Is RF full of it regarding HO alt need

sonso_chi · Post by **sonso_chi** » Tue Apr 25, 2006 8:28 pm

Per RF, for a street driven car running a 1500w amp, a 100A alterator is all that is needed. Granted for a competition car running the same amp they recommend a 200A alt.

Regardless, from my limited understanding the knowledgable people here would recommend around a 150A increase to whatever the stock alternator is in purchasing a needed HO alternaator, eg. if my stock alt were 90A I should get a 240A HO alternator.

I am sure that the people at RF know that people who do not compete (street driven cars) with a 1500w amp are still going to utilize that amount of power (wattage).

I will say that RF is at least paritally full of stuff as they mass produce capacitors and in turn recommend them as well.

PDF of owners manual for 1500w RF amplifier, see page 9.

http://www.rockfordfosgate.com/scripts/ ... 1083256070

Input?

Yes, I did just purchase this amp but still in pursuit of knowledge and understanding.

BTW as I have mentioned in the past, my old car had a 90A stock alternator and I ran a 2003 HiFonics amp that claimed to put out 1500W at 1 ohm (that's how I ran it). Based on it's performanc I'm sure it put out at least 1200w and the 3 years I had it I didn't have any apparent problems with my electrical system. The stock alt in my present car is 140A. I know this testimny holds no weight, I just thought I'd throw it in.

Lastly, RF amps are more often than not underrated (per their birth sheets).

A simple yes or no to the initial question will do. Just wanted to call attention to what the people at Rockford Fosgate think regarding this subject.

Justin from Detroit1 · Tue Apr 25, 2006 8:46 pm

Well a TRUE 1500w amp will pull 107 amps. So no, a 100A alternator is not enough.

sonso_chi · Post by **sonso_chi** » Wed Apr 26, 2006 7:59 am

^I have been doing some research on this (read perusing car audio forums) and I can see that it is somewhat controversial.

My mathmatics are off in calculating the size alt needed, but the simple counter argument is that the bass is not always hitting hard giving the alt time to charge the battery (after it gets dipped into, for what the alt can't supply).

Per Fosgate, see link page 9, the typical current draw for a 1500w amp is only 90A, I am assuming this is when the bass notes aren't hitting hard...

solacedagony · Post by **solacedagony** » Wed Apr 26, 2006 8:13 am

If you don't turn your system up to the point where your alternator is over taxed, then it doesn't matter. My calculations 1500w/13.5v=111.11A at full power. Another semi valid way to tell current pull is by the fuses on the amp.
I'm running 1700W on my stock alt (cause I'm a po boy until I pay some stuff off) but I don't turn it up to the point that my alternator wants to jump out from under my hood.

OnYrMrk · Post by **OnYrMrk** » Wed Apr 26, 2006 8:20 am

You must also take into account the other things a car can tax on an alternator. Like HID headlights, air suspension, multiple processors, aux lighting, fog lights, and so on. So for them to say that a 1500w amp will only need 100amps to run it, is if you have a 250a alternator to handle the rest of the electrical needs.

Bwcad1 · Post by **Bwcad1** » Wed Apr 26, 2006 8:32 am

your going to have electricle issues your lights will dim and the alt will die within 6 months i would almost gurantee that. just like joe said dont forget about everything else in your car that uses that power you will have only about 40 amps to use for your stere and that isnt enough.

Justin from Detroit1 · Wed Apr 26, 2006 9:44 am

Exactly. You may think "Well, I have 100a, and it will only pull 107a at peak times, so I am fine". Not true. If your car came stock with 100a alt, then your car requires close to that just to power your car. So you would need, ideally, a 200a.

Bwcad1 · Post by **Bwcad1** » Wed Apr 26, 2006 9:51 am

lol or you can be like my dumbass and run 8 kw on one battery and one 200 amp alt!

High Society · Post by **High Society** » Wed Apr 26, 2006 9:52 am

wow, you are a dumbass!! lol :)

Bwcad1 · Post by **Bwcad1** » Wed Apr 26, 2006 9:54 am

yea well what can you do! but the new battery will be here! but this bat is a team secret!!! and damn its bad ass! anything that can power 8kw and only drop .2 v is a bad ass battery.