with a CPU chip was rated at 500Mhz this was a true rating.

    It goes without saying that they are still working on faster and smaller transistors. This is what is driving the power increases in modern computer. If you go to the Science forum you will see I've started a thread concerning Graphene. If it lives up to its promise it will be the next high speed semiconductor material, with corresponding increases in switching speeds. The ultimate may be superconducting transistors, but who is to say at this point?
  17. doinky

    doinky New Member

    Joined:
    Jul 19, 2011
    Messages:
    12
    So much theory for such a simple mechanism as foil.
  18. #12

    #12 AAC Fanatic!

    Joined:
    Nov 30, 2010
    Messages:
    9,586
    Location:
    15 miles west of Tampa, Florida
    Referring to post #8, point #5

    There is a property called dielectric absorbtion. This means that power is used up (lost) in heating the insulating layer in a capacitor. It is a bad thing. Electrolytic capacitors have more dielectric absorbtion that any other type of capacitor. This is a good reason to NOT use them to pass a musical signal through.

    The metal film capacitors are much better at this property. Most famous are Sprague brand "Orange Drops". When designing music amplifiers, this is very important.
  19. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
    Thank you, #12, for your input.

    Thanks a lot, Bill. I really appreciate your effort to help me. Unfortunately, some of the things I didn't understand because of my very limited knowledge. I'm very naive with this technical stuff. These days I'm trying to grasp the bigger picture of how these things work without getting into very technical details.

    1: I should try to rephrase my original query to make it more clear:
    Suppose a modern day processor (IC) takes an area of 3 sq. inch, then how much area or space an equivalent circuit of that processor had taken if it were made before IC evolution? A room? Please watch the video in the post #13 from 3.00 onward.

    2: I think I should also rephrase the query about the frequency rating, MHz, GHz, etc. In my practical life I have never seen a square wave. What I understand so far is that the frequency rating only tell the maximum rate at which transistors in the chip can work. If the frequency is 20 Hz then that would mean that a transistor could turn on and off 20 times a second. And if we try to run transistor at a frequency larger than the specified then it would get damaged. Do I make any sense? I don't know any exact search terms to search this topic on UTube, could you please help?

    3: In the linked diagram I have tried to show that how, in my opinion, an IC is made. It's only a very, very 'rough' attempt. Please let me know if I have it right. Thanks.

    Link: http://img96.imageshack.us/img96/7445/imgtp.jpg

    I offer my thanks for all the guidance and your time.

    Regards
    PG
    Last edited: Aug 4, 2011
  20. PG1995

    PG1995 Thread Starter Active Member

    Joined:
    Apr 15, 2011
    Messages:
    753
Similar Threads
Forum Title Date
General Electronics Chat Mixing electrolytic capacitors Oct 6, 2014
General Electronics Chat Which series Electrolytic Capacitor to use Mar 7, 2014
General Electronics Chat Electrolytic Capacitor life time calculation Oct 12, 2013
General Electronics Chat Reflow ovens and electrolytic capacitors Oct 5, 2013
General Electronics Chat ELectrolytic Capacitor for Reducing Wiring Effective Inductance Oct 2, 2013

Share This Page