80A vs 140A alternator

[m3f_das borgen]

For the record, 80A/140A is a _current_ rating. It only matters if you have something to sink that much current. 140A and 80A will behave exactly the same with a 5A load, for example. So unless you're drawing a good deal of power, 140A doesn't buy you much except possibly slightly more drag.



As for HID, your battery will provide the instantaneous current bump to handle your HID ignition. You can weld with a car battery, it will have no problem handling the load unless the wires going to your lights are just too small, or there's some other factor limiting the current. I run HID Boschs and fogs with no issues, and I'm pretty sure I have an 80A unit.



Now, the _voltage_ ratings do have to match (12V system), but since these are both OE spec parts, that part is true implicitly.





Oh, and assuming you meant ! as the factorial operator, 5!/1! = 120.

nerd (last sentence)!!!!!!!!!!!





I have no idea how most people give themselves trouble over 140A when their car will most likely not have near the current draw to warrant needing one. If someone has a giant sound system, buy a 0.5Farad capacitor and call it good.



you deserve this comic for a 100% accurate answer.



ever heard of direct exhaust ignition guys?

[m3f_mmenefee]

nerd (last sentence)!!!!!!!!!!!

That has been obvious around here for quite some time....

I have no idea how most people give themselves trouble over 140A when their car will most likely not have near the current draw to warrant needing one. If someone has a giant sound system, buy a 0.5Farad capacitor and call it good.

An understanding of basic electrical concepts is not very common. Even people who are very good mechanics (pro or otherwise) don't necessarily need to (or have the inclination to) read up on this sort of stuff. You can go a long way wrenching on a car just knowing the difference between black wire and red wires. This is one of only a handful of situations where that sort of knowledge comes in handy.

you deserve this comic for a 100% accurate answer.



ever heard of direct exhaust ignition guys?

Uh, I, er... wut?



Quick! Someone call the treehuggers! We've invented a zero-emission engine!

[m3f_das borgen]

Uh, I, er... wut?



Quick! Someone call the treehuggers! We've invented a zero-emission engine!

still working, 1st prototype done blowed up

[m3f_fiveightandten]

nick, i don't see any problems running a larger alt

Thanks.


I've been running the 140A since I replaced it in May of 2008, when this thread was started. I love looking at old threads of mine. I was such a noob.

[m3f_pbonsalb]

nerd (last sentence)!!!!!!!!!!!





I have no idea how most people give themselves trouble over 140A when their car will most likely not have near the current draw to warrant needing one. If someone has a giant sound system, buy a 0.5Farad capacitor and call it good.

The 140A is not a bad or incorrect choice given that BMW factory fitted it to many of the M3. I have never been able to figure out which models got it, though. There are convertibles and luxury models with 80A and standard M3 with 140A. I see no method.

[m3f_OahuMPower]

I replaced my 80A with a 140A when I used to have my HUGE stereo in the trunk. Never had any issues, and the alternator definitely made a huge difference.



Even though the stereo is long gone, I still have the 140A alternator and everything has been GTG

[m3f_kaivonp]

For the 140 Amp alternator to put out more current than the 80A alt, I'm guessing it requires more power from the engine. So that would lead to some loss of horsepower, right? How much?

Also, would the greater demands on the engine be continuous? Or would the 140A only require more power from the engine, relative to the 80A alt, when the current draw exceeds 80A? Exceeding 80 amps probably doesn't occur often, so if the greater demands of the 140A alt are transient then there wouldn't really be a cost to installing one because you wouldn't experience a continuous loss of hp.

(sorry for resurrecting this old thread, but it seemed like there were some people here with electrical knowledge)

[m3f_salty]

For the 140 Amp alternator to put out more current than the 80A alt, I'm guessing it requires more power from the engine. So that would lead to some loss of horsepower, right? How much?

Also, would the greater demands on the engine be continuous? Or would the 140A only require more power from the engine, relative to the 80A alt, when the current draw exceeds 80A? Exceeding 80 amps probably doesn't occur often, so if the greater demands of the 140A alt are transient then there wouldn't really be a cost to installing one because you wouldn't experience a continuous loss of hp.

(sorry for resurrecting this old thread, but it seemed like there were some people here with electrical knowledge)

I believe this is correct. The 140 amp alt probably weighs a bit more.

[m3f_pbonsalb]

Theoretically, 980 watts -- the maximum output of an 80A alternator -- equals 1 horsepower. The alternator is not 100% efficient, so it probably takes more than 1 horsepower to produce 980 watts. I do not know the efficiency specs, but even if it was only 1/4 efficient, it would consume only 4 hp at peak output. A 140A unit might be more like 7 hp at peak output. Anyone have any real numbers?



Grassroots Motorsports did some dyno testing of the usual "free horsepower" tricks and found no measurable gain from disrupting the alternator field (causing it to output nothing).



http://grassrootsmotorsports.com/articles/stock-tips/



Years ago, I had a device called an Alterbreak. The FTC later went after Nutronics, the manufacturer:



http://www.ftc.gov/opa/predawn/F89/nutronics.txt



Probably pulling the belt, if an option on the car in question, would show a couple of horsepower. I would think the larger 140A unit would have more drag even at 80A or less output. Pulling the belt is not realy an option for the S52. I am running a rebuilt 140A and don't think I would bother changing it to an 80A unless it fails.

[m3f_Mad Dog 20/20]

Heated seats do not = 140A.



The 140A is significantly larger and a bit heavier, but will bolt right up - unless you have an SC or something else that needs the space.

[m3f_M3n00b]

Fawk this thread is old

[m3f_Powerverter]

I have a convertible and I'm replacing the alt with a 140A, since I read that the 140A provides power at idle, whereas the 80 needs to rev more than idle (I have no clue what rpm).



This is what I remember reading somewhere about 1 year ago...please correct me if I'm wrong.

[m3f_kingchris]

The answer is yes you can swap them, but how much more horsepower does the 140 drain? Just sayin.

[m3f_epj3]

Theoretically, 980 watts -- the maximum output of an 80A alternator -- equals 1 horsepower. The alternator is not 100% efficient, so it probably takes more than 1 horsepower to produce 980 watts. I do not know the efficiency specs, but even if it was only 1/4 efficient, it would consume only 4 hp at peak output. A 140A unit might be more like 7 hp at peak output. Anyone have any real numbers?



Grassroots Motorsports did some dyno testing of the usual "free horsepower" tricks and found no measurable gain from disrupting the alternator field (causing it to output nothing).



http://grassrootsmotorsports.com/articles/stock-tips/



Years ago, I had a device called an Alterbreak. The FTC later went after Nutronics, the manufacturer:



http://www.ftc.gov/opa/predawn/F89/nutronics.txt



Probably pulling the belt, if an option on the car in question, would show a couple of horsepower. I would think the larger 140A unit would have more drag even at 80A or less output. Pulling the belt is not realy an option for the S52. I am running a rebuilt 140A and don't think I would bother changing it to an 80A unless it fails.

I would guess we're lucky if the alternator is more than 50% efficent. Most of the mechanical energy becomes heat, not electricity.