rpm’s / Dimming lights

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=10638
Printed Date: July 29, 2025 at 2:05 AM

Topic: rpm’s / Dimming lights

Posted By: molotov_icr
Subject: rpm’s / Dimming lights
Date Posted: March 09, 2003 at 11:01 AM

My rpms fluctuate and lights dim, even when my stereo is not playing loud.

I've got an extra battery hooked up to my three amps.

Should I buy a cap? Friends tell me that won't be enough, (that I need a new high amp alternator). Or is there something else that I've over looked?

'94 accord.

What do you guys recommend?

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"If it's to loud, Then you're to old"

Replies:

Posted By: bberman1
Date Posted: March 09, 2003 at 11:11 AM

First off how many watts rms are you running? A cap is not a band aid and you probably wouldn’t see any kind of a difference adding one. But you say your rpms and lights dimm at low levels, sounds like you might have a bad or weak charging system. A high output alternator might be the answer but first I need to know the rms watts and any other accessories you may have running.

Posted By: lagatbezan
Date Posted: March 09, 2003 at 6:36 PM

are you using a isolator for your two batteries? if not, you should! i would also recomend a cap.

Posted By: molotov_icr
Date Posted: March 09, 2003 at 7:17 PM

Isolator?

I'm not sure how many watts, but i've got one beefy amp, used to power my 15w3's(500w rmsx2). The other two amps have a low rms, I'll Guess 90 combined. I'm also running an equalizer and 80watt halogen bulbs.

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"If it's to loud, Then you're to old"

Posted By: donkason
Date Posted: March 10, 2003 at 8:08 PM

It sounds like you definately need to get a high amp alternator. I would also install an isolator, it is just a relay that "isolates" your secondary batteries from your primary one. You can pick up a nice stinger 200 amp relay on ebay for about 50 bucks or an 80 amp one for about 20.

Posted By: the12volt
Date Posted: March 10, 2003 at 8:46 PM

Hi donkason, I agree with your suggestion to get a high output alternator, but here's a tip: an isolator is not a relay. It's essentially a pair of large diodes (typically rated at 70 amps each and higher) with an input terminal (the two anode ends together) and two output terminals (each cathode end). It's purpose is to prevent each battery from discharging or drawing current from the other. A 200 amp relay is another way to prevent one battery from discharging the other when the coil of the relay is not energized, but it will allow one to draw current from the other when the coil is energized if an isolator is not used.

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