low voltage at idle...

[03ozwhip]

i have a stock 78 amp alternator and an optima red top battery running 2 compressors for air and a 1 Kicker L5 system setup. when my comps are on and im listening to music and im at idle my volts drop down to around 9.7 at its lowest point. i was wondering if upgrading to a 94 amp alternator will help my situation. if not aside from running another battery, what are my options. thanks.

[Redlyne_mr2]

That sounds like a battery issue... I have a small racing battery in my mr2 and when i turn on my engine lid fans the voltage light comes on telling me that the voltage dropped below 11V. If I floor the car with the engine lid fans on then all the interior lights and gauge cluster dim because of the huge draw on the battery/ignition system.

[gretz]

sounds like you need an alternator - chances are it is undercharging, since it is a stock alt., the brushes are likely worn right the fk down. If your battery isnt reading over 13V, its the alt. 99% of the time.
Changing your alternator will fix this (sell the core back to save $$)

[03ozwhip]

Redlyne: it sounds about the same, i have a switch for my comps, and when i turn them off i suddenly have about 2 more volts. this red top is pretty new, only a few months old...should i take it back?

Gretz: if i drive it for a half hour or more straight without the comps on, my volt meter will go back to the high 13 mid 14 marks.

[gretz]

no, how likely is it that your new redtop battery is pooched when your running a stock alternator with 2 compressors and a stereo? C'mon man, check your alternator first

[03ozwhip]

thats what i was looking into first, i guess my real question would be is, are 15 amps sufficient enough to rectify this issue?

[Grogador]

I've always had this in several vehicles, granted with stock alts, just assumed it was normal that at idle it wouldn't provide full juice. Not with compressors but fogs, stereos, computers, inverters... Battery should be reading "13V" open-circuit but when you're pulling like 20A it's gonna drop. Right now with stock alt/batt and a single 500W Jensen my voltage dips to 10.4V on the heavy basslines, closer to 15V when revving. Kinda why you need to rev your engine when boosting someone... mad current draw + idling alternator = voltage dips.

[Redlyne_mr2]

Originally posted by 03ozwhip
Redlyne: it sounds about the same, i have a switch for my comps, and when i turn them off i suddenly have about 2 more volts. this red top is pretty new, only a few months old...should i take it back?

Gretz: if i drive it for a half hour or more straight without the comps on, my volt meter will go back to the high 13 mid 14 marks.

I dont know a lot about hydros but dont people usually run more than one battery? I would suspect that the battery just isnt up to the amount of drain being put on the system.

[gretz]

its a new redtop - unless its the size of a lawnmower battery

[Grogador]

Had an extra heavy duty battery for a 1000W inverter, it helped immensely but still dipped when powering... a lot of stuff.

[gretz]

ALTERNATOR - your running hydros on a stock alt

[03ozwhip]

im not running hydros, im running air its completely different. i understand my charging system is lacking, thats why i got a red top, however no one answered my question. is 15 extra amps really gonna help that much or not?

[Grogador]

imho, it won't make a difference at idle. Unless your battery gets drained during regular commuting (insufficient juice for charging), what's the point? Voltage dips aren't really dangerous, otherwise your ECU or whatever would fry every time you cranked over. You won't get much more juice out of the alt at idle, and the voltage will still dip. A cap for your stereo might help smooth things out for transients but once that's discharged the voltage will still dip.

You probably don't have a 270A 24V oil-cooled alternator but here's the basic idea for alternators in general:

[03ozwhip]

doesnt really help me. it still doesnt answer my question/.

[Supa Dexta]

As everyone has been trying to tell you, your alt puts out more amps as your rpm's increase, it's the regulators job to keep it at 14v. You're trying to ask too much of it (the alt), when it's not designed to do it at idle. Get a better alt, not just a higher number amperage, but one that puts out more amps at a lower rpm, and also raise your idle some to get more out of it. Your battery really isn't the problem, it's really just there for starting the car, then it's the alt's job to run stuff and keep the battery topped up.

[Grogador]

2nd battery in the trunk would provide more juice as well, not having to rely on the alternator.

[03ozwhip]

thats what im looking for, but how can i find out if one is better at lower RPMs? i have been looking around at alts, but all i hear is "this alt has so many amps, bla bla bla" if its not the amps that will help how do i find that out?

[03ozwhip]

dont want a second battery if i dont have to.

[benyl]

Originally posted by Grogador
2nd battery in the trunk would provide more juice as well, not having to rely on the alternator.

But it is the alt that charges the second battery.

Once you start the car, in theory, you should be able to run the car and all accessories with the battery disconnected. If you can't, then your alt isn't doing a good enough job.

[Grogador]

Assuming it's charged already, it'll provide enough juice at idle to keep your voltage from dropping... much... but yeah, alt will have to charge it eventually