The cap voltage is whatever the overall system voltage is. It can't supply any usable current as a result. It simply can't store enough.



Unlike a battery, the cap is never a load on the alt. However, also unlike a battery, it cannot store enough energy to make a real contribution to the overall situation. The biggest cap made might be able to help a tiny bit. The usable energy stored in a cap in a lossless environment (which we all know doesn't exist) is 0.5 amp-seconds per Farad. Now compare that to the multi- amp-hour capacity of even the smallest battery and it should be obvious what makes more sense to add you think that you need an electrical upgrade. Couple that with the fact that a good battery costs significantly less than a useless cap and it becomes a real no-brainer. Basic electrical theory tells us that with a high powered system, barring a large reserve buffer (read: battery bank), the lights are going to dim. No way around it. Even with a big alternator, it's pretty much unavoidable.
More like spitting in the ocean...

 

Technically, I didnt get fired. I was laid off and found humor in the play on words. But will have you know that I have not updated my signature in a while and am no longer "fired". Oh and thanks for pointing that out to me, ill have to update that for ya...

Next time, lets help the thread move along in a positive direction.
Thanks, F150Online.

 

Helotaxi, everything I said is correct. A cap is a load on your system when it needs to be charged. A cap gets its charge from your highest voltage source which should be your alternator if your system is working correctly. A cap will only charge to the highest voltage in the system. You are also correct, a capacitor will not store enough charge to fix a problem and it discharges too quickly in most cases to be of any use. Basic electronic theory says that if your supply is big enough for your loads you will not have any dimming. No need to argue the same side of the story.