Capacitors. The math behind the myth!

[SterTheDer]

To say caps don't work is false. Caps do work and have a place i'm car audio. They are not a fox soul for voltage drop but with a strong electrical a cap bank can help stiffen voltage and help sustain voltage for longer time periods. A 1"farad bank can be made for around $400-500 and with a nice ho alt can power a fairly decent size system. Right now a battery is cheaper but as technology advances and the price to manufacture caps drop so will the price of caps. The biggest issue with caps is people usually only know about the cheap ones that shops try to push out the door with a fancy volt meter on it. A real cap that will benefit a system are the carbon caps/Supercaps/ultra caps.

To say that caps dont work is to say that high octain fuel is useless.... for the majority of people that will be the case, but only because they are using it wrong!

Please exsplain how they "stiffen voltage and help sustain voltage for longer time periods"?

I believe i have already shown how absolutely pathetic small capacitors (sub 10farad) are, giving very few watts of usable power...

You are correct that they do stiffen and sustain, because they resist the change in voltage.. but for small capacitors this resistance to change in voltage (Capacitance) is so small as to be nearly negligable.

a 1 farad bank can be had for under $50 if you buy from Boss audio XD

Ebay has some nice deals on super caps, from Maxwell.. for less than 300...

http://www.ebay.com/itm/181238407262

380 Farad cap bank for $200

I completely agree with your last statement, the amount of miss-information and speculation is absolutely astounding, hence why i made this thread

More math (For the 380 farad cap)

E = (1/2)* C * V^2

Joules(Watt-seconds) = (1/2) * Capacitance (Farads) * Voltage^2

380 farad capacitor:

E= (1/2) * 380 * 14.8^2

E = ~41,617 Joules of energy.

This is how many Watt-Seconds the 1farad capacitor can supply from 14.8 volts down to 0 volts.

to figure out how much power would be supplied to the system, we calculate the difference in stored power across our voltage drop.

380 Farad capacitor:

14.8v = ~41,617.6 Joules. <- Vehicle charging voltage. The ideal maximum voltage your car will see.

12.8v = ~34,129 Joules <- Battery voltage. The maximum voltage your batteries can supply.

Now, we calculate the voltage drop and receive the amount of power the capacitor contributed to the system!

(Drop from 14.8v -12.8 ) 10,488 Watt seconds.

10kw for 1 second

5kw for 2 second

2.5kw for 4 seconds

1,250w for 8 seconds

675w for 16 seconds

That cap.. for 200... i am fully planning on getting myself one or more to go with my DC XP270 When i get it... instead of dumping more batteries into my poor car

[alaskanzx5]

honestly I cant tell you the math behind it or how it works. I can just say that I have seen it work. now it never fully took care of the issue but it was a starting point.

imo, if your pulling say 300amps with your stereo and 50 for the car and have a 350amp alt with an agm battery but voltage will sometimes fall to battery voltage a nice 500+cap bank would work nicely. sure you could add another batt but the amp wont pull power from the batt until you get down to battery voltage again. the added batt will just sustain you at battery voltage longer. a cap will "stiffen" voltage to keep you above battery voltage for a longer period of time. between moments where the amp is really drawing power and not (breaks in lows for example) will allow 4-5 sec for that cap to charge and it will charge faster then a battery in those 4-5 sec. might not completely charge but enough to help hold you above battery voltage longer. by stiffening I mean they help keep voltage with in a smaller range while slowly dropping down lower. might not last long but for those bursts of power needed to keep things above voltage on music it will work. that's all assuming your power supply can keep up or only needs help on the short bursts.

if you haven't yet check out the Maxwell 3000bcap on ebay. think they are around 50 each right now. 6 in series is a 500f bank charging voltage up to 16.2 if I remember right. that with a nice agm battery and ho alt and you could run 1.5-3krms... would have roughly 330 amperage draw and a 300 amp alt could just about power that. add in a 100ah battery and a 500farad cap and your good to go. should stay above 13v easily maybe even in the high 13s if the wiring is solid.

[SterTheDer]

honestly I cant tell you the math behind it or how it works. I can just say that I have seen it work. now it never fully took care of the issue but it was a starting point.

imo, if your pulling say 300amps with your stereo and 50 for the car and have a 350amp alt with an agm battery but voltage will sometimes fall to battery voltage a nice 500+cap bank would work nicely. sure you could add another batt but the amp wont pull power from the batt until you get down to battery voltage again. the added batt will just sustain you at battery voltage longer. a cap will "stiffen" voltage to keep you above battery voltage for a longer period of time. between moments where the amp is really drawing power and not (breaks in lows for example) will allow 4-5 sec for that cap to charge and it will charge faster then a battery in those 4-5 sec. might not completely charge but enough to help hold you above battery voltage longer. by stiffening I mean they help keep voltage with in a smaller range while slowly dropping down lower. might not last long but for those bursts of power needed to keep things above voltage on music it will work. that's all assuming your power supply can keep up or only needs help on the short bursts.

if you haven't yet check out the Maxwell 3000bcap on ebay. think they are around 50 each right now. 6 in series is a 500f bank charging voltage up to 16.2 if I remember right. that with a nice agm battery and ho alt and you could run 1.5-3krms... would have roughly 330 amperage draw and a 300 amp alt could just about power that. add in a 100ah battery and a 500farad cap and your good to go. should stay above 13v easily maybe even in the high 13s if the wiring is solid.

For sure! The capacitor resists change in voltage. The cap will store "extra" power from the altnerator when the demand from the system is less than the output of the alternaot (Ie, inbetween beats) and release that stored charge when the demand is high. This is certanly not new information by any means.. but.. Many people dont know just how much/little energy that is.. In your example with the current generated being exactly what the current demand is, a large capacitor bank would work wonders, it wouldnt need to do much as the demand = the supply.

If you had a 50 amp difference, you would be able to support that additional 50 amps for ~19 seconds. Plenty of time

Even if you had, say a 100 amp deficit (maybe you added another 1200w amp or smt) you could hold voltage for ~ 9 seconds

Capacitors are quite usefull IF USED PROPERLY! Batteries are quite usefull when USED PROPERLY!

Here is another usefull resource for calculating the same equations, but in terms of Amps instead of Watts.

http://www.circuits.dk/calculator_capacitor_discharge.htm

(remember that 1 amp = 1,000,000 uA)