Caps and Farads explained

[Intercooler 10+ year member]

So I added a 1 farad on the advice of the audio shop but want to understand them fully. Supposedly some have less noise level rating or something? How will adding extra capacity help you? What are the best brands to get? Just wondering if stepping up to a 5 farad or larger would help with lights flickering?

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[bikejunkie223 10+ year member]

You get a cap based on the amps you are running. The more watts you are running, the bigger the cap needs to be to stabilize voltage. Think of the cap as a buffer between the battery and your amp. It stores voltage when demand is low, and outputs it faster than the battery can to meet demand. The higher the farads, the greater the storage.

 

[Intercooler 10+ year member]

How about the ratings on them? Look like I need more?

I see the voltage on the one I have go down to low 11's. Is that what everyone else is seeing on their caps?

 

[iceteebone 5,000+ posts]

caps are useless if you are using them to fix a weak electrical system. basically what a cap does is store energy so it can realse it quickly. this comes in handy on big bass notes. a cap can only disperse current for like a second then needs to recharge. a cap is for sq. it is intended to be used with an adequet electrical system. on the big bass notes a good electrical system may not be able to get the current quick enough so the cap can release a seconds worth of current so basically the electrical system can catch up. anything more then 1 farad is just a gimmick.

 

[iceteebone 5,000+ posts]

How about the ratings on them? Look like I need more?
I see the voltage on the one I have go down to low 11's. Is that what everyone else is seeing on their caps?

that is bad. your voltage should be 13.5-14.5 volts. a cap doesn't help low voltage problems. your alt will die soon.

 

[skmfkr 5,000+ posts]

doesnt sound like its helping any with 11v

 

[bikejunkie223 10+ year member]

It could be 11 with the car off. Just know a good battery is 12.6v at rest, and your '98 Civic will charge at around 13.8 volts, but because of ELD operation, it may not charge much right after startup. (this is part of why Civics are notorious for dimming headlights when the a/c compressor clutch engages)

 

[Intercooler 10+ year member]

that is bad. your voltage should be 13.5-14.5 volts. a cap doesn't help low voltage problems. your alt will die soon.

Wouldn't you have to measure pre and post to determine? I could have 13.5v going to the cap and on big bass it is measuring 11v on the downstream side but still have 13.5v on the upstream side. Where does the digital readout give it's reading from?

 

[DiamondFanatic 10+ year member]

input. You probably do need a new alternator if that 11v was with the car running. Another thing you could look into is getting an optima for under hood.

 

[iceteebone 5,000+ posts]

Wouldn't you have to measure pre and post to determine? I could have 13.5v going to the cap and on big bass it is measuring 11v on the downstream side but still have 13.5v on the upstream side. Where does the digital readout give it's reading from?

your voltage should be constant

 

[Intercooler 10+ year member]

What did you mean by anything over 1 farad is a gimmick?

 

[bikejunkie223 10+ year member]

Unless you are running massive wattage, 1 farad is plenty for up to probably 1000wRMS, especially since at that wattage, a cap isn't even really nec.

 

[bigbangtheory 5,000+ posts]

You are saying your cap reads 11v when the big bass notes hit right? I am with the one guy if your car is off and it is reading 11v then that is bad.

 

[M@nJo 10+ year member]

i have a honda civic with OEM 70a alt. im running 1000rms (overrated hifonics amp) and when the bass hits, lowest ive ever seen was 11.8v but thats rare and less than a quarter second. if im bumping for a moment of time, lowest it stays at is 12.8v on the hard bass notes, again, thats for a split second. with the system off, engine on, it goes 13.6/13.8v when i accelerate. 14.4 when idle.

your car must be off when your testing your cap. if it was, turn it on then see what the voltage reading is off the cap on big bass hits.

 

[Intercooler 10+ year member]

I am getting 14.2-14.4 at idle with nothing on. With the car turned off I have 13.2. With the system on but not cranking it is 11.9-12.8. With it turned up and bass hitting 11.4-12.0.