Alternator

[Mattitjah]

I just want to know if sombody could tell me what amp rating there is on a stock alternator for a `95 325i?

[El Presidente]

BMW used different brand alternators on certain cars, but it should be either 120 or 140. It should say on it.

[bitcore]

I've got 80 on a 98 323is? This normal because of the smaller engine or is it somthing else?

[Mattitjah]

OK, I am planing on adding an amp and some subs. I allready have the amp, a 800W (or so it say on the amp), now I am not sure if that is RMS or peak, but if it is RMS then that would ad about 60 more amperes of current drawn from the alternator according to my calculations. If my alternator is a 140 amp, would it be able to draw this size amp?

[Mattitjah]

OK, Just checked my amp and it is a 140 amp. That should be big enough, right?

[bitcore]

thats plenty..
Remember, you do have a battery to act as an alternate power supply when the alternator can't produce the load.

also, remember that the alternaor wont produce that many amperres at engine idle. It will be significantly less than that.
BTW do not EVER go by peak ratings on an amplifier, peak is purly a marketing term and your amp will only "peak" when it's outputting TERRIBLE signals.

[El Presidente]

are you sure its 80 amps? My understanding was the the 1.8s had a 90A alt, and the 325/328 had 120A or 140A alt. The 232 really has the 2.5L engine, so I can't imagine why it would be that way. I'll check my books again and make sure I have my numbers right.

Also, if you're running over 500W then a cap is in order. it will reduce or eliiminate strain on the alt and bat.

[bitcore]

general rule of thumb is 0.1 farads per 100W of wattage produced (given the amp is at least 80% efficent, most class D or better are) I'd go ahead and get a 1 farad cap if you like boom boom music.

El Presidente: The thing says 80 on it.. I'll go take a look again real quick
Edit: Yah I think thats what I have... here's my alternator...

[Mattitjah]

Cap? As in capasitor?

[bitcore]

and here's a closeup of the big 80 stamped on it... (air filter's in the way and I dont feel like tearing apart my engine compartment right now)

Yes, cap as in capacitor. Get a used one on ebay for like 50-100$... Don’t worry about name brands, a capacitor is a capacitor as long as it's electrolyte (EG: a modern one) and dosn't look damaged.

Edit: A farad is a unit of measurement to measure the amount of electrons a device can store. A car battery can hold hundreds of thousands of farads (I think maybe a few million but I don’t remember exactly. It’s a lot compared to a capacitor), but it's ability to release the energy quickly is very poor, so you need a capacitor that can hold a farad or two, which can release all of it's energy almost instantaneously, to help out with the electrical demand while the battery catches up in releasing it's own energy to re-charge the capacitor for the next sudden burst of energy demand. (wow what a run-on sentence)

Edit2: El Presidente, it wont ELIMINATE the strain on the alternator, it still has to produce the same amount of energy, it just wont have as hard of a time doing so because the energy demand will be more constant than without a capacitor. It's still easier on your car's electrical system none the less. BTW, Do you think my original alternator failed and was replaced with a smaller one because it was cheaper for the previous female owner? This hacks me off.

Edit3: Damn I shoulda just pointed to this thread... :P

[Furious]

there is two main brands of alternators used for e36's one is bosch (the german brand) and Valaeo (french brand bad spelling of the name btw)

i thiink the 3 types ive seen are 80, 90 and 140 amp.

[Mattitjah]

THIS is the amp I got. It was cheap and looks nice and produces the amount of amplification I was looking for. Other than that I do not know a lot about car stereos. I think I will get a capasitor just in case it will save my electrical sys. in the car.
Does any one know where I can find a diagram on hooking up amp/subs/caps in a car? I do have a degree in instrumentation so I could probably figure it out myself but I would rather go by a diagram or something.
Thanks.

[bitcore]

specific ways of wiring 2 subs can produce different results.
Your Amp appears to be 2 ohm stable, so you should wire it as such. Don't wire it any lower than 2 ohms or you could quickly kill your amplifier AND drivers if the amp dosn't have any protection circuity.
Lightning Audio Wiring Wizard Good method to figure out how to wire your subs to specific ohm loads.

I dont see any THD or SN ratings on the amp so it could be crap, it could be great, I wouldn't be able to tell you by just looking at it.

[Mattitjah]

Yea, I don't expect TOO much from it. It was cheap! And it is SHINY!!!
All I need is THUMP. I listen to rap, techno, heavy metal and old rock.
My plan was to use two 8" subs to save on weight and space.

I don't see any THD or SN ratings on the amp so I can't say what they are but I am not building a super HI-FI system so...

[bitcore]

if it works, its all good