I just upgraded my stereo and my sub amp is going to be a Rockford Power 750s. It is rated at 750 watts RMS bridged at 4 ohms. Can I get away with a 1 farad, or do I need a bigger one? I already have a 1/2 farad, but I don't think that one will cut it, so I'll probably just hook that up to the 4-channel I have runnign my speakers.

Thanks,
Eric

 

you dont need a cap, caps are the devil mmmk?

upgrade the big three, if that dont solve your problem...
upgrade your battery, if you still have problems...
upgrade your alternator

 

I'm sorry, I don't understand what you mean. "The caps are the devil mmmK," "upgrade the big three." Please clarify.

Eric

 

Link to Big 3 Upgrade

Seriously, don't bother with a cap. They're pretty much useless. Definatly do the big 3 upgrade, then maybe a red/yellow top Optima battery, and a bigger amp alternator.

Although, I'd suggest doing the battery/alternator at the same time. The alternator is what "recharges" the batter, and if you get a bigger battery w/o getting a higher alt amp, you're eventually gonna be back to where you started.

Also, if you have ever deep-cycled your battery, you can have power loss because it might not be putting out all 12v anymore.

Hope this helps!!

 

You should definately do the Big 3 upgrade, but a cap is not "useless" . It will spread out the load on your alternator and battery, if you can't afford to upgrade both now.

 

although upgrading the big 3 is always a good thing, a cap has its place in a properly designed audio system also. Getting back to your original question, the general rule is that 1 farad for every 1000 watts RMS is adequate. Considering that most modern amps come with large capacitor banks already, you can usually get away with less.

 

Yup exactly what I was thinking Jim.

 

I understand the point in doing this, however, my concern is that lowering the resistance this much on the charging system will put a huge strain on the alternator. On a cheap, stock alternator from Auto Zone, can it really handle that much output without burning out? Also, Jim, you pointed out that new amps have a large capacitor reserve in them already. If I did the big 3 upgrade, could I get by with just using the 1/2 farad cap on that Power 750s amp? I also have an Eclipse 3442 that I was planning on using the 1/2 farad cap for if I needed to get a larger cap for the sub amp. So, if I upgrade the cables under the hood and put the 1/2 farad cap on the sub amp with nothing on the 4-channel amp, should this work? I know there will be some trial and error, but I'm just keeping my eyes open on ebay for a larger cap if I need one.

Thanks for all the input guys,

Eric

 

I can't say for sure, but with a healthier alternator, and if Rockford does in fact use as much capacitance as some other brands, then you can probably get away with .5 farad.

On the other hand, caps have gotten so cheap lately, that the difference between .5 farad and 1 farad is very small.

 

This is very true. If you are running an high-wattage SPL system, a cap does have it's place, most people are not running an SPL system for daily driving though. Most people are mislead on how to properly use a cap.

 

I don't mean to be mean, but I am pretty sure a deep cycle battery is a battery with a slower discharge rate. They are normally used to run small electric motors in boats. But because of their ability to hold a charge so long, they became popular in car audio as a secondary battery.

I think maybe you ment just running the battery really dead a few times too often, that would definately affect its ability to hold a charge and maybe its ability to provide 12VDC. Of course this would also be hard on the charging system too, which would also play a part in the whole scheme of things.

 

A deep-cycle battery is meant to be discharged SEVERELY, like on old marine outboards that had no generators or alternators, thus taking a lot of abuse without a recharge.

 

I'm not using my system for competition, just for my enjoyment when I'm in the car. I just don't want my charging system to drop down to 8 volts every time the bass hits. I basically want to do whatever I need to do so I can drive the car with the system on and not have it put a huge stress on my charging system.

 

Me, too. I've got 1040 watts (2 amps 440 and 600) and I have a 2 farad cap, and it helps!

 

if you're only running 750 watts i think you should be ok with just upgrading the magic three wires...make sure all your grounds are done well and you should be set

having a strong electrical system is the most important and most overlooked aspect of a car audio system

 

always do the "big 3" first. it will make a difference. caps are done all too often as an easy way out (yet much more expensive). there are quite a few things to look into when purchasing a cap (a last resort). getting the digital display looks nice, but is more detrimental to the caps operation. i believe they also need to be rated to 20 or 24 volts, cant remember off the top of my head.
in my current setup, have a 50x2 rms amp and 600x1 rms amp, both class AB. i have a stock alt (105amp i believe), upgraded the wiring. i have yet to see lights dim in my car. there's a decent size battery under the hood (850 cca, soon to be replaced by a red-top). no cap. havent needed one, dont see one in the future either.

 

I just don't understand how upgrading those wires isn't hard on the alternator. To me, it seems like it will be overworking the alternator and will just burn it out. Can someone explain to me if/why I'm wrong.

Eric

 

Larger size wire will not overwork the alt. Larger size wire helps the current flow....
Think of it as water flow.... With the alt. being the pump... Wire's being the pipe.
Say you need to flow 100 cfm at 12 psi... A smaller diameter pipe would put more strain on the pump to get that 100 cfm than a larger pipe would.... The larger the pipe the easier the water can flow through it....
Same goes with electricity....
The larger the wire, the easier the amperage can flow....