# Do I need a SUPER CAP?



## Truthman (Dec 13, 2008)

I will be running battery (RCC) eventually and was wondering if I will need a super cap on my QSI sound decoder boards? I have two GP40's with QSI now and no super caps installed. The sounds cuts out at about 6 volts or when I reverse direction on straight DC. Does anyone know what type of capacitor this is? Can it be purchased somewhere?


----------



## Nicholas Savatgy (Dec 17, 2008)

I use the caps on all my QSI boards and they work great, i run DC only. they cost about 16.00 each and soder on to the board easy, you can get them at any QSI dealer....


----------



## eheading (Jan 5, 2008)

Nick, what kind of idle time do you get with the super caps??

Ed


----------



## pimanjc (Jan 2, 2008)

Do you have pictures of the super cap installation?
JimC.


----------



## Greg Elmassian (Jan 3, 2008)

QSI site JC 

http://www.qsisolutions.com/products/techinfo/other/supercap_wiring.html 


If you don't reduce the voltage below 6 volts, the sound will stay on, and you can reverse the loco and take off.

If it's difficult for you to do this, you can add the supercap.


It can interfere with your using the reversing switch to run the horn or bell.... 

Regards, Greg


----------



## Nicholas Savatgy (Dec 17, 2008)

Ed, about 30 seconds or so. Jim, if when you said you? you ment me, why yes i do have a picture for you













Jeez i just looked at this photo and i really need to get my nails done.................. HAAAAAAAAAAA







he he he


----------



## acmartina (Jan 6, 2008)

Ok. I'll bite. What is a super cap?







Thanks,
Steve


----------



## altterrain (Jan 2, 2008)

Posted By acmartina on 03/30/2009 7:50 PM
Ok. I'll bite. What is a super cap?







Thanks,
Steve




cap = capacitor


----------



## Greg Elmassian (Jan 3, 2008)

large capacity in a small size... 

Stores enough energy to run the sound board for about 20 seconds when you go to zero volts and then into reverse.. 

Regards, Greg


----------



## Semper Vaporo (Jan 2, 2008)

A Capacitor is any two electrical conductors separated by an insulator. The "Capacitance" is directly proportional to the area of the two conductors and inversely proportional to the thickness of the insulator between them. The "Capacitance" is measured in "Farads".

The two wires in the extension cord to your reading lamp are a capacitor, but the area of the wires is really small and the insulator is relatively thick, thus the "capacitance" of the extension cord is really, really small... on the order of just a few nano-nano-nano-Farads... i.e.: so small as to be totally ignored except in some really esoteric and extremely rare circumstances.

Substitute the wires with two 1-ft square conductive plates and separate them with a sheet of thin glass and the capacitance ups to just a few nano-Farads. I have used one of these to store the charge from a Whimhurst machine (static electric discharge generator) and as part of the oscillator for a Tesla coil (generates extremely high Voltages... like... greater than 50,000 Volts.. pszap!







pszap! ) 

Substitute Mica for the insulator and you can get it really thin and the capacitor can be in the Pico-Farad range. These are rugged enough to use in radios and TVs in the Radio Frequency areas.

Change the plates to thin sheets of metal foil 2 inches wide and 100-ft long and the insulator to very thin sheets of wax paper the same size and roll it up tight in a small roll and you can get into the micro-Farad range and have a component that is small, and rugged enough to use in the power areas of radios, TVs, etc.

The down side to this miniaturization is that the thinner the insulator (known technically as the "Dielectric") the less Voltage it takes to jump an electrical spark through it and ruin its insulating properties and "short out" the capacitor. The sheet of glass can take 100,000's of Volts to short through. Mica may take 1,000's of Volts and wax paper can take maybe 100's of Volts to punch through.

An "Electrolytic capacitor" is one that has one metal plate (a thin foil roll) and the other conductor is made up of a chemical that reacts with the metal to produce the insulator on the surface of the metal. All it takes is a sheet of wax paper to keep the rolled up coil of metal foil from shorting to itself. These capacitors can range in the 100's of Farads. The working Voltage is in the 100's of Volts, but if you reverse the polarity of the Voltage applied to the device between the metal and the chemical, the insulating properties dissolves and the device is ruined.

I remember when we were studying capacitors in Tech school, someone asked how big a 1 Farad capacitor would be and the instructor scoffed at the question, saying that it would be so big as to be too big to work with and "there would be no possible use for it... except as maybe some sort of lousy short lifetime battery".

A year later I saw a display at Graham Electric (a radio/TV parts supply retailer) that was made up of one thousand capacitors connected in parallel that were rated at 1,000 micro-Farads each... thus it was a ONE-Farad capacitor... it covered the "end cap" of a display aisle of parts bins at the store... about 4-ft wide and 6-ft tall!

Several years ago someone figured out how to replace the foil and the paper with a semi-conductor growth that becomes the equivalent of the two conductors and the insulator. All three of the components (2 conductors and the insulator) are only a few atoms thick and the area of the conductors in on the order of thousands of square feet. Since the area is so large and the insulator is so thin the capacitance is into the 1,000's of Farads, but the component is just about the size of the last segment of your little finger. The working Voltage is often very small... on the order of just 10's of Volts.

BUT, because these capacitors are so huge (value-wise) they became known as "Super Caps". Charge-wise, they are beginning to rival some of the original carbon batteries, so their major use has been in surge suppression and power sustaining circuitry.


----------



## Truthman (Dec 13, 2008)

Good information thanks! Will I need a Super Cap to enjoy uninterrupted sound when under battery and radio control?


----------



## Semper Vaporo (Jan 2, 2008)

Posted By Truthman on 03/31/2009 10:59 AM
Good information thanks! Will I need a Super Cap to enjoy uninterrupted sound when under battery and radio control?


I wouldn't think so, unless you want the sound to continue after you disconnect/remove the battery. I suppose it could also be in the circuitry to act as some sort of filter to remove RF noise, but a regular capacitor should suffice for that. if it comes with the sound card, so-be-it, but if you are building all this stuff on your own, I don't think it would be necessary, at least for the purposes discussed here so far.


----------



## Greg Elmassian (Jan 3, 2008)

If you mean Gwire + QSI + Battery.... no... you don't need it. 

It's only needed when you are on track power and you go to 0 volts... then there is no power and the microprocessor resets... just like the rest of the sound systems, they have to have a backup battery if you go to zero volts on the rails. 

Regards, Greg


----------

