I just picked up an Alpine MRV-F450: 850W unit. Is 8 guage wire enough or should I use 4 gauge for power. The amp will have a 50A fuse inline with it. Thanks

Do I need a capacitor to? If so what kind/type?

 

I'd say go with the 4 guage wire, and def use a capacitor. Unless you want to have a 2nd battery.

 

With this formual would 1F be enough? One Farad of capacitance per 1,000 watts of power with a minimum of one Farad.

 

I'm not no expert but 4 gauge would do you pretty good I think . I have a 750watt JBL amp and I got 4gauge wires

 

Voltage X Amps = Watts
Or what you want to know,
Watts divided by voltage = Amps

850 divided by 12 volts = 70.83333333 Amps

Wire being what it is and the usage in your case, by gauge 12 gauge = 20 amps
10 = 30
8 = 40
6 = 60
4 = 80

As far as wire for this purpose you want a fine stranded 4 gauge wire like as in a welding cable or heavy duty jumper cable. I would also solder the connectors rather than just crimp them.

 

You'd also want to keep the distance in mind as well. I've enclosed a chart for reference (on this or other projects).

 

never hurts to run bigger than u need right now you never know if u might upgrade!!! ive also found all wire is not created equal cheep brand 4 gague is smaller then rockford fosgate 4g wire i usualy go for big and cheep like my...... ahhh thats another discussion

 

Not trying to step on anyone's toes, but a good formula for finding what ampere fuse to use is Wattage / Voltage / Amplifier Efficiency.

As a rule of thumb, Class AB amps are ~65% efficient. Class D ~80%

I normally use 13.6 volt DC because a fully charged battery will cause the alternator to put out about that voltage. Even if the alt is putting out max voltage, it's not uncommon to see ~1 volt drop with hard bass notes.

850 watts RMS / 13.6 volts = 62.5 amperes

62.5 amperes / .65 = ~96 amperes (Class AB)
62.5 amperes / .80 = ~78 amperes (Class D)

That's why Class D amps are more desirable for bass. They make more wattage with any given amperage.