Quick Cap. Questions

[`pr0digy 10+ year member]

Two questions on caps.

First, do they degrade over time like batteries ? Is buying a used one okay ?

Second, if my alt is regulated to do only, say, 13.5, will the cap always discharge to try and keep 14.4V ?

Click to read more...

 

[`pr0digy 10+ year member]

Not to be arogant, but if someone could answer, I'd be greatful. Need to know for a deal that may go down in a few hours.

 

[DBfan187 5,000+ posts]

This help any? - http://www.welcometotheden.8k.com/caraudio/Captest.pdf

 

[JimJ 5,000+ posts]

caps do go bad over time, but it takes a lot longer than batteries. They don't have a surface charge to degrade, but over 20+ years big electrolytics tend to dry up, causing fun explosions if you try to power everything up at once.

Standard procedure for reviving old electrolytics is to bring them up slowly on an AC variac (basically a big honking potentiometer that slowly raises the AC line voltage up to 110V or something). Otherwise they tend to explode...leaving a bubbly, oily, gooey mess.

 

[JimJ 5,000+ posts]

since caps don't have a surface charge to deal with, you don't need to worry about maintenance like you do with batteries. A cap that you leave sitting there will work perfectly in a year...while a battery that you leave sitting for a year will make a nice paperweight.

 

[squeak9798 5,000+ posts]

Second, if my alt is regulated to do only, say, 13.5, will the cap always discharge to try and keep 14.4V ?

A cap will only charge as high as the rest of the system. If you're systems running 13.5V, then the cap will also run at 13.5V.

But be sure to read the link that DBfan posted //content.invisioncic.com/y282845/emoticons/popcorn.gif.32dd9e22fd77e77bc3c907062768fcd2.gif

 

[JimJ 5,000+ posts]

but batteries won't //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif funny little property of them.

 

[`pr0digy 10+ year member]

Thanks for the info guys. The cap is 1 farad for $20, so I think I'll get it. Might not do much, but it won't hurt, seeing as my charging system handles my amps well so far.