525i/ new audio system

[rob]

Hi,

I'm spec'ing out a system for my 2001 525i and I've got some questions.

Primarily I'm concerned with overstressing the car's electrical system. The stock alternator is 120-Amp and I've been told that the max it can handle is 1500 watts RMS... But I'm not sure if AC and other electrical systems would lower this RMS number. Here's what I'm thinking about installing:


SQ system:

CD- Changer:
Alpine + blitzsafe

Head Unit:
Mark 3 Nav Widescreen (crap HU, but I like my Nav and have to have hands free cell phone for DC now).

Front Stage:
Boston Z5's powered by a bridged Boston GT-42 amplifier (300 watts RMS per channel @ 3 ohms)

Rear Stage:
No rear fill

JL 12w6v2 Subwoofer powered by a JL Audio 500/1 amplifier @ 4 ohms.

---

The bass from the sub will enter the main cabin through the 5.25" holes in the rear deck where the factory speakers were (the grills will remain) I'm also toying with the idea of tearing out the backing behind the rear seat arm rest in case I need more bass.

So I'm looking for advice here on whether or not this system will draw too much current, and opinions on the overall setup based on your experiences w/ BMWs.

thanks.

 

[rob]

is this forum dead?

 

[jszar]

sorry man, i am usually around a lot here, been busy though.

that will sound sweet ass if you want my opinion. boston's stuff is pretty nice.

1500wrms / 14.4 = 104A.....NO! that alt CANNOT handle 1500RMS, no way no how, your car will need at least 80A to run and have lights, heated seats etc... you'll need to upgrade if you are looking for lots of power.

i estimate 700wrms in reality for that JL amp, they are WAY underrated, go get it bench tested if you dont believe me. that boston should be right on. so figure 1300wrms, divide that by the voltage (ohms law) and those amplifiers will draw 90 amperes of current. TOO much! you should get a high output alt, around 180-200A for that system, and not be stressing it.

i'm around more, so if you have any more Q's hit me up or just post!

 

[rob]

jszar,

I changed my setup a bit (all parts ordered and on the way...):

Boston 10.5LF (2 ohm model) Sub (will put in custom enclosure firing through rear seat arm rest)

Z5s -- 3 ohms (front stage only, no rearfill)

JL 300/2

JL 500/1

Will this setup still require an alternator upgrade?

Thanks.

 

[jszar]

well after doing some thinking, as long as you dont turn it up to full volume, you should be ok. keep it under 3/4 volume.

 

[jszar]

technically though, you're still at the same amount of power.

 

[rob]

I talked to this guy at www.h-o-alternators.com and he said they have a bosch 200-amp alternator that'll fit my car. you know anything about this? I talked to bosch tech support and they didn't know about it...


300/2 puts out the same amount of power as a bridged GT-42? mmmm how's that work?

 

[jszar]

if they say it fits, i am sure it fits. i might check that out, i was looking for a 200A alt also. so far the best i can find is 140.

that 300/2 is 300 x 2 channels, correct?

 

[rob]

well 300/2 = 150 watts per channel (2 channel amp).

Well I'm wondering if the bosch 200A they have is manufactured that way or a modified 120A.

It took a lot of looking to find this 200A. Nobody seems to deal with BMW HO Alternators... BMW was no use when I contacted them (blah blah, void your warranty, blah blah) and most of the sites out there are Jap and American cars only...

Just so you know, They quoted me $700 on this Bosch 200A, not sure that's doable if you're in college.

 

[jszar]

ouch. yeah, no way for me.

1000 / 14.4 = 70A at full volume. You're fine there with a 140A.

It is definetly a modified alt. NO ONE makes alt's that big stock, its always a shop that enlarges the case etc.

 

[rob]

jszar,

Sadly, my 525i comes with a 120A alternator, not 140A. I may just go ahead and order the 200A alternator just so I don't have to worry.

Another option I've heard is get a Optima Yellow Top and farad caps... but I can't see how this would help generate power, just store it, so it's really no solution.

 

[jszar]

yes, caps only smoothen out the draw from the alt, and reduce engine noise. they are also a nice cosmetic feature. but dont mistake them for more power, they get their power from the alt.

i would say get the 200A if its feasable. I wish i had enough to get one for my car. i have a 140 stock, on a 3 series though. it might handle the 1200 i put on it.

yellow tops are nice, get the multi purpose yellow top if you plan on replacing your starter with it. otherwise the regular yellow top's warrenty might void. if you just want a better battery that isnt deep cycly, get the red top, its a starter with all the goodies.

 

[rob]

Cool.

I'm gonna get that alternator, I hate having to worry about sh{t, like can I turn my ac up or not, blah blah.


I think i'll skip the battery, as I just use the radio to drive down to dodge city (wash dc) and don't listen to it when the engine is off -- I have a massive adcom seperates systems w/ infinity studio monitors for home listening -- but I did buy a 1.5 farad cap that I'll probably put in.

thanks for you help man. GL in college. Go w/ that Air Force route maybe by the time your manditory time expires (2012) the economy will have picked up. LOL.

 

[jszar]

yeah, a cap will prolong the life of a alt like that, and kill engine noise.

thx. hopefully it will soon.