Im getting a new amp tomorrow and im going to be installing it. I have a 2.5 farad cap and when i disconect the battery so i can change the power wires the cap will lose its charge. I dont have a recharging key or whatever its called and im not exactly sure waht do. Do i need to use a charger that is specific to my cap? or can i get around changing the amp without disconecting the battery? thanks.
Actually it won't lose its charge, at least not right away. That thing will be "loaded" and if you accidentally touch a pos lead off that thing to ground(chassis metal) your gonna have hella sparks which may result in your red wire welded to your chassis.
I'd disconnect the power wire at the pos terminal of the cap as well. I'd use a "key" as you call it too hook it back up. All a "key" does is get the voltage at your cap equal to the voltage at your battery. If they're unequal when you hook it up you're gonna get sparks.
All you need is a small 12 volt light bulb and socket. You can use a resistor instead but you won't know when your cap is fully charged/discharged.
To recharge your cap(with power disconnected at battery and cap hooked back up again) just connect the power wire to one end and touch the other end to your battery's pos teminal. Once the light bulb quits glowing its safe to go ahead and reconnect power to your battery.
To charge the capacitor, the light bulb acts as a "curent limiter" and as you mentioned and is connected in SERIES between the battery and capacitor, It don't matter if the light bulb is in series with the positive or negative lead.