# Capacitors Sort of Explained, Maybe



## Bwells (Mar 30, 2014)

Caps

DISCLAIMER: do not believe what follows as it was written by someone that is a newbie to the field of electronics. Written solely to gain some insight from those that understand the actual functions of a capacitor and as a platform to correct anything that is stated.


Okay follow along with my silly reasoning. First off, a cap is a “smoothing device” in that it absorbs any ripple current and provides a more uniform current, possibly acting as a filter. Here is my reasoning. Remember when you had a Yamaha Twin 100 and the battery was dead so you pulled it out and stuck it in your pocket. Backpacks hadn’t been invented yet. You knew the bike would run so you took your 5 dollar allowance and the battery and headed to the motorcycle shop, bought a new one with 37 cents change and headed home. However it was getting dark so you clicked on the lights which worked fine until you brought up the R’s, POOF, out goes the lights. Why? The battery was acting as a smoothing capacitor to prevent surges . Here is another one, although a stretch, but you have all been in an old house that when you turn off the water and immediately you hear a bang bang briefly. This is due to “hammering” as the flow was abruptly stopped and the pipes will bang against nearby wood framing. This can be eliminated with the use of an air lock, kind of like a shock absorber and slow the flow down and smooth it out (capacitor). Next, my favorite, is a capacitor as a battery. The bigger the better! They will store voltage for future use or to supply for intermittent outages (keep alive). This is my main use for a capacitor. They do seem to hold the stored charge for quite awhile, I would expect it to leak out somewhere but it stays put.

Okay folks, lay it on me as I’m sure I screwed up!:dunno:


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## wvgca (Jan 21, 2013)

decent explanation ...


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## Bwells (Mar 30, 2014)

Really? Okay, how about this one. Unfiltered DC is what comes out of a bridge rectifier (spikes and all) however by placing a capacitor in parallel with the leads will transform it into filtered DC. In this case, the capacitor is now acting as a filter. This could be the same as the smoothing function above but with a different name. It appears there are many names for the same device depending on what you are using it for.


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## time warp (Apr 28, 2016)

Bwells said:


> Really? Okay, how about this one. Unfiltered DC is what comes out of a bridge rectifier (spikes and all) however by placing a capacitor in parallel with the leads will transform it into filtered DC. In this case, the capacitor is now acting as a filter. This could be the same as the smoothing function above but with a different name. It appears there are many names for the same device depending on what you are using it for.


 Basically a capacitor resists change, evident even in the battery comparison.
EVERYONE PLEASE NOTE THAT THE CAPACITOR IS PLACED IN PARALELL IN THE ABOVE EXAMPLE. NOT SERIES.
If you don't know the difference between series and parallel circuits please ask. A lot of confusion will be avoided that way.


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## Bwells (Mar 30, 2014)

Yes, caps in parallel. Ed is the only one that can take a sound cap and put it in series with a single speaker lead and have good results. (just kidding). This bring us to our next topic, super capacitors. These are rated a low voltage, 5 or less. Not really good for anything above that unless you put two in series Say you want giant capacitance. You aren’t going to get it with electrolytic caps unless you have a lot of room. Super capacitors are the answer (SC). The problem is their voltage rating. Usually too low for a small MR project unless you put two in series. Take an 8 volt circuit, one won’t do but if you series two you have increased their maximum voltage rating to 10. That is running them at 80% which is plenty of headroom. Problem is the trade off. Caps in series lowers the total capacitance to half. So two 5v 1F SC in series gets you 10 volts and .5F. If the circuit is 12 volts, you need three to get to 15v but your total capacitance is now .33 . Super caps are small for what they do but they aren’t cheap. The above numbers are assuming you are using the same capacitance rating for all in series. You can mix and match them but then you need to use a formula to find the total capacitance. It will always be less than the smallest one.
Even though you have series two SC together they will still need to be installed in parallel with the circuit.
Here is a quick drawing using 2 SC in series and then paralleled with the circuit. I drew in two resistors which I understand are for balancing the voltage between the two SC. This is done to avoid one from getting more than it’s allotted amount. In this case a resistor has now become a balancing resistor, still a resistor but with a new name. 







From what I understand, the resistors are not the best way to go but a zener diode would work much better. Well I have heard the term zener diode but not sure what it does so I googled it and used wikipedia. Here is an excerpt:
The device was named after Clarence Melvin Zener, who discovered the Zener effect. Zener reverse breakdown is due to electron quantum tunnelling caused by a high strength electric field. However, many diodes described as "Zener" diodes rely instead on avalanche breakdown. Both breakdown types are used in Zener diodes with the Zener effect predominating under 5.6 V and avalanche breakdown above.
Okay, cool, that helped! Clear as mud now, eh. To be continued, maybe.


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## traction fan (Oct 5, 2014)

*Capacitor stories*



Bwells said:


> Caps
> 
> DISCLAIMER: do not believe what follows as it was written by someone that is a newbie to the field of electronics. Written solely to gain some insight from those that understand the actual functions of a capacitor and as a platform to correct anything that is stated.
> 
> ...


 First you are correct that a capacitor is like a battery in that it stores an electric charge, and both can hold the charge for a long time. The difference between the two is the way they release their charges. A battery lets its charge out slowly. A capacitor lets its charge out much faster, often all at once. 
Here are a pair of "sea stories" related to capacitors. One from my older brother's navy service, and the other from my own. (We were both navy electronics techs though at different times,) Sailors get bored on long cruises. They have been known to relieve the monotony by pulling pranks on their shipmates. My brother was no exception. He would charge up a capacitor with a suitable voltage, then leave it lying around where someone was likely to pick it up. When the victim managed to touch the terminals of said capacitor in the process of moving it he would receive a painful, but not dangerous, electric shock. This would cause the "shockee" to leap about screaming things like"Oh my goodness I have received a shock"; and related things a sailor might say under such trying circumstances! This caused great amusement among my brother's colleagues, who were waiting to see the show. They developed the following motto and later, (when they had run out of potential victims) posted in the electronics shop. "beware ye of the un-discharged capacitor! Lest it cause you to fall upon thy buttocks in an un-seaman like manner thereby incurring the scorn of thy fellows!" 

My own "capacitor" story involves a brash young sailor from NEW YORK CITY, as he proudly boasted to anyone who would listen. This guy absolutely knew it all, at least in his own mind!
He was one of the techs in our radar shop. We repaired radar on the F-4 Phantom jet fighters of our squadron. Now in these radars there is a notorious part called a klystron. It acts like the "capacitor from hell." A klystron stores about 10,000 volts. Fortunately the current from it is low enough that it won't kill you, but it will hurt a lot and cause you to jump if you are dumb enough to touch it! This hazard is well known among the people who work on radar.The part is painted bright red and carries a clearly visible, printed warning label. There is an adjustment on a klystron which you should only adjust with an insulated screwdriver not your fingers. Also, like its cousin the capacitor, a klystron dumps its entire charge instantly. Once discharged it can't shock you again until it;s recharged. 
Well our arrogant, Mr. know-it-all from NYC, put a bit too much faith in that last characteristic of a klystron one day. He was adjusting the klystron, after supposedly discharging it, and suddenly jumped back yelling that he'd been shocked ( in naval language!) Then he brilliantly stated that, " It must be discharged now!" and proceeded to repeat his athletic and verbal performance! As he was scrapping his sorry body off the flight deck for a third attempt; some of us managed to stop laughing long enough to point out the large cable extending down from the aircraft. It was basically a giant extension cord that supplied (constant) power from the ship to the plane's electrical system. We pointed out to or worthy fellow technician that since electricity travels at 186,000 miles per second; It could probably recharge the klystron before he could get up and go grab it again!:smilie_auslachen:


Traction Fan:smilie_daumenpos:


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## Tom_C (Jan 8, 2016)

Brian, this reminded me of the buck-boost discussion, so I went back to that thread to read you updates....

Anyway. This looks like a good place for a buck-boost (or just a buck) circuit. Adjust it down to 4-5v and then use it to drive your LED and SC.


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## gunrunnerjohn (Nov 10, 2010)

Don't forget that with EDLC capacitors (supercaps), the internal resistance is all important to note, depending on your application. The small coin style units have very high capacitance and 5V ratings, but the internal resistance is many ohms, so they will only deliver a few milliamps before losing a lot of their voltage to the internal resistance. It's not as simple as selecting the capacitance and voltage rating like using a standard electrolytic capacitor.


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## Bwells (Mar 30, 2014)

I was wondering about that. I noticed for a 5v radial can, the ESR ranges between 8mΩ to 500mΩ yet a 5.5v button ranges from 3.5Ω to 75Ω. Which is better?


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## gunrunnerjohn (Nov 10, 2010)

Note that the 8M ohms is eight milli-ohms, or .008 ohms! Obviously, the lower ESR will deliver more current. Let's say you wanted 250ma and you could only handle a .2 volt drop of your 5V capacitor. Simple ohms law says you could tolerate a maximum ESR of 800mΩ.


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## Tom_C (Jan 8, 2016)

I really didn't know about SCs so I just did a very quick read on them, and IMO they may not really be useful in a circuit like you want to use, IE, supplying current for an extended period of time in the event of losing power.

ADDED: Perhaps I'm wrong based on this... need to read more.

http://ieeexplore.ieee.org/abstract/document/1218178/?reload=true


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## gunrunnerjohn (Nov 10, 2010)

That really depends on what you're trying to power. I have designed a replacement battery for the RailSounds in Lionel based locomotives that uses the supercap for power storage. This powers the sound when running in conventional mode for direction changes, etc. and replaces the alkaline batteries that tend to leak when they get a couple years old.

New JWA Project, TMCC Permanent Battery

Once the cap is charged, it'll power the RailSounds board for around 12 seconds.


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## Tom_C (Jan 8, 2016)

Lets see the circuit!


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## gunrunnerjohn (Nov 10, 2010)

Sorry, you have to buy one to get the circuit. 

There's more in there than you might imagine, two complete voltage regulator circuits as the first charges the capacitor to 5V, the second is a boost supply to output the 9V battery voltage.


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## Tom_C (Jan 8, 2016)

Buy it, where?


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## Bwells (Mar 30, 2014)

gunrunnerjohn said:


> Note that the 8M ohms is eight milli-ohms, or .008 ohms! Obviously, the lower ESR will deliver more current. Let's say you wanted 250ma and you could only handle a .2 volt drop of your 5V capacitor. Simple ohms law says you could tolerate a maximum ESR of 800mΩ.


Thanks John for that info, makes sense. Looks like the cans are the way to go over the buttons but the extra .5 volt would be handy. Always sacrifices.


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## gunrunnerjohn (Nov 10, 2010)

Tom_C said:


> Buy it, where?


It will appear in the Henning's Trains Web Store when they're in stock. Should be within a couple of weeks.


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