what size capacitor?

i will be getting a system soon and i wanted to know what size capacitor i should get. i will have 1400 watts. my friend says i should get a 20 farad cap. i've heard that you only need 1 farad per 1000 watts. is that true? if going off of that should i only need 2 farad cap? one other question. will a cap keep my system running smoothly or should i upgrade my alternator? either bigger alternator or both bigger alternator and a cap? any help would be great thanks.

If you upgrade you alternator properly you shouldnt even need a cap. If anything you should get a second battery along with the alternator upgrade - one for the stereo and one for the car itself.

You only need a second battery if your going to listen to your system with the car off. Otherwise having multiple batteries wont benefit you. HO alternators can be very expensive, but with 1400 watts, you really need one.

caps do crap all, get a HO alt, best value for money when ur dealing with large power requirmentsClarion DB36MP

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And depending upon what that output rating really means, you may not need an upgraded alt either.  Initially, spend your money on upgrading the wiring with extreme detail (see the Big 3 sticky).  Install sound damping with equal detail.  After the install is complete you will know if an alt upgrade is necessary.  And also, if you have an older car with a 3- or 4-year old battery in it, replace the battery right from the start.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

do a search on this forum about capacitors, and read this it will help you understand more about caps. Shaking The Neighborhood

if i get a bigger alternator what is a good size to go to?

Basically the biggest one you can afford. Another way - figure out how many amps your alternator puts out now and then add the amps that your amplifier pulls (look for the fuses on the amp if there are any), and add in how many amps you plan to use for an upgrade later, if you can afford it. Example Your car puts out 60 amps now Your amplifier has two 30 amp fuses (60 amps) You're thinking of adding a 4 channel amplifier in the near future that pulls 40 amps so: 60+60+40=160 look for a 160 amp alternator, get it if you can, if not, get the largest you can afford.

drewt don't forget what the cars electronics already draw. ex. headlights draw about 30 amps. plus the heater and other things. so make sure to add those to the total